Material Selection for Soil Remineralization: Mineralogical, Agronomic and Environmental Perspectives on Crushed Rock Wastes

Abstract

The increasing interest in the use of crushed rock wastes as soil remineralizers has created a need for a more rigorous evaluation of these materials. This evaluation should go beyond total nutrient content and consider the factors that may determine their performance under agricultural conditions. Therefore, this review aims to analyze these wastes from an integrated perspective, considering their potential for nutrient supply, their possible agronomic responses, and their environmental and operational feasibility. The literature was selected using different research platforms, prioritizing recent scientific studies directly related to the scope of the review. The selected studies indicate that high nutrient contents in rocks do not necessarily guarantee their availability, while mineralogy, pH, water availability, temperature, and microbial activity are among the factors that determine the rate and duration of nutrient release. These differences are also reflected in crop responses, which vary according to the type of rock material, soil conditions, application rate, and crop species. While some studies report improvements in soil fertility and crop yield, others show changes in soil chemical properties and evidence of mineral weathering without corresponding increases in productivity. At the same time, strategies used to increase material reactivity, such as reducing particle size, may lead to greater energy demand and potentially higher CO₂ emissions associated with grinding. Another important aspect is that materials with favorable nutrient composition may have their agricultural use limited by the presence and mobility of potentially toxic elements. Based on these findings, this review organizes the selection of crushed rock wastes through a critical assessment of their reactivity and compatibility, while also considering environmental safety and conditions that may determine their agricultural feasibility.

1. Introduction

Agricultural production depends directly on nutrient availability in the soil and on the use of fertilizers to maintain crop productivity. However, the prolonged use of mineral fertilizers may be associated with environmental impacts, including soil acidification, nutrient losses through leaching, and eutrophication. In addition to these environmental concerns, dependence on conventional fertilizers also makes some agricultural systems more susceptible to fluctuations in prices, availability, and imports of these products. In this context, the search for alternative nutrient sources has increased, particularly those that can combine nutrient supply with the reuse of materials that are already available [1,2].

In line with this need, wastes generated from mining and rock processing have gained attention as alternative nutrient sources for agriculture. In addition, mining activities are estimated to generate approximately 8.9–14.4 billion tonnes of tailings annually worldwide, with a large proportion remaining stored in disposal piles, which may favor the mobilization of elements from these materials into soil and water [3].

The reuse of these wastes represents a promising alternative when associated with their application in agriculture, providing a more appropriate destination while contributing to nutrient supply to the soil. These materials commonly contain Mg, K, P, Si, and Ca, as well as different micronutrients important for plant growth. Silicate materials can provide benefits beyond fertilization, contributing to soil acidity correction and the formation of secondary minerals. In addition, they may increase plant resistance to biotic and abiotic stresses by strengthening plant tissues. Another important aspect is the gradual release of nutrients, allowing part of these minerals to remain as a nutrient reserve in the soil and continue to be released over time. Ca- and Mg-rich silicate remineralizers may also contribute to atmospheric CO₂ removal through enhanced weathering, although the magnitude and permanence of this effect depend on mineral reactivity, soil conditions, hydrological pathways, and the fate of dissolved inorganic carbon [4,5].

Recent studies have provided more direct evidence of the behavior of remineralizers shortly after their application to soil. Kurokawa et al. [6] used quantitative X-ray diffraction analysis and observed a significant reduction in minerals such as plagioclase and pyroxene present in basalt after cultivation, with weathering being approximately 8.5 times greater in the root-influenced zone. The authors also observed that the minerals behaved differently even after only 2.5 months of cultivation, confirming that different mineral phases can undergo changes to different extents after their application to soil. Therefore, evaluating these factors together is important for understanding the actual agricultural potential of each remineralizer.

Considering these different possibilities, this review aims to provide an integrated analysis of the use of crushed rock wastes as soil remineralizers, linking material characteristics to nutrient release mechanisms and their potential direct and long-term effects on the soil–plant system. In addition, the agricultural and environmental benefits are discussed together with the potential limitations that still restrict the large-scale application of this approach. Based on this discussion, a framework is proposed that brings together the main criteria related to material selection, reactivity, and compatibility, aiming to support the identification of rock wastes with greater potential for agricultural application under different conditions.

2. Materials and Methods

The literature search was conducted using different scientific databases and research platforms, including Scopus, ScienceDirect, Springer Nature Link, Taylor & Francis Online, and Google Scholar. The search terms included combinations of “crushed rock waste”, “rock powder”, “soil remineralization”, “enhanced weathering”, “mineral weathering”, “agricultural application”, “nutrient release”, “carbon sequestration”, and “potentially toxic elements”.

Publications in English were considered, prioritizing recent scientific studies, particularly those published within the last five years. Older studies were also included when relevant to the conceptual basis of soil remineralization and mineral weathering. Studies were initially screened based on their titles and abstracts, followed by full-text assessment of publications considered relevant to the scope of the review. Studies not directly related to the agricultural application of rock-derived materials, soil remineralization, or the main topics addressed in this review were excluded.

Original research articles and review papers were considered when they provided relevant information on the topics addressed in this review. The selected studies were evaluated considering mineralogical and chemical composition, mineral reactivity and nutrient release, particle size, soil and climatic conditions, agronomic responses, environmental safety, and technical and economic aspects related to the agricultural use of crushed rock wastes.

3. Material Selection Criteria for Soil Remineralization

Rock-derived materials used in agriculture are described by different terms depending on their origin and processing. Mining wastes include materials generated during mineral extraction and processing, while tailings are residues remaining after mineral processing. Quarry wastes and crusher dust are generated during rock extraction and crushing, respectively. Rock powder generally refers to ground rock material that can be applied to the soil. In this review, the term crushed rock waste is used more broadly to include these different materials when they are evaluated for agricultural use. However, when discussing individual studies, the terminology used by the original authors was maintained.

The effectiveness of remineralizers does not depend directly on the amount of nutrients present in the rock, although this is one of the first characteristics considered when evaluating these materials. Therefore, chemical composition alone is not sufficient to predict their behavior in soil. Therefore, mineralogical and geochemical characterization should be considered together, since the total elemental composition alone does not indicate the mineral phases in which potentially available nutrients and other elements are present. In this context, the combined use of XRD and XRF can provide complementary information on the mineralogical composition and bulk geochemistry of these materials [7]. Mineralogy, particle size, mineral reactivity, soil and climatic conditions, and biological activity also play important roles in determining how these materials behave after application. In this context, the selection of a material as a remineralizer should consider these factors together, as they can determine its agricultural potential and performance over time [8,9,10].

Materials used as remineralizers are generally obtained from by-products of mining activities, quarries, and crushing processes. These materials can act as sources of gradual release of macro- and micronutrients essential for plant growth. In addition, they can contribute to improving the physical, chemical, and biological properties of the soil, supporting more sustainable agricultural systems and reducing dependence on conventional fertilizers.

For this reason, the selection of a remineralizer should be based on a careful evaluation of mineralogical, physical, chemical, biological, environmental, and economic factors. Considering these factors together provides a more consistent assessment of the agricultural potential of the material than the use of isolated parameters, such as total nutrient content. Therefore, based on the available literature,

Table 1. Selection and evaluation of rock wastes as agricultural remineralizers.

Selection Criterion	Indicators	Influence on Performance	Practical Implications	References
Predominant mineral type	Highly reactive minerals: nepheline, anorthite, glauconite, wollastonite, leucite, olivine, and pyroxenes	More reactive minerals generally favor faster nutrient release during weathering.	Mineralogy should be evaluated together with the nutrient content of the material.	[11,12]
Dissolution rate	Dissolution rates vary among minerals, with nepheline, anorthite, glauconite, wollastonite, and leucite generally showing faster dissolution than K-feldspars	Higher dissolution rates may increase nutrient availability in the short and medium term.	Rocks containing feldspathoids, glauconite, or more reactive mafic minerals may be more suitable when faster nutrient release is expected.	[11,12]
Rock reactivity	Mafic and ultramafic rocks, such as basalts and dunites, tend to be more reactive than granites.	More reactive rocks can favor the release of Ca, Mg, Fe, Si, and micronutrients.	Basaltic and ultramafic wastes are promising alternatives when their environmental safety is confirmed.	[11,12,13]
Total nutrient content	Presence of K, Ca, Mg, P, Si, Fe, Mn, Zn, and other micronutrients	Total nutrient content indicates the nutritional potential of the material but does not necessarily represent nutrient availability.	Chemical composition should be evaluated together with XRD, petrographic characterization, and dissolution tests.	[7,8]
Particle size	Studies report particles ranging from <74 µm to <2 mm. Finer particles generally have a larger specific surface area.	Smaller particles favor mineral dissolution, although finer grinding requires greater energy consumption.	Particle size should be selected considering both mineral reactivity and the energy required for processing.	[14,15]
Application rate	Most studies have evaluated rates between 1 and 20 t ha−1, although rates of 50–100 t ha−1 have also been reported.	Soil responses vary according to the applied rate, while very high rates may increase costs and lead to nutrient imbalances.	The application rate should be adjusted according to the material, soil characteristics, and crop requirements.	[16]
Soil type	Latosols, Argisols, Oxisols, and Ultisols, particularly acidic and highly weathered soils, have been evaluated in different studies.	Acidic and highly weathered soils may favor the dissolution of some minerals and the release of nutrients.	Soil characteristics should be considered when selecting the material and defining application conditions.	[13,14]
Soil pH	Acidic and moderately acidic soils	Soil acidity can favor silicate mineral dissolution and the release of base cations.	Remineralizers may contribute to soil conditioning, although they do not necessarily replace liming.	[17]
Climate	Warm and humid conditions favor mineral weathering.	Temperature and water availability directly affect mineral dissolution and nutrient release.	Climatic conditions should be considered when estimating the expected weathering rate after application.	[18]
Plant species	Maize, soybean, cocoa, coffee, black oat, eucalyptus, rice, tomato, and apple have been evaluated in different trials.	Plant species differ in their interaction with minerals and their ability to promote weathering and nutrient uptake.	The response to remineralizers should be evaluated according to the crop and management system.	[19,20]
Interaction with organic matter	Kamafugite: 40 t ha−1 + organic compost: 80 t ha−1 in leaching columns; increases in Ca, Mg, K, S, pH, and electrical conductivity were reported in the leachates.	Organic matter can favor biological and chemical processes involved in mineral weathering.	The combination with organic materials may increase nutrient release from some remineralizers.	[21]
Agricultural response	Trials with basalt, dacite, phonolite, glauconite, and mineral mixtures have reported changes in crop yield, soil pH, K, Ca, Mg, Si, Al, and Mn.	Positive effects on soil fertility and crop development have been reported, although the magnitude of the response varies considerably among studies.	Local trials remain important before these materials are applied on a larger scale.	[19,22,23]
Carbon removal and enhanced weathering	Basalt and other Ca- and Mg-rich rocks have been investigated for CO2 removal. Field studies have evaluated basalt applications of up to 50 t ha−1 f 50 t ha−1, with higher rates also reported in the literature.	Silicate weathering can contribute to CO2 removal, but long-term field evidence is still limited and mineral dissolution does not always correspond directly to CO2 removal.	Carbon monitoring should be considered together with soil and crop responses.	[16,24]
Environmental risk	Elements of concern include Cd, Cr, Ni, Pb, As, Hg, Cu, and Co.	The presence and mobility of potentially toxic elements may limit the agricultural use of some wastes.	Geochemical characterization and leaching tests are important before field application.	[25]
Economic feasibility	Costs are mainly associated with grinding, transport, application rate, and regional availability of the material.	Locally available wastes can reduce transport costs, whereas intensive grinding and high application rates may reduce economic advantages.	Techno-economic and life cycle assessments should be considered when evaluating large-scale application.	[15,25]
Contribution to the circular economy	Reuse of wastes from quarrying, mining, and crushing activities	Provides an alternative use for mineral wastes while generating an agricultural input.	Regional use can reduce waste accumulation and support local agricultural input chains.	[1,2]

summarizes the main factors that should be considered when selecting rock wastes for agricultural use and their influence on nutrient availability.

Thus, a K-rich rock dominated by low-reactivity alkali feldspars may have lower potential for agricultural application than a rock with a lower total nutrient content but composed of minerals that are more susceptible to weathering. Although several studies have demonstrated the importance of total nutrient content and mineralogical composition, recent findings indicate that mineral dissolution rates also play a key role in the performance of these materials. Considerable differences in dissolution rates have been reported among the main minerals found in silicate rocks. Minerals such as anorthite, nepheline, and glauconite dissolve considerably faster than K-feldspars, indicating a greater potential for nutrient release in the short term [11,12]. However, these differences in dissolution rates can vary depending on the conditions under which they are evaluated, particularly pH, temperature, reactive surface area, solution chemistry, and saturation state.

In addition to mineralogical characteristics, the performance of remineralizers also depends on the interaction between material properties and soil and climatic conditions. Highly weathered tropical soils, such as Latosols and Argisols, may show a greater response to the nutrients released from these materials due to their low reserves of primary minerals, high acidity, and nutrient losses through leaching. When applied to highly weathered soils, rock powders can promote the gradual replenishment of Ca, Mg, K, Si, and micronutrients, while also contributing to an increase in soil pH and, consequently, to a reduction in aluminum toxicity in certain agricultural systems [13,26].

Particle size is one of the most relevant physical factors affecting the performance of these materials. Finer particles, for example, have a larger specific surface area and therefore greater contact with the soil solution, favoring mineral dissolution reactions. Rinder von Hagke [27] reported that reducing the particle size of basalt (<100 µm, <10 µm, and <1 µm) can increase its weathering potential and, consequently, its capacity for CO₂ removal through enhanced rock weathering. The authors found that approximately 16% of particles smaller than 100 µm were dissolved, whereas this value reached about 55% for particles smaller than 10 µm and nearly 100% for particles below 1 µm. Similarly, experimental weathering tests showed that silt-dominated basalt powders (<45 µm) weathered approximately twice as fast as coarser sand-dominated fractions [14]. However, it is important to note that the relationship between surface area and weathering rate is not always linear. In other words, an increase in surface area does not necessarily mean that mineral dissolution will increase in the same proportion, since dissolution may preferentially occur at more reactive regions, such as crystal defects, fractures, and specific reactive sites on the mineral surface [11]. Finer particles require more energy to be produced, which can increase processing costs and associated CO₂ emissions. Therefore, these limitations should also be considered during the production and application of the material.

The combination of remineralizers with organic matter represents a promising strategy to increase nutrient release and improve soil quality. Medeiros et al. [21], for example, evaluated kamafugite applied at a rate equivalent to 40 t ha⁻¹, either alone or combined with organic compost at 80 t ha⁻¹, and observed significant differences in Ca, Mg, K, and S concentrations, as well as pH and electrical conductivity, in the leachates from treatments containing rock, particularly when combined with organic compost. In addition, the authors reported increased Mg, K, P, and Mn contents in the soil treated with rock and greater inorganic carbon capture when the remineralizer was associated with organic compost. These results indicate that organic matter can intensify mineral weathering and favor nutrient release.

Recent studies have shown that these effects extend beyond soil chemical fertility, also influencing biological characteristics. Razera et al. [28] verified that remineralizers produced from mining wastes promoted significant changes in the fungal biodiversity of a Quartzipsamment, including an increase in beneficial fungi belonging to the genera Mortierella and Trichoderma, as well as more complex microbial interactions. According to the authors, calcium, manganese, and organic carbon were the main factors associated with the observed changes in fungal community structure. Moscatelli et al. [29] demonstrated that the combination of basalt rock powder with a microbial consortium significantly increased microbial biomass and enzymatic activity associated with biogeochemical cycles. In addition, the authors observed that biological attributes responded more rapidly to remineralizer application than soil chemical properties, suggesting that microbial activity may act as an early indicator of soil quality recovery. Therefore, changes in microbial and enzymatic activity have received increasing attention, since the production of organic acids can accelerate the weathering of silicate minerals. This enhanced weathering can contribute to atmospheric CO₂ removal and carbon storage and, consequently, to climate change mitigation [9,16,30].

In addition to agricultural performance, the large-scale use of remineralizers also depends on technical aspects, environmental safety, and economic feasibility. Highly reactive materials may favor greater nutrient release; however, they may require higher energy consumption during grinding or involve higher transportation costs, depending on the region where they are used. The presence of potentially toxic elements should also be evaluated, and environmental monitoring should be considered throughout the process. Therefore, these aspects show that the selection of rock wastes for soil remineralization requires an integrated assessment of mineralogical, agricultural, environmental, and economic criteria. In this context, Figure 1 presents a conceptual framework that summarizes the main factors involved in selecting rock wastes for use as soil remineralizers. The framework considers the main characteristics of the material together with soil and environmental conditions and practical aspects that can influence its agricultural use. Figure 1 was prepared by the authors based on the literature reviewed in this study.

4. Controls on Nutrient Release from Crushed Rock Wastes

4.1. Mineral Weathering and Dissolution

Section 2 addressed the main criteria for selecting rock wastes as remineralizers, considering their mineralogical, agricultural, and environmental characteristics. However, the performance of these materials also depends on the processes that control nutrient release after their application to soil. In this context, this section further explores the mechanisms of mineral weathering and dissolution, as well as the influence of soil properties and physicochemical and biological interactions on nutrient availability.

Nutrient release from remineralizers occurs mainly through the weathering and dissolution of the minerals that make up the rock. During weathering, nutrients contained within the mineral crystal structure are gradually released into the soil solution, where they can become available for plant uptake. The rate of this release is not uniform and is influenced by both the mineralogical properties of the material and the environmental conditions under which it is applied [31,32].

In basalt rock powder, mineral dissolution is one of the main mechanisms involved in weathering. However, the dissolution process depends not only on mineral reactivity but also on the interaction between chemical reactions occurring at particle surfaces, the transport of dissolved species by water (advection), and their dispersion through the porous soil medium. Therefore, the observed dissolution rate results from the combined action of these processes, which control the release of elements into the soil environment [18].

The influence of mineralogical composition on weathering behavior can also be observed in other volcanic rocks. For example, andesite is a volcanic rock occurring in southern Brazil that is traditionally exploited for use in civil construction. The presence of volcanic glass may enhance weathering because amorphous phases lack the long-range structural order of crystalline minerals and can therefore exhibit higher reactivity under suitable geochemical conditions. As a result, andesite weathers more rapidly, promoting the release of Ca, K, Na, and Mg into the soil [33]. Together, these examples demonstrate that differences in mineralogical composition directly influence weathering intensity and nutrient release, even among rocks of volcanic origin.

It is important to distinguish the different processes involved in carbon capture through rock weathering, since they are related but not equivalent. Mineral weathering refers to the alteration and chemical dissolution of minerals, which may involve H⁺ consumption and the release of ions and silica, whereas CO₂ consumption is associated with reactions between dissolved CO₂ in the aqueous system and minerals, which are favored by H⁺ consumption during weathering [31,34]. These reactions contribute to the formation of dissolved inorganic carbon (DIC), mainly in the form of bicarbonate, which constitutes a dynamic transport phase and does not, in itself, imply permanent carbon retention. Carbon sequestration, in turn, refers to the retention and stabilization of carbon in long-term reservoirs, whereas net atmospheric CO₂ removal represents the final balance between CO₂ removed from the atmosphere and the emissions associated with the implementation and life cycle of the technology [31]. Therefore, the occurrence of weathering, CO₂ consumption, and DIC formation does not necessarily imply effective carbon sequestration or positive net atmospheric CO₂ removal.

The intensity of mineral dissolution tends to be even greater in the rhizosphere, the region surrounding plant roots, where the continuous uptake of nutrients maintains the soil solution in an undersaturated state. Under these conditions, minerals continuously dissolve to re-establish the chemical equilibrium of the system [34]. In addition, plants release exudates rich in organic acids, enzymes, and carbohydrates, which stimulate microbial activity and contribute to nutrient availability [31]. In this environment, roots and microorganisms also release CO₂ and organic acids, intensifying chemical weathering and enhancing nutrient availability for plants [34].

As a result of this process, primary minerals that compose the original rock, such as plagioclase and pyroxene silicates, undergo decomposition of their crystalline structure. This transformation leads to the formation of secondary minerals, which correspond to more stable phases under the conditions found in the soil environment [34,35].

In this context, Cardozo et al. [33] highlight that the deliberate application of rock powder triggers an accelerated weathering process, enhancing a natural mechanism associated with nutrient release and potential CO₂ removal. Supporting this perspective, Medeiros et al. [] demonstrated that the application of crushed kamafugite rock, an alkaline volcanic rock, has the potential to promote CO₂ capture, especially when associated with organic matter. Together, these studies indicate that accelerated weathering contributes to gradual nutrient release and may also contribute to CO₂ removal; however, mineral dissolution alone does not necessarily result in net carbon sequestration, as this depends on the fate and long-term stability of the resulting dissolved inorganic carbon.

The intensity of these processes depends not only on mineral characteristics and biological activity but also on the environmental conditions to which the system is subjected. Climate is considered one of the main factors controlling the rate and extent of weathering, and under arid conditions, mineral alteration rates tend to be significantly lower [31]. Consistently, Kurokawa et al. [34] emphasize that humid regions at low and middle latitudes favor mineral dissolution due to high leaching rates, which maintain the soil solution in an undersaturated state. In this context, Cardozo et al. [33] point out that the Brazilian climate provides favorable conditions for weathering processes, contributing to the efficiency of soil remineralization.

4.2. Factors Regulating Nutrient Availability

Soil pH directly influences nutrient uptake by plants and the rate of weathering processes. Under more acidic conditions, mineral dissolution is favored because silicate hydrolysis occurs more rapidly, promoting the release of nutrients present in rock powders [17]. As these minerals dissolve, soil acidity is consumed and pH gradually increases, reducing the dissolution rate over time and contributing to the establishment of chemical equilibrium within the system. However, in regions with high rainfall, the leaching of buffering elements promotes soil acidification, a process that the application of nitrogen fertilizers and the production of organic acids may also intensify. However, effective CO₂ capture does not depend solely on the availability of cations released through weathering, since these elements may follow different pathways in the soil. In addition, the pH conditions that favor silicate hydrolysis may differ from those required for the formation and stabilization of carbonates, as demonstrated by Medeiros et al. [], who observed that although the application of a remineralizer increased soil pH, the resulting values were insufficient to favor carbonate formation and stabilization, which may limit the efficiency of this capture mechanism. Thus, although silicate rock powders have potential for CO₂ sequestration, their effective magnitude may be lower than that estimated based on the mineralogical composition of the rock [31,,].

Just as pH regulates the rate of dissolution reactions, water availability also plays a determining role in weathering and nutrient release processes. Moisture is one of the main factors controlling weathering, influencing both the rate of chemical reactions and the transport of products generated during these processes []. Since mineral weathering depends on the interaction between water and CO₂, water availability is essential for nutrient release from rock powders [36]. Under conditions of high rainfall, such as those found in tropical regions, chemical weathering tends to occur more intensely, favoring mineral dissolution and increasing nutrient availability in the soil [18,31]. In addition to participating directly in dissolution reactions, adequate moisture sustains the activity of roots and soil microorganisms, which release exudates and organic acids capable of accelerating mineral decomposition [31,37]. Other environmental factors, such as precipitation, wind, and microbial activity, may also influence the efficiency of this process [18]. However, although water is indispensable for nutrient release, excessive rainfall may promote the leaching of dissolved elements, reducing their retention in the soil and their availability to plants []. In addition to water availability, temperature is another important factor controlling mineral weathering.

Temperature directly influences mineral weathering by affecting reaction kinetics. Under comparable conditions, higher temperatures generally favor mineral dissolution and may increase nutrient release into the soil solution. However, the magnitude of this effect also depends on mineralogy, solution chemistry, and saturation state. Consequently, remineralization processes tend to occur more rapidly, increasing the availability of these elements to plants. This behavior was observed in studies involving basalt, in which mineral dissolution was significantly greater at 25 °C than at 10 °C, highlighting the importance of temperature in mineral dissolution kinetics [18]. However, mineral dissolution processes are not controlled solely by physicochemical factors. Soil biological activity also plays a fundamental role in nutrient availability [].

Soil microorganisms play a central role in nutrient cycling and fertility maintenance, acting in the transformation of minerals into bioavailable forms for plants. In this context, rock powders provide minerals that serve as substrates for biological activity and promote interactions among soil, roots, and microbiota. Microbial colonization of mineral fragment surfaces can intensify localized weathering, promote gradual mineral dissolution and increase nutrient availability in the soil [31,35,38]. This process is particularly relevant in the rhizosphere, where biological activity is more intense. In this region, the release of organic acids and enzymes by roots and microorganisms promotes mineral dissolution, resulting in higher weathering rates compared with areas not influenced by roots. Furthermore, the secretion of these compounds occurs according to plant demands, conferring a self-regulating character to nutrient release from minerals [31,34].

4.3. Nutrient Retention and Soil Fertility Enhancement

Among the soil properties influencing the long-term performance of remineralizers, cation exchange capacity (CEC) deserves particular attention because it directly affects nutrient retention and availability. CEC is a soil property related to its ability to adsorb, retain, and exchange cations, playing a fundamental role in nutrient dynamics and availability for plants [39]. CEC is mainly influenced by clay mineralogy, soil organic matter, and pH-dependent surface charges. Permanent negative charges are particularly important in 2:1 phyllosilicates, whereas Fe and Al oxides generally exhibit variable surface charges that depend strongly on soil pH [18].

Different clay minerals exhibit different charge characteristics and, consequently, influence CEC differently. Permanent negative charge is mainly associated with isomorphic substitution within the mineral structure. This substitution results in a permanent negative charge in the mineral structure, does not directly depend on pH, and favors cation adsorption on the mineral surface [40,41]. In contrast, surface negative charge depends on the chemical conditions at the mineral surface. As pH increases, protonated species present on the surface are converted into negatively charged species, increasing the magnitude of the surface charge and favoring cation adsorption. Under acidic conditions, on the other hand, H⁺ adsorption onto the mineral surface reduces the negative surface charges, resulting in a lower capacity for ion adsorption [41,42].

The contribution of these mechanisms to CEC varies among different soil groups. Clay minerals, such as smectite (2:1), generally exhibit a high density of constant charge and can contribute significantly to CEC, whereas kaolinite (1:1) exhibits a low density of constant charge and low CEC. In addition to the mineral fraction, organic matter is directly related to CEC because it contains several functional groups that can develop negative charges. Thus, organic matter constitutes an important source of pH-dependent variable charge. Therefore, the relative contribution of constant and variable charges to CEC depends on mineralogical composition and organic matter content, as well as environmental conditions [43].

Soil mineralogy can change over time as a function of environmental conditions. Long-term acidification may favor the transformation of 2:1 minerals into 1:1 minerals, resulting in a reduction in permanent negative charge and soil CEC [40]. In addition, climatic and moisture conditions influence the distribution and formation of clay minerals, resulting in differences in soil mineralogy. These climatic variations, in turn, are associated with the distribution of clay minerals and the charge characteristics that contribute to CEC [43]. Thus, the formation of secondary clay minerals depends on local environmental conditions. In humid tropical climates and under intense weathering, leaching favors the formation of kaolinite and Fe/Al oxides [44]. In semi-arid environments or under limited drainage, lower leaching favors the formation of 2:1 clay minerals, such as smectites, associated with a predominance of higher CEC [45].

The application of rock powders may contribute to increasing CEC through mineralogical transformations promoted during weathering. In this process, primary minerals are gradually altered, favoring the formation of secondary clay minerals and the release of elements such as Ca, Mg, K, Fe, and Si into the soil solution. Therefore, base saturation increases, soil acidity decreases, and nutrient retention capacity improves [35]. Similarly, Cardozo et al. [33] highlight that the use of remineralizers has the potential to increase CEC, soil pH, and soil aeration, since the mineral constituents of rock powders may contribute to the formation of secondary clay minerals over longer timescales, depending on local soil and environmental conditions. Therefore, soils with higher CEC tend to retain greater quantities of nutrient cations, functioning as reservoirs capable of gradually supplying these elements to plants according to their demand [,39].

Cation exchange capacity constitutes one of the main mechanisms responsible for nutrient retention in the soil. However, this process does not depend exclusively on CEC but also on factors such as soil texture, pH, interactions between mineral particles and cations, and organic matter content. High concentrations of divalent cations, such as Ca²⁺ and Mg²⁺, favor particle flocculation and aggregate formation, contributing to improved soil structure and reduced nutrient losses [18,46,47].

A slower nutrient-release rate from remineralizers may reduce transient solute concentrations in the soil solution and, under suitable soil and hydrological conditions, decrease leaching losses compared with highly soluble nutrient sources [,48]. Beyond supplying nutrients, remineralizers can improve cation retention and enhance soil chemical properties, allowing their benefits to persist over time. Consequently, their role extends beyond nutrient supply, contributing to the long-term maintenance of soil fertility and more sustainable agricultural production.

5. Agronomic Performance of Crushed Rock Wastes

The use of crushed rock wastes in agriculture has been investigated under different cultivation conditions and crop species. Although improving crop productivity remains the main objective, recent studies have also demonstrated their potential when associated with soil amendments and in strategies aimed at pest management.

Table 2. Main agronomic responses reported for the application of crushed rock wastes in different crops.

Crop	Rock Material	Main Findings	Main Mechanism	Ref.
Tomato	Rock dust	Increased plant growth, reduced disease incidence, improved soil fertility	Gradual nutrient release, pH correction and improved nutrient availability	[19]
Cabbage	Granite rock dust	Reduced feeding damage by Plutella xylostella	Silicon supply and abrasive effect on insects	[22]
Bean	Siltstone + limestone	Higher Ca, Mg, K and P availability, greater biomass production	Slow nutrient release and improved soil chemical properties	[23]
Maize	Basalt rock powder	Greater biomass and nutrient accumulation	Mineral weathering and continuous nutrient release	[49]
Lily	Granite rock dust	Lower pest damage	Silicon-mediated plant resistance	[50]
Squash	Granite rock dust	Higher fruit production	Improved plant nutrition	[50]
Amaranth	Silicate rock powder + manure	Increased yield and microbial activity	Synergistic effect between organic matter and mineral weathering	[24]
Watermelon	Rock powder + poultry manure	Reduced nematode infestation and increased productivity	Improved soil fertility and biological activity	[51]
Sorghum	Basalt	Greater biomass production and CO2 sequestration potential	Enhanced rock weathering	[24]

Responses reported in the literature vary according to crop species, rock type, application rate, soil properties, and environmental conditions.

summarizes the main agronomic responses reported in the literature.

Rock dust developed from quartz, abundant biotite, equivalent proportions of potassium feldspar, plagioclase, olivine, and rice straw was applied to tomato growth (Solanum lycopersicum L.) in a greenhouse. The results showed that rock dust promoted higher plant growth, with a height of 49.78 cm compared to 33.28 cm, and decreased bacterial wilt severity from 68.33 ± 1.44% to 14.16 ± 3.81%. The results were attributed to a change in the soil pH from acidic (5.13) to neutral, since acidic soils can lead to mineral deficiencies, such as Ca, Mg, and P, among others, and to toxic levels of Mn and Al. Another factor was the higher presence of Ca in the soil amendment, since Ca is responsible for plant membrane stability and functionality, decreasing plant disease susceptibility. Better results were also observed combining organic fertilizer with rock dust for most parameters, including overall plant health measured by chlorophyll content and photosynthetic rate, suggesting rock dust application as a soil amendment [19]. Uchibayashi et al. [20] verified that the basalt application rates range from 5 to 100 t ha⁻¹ in paddy rice and indicated that the amount of basalt applied influences soil chemical properties and the uptake of different elements by plants.

The study conducted by Faraone et al. [22] specifically explored the application of rock dust for insect pest management. The chemical analysis of granite dust composition showed high levels of silica and other oxides, suggesting that the mode of action and efficiency, in this application context, may be similar to diatomaceous earth [52]. The foliar application of granite dust was able to reduce larval feeding damage, produce an insecticidal effect on larvae, and reduce the number of eggs oviposited on cabbage leaves of Plutella xylostella. The foliar application was also tested against Trichoplusia ni on cabbage leaves, reducing only larval feeding damage, suggesting that granite dust application can vary according to the target pest species.

Similar results were found by Oliveira et al. [23] when applying a blend of siltstone powder and limestone, derived from mining waste, for bean (Phaseolus vulgaris) and maize (Zea mays) cultivation. Rock dust application resulted in an increase in Ca, K, P, and Mg contents, as well as the pH neutralization in soil. In addition, the use of silicate rocks provides higher silicon (Si) uptake by plants, promoting higher tolerance to biotic and abiotic stresses. It is important to highlight that these nutrients are released gradually into the soil due to mineral degradation processes, contributing to a residual effect of this soil amendment and maintaining the nutrient levels even after crop removal. Finally, the results showed an increase in shoot dry mass, height, and stem diameter of 126, 83, and 35%, respectively, for bean and of 40, 63, and 61%, respectively, for maize due to the lowest rate of rock dust application (4.0 t ha⁻¹).

A similar study conducted by Conceição et al. [49] applied basalt rock dust to maize (Zea mays) and bean (Phaseolus vulgares—cv Perola) cultivation. Basalt rock dust increased Ca, K, P, and Mg contents in soil, increasing its pH level, as already discussed in the studies above. Both maize and bean plants supplemented with this soil amendment soil exhibited an increase in shoot dry mass of 200% and 300%, respectively, and an increase in micro- and macronutrient accumulation, provided by the rock dust, when compared to control plants. A residual effect in the soil was also observed, increasing the overall mineral content and soil quality parameters that may enhance future crops, due to the same reasons discussed above.

It is important to note that the rock dust application may vary depending on the crop planted. In the study conducted by Faraone and Hillier [50], granite rock dust showed divergent results when applied to lily (Lilium spp.), squash (Cucurbita pepo var. turbinata L.), and cabbage (Brassica oleracea L.) plants. Regarding abiotic stress, such as herbivore damage, the rock dust treatment reduces damage from 30% (control without rock dust) to almost 0%, effectively managing lily beetles in lily plants. On the other hand, no statistically significant differences in herbivore damage were achieved for cabbage and squash plants against lepidopteran and coleopteran pests, respectively. However, the foliar application increased squash fruit growth by 2.5-fold when compared to the control squash fruit group. Elemental analysis showed a high content of silicon in the rock dust, present in the form of SiO₂ (around 60% of the rock dust composition). The authors suggest a positive correlation between the silicon presence and the results obtained, since silicon has already been reported as an active ingredient for pest control in similar organic materials. However, more studies are needed to better understand its applicability and variation among different target pest species and different plant species.

A different approach relies on the synergistic effect of rock dust combined with manure. The combination of silicate dust and manure proposed by Oladele et al. [53] led to improvement in different parameters regarding soil health and crop production. In this approach, the application of rock dust can help stabilize manure-derived organic matter, due to its silica and inorganic C content. On the other hand, manure application can stimulate the mineral weathering of rock dust through organic acid production or microbial exudates [54]. This combination increased nitrogen availability and microbial activity, as well as different soil physical parameters, achieving a vegetable fresh herbage yield 19% higher than that of the control group for the Amaranth cruentus species. It is important to highlight that this study also showed the application of rock dust for capturing and storing atmospheric CO₂ as inorganic carbon, mitigating CO₂ emissions.

Another study conducted by Oladeji et al. [51] applied rock dust combined with poultry manure in watermelon (Citrullus lanatus Thunb) fields. This combination was able to suppress the root-knot nematode population by 99%, reducing root galling by 60 to 89% according to the different trials and significantly increasing the watermelon fruit yield. The best case scenario showed an increase in yield up to 46.5 t ha⁻¹ when compared to the control group (20.9 t ha⁻¹).

The study conducted by Kelland et al. [24] also explored the CO₂ sequestration through silicate dust application in agricultural soil. After a single application of rock dust (10 kg m⁻²), CO₂ sequestration levels achieved rates of 2–4 t CO₂ ha⁻¹ over 5 years. Overall, the basalt dust treatment increased the seed dry mass per plant by 21 ± 9.4% for the cereal Sorghum bicolor.

Taken together, these studies show that the agronomic response to crushed rock materials depends on crop species, material composition, application rate, soil properties, and the use of complementary organic amendments. Positive responses are not uniform, and improvements in soil properties or mineral weathering do not necessarily result in proportional increases in crop productivity.

In fact, other studies have pointed out the advantages of crushed rock application in agriculture for remineralizing soils, restoring their fertility and structure, and consequently improving crop production. As discussed above, these soil amendments can be obtained from mining wastes and may reduce the need for conventional fertilizers under suitable conditions, while also providing economic benefits associated with their use.

Due to its high mineral content, this soil amendment also acts as an inert dust capable of increasing the adsorption of the insect wax coating, leading to desiccation and, consequently, pest management. In addition to the direct increase in productivity, due to concerns about climate change, a strategy that allies productivity with CO₂ mitigation needs to be further explored and encouraged. Further studies are needed in this field in order to better comprehend the variability among the vast diversity of crops, soil conditions, and pest management strategies, among others, to allow this approach to be fully widespread and applied, looking not only for financial compensation and environmental preservation but also possibly playing a key role in global food security in the near future [55,56].

6. Environmental and Sustainability Perspectives

The agricultural application of crushed rock may provide environmental and sustainability benefits, provided that the materials undergo proper geochemical characterization, safety screening, and physical processing prior to field placement. Figure 2 summarizes these main benefits, which include the valorization of industrial and mining by-products through regulated processing pathways, reduced dependency on imported synthetic inputs, and potential atmospheric CO₂ removal via soil–mineral interactions. Figure created by the authors based on the reviewed literature.

6.1. Circular Economy and Waste Valorization

Sustainable mining can be used to mitigate anthropogenic climate change, presenting great potential to supply agriculture in a complementary and synergistic way, with fertilizers already in use []. The use of already extracted residues, such as basalt rock powder (PRB) [25] and silicate rock powder (SRP) [], can reduce the demand for primary mineral extraction specifically targeted for agricultural inputs. These by-products, often accumulated in global stocks for decades, allow for resource efficiency without the environmental footprint of dedicated new extractions [57]. However, rather than an immediate or direct field application, transforming these materials into safe remineralizers follows a regulated circular-economy route. This process requires essential preprocessing steps, including geochemical characterization, ecotoxicological screening to ensure trace elements remain within safe regulatory limits, and physical processing (such as grinding and particle-size standardization) prior to soil application [25].

In this sense, materials that would otherwise end up in landfills or stored in waste piles are transformed into valuable commodities. The implementation of the life cycle assessment (LCA) methodology allows us to quantify how the application of this circular model preserves natural resources and mitigates the risks of pollution and soil degradation [57,58].

Chami et al. [58] conducted groundbreaking research on the LCA of fertilizers, aiming to show that adopting a circular economy model in the sector is essential to reduce pressure on natural resources and mitigate the effects of climate change. By reformulating products through waste valorization, replacing virgin and imported raw materials (such as urea from North Africa) with local industrial by-products (such as ammonium sulfate from the plastics industry), the study found a considerable decrease in global warming potential, ranging from 4.4% to 9.2%.

Furthermore, the use of local materials or materials sourced from nearby locations significantly reduces emissions associated with transportation. Russell et al. [59] confirmed that ameliorated mining waste product can be applied to promote inorganic carbon sequestration, with a carbon capture rate 4.5 times higher than that of untreated soils and improve the fertility of acidic soils.

6.2. Reduction in Fertilizer Dependence

Reducing dependence on fertilizers makes agriculture safer, more stable, and more economical. The main reasons for this strategy include reducing external vulnerability and costs for producers, strengthening food security, promoting local sources, and fostering sustainability.

Dependence on conventional fertilizers involves interconnected economic, logistical, and environmental challenges. Studies addressing fertilizer supply indicate that reliance on imported inputs increases the vulnerability of agricultural systems to price fluctuations, geopolitical conflicts, sanctions, exchange-rate variations, and logistical disruption [60]. These constraints may be further intensified by the distance between fertilizer production centers and agricultural regions, which increases transportation requirements and associated costs []. At the same time, the environmental impacts associated with the inappropriate or excessive use of conventional fertilizers, including soil and water contamination, eutrophication, and greenhouse gas emissions, reinforce the need to diversify nutrient sources [60,61].

Taken together, these findings suggest that locally available mineral resources, including suitably characterized crushed rock wastes, may contribute to reducing some of these vulnerabilities by complementing conventional fertilization [25,60,61]. However, their contribution should not be interpreted as a complete replacement for conventional fertilizers, because their agronomic effectiveness depends on mineral composition, nutrient-release kinetics, soil properties, crop requirements, and local availability. Therefore, the main potential of crushed rock wastes lies in diversifying nutrient sources and partially reducing dependence on external inputs within regionally adapted fertilization strategies.

6.3. Potential CO₂ Removal Through Enhanced Weathering

Enhanced Rock Weathering (ERW), based on the incorporation of crushed calcium and magnesium-rich silicate minerals into soils, has been investigated as a potential strategy for atmospheric CO₂ removal [62]. During silicate weathering, minerals may react with CO₂ and water, releasing base cations and converting part of the carbon into dissolved inorganic carbon, mainly bicarbonate ions (HCO₃⁻) [63,64]. However, the magnitude and persistence of CO₂ removal depend on rock geochemistry, mineral dissolution rates, soil properties, climatic conditions, and the fate of dissolved carbon. Therefore, mineral weathering should not be interpreted as direct evidence of equivalent or permanent CO₂ removal [62].

In the United Kingdom, Harrington et al. [65] found that ERW could remove 4.9 to 8.1 Mt of atmospheric CO₂ annually. The authors carried out an analysis and found that 7% of the main cations present in UK rivers come from the weathering of silicate rocks and 49% come from carbonates. Also in that region, Buckingham et al. [] concluded that five years of annual basalt application at 100 t/ha has the potential to sequester 1.3 Mt of atmospheric CO₂ annually on agricultural land, which is equivalent to 3% of current CO₂ emissions from British agriculture.

Direct measurement of CO₂ removal in the field using ERW is a strategy associated with carbon farming, which consists of a set of agricultural practices that seek to increase carbon storage in the soil and/or remove CO₂ from the atmosphere, while maintaining agricultural production [66]. There are still few field studies on this practice.

Holden et al. [67] applied 50 t/ha of ground basalt to agricultural soil cultivated with sugarcane in an acidic tropical soil in northeastern Australia from 2018 to 2022. The authors found an increase in soil pH and extractable Mg and Si at a depth of 0–0.25 m, indicating significant weathering of the basalt, but showed no increase in crop productivity and no significant CO₂ flux (0.026 t/ha). These findings illustrate that evidence of mineral weathering does not necessarily translate into measurable atmospheric CO₂ removal under field conditions.

The study conducted by Wu et al. [63] in a 20-year-old larch (Larix olgensis) plantation in northeast China investigated the effects of ERW via wollastonite (CaSiO₃) application on carbon sequestration and forest growth. In the first year, the application reduced soil CO₂ flux by 16.5% (5 t of CaSiO₃/ha) and 15.4% (10 t of CaSiO₃/ha). In the second year of application, there was an increase of 4.1% (5 t of CaSiO₃/ha) to 5.1% (10 t of CaSiO₃/ha) in CO₂ fluxes compared to the control. The authors attributed the differences found to the greater stability of soil organic carbon and to the fact that wollastonite weathering reacts with CO₂ derived from root and microbial respiration. Regarding forest growth, tree biomass exhibited an upward trend, indicating a possible contribution of vegetation growth to carbon sequestration in the ecosystem.

These studies show that agricultural use of rock wastes may combine soil improvement with potential climate mitigation benefits. The strategy includes adding value to waste from mining and industrial processes, reducing improper disposal and encouraging a circular route for the reuse of materials.

7. Current Limitations and Future Challenges

7.1. Potential Release of Toxic Elements

The agricultural use of crushed rock wastes as soil remineralizers can provide macro- and micronutrients and promote the valorization of mineral residues. However, an important drawback is the possible presence and release of potentially toxic elements, including Cd, Cr, Ni, Pb, As, Hg, Cu, and Co. Their environmental risk depends on their concentrations, speciation, mobility, and bioavailability. Elevated concentration and bioavailable fractions can affect soil quality, crop safety, and human health. In addition, the release of metals during rock weathering can transfer them from soil to cultivated plants. Indeed, the composition of crushed rock waste depends on the mineralogy of its original geological source [,68,].

Wang et al. [69] investigated the distribution and accumulation of Cd, As, Hg, Cr, Ni, Cu, Zn, and Pb in basalt bedrock, basalt-derived topsoil, and cultivated crops in western Jiangsu Province, China. Their results showed that basaltic bedrock contained high concentrations of Cr (176–416 mg kg⁻¹), Ni (72–280 mg kg⁻¹), and Zn (97–131 mg kg⁻¹) and moderate concentrations of Cu (48.7–97.7 mg kg⁻¹). These elements were also detected at elevated levels in the corresponding agricultural topsoils, especially Cr (86–279 mg kg⁻¹), Ni (45–269 mg kg⁻¹), Zn (57–127 mg kg⁻¹), and Cu (27–80 mg kg⁻¹). Therefore, these results indicated that the metals were transferred from the basalt to the soil during weathering. Moreover, the presence of these metals was attributed to mafic minerals, such as olivine and pyroxene, in which elements, such as Cr, Ni, and Cu, can substitute for Mg and Fe in the mineral lattice. Indeed, the study demonstrated that total soil metal concentrations were insufficient to predict crop contamination. For Ni, grain accumulation was more influenced by soil pH and bioavailable fractions than by total Ni concentration, with lower pH favoring greater metal availability and transfer to plants. The rice grains accumulated higher Ni concentrations than wheat grains, with values of 1.22–9.34 mg kg⁻¹ in rice compared with 0.41–3.46 mg kg⁻¹ in wheat.

For instance, the environmental risk associated with crushed rock wastes should be determined based on the total concentration of toxic elements in the crushed rock wastes and their speciation, mobility, and bioavailability. This information can be used to understand metal desorption from soil particles and, consequently, plant uptake and grain accumulation. Moreover, it is important to comprehend how plant physiology and rhizosphere conditions affect the accumulation of potentially toxic elements. These processes are controlled by several factors, including mineralogical composition, particle size, weathering rate, soil pH, organic matter, redox conditions, microbial activity, and crop species. Environmental risk assessment of crushed-rock wastes should consider not only the total concentrations of potentially toxic elements but also their mineralogical occurrence, chemical speciation, mobility, leachability, and bioavailability. Therefore, before their use as soil remineralizers, crushed rock wastes should be studied considering chemical and ecotoxicological characterization, including total elemental analysis, leaching assays, bioavailability tests, plant uptake studies, and long-term field monitoring.

It should be mentioned that quantitative scenario analyses of trace element accumulation in conventional agricultural remineralization remain scarce. However, studies developed for high-rate enhanced rock weathering could be adapted to evaluate the use of crushed rock waste at lower rates and with longer reapplication intervals. Dupla et al. [70] estimated trace element accumulation by combining rock composition, application rate, initial soil trace element concentrations, soil incorporation depth, weathering assumptions, leaching, crop removal, and regulatory thresholds. This information was used to estimate the time required for soil trace element concentrations to exceed regulatory thresholds. Similar calculations could be performed for crushed rock wastes applied at lower and less frequent agronomic doses than those commonly proposed for enhanced rock weathering. Therefore, hypothetical low-, moderate-, and high-dose remineralization scenarios could be simulated by varying the application rate, reapplication interval, and number of consecutive applications, based on measured concentrations of potentially toxic elements. This would allow the estimation of cumulative metal inputs over successive applications and could support decisions on maximum application rates, reapplication intervals, and long-term monitoring requirements. Indeed, long-term monitoring should include soil background metal concentrations, cumulative metal loading, soil pH, organic matter content, leachable and bioavailable fractions, and metal accumulation in edible plant tissues. Considering that uptake of potentially toxic elements can vary among crop species and cultivars, monitoring should be crop-specific. If these indicators show increasing bioavailability, crop accumulation, or values approaching regulatory limits, application rates should be reduced, reapplication intervals extended, or the material should be discontinued.

Based on the whole discussion in this section, a simple risk-screening process can be proposed to guide the evaluation of crushed rock waste for agricultural use. This process summarizes the main risk factors discussed in this section and integrates source identification, total elemental composition, mineralogical occurrence, mobility, bioavailability, plant uptake, and cumulative loading under repeated applications (

Table 3. Simple risk-screening process for crushed rock wastes before agricultural use.

Step	Screening Parameter	Purpose	Practical Decision
1	Geological origin and processing history	Identify materials that could contain higher concentrations of potentially toxic elements	Use as a preliminary warning step; prioritize detailed assessment when high-risk sources are identified
2	Total elemental composition	Determine whether the material contains useful nutrients and whether potentially toxic elements, such as Cd, Cr, Ni, Pb, As, Hg, Cu, and Co, occur at concentrations that could limit agricultural use	Compare with regulatory limits; materials exceeding legal thresholds should be restricted or excluded from agricultural use
3	Mineralogical occurrence	Evaluate whether nutrients and potentially toxic elements are present in resistant phases or in minerals that may weather more easily	Apply greater caution when potentially toxic elements are associated with reactive or easily weatherable minerals
4	Mobility and leachability	Estimate the potential release of potentially toxic elements into soil solution	Restrict application when leachable fractions are high, particularly in soils where pH, redox conditions, or low adsorption capacity could favor the mobility of potentially toxic elements
5	Bioavailability	Estimate the fraction of potentially toxic elements that could become available for root uptake	Require crop-specific evaluation, dose reduction or longer reapplication intervals when bioavailable fractions are high
6	Plant uptake	Verify whether potentially toxic elements are transferred to roots, shoots or edible tissues	Compare concentrations in edible tissues with applicable food safety limits; restrict or discontinue use when crop accumulation exceeds or approaches regulatory thresholds
7	Repeated-application risk	Estimate cumulative metal loading over successive applications	Define maximum application rates, reapplication intervals and monitoring frequency
8	Long-term field monitoring	Follow changes in soil pH, organic matter content, total concentrations, leachable/bioavailable fractions and crop tissues	Reduce dose, extend reapplication interval, or discontinue the material if risk indicators increase or approach regulatory limits

).

7.2. Technical and Agronomic Limitations

The agronomic efficiency and large-scale application of crushed rock waste have some limitations that should be addressed. Their performance is controlled by the interaction of several factors, including mineralogical composition, particle size, soil pH, moisture availability, weathering rate, climatic conditions, and crop species. Therefore, the nutrient release capacity of these materials depends on the type of minerals present, their dissolution kinetics, and the environmental conditions. The weatherability of minerals is related to their crystallization history, chemical composition, crystal structure, and structural defects. Minerals that crystallize at high temperatures, such as olivine and anorthite, are less stable in a weathering environment. Their structures and chemical compositions result in enhanced susceptibility to hydrolysis, cation leaching, and transformation into secondary minerals. In contrast, minerals that crystallize at lower temperatures, such as quartz, muscovite, and K-feldspar, are more resistant to weathering. Their higher resistance is related to their more polymerized silicate structures, stronger Si–O and Al–O bonds, and lower amount of easily leachable cations, such as Ca²⁺, Mg²⁺, and Fe²⁺. For this reason, under similar physicochemical conditions, basaltic waste would be expected to weather faster and release nutrients more readily than granitic waste. As previously mentioned, this behavior can be associated with its mineralogical composition, which usually includes more weatherable minerals, such as olivine, pyroxene, Ca-rich plagioclase, and amphibole. Nevertheless, granitic waste is usually composed of more resistant minerals, including quartz, K-feldspar, Na-rich feldspar, muscovite, and biotite [,71,72].

The chemical speciation of elements released from crushed rock wastes also controls their mobility, saturation state, secondary precipitation, and bioavailability in soil. Ionic speciation is pH-dependent; thus, soil pH can affect mineral dissolution kinetics and weathering reactions by influencing both surface reaction mechanisms and the release of ions in solution. Particle size is one of the main physical factors controlling the weathering of crushed rock wastes because it influences the mineral surface area exposed to soil solution. In general, finer particles are expected to weather faster than larger particles due to their higher surface area per unit mass. It should be mentioned that the effective reactive surface area also depends on the porosity and microstructure of crushed rock waste, due to the fact that some surfaces can be unreactive, coated, or physically inaccessible to soil solution. Moreover, the dissolution usually occurs at reactive sites, such as defects, dislocations, fractures, and microstructural heterogeneities [72,73,74]. Although grinding can enhance nutrient release from crushed rock wastes, particle size alone is insufficient to predict weathering kinetics. Therefore, the advantages of grinding should be balanced against the energy demand, cost, and dust-generation risks associated with producing very fine powders.

Biological and climatic factors also influence the weathering of crushed rock wastes. In agricultural soils, mineral dissolution is influenced by plant roots, microorganisms, and organic matter, which can modify rhizosphere pH, release organic ligands, complex dissolved ions, and remove nutrients from the soil solution through plant uptake. These processes can maintain chemical disequilibrium and promote further mineral dissolution. Climatic conditions, including temperature and precipitation, also regulate weathering rates because temperature affects reaction kinetics, whereas water availability controls hydrolysis, solute transport, and the removal of weathering products [,71,75]. Therefore, warm, humid, and biologically active soils may provide more favorable conditions for mineral weathering than cold and dry environments. This reinforces the need for further studies to evaluate rock powders under site-specific soil, crop, and climatic conditions rather than assuming universal performance.

Among the strategies proposed to overcome the low dissolution rate of rock powders, biological treatments have attracted increasing attention due to their sustainability and potential economic feasibility. Unlike chemical or thermal activation, which can require high energy inputs or generate wastewater, biological approaches rely on microorganisms, organic compounds, and rhizosphere processes to promote mineral weathering under mild conditions. These mechanisms include chelation, pH modification, redox reactions, biofilm formation, and physical disruption by roots and hyphae [75,]. However, the biological contribution to weathering is context-dependent, and organisms can either enhance weathering or, under some conditions, inhibit abiotic dissolution through bioprotection. Therefore, the use of biological treatments to improve nutrient release from crushed rock wastes should be evaluated under realistic soil–plant–microorganism conditions, considering mineral type, microbial community, carbon availability, moisture, pH, and long-term field performance.

Zhang et al. [76] studied bacteria capable of co-solubilizing P, K, and Si isolated from acidic forest soil and evaluated their effect on nutrient mobilization and rice growth. The soil used in the study had low available P, K, and Si contents of 4.9, 34.5, and 23.0 mg kg⁻¹, respectively, and a pH of 4.95 ± 0.03. Six isolates belonging to Pseudomonas, Agrobacterium, Collimonas, Burkholderia, and Paraburkholderia reduced pH by up to 4.6 and solubilized up to 400 mg L⁻¹ P, 12.7 mg L⁻¹ K, and 92 mg L⁻¹ Si. When inoculated into soil at 1 × 10⁷ CFU g⁻¹, these bacteria increased rice seedling dry weight by 26–163%, P accumulation by 24–215%, K accumulation by 36–170%, and Si accumulation by 24–177% after 35 days. These results indicate that mineral-weathering bacteria can represent a biological strategy for improving nutrient mobilization from poorly soluble mineral sources without requiring external chemical acidification treatments.

Despite the growing number of studies evaluating crushed rock waste as soil remineralizers, comprehensive LCA and TEA remain limited. Most studies focus on mineralogical composition, nutrient release, soil fertility, and crop response, whereas fewer studies quantify the environmental burdens and economic feasibility associated with processing, grinding, transport, and large-scale field application [77,78,79,80]. This represents an important gap because the sustainability of rock powder use depends not only on agronomic performance, but also on energy demand, transport distance, application rate, replacement of conventional fertilizers, potential CO₂ removal, heavy metal monitoring, regulatory costs, and farmer adoption costs. Therefore, future studies should integrate agronomic research with LCA and TEA to determine whether the use of crushed rock waste provides environmental and economic advantages under realistic regional conditions.

8. Conclusions

The studies addressed in this review show that crushed rock wastes, when directed toward agricultural application, have a potential that goes beyond their use as an alternative source of nutrients. These materials may contribute to soil fertility, partially reduce dependence on conventional fertilizers under suitable agronomic conditions, and, when sufficiently reactive Ca- and Mg-bearing silicates are used, potentially contribute to net CO₂ removal. However, the results do not show a consistent response, as some studies report that, after remineralizer application, material weathering and the resulting changes in soil chemical properties do not always lead to productivity gains. Therefore, the studies show that nutrient release or even rock dissolution alone is not sufficient to determine the effectiveness of a remineralizer.

As a first research priority, future studies should focus on long-term field trials to assess residual effects and better represent real conditions of use, considering different crops, soils, application rates, and application methods. Along with this, greater standardization of experimental designs, cultivation conditions, application rates, and evaluation periods would further improve the characterization of these materials and allow more consistent comparisons among studies. Although Brazil already has specific criteria for the registration and use of remineralizers, regulatory and experimental differences at the international level still make it difficult to compare results and establish broader parameters for the use of these materials. In this context, parameters such as mineral dissolution rates and acceptable limits for potentially toxic element leaching still need to be better standardized for the evaluation of these materials.

Thus, advances in soil remineralization using rock wastes do not simply depend on finding new materials, but on better selecting and characterizing those that are already available. In addition, studies on the economic feasibility of applying these wastes on a large scale are still limited, particularly when considering the availability of large quantities of the same type of waste, transport distances to the application site, their use under different crop rotation systems, and variations in environmental conditions over time. Processing and application costs should also be considered, since a material that shows promising results under experimental conditions may not provide the same advantages when applied under real conditions and at a larger scale. Therefore, as a second research priority, life cycle assessments combined with techno-economic analyses should be further developed to identify the conditions under which the use of these wastes is actually viable. This approach could help bridge the gap between results obtained at the experimental scale and their potential application under real conditions, while supporting the regional use of these materials in agriculture. Finally, biological approaches, particularly those involving mineral-weathering microorganisms and their association with organic amendments, should be further investigated as strategies to improve mineral dissolution and nutrient availability.