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Article

Cultivating Lavandula dentata in Coal-Waste Technosols: Implications for Essential Oil Production and Post-Mining Restoration

by
Arthur Cesa Venturella
1,
Eduardo Kercher de Oliveira
1,
Jéssica Weiler
2,
Eduardo Miranda Ethur
3 and
Ivo André Homrich Schneider
1,*
1
Laboratório de Tecnologia Mineral e Ambiental, Programa de Pós-Graduação em Engenharia de Minas, Metalúrgica e de Materiais, Escola de Engenharia, Universidade Federal do Rio Grande do Sul (UFRGS), Av. Bento Gonçalves 9500, Bairro Agronomia, Porto Alegre CEP 91501-970, RS, Brazil
2
Laboratório de Estudos Ambientais, Universidade Federal do Pampa, Av. Pedro Anunciação 111, Vila Batista, Caçapava do Sul CEP 96570-000, RS, Brazil
3
Programa de Pós-Graduação em Biotecnologia, Universidade do Vale do Taquari, Av. Avelino Talini 171, Bairro Universitário, Lajeado CEP 95914-014, RS, Brazil
*
Author to whom correspondence should be addressed.
Mining 2026, 6(1), 25; https://doi.org/10.3390/mining6010025
Submission received: 24 December 2025 / Revised: 6 March 2026 / Accepted: 16 March 2026 / Published: 21 March 2026
(This article belongs to the Topic Environmental Pollution and Remediation in Mining Areas)
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Versions Notes

Abstract

This study assessed the feasibility of cultivating Lavandula dentata in Technosols produced from fine and coarse coal mining waste, focusing on plant development, substrate functionality, essential oil production, and post-mining ecosystem restoration. The Technosols were formulated using coal waste from the Moatize Coal Mine, Mozambique, combined or not in different configurations with agricultural soil and amended with sewage sludge (3% organic matter) and chemical fertilizer to ensure adequate nutrient availability. The experiments were conducted in 30 L containers, performed in triplicate for each experimental group. All settings allowed good plant growth, although the treatment that used only fine waste presented the closest performance to agricultural soil in terms of the production of aerial biomass. In this case, the dried biomass production of the shoots reached an average of 165 g per pot over 8 months (with a standard deviation of 20.3). The study showed a positive correlation between plant development and the available water capacity of the substrates. The plant tissue of L. dentata, in all the Technosols configurations studied, presented a similar composition to the control, with a biomass composition within the standard range established by the literature. The essential oil production ranged from 0.3 to 0.7% (m/m), averaging 0.5% (m/m), with chemical characteristics also alike the control trial. Technosols composed of coal waste from Moatize appear to be an alternative, both to provide a suitable destination for mining waste and to provide conditions for the revegetation and recovery of degraded areas by coal mining. This avoids the commissioning of nearby areas to supply soil for the restoration process. L. dentata, in addition to its various medical, ornamental, and aromatic uses, has potential as an “ecological trigger” in the restoration process with environmental and socioeconomic benefits.

Graphical Abstract

1. Introduction

Coal is one of the top two sources of primary energy worldwide [1]. Its exploration has been responsible for serious environmental degradation, such as landscape and vegetation modification [2,3], the physical and chemical deterioration of soils [4,5,6], and changes in water quality and hydrological cycle at a watershed scale [7,8]. In all continents, coal mining has caused severe environmental disruption, highlighting the urgent need for policies and appropriate mitigation and rehabilitation strategies [9]. It is imperative to develop and promote sustainable recovery techniques, minimizing additional environmental damage, while restoring the functionality of the mining territory [10].
The use of Technosols emerges as a promising solution for the rehabilitation of mined lands [11]. Scientific publications have addressed the advances to those produces with coal waste [12,13,14,15,16,17,18,19,20,21,22]. Physical processing for the removal or chemical transformation of sulfides (e.g., pyrite) as well as particle size adequacy might be necessary. Monitoring pH and/or the use of amendments for acidity control as well as the addition of organic matter and nutrients are crucial. Among the organic additives, sewage sludge [12,15,16,17,20], organic compost from urban waste [13,22], brewery waste [14], spent mushroom compost [17], rice and poultry agro-industry waste [18,19], and biochar [21] have been some of the choices. This approach reduces the demand for natural topsoil and contributes to sustainable waste management. When implemented in ecosystem restoration projects, these constructed soils can serve as effective substrates to initiate ecological succession [23] or to turn mined brownfield areas into green spaces for the sustainable development of urban areas [24].
The province of Tete, Mozambique, in Africa, is recognized as one of the largest coal deposits in the southern hemisphere [25,26]. Coal waste from the Chipanga Seam reveals distinctive characteristics, including low acid generation potential, due to the presence of carbonates and a low concentration of pyrite [27,28]. This behavior enables its use as a substrate for plant growth, avoiding the haulage of topsoil, a practice increasingly criticized for its environmental impacts.
A previous study considering various compositions of coarse and fine tailings from the Moatize Mine indicated that the materials served as a substrate for the sequential growth of species such as alfalfa, corn, teff, and even opportunistic species (during the pandemic period) (Figure 1). The different material compositions make up well-drained substrates, with distinct water retention capacities [20]. However, it is still important to understand how coal waste particle size (fine vs. coarse) might interact with water retention capacity, microbial communities, and consequent plant growth. Besides this, most of the previously introduced species were small in size or had short life cycles.
Some authors have suggested phytoremediation using aromatic plants as a safe approach for the recovery of degraded areas with potential economic return through the production of essential oils [29,30,31]. Herein, we decided to introduce Lavandula dentata, a shrubby species adapted to well-drained soils with multiple uses in pharmaceutical and personal hygiene products. It belongs to the genus Lavandula, which contains 47 known species of the family of Lamiaceae. It is an evergreen and perennial plant, native to Mediterranean regions such as France, Italy, Spain, and Andorra [32,33]. It is also cultivated in many other countries around the world, due to its broad adaptability to diverse edaphoclimatic conditions, drought resistance, and capacity to accumulate heavy metals without compromising the quality of the extracted essential oil [34,35,36].
Concerning Lavandula growth in coal-mined areas, previous work carried out by the Appalachian Botanical Company, in West Virginia, USA, reported the success of the recovery of areas degraded by coal mining and an economic “just transition” with job offers for local communities [37]. Another recent work was reported in Serbia, growing Lavanda augustifolia on reclaimed soil from coal mining with the aim to produce and characterize L. augustifolia essential oil [38].
Within this context, the present study investigated Technosols formulated from the coal waste of different particle sizes combined with sewage sludge and agricultural soil, aiming to assess their viability as substrates for the growth of Lavandula dentata. The chemical properties of the Technosols and the vegetative performance of the species under different substrate configurations were monitored. Furthermore, the biological activity in the substrates was evaluated by measuring the microbial biomass carbon (MBC) and the soil microbial respiration (SMR), as well as the effect of the available water capacity (AWC). By exploring the cultivation of a commercially valuable plant in constructed substrates, this study contributes to the advancement of innovative and sustainable solutions for the restoration of coal-mined degraded areas.

2. Materials and Methods

2.1. Coal Waste and Sewage Sludge Samples

The coal wastes utilized in this study originated from the province of Tete, Mozambique, in Africa (16°07′54″ S, 33°46′00″ E). They were collected during the coal preparation process of the Chipanga Seam, with coarse particles (1 mm < d < 50 mm) generated from dense medium cyclone operations, and fine particles resulting from processing through spirals, elutriation (0.25 mm < d < 1 mm), and flotation (d < 0.25 mm). The characteristics of both materials in terms of their proximate analysis, sulfur speciation, mineralogical composition, and acid generation behavior can be found in [27]. In summary, they contain 58 to 59% ash, about 1% sulfur, half of which is pyritic sulfur, and a balance between acid and alkaline minerals that leads to neutrality. Metals are present at levels that would not restrict their use as agricultural soil (according to the standards of various countries).
The source of organic matter was the sludge from the activated sludge process of a municipal sewage treatment plant, after aerobic digestion to remove pathogens. The sludge contained 52.5% organic matter (OM) and 0.5% organic nitrogen. Details on the collection, preparation, and other characteristics of this treatment plant residue are described in the previous work by Firpo et al. [15]. Agricultural soil was used as the control, and it was classified as a Red Nitisol [39].

2.2. Technosols Manufacture and Their Characterization

All Technosols were manufactured in 2018 through the combined use of coal waste as raw material and sewage sludge as the source of organic matter and nutrients. Plant growth experiments, with successive cropping cycles, were conducted in 30 L polyvinyl chloride (PVC) containers 35 cm high and 30 cm in diameter, to which about 20 kg of material was added, as shown in Figure 2. It is important to note that, although the cultivation of L. dentata was carried out from November 2021 to May 2024, the present study focuses exclusively on the cultivation period from November 2021 to June 2022.
The soils were designed comprising seven configurations, each one performed in triplicate with the following compositions (Figure 2):
  • Fine coal waste;
  • Fine coal waste and coarse coal waste, composing two seams;
  • Fine coal waste and coarse coal waste as a mixture;
  • Agricultural soil, fine coal waste, and coarse coal waste, composing three seams;
  • Agricultural soil and a mixture of fine coal waste and coarse coal waste, composing two seams;
  • Agricultural soil, fine coal waste, and coarse coal waste as a mixture;
  • Agricultural soil used as the control.
Sewage sludge was added to all the containers to obtain 3% of soil organic material (SOM). This amount of SOM is suitable for most soils and sufficient to support plant development [40]. Table 1 depicts the composition of the Technosols in terms of the mass of the materials utilized.

2.3. Growth Study of Lavandula Dentata

Since the establishment of the experimental design in December 2018, several plant species have been cultivated in succession, including Medicago sativa, Zea mays, Eragrostis tef, spontaneous vegetation, and, most recently, Lavandula dentata, which is the focus of this study. In November 2021, prior to the introduction of L. dentata, all spontaneous vegetation was removed. Each pot was chemically fertilized with 15 g of NPK 10:10:10, followed by the transplantation of an L. dentata seedling approximately 7 cm in height. To simulate the leaf litter layer and aid in moisture retention, approximately 20 g of dry leaves from the gardening of the university campus were added to the surface of each pot.
The cultivation was carried out in Rio Grande do Sul, southern Brazil (30°04′33″ S, 51°07′06″ W). Soil samples were collected in March 2022, and plant shoots were harvested in June 2022. After pruning, the plants sprouted again and resumed their growth. They remained until May 2024, when the experiment was interrupted by the unprecedented flood that hit the state of Rio Grande do Sul [41,42]. The region features a humid subtropical climate (Cfa, Köppen classification), with temperatures ranging from 14 to 29.5 °C, an annual mean of 19.7 °C, relative humidity between 72% and 82%, and a monthly precipitation between 109 and 144 mm. Throughout the experiment, the pots were arranged in a randomized layout and exposed to natural environmental conditions, including direct sunlight and rainfall. Local precipitation records between an experiment in November 2021 and June 2022 indicated an average of 117.3 mm per month [43]. Irrigation with rainwater was applied only when necessary and did not exceed 20 mm above natural rainfall levels. Figure 3 provides images of Lavandula dentata growth.

2.4. Soil, Plant Tissue, and Essential Oil Analysis

For the fertility analysis of the soil, samples were collected using a tubular sampler with a diameter of 3 cm, capturing material from the entire soil profile. For each configuration, one sample was taken per pot, totaling twenty-one samples (three per configuration). All samples were homogenized to ensure the representation of all soil horizons for subsequent analyses. Samples were analyzed for pH, soil organic matter (SOM), cation exchange capacity (CEC), aluminum saturation, macronutrients (nitrogen, phosphorus, potassium, calcium, and magnesium), and micronutrients (copper, zinc, manganese, iron, and boron), following the analytical procedures established by Embrapa [44]. The same tubular sampler was used to collect the 10 cm topsoil to measure microbial biomass carbon (MBC) [45], and soil microbial respiration (SMR) [46]. Based on these data, the microbial metabolic quotient (qCO2), defined as the ratio between SRM and MBC was calculated [47].
The bulk density of Technosols was determined previously [20] under two conditions: After a dry period (dry bulk density) and after a period of heavy rainfall (saturated bulk density). The difference in mass between the two conditions was converted into water volume, using the assumption that water has a density of 1 kg L−1, and expressed as liters of water retained per cubic meter of soil, an estimate of the Available Water Capacity (AWC) (also named Field Capacity) [48]. Although this procedure was carried out on a larger scale and using rainwater, it followed the methodology described by Amaral Filho et al. [14].
We also evaluated the plant tissue in terms of the shoot mass and composition. After 223 days of cultivation, the pruning of the apical and basal branches, containing leaves and flowers, was carried out. The collected shoots were dried at 60 °C in a constant flux oven, weighed, and analyzed in terms of the plant tissue composition. The concentrations of macro- and micronutrients were analyzed and compared as recommended by the Handbook of Reference Methods for Plant Analysis [49].
The essential oils (EOs) were extracted according to the methodology presented in the Brazilian Pharmacopoeia [50]. The dried plant materials were chopped into fine fragments in a cutting mill. EOs were obtained from hydrodistillation performed in a modified Clevenger apparatus. The modification was the introduction of a Graham condenser at the air outlet by means of ground joint NS 14/23 (Figure 4). Each sample was subjected to an extraction period of 3.5 h. Then, the extracted liquid was left to rest for phase separation, and, with the aid of anhydrous sodium sulfate (Synth®), the residual water was removed. The EOs were stored in amber bottles under refrigeration (approximately 6 °C).
The yield of the EOs was represented as a percentage (%), where the total amount of biomass used in the extraction represented 100% and was calculated using Equation (1).
Y = m E O S ·   100 m b ,
where
Y = yield (%);
m E O S = mass of essential oil (g);
m b = L. dentata biomass (g).
The identification of the chemical constituents present in the EOs was performed using a gas chromatograph with a temperature gradient, coupled to a mass detector. The analysis was performed at the Instrumental Center of the Technological Center for Food Research and Production (CTPPA) of Univates. Aliquots of 1.5 μL of the EOs were solubilized in 1.5 mL of double-distilled n-hexane (Merck, Darmstadt, Germany) and injected into a gas chromatograph (model GC2010 Plus, Shimadzu, Kyoto, Japan) coupled to a mass detector (model GCMS-QP2110 Ultra, Shimadzu), operated at 70 eV, in a fused silica capillary column (Rtx®, 5MS − 30 m × 0.25 mm × 0.25 μm). Helium was used as the carrier gas. The samples were injected in the order of 1 μL, using an autoinjector (AOC-5000 Plus, Shimadzu, Kyoto, Japan). The following conditions were used for the analysis: Injector temperature: 240 °C; injection mode: Split ratio 1:20 with a purge of 3.0 mL min−1; gas flow control: linear speed; carrier gas flow: 1.0 mL min−1; program: 50–290 °C (4 °C min−1); mass spectrometer interface temperature: 280 °C, ion source temperature: 260 °C [51]. The constituents were identified using the Kovats Retention Indices (RIs), with reference to a homologous series on n-alkanes, from the mass spectral database (NIST MS Library v.2.0), and comparison with the mass spectra found in the literature [52,53].

2.5. Statistical Analysis

The results of the plant growth and the yield of essential oil extraction were expressed as the mean percentage ± standard deviation. Analysis of variance (ANOVA, single factor) with a significance level of α ≤ 0.05, followed by Tukey’s Honestly Significant Difference (HSD) post hoc test for multiple comparison of means to identify significant differences among the different Technosols configurations studied. Statistical analysis of the data was performed using OFFICE EXCEL® software.

3. Results and Discussion

From their initial preparation, the Technosols provided conditions for plant development. The pH remained within a suitable range for plant growth—between pH 5.7 and 6.5—and the SOM, CEC, and micro/macronutrient values were also within the established reference ranges [54,55]. However, during the planting of teff, a decline in phosphorous and potassium was observed [20]. To overcome this deficiency, chemical fertilization was carried out with NPK 10:10:10 three months before introducing the L. dentata seedlings, and a new soil analysis was carried out (Table 2).
Compared to the previous soil analysis, there was an increase in the SOM and CEC, provided by past teff (2019 and 2020) and spontaneous vegetation (2020 and 2021) growth, while nutrients were retained in favorable concentrations. The pH was shown to be slightly below the range of 6.0 to 6.5 [54] for optimal nutrient absorption by most commercial crops. However, Wiethölter [55] considered the range of 5.5 to 6.0 also acceptable; in this case, treatments I and VII fell within this range, and treatments II, III, IV, V, and VI were borderline. The concentration of organic matter (SOM) and cationic exchange capacity (CEC), in all situations, was compatible with that of healthy soil. The concentrations of the macronutrients N, P, and K were adequate, while Ca and Mg exceeded the reference values. The micronutrients Fe and B were in the expected range, and the Cu, Zn and Mn levels surpassed those necessary for vegetation development [54]. The aluminum levels, which can be a limiting factor for plant growth, were zero or very low in all treatments.
Information regarding the microbial biomass carbon, soil microbial respiration, and microbial metabolic quotient in experiments I, III, and VII is presented in Figure 5a–c. The soil microbial biomass carbon (MBC) represents the total carbon content of the microbial community present in the system and may range from 30 to 2780 mg C kg−1 soil in natural soils [56]. Herein, the values found were 426 mg C kg−1 soil in treatment I (containing only fine coal waste), 595 mg C kg−1 soil in treatment III (with both fine and coarse waste) and reached 716 mg C kg−1 soil in the control. These values are high compared with those reported for other coal waste bearing Technosols. For instance, Weiler and Tassinari [21] reported values ranging from 180 to 310 mg C kg−1 soil after 120 days of experimentation using effective microorganisms as inoculants. Likewise, Moreno-Barriga et al. [57] presented data for Technosols amended with biochar, with a MBC ranging from 150 to 300 mg C kg−1 soil in 90 days. This may be attributed to the longer duration of the herein experiment, which has allowed for the development of a more established root system and the accumulation of stable organic matter, both of which contribute to a more mature and stable microbial community.
In turn, the soil microbial respiration (SMR) also showed satisfactory values, ranging from 80 to 94 mg CO2 kg−1 soil a day−1. These results are very similar to those reported by Weiler and Tassinari [21], who observed values between 80 and 190 mg CO2 kg−1 soil a day−1, as well as to the findings of Zornoza et al. [58], which ranged from 20 to 200 mg CO2 kg−1 soil a day−1. This parameter is particularly important because it reflects the abundance and functional quality of the soil microbiota. Respiration levels are strongly influenced by microbial community composition and substrate quality, thereby directly affecting nutrient cycling and organic matter stabilization processes [59].
Furthermore, the metabolic quotient (qCO2)—ratio between microbial respiration and microbial biomass—resulted in mean values of 1.83, 1.85, and 1.49 mg C-CO2 g−1 MBC h−1 for treatments I, III, and VII, respectively. These values are within the healthy range of qCO2 for agricultural soils—between 0.5 and 2.0 mg C-CO2 g−1 MBC h−1 [47,59]. Mature soils with qCO2 values higher than 2.0 mg C-CO2 g−1 MBC h−1 can be considered as an unhealthy rate of qCO2. It is interesting to mention that Anderson and Domsch [60] described the critical value for agricultural soils as 1.83 mg C-CO2 g−1 MBC h−1, the same value found in this work for Treatments I and III. Higher qCO2 values reflect CO2 emission higher than the maintenance requirement of microbial populations, which reduces the ability of a soil to sequester C.
After 223 days of cultivation, Lavandula dentata plants were harvested through drastic pruning, and the aboveground biomass—including apical and basal branches with leaves and flowers—was dried and weighed. The biomass production values are presented in Figure 6. Triplicates were used for biomass quantification, and the statistical significance was assessed via one-way ANOVA (α ≤ 0.05). The results revealed statistically significant differences in the aboveground biomass among the different treatments. Clearly, the best performance was obtained in treatment I, comprising only fine coal waste, with aboveground biomass productivity similar to the control performed with native soil. The presence of coarse coal waste was found to negatively impact the biomass production.
It is interesting to note that the biomass production by L. dentata was not markedly influenced by the chemical and microbiological activity variations among different Technosols configurations. The parameter that showed notable influence was the available water capacity (AWC) (Figure 7), with an almost linear relationship between L. dentate dry mass production and field capacity. The results show that the aboveground biomass increases as the AWC of the Technosols rises. Similarly, in the experiment conducted by Du and Rennenberg [61] and Saunier et al. [62], Lavandula spp. subjected to a water deficit exhibited reduced leaf hydration, growth, and aboveground biomass production. Therefore, the higher development observed for L. dentata cultivated in Technosols with higher water retention capacity suggests that these substrates provide more stable moisture conditions that prevent water stress, thereby supporting photosynthesis, shoot growth, and biomass accumulation, resulting in performance comparable to that observed in well-irrigated natural soils.
The results of the vegetal tissue analysis of Lavandula dentata for each treatment are presented in Table 3. The shoots collected from plants grown in coal tailings showed equivalent values of N, P, Ca, Fe, and B, a higher concentration of Mg, Mn, Zn, and Cu, and a slightly lower concentration of K when compared to the soil used as a control. In general, the concentration of macronutrients in the shoots are in the range of other analyses performed on species of the genus Lavanda mentioned in the literature, including hydroponic [63] and soil growing conditions [64,65]. However, we observed, particularly in the case of micronutrients, a higher concentration of Mn and Zn in our experiment, which is probably related to the higher availability of these elements in the substrates containing coal tailings (Table 2).
Essential oils (EOs) were extracted from Lavandula dentata cultivated in different coal-mining Technosol configurations. All yield values (Figure 8) were determined using triplicates and analyzed using ANOVA (α ≤ 0.05), with no statistically significant differences observed between treatments. Even so, treatment I showed the highest EO yield (mean of 0.76%), while Treatment V presented the lowest (0.32%). Treatment VII (control) provided a mean extraction of 0.65%. Overall, the results fall within the range reported in the literature for cultivated L. dentata in the state of Minas Gerais, Brazil (0.46 to 0.50%) [66] and wild and cultivated L. dentate in the rural commune of the Ouirgane region in Marrakech-Safi (0.49% and 1.11%, respectively) [67].
Chemical characterization of the EOs revealed the identification of 96.93% to 99.67% (Supplementary Material Table S1) and the major constituents found across treatments are listed in Table 4. The major compound in all samples was 1,8-cineole (~20–25%), followed by camphor (~17%), fenchone (~15%), and endo-fenchol (~10%). The EOs were dominated by oxygenated monoterpenes (~65%), followed by monoterpene hydrocarbons (~22%), oxygenated sesquiterpenes (~8%), sesquiterpene hydrocarbons (~2%), and other oxygenated compounds (~0.5%). The chemical composition of the EOs obtained in this work is distinct from that of other works we consulted [38,67,68,69]. It is a consensus that environmental and climatic factors (temperature, day length, light, season, substrate, fertilization) changes significantly the quantitative composition of essential oils while management practices such as pruning and harvesting during dry, sunny conditions help preserve oil quality. All these factors result in variations in secondary plant metabolite content during the plant’s vegetative cycle [38,67]. In this study, we did not find substantial differences in the composition of the EOs in the vessels containing coal tailings (I, II, III, IV, V, and VI) compared to agricultural soil (VII), indicating that geographical and climatic conditions predominate over the substrate in the composition of the EOs.
Agronomically, L. dentata shows adaptability to diverse climatic conditions, including regions of America, Europe, and Africa, and is characterized by drought tolerance and efficient nutrient uptake [32,33]. Productivity increases as the plants mature, with optimal yields occurring between the second and fifth years of cultivation. In this study, the results demonstrated that the lavender growth in coal tailings was slightly lower than in agricultural soil. Considering the average annual dry matter productivity of 14.7 t of L. dentate shoots per harvest for one hectare of Technosols, the average essential oil production yields 0.5% (weight of EOs/weight of L. dentata dry mass), and the retail value of the lavender essential oil of USD 18–25 per kg, the potential gross income ranges from USD 1300.00 to USD 1800.00 ha−1 harvest−1. This estimate was carried out on the first harvest, which is typically less productive than subsequent ones. Up to two harvests per year may be feasible, enhancing the socioeconomic potential of this cultivation system.
Although the sample of coal waste from Tête, Mozambique, used in this study does not pose a concern regarding toxic metals, Lavandula sp. also demonstrates suitability for phytoremediation. Lavandula vera (syn. L. angustifolia) has been shown to accumulate Pb, Cd, and Zn, enabling its use in the remediation of metal-contaminated soils [34]. Importantly, studies indicate that metal accumulation in plant tissues does not translate to the contamination of the essential oil. Bozhanov et al. [35] found no strong correlation between the metal content in inflorescences and the oil, and Zheljazkov and Astatkie [36] confirmed the absence of toxic metals in the distilled oil. This reinforces the feasibility of integrating lavender into phytoremediation systems without compromising the product safety or market value.
During the cultivation process of Lavandula dentata, several environmental benefits were observed. These included excellent root development, which contributes to erosion control and organisms’ development. The emergence of active microbial life, essential for the decomposition of organic matter, and the potential reactivation of pedogenic processes, are indicative of the establishment of fundamental soil functions. Additionally, the presence of pollinating insects (e.g., bees, butterflies, flies) was noted, indicating an increase in biodiversity and the potential for the restoration of complex trophic interactions (Figure 9).
Recent findings by Yang et al. [8] highlight that coal mining produces far-reaching hydrological alterations at the watershed scale, affecting infiltration, runoff patterns, and groundwater dynamics. Their global meta-analysis demonstrates that mining-induced disturbances disrupt key components of the hydrological cycle, intensifying erosion processes, altering soil–water interactions, and reducing ecosystem resilience. As vegetation plays a crucial role in restoring water regulation functions, studies highlight the relevance of strategies that reestablish vegetation cover and soil functionality in post-mining environments [70,71].
This work validates other initiatives [37,38] for the use of lavender in the rehabilitation of areas degraded by coal mining. In turn, it advances the knowledge of the cultivation in Technosols constructed with the coal tailings themselves. L. dentata can generate socioeconomic benefits within ecosystem restoration projects. The plants may be used as a facilitator, acting in erosion control, initiating successional pathways, restoring lost ecosystem functions, and promoting the reestablishment of local resilience and landscape functionality. Furthermore, the use of this species in intercropped systems could strengthen local livelihoods, enhance income-generation opportunities, and align with the goals of a just transition in post-coal mining endeavors [72].

4. Conclusions

The results confirm the feasibility of using coal waste from the Moatize Mine in the formulation of Technosols. All configurations evaluated in this study proved suitable for supporting the growth of Lavandula dentata. The plants grew continuously, producing healthy shoots and inflorescences. In general, the substrates exhibited pH, organic matter, macro- and micronutrient, and microbial activity at levels recommended as appropriate for plant growth. The dry biomass production of the shoots ranged from 70 to 170 g per pot over 8 months. The substrate composed solely of fine coal waste and sewage sludge yielded aerial biomass levels comparable to those obtained with agricultural soil (≈170 g pot−1 in the first harvest). Technosols incorporating coarse waste showed slightly lower biomass productivity, even with the addition of natural soil. The production of dry biomass in the study was shown to be positively related to the available water capacity of the substrate.
The chemical composition of L. dentata biomass across all substrates was consistent with the literature standards, indicating that the plant quality was not compromised by the substrate type. The essential oil yield ranged from 0.3 to 0.7% (averaging 0.5%), which is comparable to values reported for commercial cultivations. No significant differences in EO composition or yield were observed among treatments or when compared to agricultural soil control. Based on the yield data and retail prices, L. dentata cultivation on Technosols has the potential to generate a gross revenue from USD 1300.00 to USD 1800.00 ha−1 harvest−1, which can be socioeconomically beneficial in the use of the area in post-coal mining in Mozambique and in other parts of the world.
Lavender exhibited robust root development, contributing to substrate stabilization and erosion control, key prerequisites for initiating soil formation in post-mining environments. In this context, Technosols developed from coal mining waste represent a viable solution not only for the environmentally appropriate disposal of such residues but also for the formation of new functional soils, enabling the revegetation and ecosystem restoration of depleted or abandoned mine sites.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/mining6010025/s1, Table S1: Essential oil components.

Author Contributions

Conceptualization, J.W. and I.A.H.S.; formal analysis, A.C.V. and E.K.d.O.; methodology, A.C.V., E.K.d.O., J.W., E.M.E. and I.A.H.S.; investigation, A.C.V., E.K.d.O., J.W., E.M.E. and I.A.H.S.; resources, I.A.H.S.; data curation, A.C.V., E.K.d.O., J.W. and EME; writing—original draft preparation, A.C.V., E.K.d.O., J.W. and I.A.H.S.; writing—review and editing, A.C.V., E.K.d.O., J.W., E.M.E., I.A.H.S. and J.W.; funding acquisition, E.M.E. and I.A.H.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Brazil National Council for Scientific and Technological Development (Conselho Nacional de Desenvolvimento Científico e Tecnológico—CNPq: 314880/2020-8) and the Vale Institute of Technology.

Data Availability Statement

The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding author.

Acknowledgments

The authors acknowledge the support of CNPq, CAPES, FAPERGS, UFRGS, UNIVATES, and VALE for the development of this work. We also thank Esher Kern Pires, Laura Zannata Lermen, and Thomás Prates da Silveira Schneider for their help with the experimental work.

Conflicts of Interest

The authors declare no conflicts of interest.

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Mining 06 00025 g001
Figure 1. Timeline of pot-cultivated vegetation in Technosols formulated with coarse and fine tailings from the Moatize Coal Mine, Mozambique.
Figure 1. Timeline of pot-cultivated vegetation in Technosols formulated with coarse and fine tailings from the Moatize Coal Mine, Mozambique.
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Figure 2. Configurations of the Technosols produced with fine and coarse coal waste and natural soil in different configurations.
Figure 2. Configurations of the Technosols produced with fine and coarse coal waste and natural soil in different configurations.
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Figure 3. Images of Lavandula dentata growth.
Figure 3. Images of Lavandula dentata growth.
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Figure 4. Hydrodistillation of Lavandula dentata.
Figure 4. Hydrodistillation of Lavandula dentata.
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Figure 5. Mean and standard deviation of the results of microbial activity in Technosols (I and III) and native soil (VII): (a) microbial biomass carbon (MBC); (b) soil microbial respiration (SMR); and (c) soil microbial metabolic quotient (qCO2).
Figure 5. Mean and standard deviation of the results of microbial activity in Technosols (I and III) and native soil (VII): (a) microbial biomass carbon (MBC); (b) soil microbial respiration (SMR); and (c) soil microbial metabolic quotient (qCO2).
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Figure 6. Mean and standard deviation for Lavandula dentata aboveground biomass yield after 223 days of cultivation in the Technosols and the native soil used as control. Means that differ significantly are indicated by different lowercase letters (Tukey’s test, p < 0.05).
Figure 6. Mean and standard deviation for Lavandula dentata aboveground biomass yield after 223 days of cultivation in the Technosols and the native soil used as control. Means that differ significantly are indicated by different lowercase letters (Tukey’s test, p < 0.05).
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Figure 7. Effect of the available water capacity (AWC) of the Technosols on the aboveground dry biomass of Lavandula dentata after 10 months of cultivation.
Figure 7. Effect of the available water capacity (AWC) of the Technosols on the aboveground dry biomass of Lavandula dentata after 10 months of cultivation.
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Figure 8. Yield (g of EOs per 100 g per dry biomass) of essential oil extracted from the aerial parts of Lavandula dentata in different Technosol configurations.
Figure 8. Yield (g of EOs per 100 g per dry biomass) of essential oil extracted from the aerial parts of Lavandula dentata in different Technosol configurations.
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Figure 9. Environmental benefits of cultivating L. dentata in coal Technosol: (a) root system promoting erosion control, (b) presence of terrestrial invertebrates, and (c) appearance of pollinating insects.
Figure 9. Environmental benefits of cultivating L. dentata in coal Technosol: (a) root system promoting erosion control, (b) presence of terrestrial invertebrates, and (c) appearance of pollinating insects.
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Table 1. Mass of components used in each composition of Technosols.
Table 1. Mass of components used in each composition of Technosols.
Main Substrate—From All Previous CulturesFor Lavandula dentata Growth
TreatmentFine Coal Waste
(kg)		Coarse Coal Waste
(kg)		Agric. Soil
(kg)		Sewage Sludge
(kg)		Total
(kg)		NPK 10:10:10
(g)		Leaf Litter Layer
(g)
I18.9--1.1201520
II7.711.2-1.1201520
III7.711.2-1.1201520
IV5.17.46.31.1201520
V5.17.46.31.1201520
VI5.17.46.31.1201520
VII--18.91.1201520
Table 2. Mean values for fertility parameters of the different Technosols configurations and native soil used as control (mean values, n = 3) and the value reference ranges [54,55].
Table 2. Mean values for fertility parameters of the different Technosols configurations and native soil used as control (mean values, n = 3) and the value reference ranges [54,55].
Treatment MacronutrientsMicronutrients
pHSOMCECAlNPKCaMgCuZnMnFeB
%cmolc dm−3%mg dm−3cmolc dm−3mg dm−3
I5.63.511.4bdl *0.55220.446.76.91.913.736.516.1>5.00.30
II5.44.210.50.10.56252.644.05.32.213.435.921.3>5.00.17
III5.23.312.00.30.54224.150.75.92.113.036.228.4>5.00.30
IV5.44.416.20.20.57201.8122.79.62.67.932.844.8>5.00.27
V5.33.018.60.30.53162.0128.011.32.96.431.3>50>5.00.23
VI5.03.917.71.00.58159.486.78.73.38.131.2>50>5.00.40
VII5.52.023.10.10.30111.8308.015.03.03.524.5>50>5.00.27
Ref.5.5–62.6–55.0–150.5–1-59–11731–1800.5–10.4–0.80.3–0.80.6–1.21.3–55–120.2–0.3
* bdl—below the detection limit.
Table 3. Mean macro- and micronutrients values for Lavandula dentata above-ground plant tissue analysis in the Technosols and native soil used as control (n = 3).
Table 3. Mean macro- and micronutrients values for Lavandula dentata above-ground plant tissue analysis in the Technosols and native soil used as control (n = 3).
TreatmentMacronutrients (g kg−1)Micronutrients (mg kg−1)
NPKCaMgFeMnZnCuB
I18.22.913.716.12.793.4105.592.19.522.3
II14.72.614.713.72.8113.1303.5125.58.521.5
III17.72.614.516.83.1128.8256.0117.79.921.5
IV17.92.818.315.42.5119.3247.195.19.919.9
V17.72.715.115.32.3103.0238.783.311.420.5
VI15.42.617.815.42.5107.1264.696.111.824.7
VII16.82.322.913.51.6112.4125.342.37.222.8
Table 4. Average values of the major chemical compounds identified in the characterization of Lavandula dentata essential oils.
Table 4. Average values of the major chemical compounds identified in the characterization of Lavandula dentata essential oils.
CompoundRI Calc.RI AdamsTreatment (%)
IIIIIIIVVVIVII
1,8-Cineole1033103321.6726.2327.3620.6922.1024.8024.94
Fenchone1091108614.0516.2416.3714.0515.6415.7915.2
Endo-Fenchol111611169.219.499.739.7810.018.398.18
Camphor1147114616.1218.9518.5116.3418.7218.0516.99
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Venturella, A.C.; de Oliveira, E.K.; Weiler, J.; Ethur, E.M.; Schneider, I.A.H. Cultivating Lavandula dentata in Coal-Waste Technosols: Implications for Essential Oil Production and Post-Mining Restoration. Mining 2026, 6, 25. https://doi.org/10.3390/mining6010025

AMA Style

Venturella AC, de Oliveira EK, Weiler J, Ethur EM, Schneider IAH. Cultivating Lavandula dentata in Coal-Waste Technosols: Implications for Essential Oil Production and Post-Mining Restoration. Mining. 2026; 6(1):25. https://doi.org/10.3390/mining6010025

Chicago/Turabian Style

Venturella, Arthur Cesa, Eduardo Kercher de Oliveira, Jéssica Weiler, Eduardo Miranda Ethur, and Ivo André Homrich Schneider. 2026. "Cultivating Lavandula dentata in Coal-Waste Technosols: Implications for Essential Oil Production and Post-Mining Restoration" Mining 6, no. 1: 25. https://doi.org/10.3390/mining6010025

APA Style

Venturella, A. C., de Oliveira, E. K., Weiler, J., Ethur, E. M., & Schneider, I. A. H. (2026). Cultivating Lavandula dentata in Coal-Waste Technosols: Implications for Essential Oil Production and Post-Mining Restoration. Mining, 6(1), 25. https://doi.org/10.3390/mining6010025

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