Search Results (23)

Economic and legal conditions of the European power industry enforce higher participation of biomass in the thermal energy mix per power unit, due to the necessity of carbon dioxide emission reduction. One of the most important features dictating the suitability of biomass fuel for utilization in pulverized fuel-fired boilers is its grindability. The grindability of biomass is a difficult parameter to estimate due to its non-uniform morphology and inhomogeneous character. Milling and co-milling of large amounts of biomass can deteriorate the mill output and make it difficult to ensure the proper particle size distribution of the pulverized fuel fed into the combustion chamber. The main objective was to determine whether torrefaction pre-treatments could increase the grindability features of various types of biomass. Investigations of raw and torrefied biomass grindability were performed with the use of a modified Hardgrove Index for alder chips, palm kernel shells, and willow chips. Additionally, semi-industrial scale milling tests were performed, which allowed for the evaluation of torrefied biomass suitability for continuous grinding installations equipped with vertical spindle mills. According to the analysis, an increase in the biomass grindability index after the torrefaction process was shown. Additionally, it was noted that for milling low-density materials (e.g., torrefied biomass), changes in the construction of the industrial mill classifier may be necessary for the proper grinding circuit operation. Full article

Determining the Bond grindability test in a ball mill is one of the most commonly used methods in the mining industry for measuring the hardness of ores. The test is an essential part of the Bond work index methodology for designing and calculating the efficiency of mineral grinding circuits. The Bond ball mill grindability test has several restrictions, including the sample’s initial particle size distribution (PSD). This paper presents a method for calculating the Bond work index when the Bond ball mill grindability test is performed on samples with non-standard PSD. The presented equation includes a correction factor (k) and is applicable only for P₁₀₀ = 75 μm. The defined method is then compared with methods proposed by other researchers, and conclusions are drawn as to which method results in less deviation. The presented model resulted in a mean square error of 0.66%. Full article

Mining is a crucial sector in the global economy, providing essential materials for various industries, including construction, electronics, and energy. However, traditional mining practices often have significant negative impacts on the environment. Therefore, integrating sustainable practices into mining has become vital. Grinding is a crucial stage in the mineral processing industry, essential in liberating valuable minerals from ore. However, it is also one of the most energy-intensive processes in mining operations, consuming a substantial amount of electricity. Understanding and optimising electricity consumption in the grinding process is essential for enhancing energy efficiency and reducing operational costs. The relationship between electricity consumption in the grinding process and the Bond Work Index (BWI) is a crucial aspect of mineral processing and energy management in the mining industry. Understanding this relationship helps optimise grinding operations and improve energy efficiency. This review paper continues a previous work, where possible alternative modified methods for estimating the BWI in a Bond ball mill are presented. An analysis of selected methods is also provided to assess and obtain an accurate value of the BWI, which is essential in the grinding process. The methods for estimating the BWI using the wet method are presented. It is shown how the BWI can be estimated using dynamic elastic parameters and how changes in the Bond ball mill affect the BWI value. New equations for calculating the BWI and alternative procedures for evaluating the BWI in samples of non-standard size are proposed. The paper presents a comparative analysis of all presented methods. Full article

The objective of this study was to evaluate the impact of various drying methods: freeze drying, vacuum drying, convection drying, and convection-microwave drying at microwave powers of 50 W and 100 W, along with process temperatures (40 °C, 60 °C, and 80 °C), on the drying kinetics, selected physicochemical properties of dried celery stems, and their grindability. The Page model was employed to mathematically describe the drying kinetics across the entire measurement range. Convection-microwave drying significantly reduced the drying time compared to the other methods. The longest drying duration was observed with freeze drying at 40 °C. The product obtained through freeze drying at 40 °C exhibited the least alteration in color coordinates, the highest antioxidant capacity, and the greatest retention of chlorophylls and total carotenoids. At a specific temperature, the quality of the product obtained from vacuum drying was slightly lower compared to that from freeze drying. The most substantial changes in the physicochemical properties of the dried product were observed with convection-microwave drying at a microwave power of 100 W. The drying method selected had a significant impact on the energy consumption of grinding, average particle size, and the grinding energy index of the dried celery stems; these parameters worsened as the drying temperature increased. The product with the best quality characteristics and disintegration parameters was achieved using freeze drying at 40 °C. Full article

The effect of microwave treatment on the grinding and flotation performance of a typical copper–nickel sulfide ore was evaluated, based on the determination of its microwave absorption capability, grinding and flotation indexes such as crack percentage, mineral liberation degree, particle size distribution, relative work index (RWI), metal enrichment ratio and recovery. There were obvious differences between the microwave absorption capabilities of the main minerals in the ore, as demonstrated by their different microwave penetration depths. They also induced temperature differences between sulfide minerals and gangue minerals which could reach 418 °C after microwave treatment for 20 s. It was shown that microwave treatment could effectively improve the grindability of the ore, as proven by the increase in fine particles smaller than 0.074 mm and the decrease in RWI after grinding due to the higher crack percentage and mineral liberation degree. Moreover, microwave treatment affected the ore floatability because of the generation of cuprite, retgersite, and rozenite with poor floatability when the treatment time was extended. By microwave treatment for a proper time, 20 s, an optimal balance between the grindability and flotation performance could be achieved. Compared with the untreated ore, the RWI of the ore decreased by 11.5%. After flotation, the Cu and Ni enrichment ratios of the flotation concentrate increased by 0.3 and 0.2, respectively. Meanwhile, their corresponding recoveries increased by 4.2% and 3.1%. This study provides new insights for the treatment of copper–nickel sulfide ore to enhance the grinding and flotation process. Full article

Understanding the mechanical properties of coal is crucial for efficient mining and disaster prevention in coal mines. Coal contains numerous cracks and fissures, resulting in low strength and challenges in preparing standard samples for testing coal fracture toughness. In engineering, indicators such as the hardness coefficient (f value) and Hardgrove grindability index (HGI) are straightforward to measure. Various experiments, including drop weight, grinding, uniaxial compressive strength and three-point bending experiments, were conducted using notched semi-circular bend (NSCB) specimens and particle sizes of 1–2 mm/0.425–1 mm. Theoretical and experimental results indicate that the hardness coefficient of coal and rock is proportional to the crushing work ratio and inversely proportional to the mean equivalent diameter. Moreover, the square of the fracture toughness of coal and rock is directly proportional to the crushing work ratio, inversely proportional to the newly added area, directly proportional to the mean equivalent diameter and directly proportional to the hardness coefficient. The Mode-I fracture toughness of coal and rock can be rapidly determined through the density, the equivalent diameter after crushing and the elastic modulus, with experimental verification of its accuracy. Considering that smaller particle sizes exhibit greater resistance to breakage, the distribution mode of new surface areas after particle breakage was established, influenced by the initial particle size and the energy of a single broken particle. This study can assist in quickly and accurately determining the fracture toughness of coal. Full article

Oxidised pellets have become an indispensable high-quality charge for blast furnaces. Nevertheless, high-quality pellet feeds are becoming scarcer and scarcer. To broaden the range of sources of pellet feeds and reduce the production cost of pellets, more steel mills are predicted to use coarse iron ore fines with a relatively low iron grade and low impurities for the preparation of desirable pellet feeds through a typical wet grinding–settling–filtering process. In this work, the grinding, settling and filtering behaviour of Brazilian and Australian iron ore fines are studied and compared, with the aim of discovering the internal relationship between the mineralogical characteristics of different iron ore types and their grinding–settling–filtering performance. Additionally, the effects of ore blending on pellet preparation were investigated. The results show that, usually, the higher the hardness of the iron ore, the more grinding energy is required. Australian and Brazilian ore fines exhibit good grindability, with a Bond work index of about 10–15 kW·h/t. Furthermore, ore blending can reduce grinding energy consumption and improve settling and filtration rates, and the addition of finely ground Australian ores improves the balling performance of pellet mixtures. At the same bentonite content, the ball drop strength of the three blends with added Australian ore is significantly higher than that of the base blend, and the fired pellets obtained from Blend 1, Blend 2 and Blend 3 blends exhibit good metallurgical properties. Full article

This study examines the grinding process of pumice based on the dry and wet laboratory measurements, scale-up method, and life cycle assessment. This research’s main goal was to set up the relation between scale-up and life cycle assessment results for the wet grinding process with the help of mathematical equations. Within the first research works, basic grinding testing in a laboratory dry Bond mill was accomplished. This step allowed the description of the estimated particle size distribution, median particle size, specific grinding work, and grindability index number of pumice. The second step was the determination of power consumption and scale-up in a laboratory stirred media mill, and it involved the assessment of resources, primary energies, and environmental impacts of wet grinding using GaBi 8.0 software. According to the results, we obtain life cycle emission factors by introducing five coefficients for grinding in laboratory and industrial conditions. These constants depend on the external dimensions of the mill and can be expressed by a derived scale constant from the scale-up. Research results enable the industry to make a prognosis for industrial plants based on the integration between life cycle assessment and scale-up of the pilot grinding processes. Full article

This study aims to evaluate the grindability and energy requirements for the liberation of quartz from blast furnace ironmaking slag. Furthermore, the study investigates the efficiency of gravity concentration method by using a shaking table and Falcon concentrator for the separation of quartz from the slag. The grindability of the slag was evaluated using the Bond’s Work Index (BWI) method. The energy required for the liberation of quartz was determined using a Modified Bond’s Work Index (MBWI) method. The results showed that the BWI of the slag was 13.5 kWh/t and the MBWI of the quartz was 22.3 kWh/t. Gravity separation tests were carried out using a shaking table and a Falcon concentrator. The results showed that the shaking table was able to recover 91.2% of the quartz with a grade of 99.5% SiO₂. The Falcon concentrator was able to recover 98.3% of the quartz with a grade of 99.7% SiO₂. In contrast, the study found that the quartz in blast furnace ironmaking slag can be physically separated using gravity separation techniques such as shaking table and Falcon concentrator. The study also provides valuable information on the grindability and energy requirements for the liberation of quartz from the slag, which can be used in the development of more efficient separation processes. Full article

This article deals with the development of an alternative method for determining the grindability index of fine-grained materials. This method is inspired by the commercially used VTI method (also known as RTI after the Russian Thermal Energy Institute), which was widely used in Central and Eastern Europe in coal grinding. The disadvantage of the VTI method is that it uses a specific grinding device that otherwise has no other use and nowadays is no longer commonly available. Through the new method, high-energy grinding was performed using a commercially available planetary mill on silicate materials such as limestone, feldspar, corundum, and quartz. The effectiveness of the method was verified on clinker as a representative of widely used materials. The deviation between the grindability index calculated by the origin VTI method and the new developed method was on average approximately 8%; in the case of clinker grinding, it was only 3%. The results showed that the VTI method could be replaced by a new method that uses a modern available planetary mill and laser granulometry to determine the grindability index. The result is a new classification of materials according to their grindability indexes, which is based on the original VTI method. Full article

Controlling the size of powder particles is pivotal in the design of many pharmaceutical forms and the related manufacturing processes and plants. One of the most common techniques for particle size reduction in the process industry is powder milling, whose efficiency relates to the mechanical properties of the powder particles themselves. In this work, we first characterize the elastic and plastic responses of different pharmaceutical powders by measuring their Young modulus, the hardness, and the brittleness index via nano-indentation. Subsequently, we analyze the behavior of those powder samples during comminution via jet mill in different process conditions. Finally, the correlation between the single particle mechanical properties and the milling process results is illustrated; the possibility to build a predictive model for powder grindability, based on nano-indentation data, is critically discussed. Full article

A very important aspect of proper preparation of the coal mixture for the coking process is its appropriate grinding. One of the parameters describing the energy input required for grinding is the Hardgrove index. This research was undertaken to determine the dependence of the Hardgrove grindability index on selected physicochemical properties of coal. The Hardgrove grindability index was determined using the available methods described in the standards, and the dependence on selected parameters was examined. A clear positive correlation with calorific value and smaller (also positive) correlations with moisture content and free swelling index was obtained. A slight negative correlation was also obtained with sulfur content. Full article

Renewable energy sources and their part in the global energy mix are beneficial to energy diversification and environment protection. However, raw biomass is characterized by low heating value, hydrophilic properties, various mechanical durability, and the logistic challenges related to transportation and storage. One frequently used process of combined biomass valorization is torrefaction and pelletization, which increase the heating value, homogeneity, and hydrophobicity of the fuel. However, industrial clients need fuel characterized by favorable grindability, whereas, the individual clients (householders) need fuel with high mechanical durability. Due to the different expectations of final customers regarding biomass fuel properties, it is necessary to investigate the influence of the torrefaction on the mechanical durability of the pellets. In this paper, five various types of pellets and their torreficates (obtained at a temperature of 200 and 300 °C) were examined. Then the mechanical durability index D_U and the grindability of the untreated and torrefied pellets were determined. The results indicated that the mechanical durability of untorrefied pellets is significantly greater than torrefied pellets. Interestingly, no significant differences in mechanical durability between torrefied pellets at 200 and 300 °C were observed, For sunflower husk pellets, the D_U index amounted to 95.28 ± 0.72 (untorrefied), 47.22% ± 0.28% (torrefied at 200 °C), and 46.34% ± 0.72% (torrefied at 300 °C). Considering the grindability, as the treatment temperature increased the energy demand for grindability decreased. For example, the grindability of pine tree pellets was 15.96 ± 3.07 Wh·kg⁻¹ (untreated), 1.86 ± 0.31 Wh·kg⁻¹ (torrefied at 200 °C), and 0.99 ± 0.17 Wh·kg⁻¹ (torrefied at 300 °C). The highest difference between raw and torrefied pellets was determined for beetroot pomace pellet: 36.31 ± 2.06 Wh·kg⁻¹ (untreated), 3.85 ± 0.47 Wh·kg⁻¹ (torrefied at 200 °C), and 1.03 ± 0.12 Wh·kg⁻¹ (torrefied at 300 °C). Full article

There is no doubt about the practical interest of Fred Bond’s methodology in the field of comminution, not only in tumbling mills design and operation but also in mineral raw materials grindability characterization. Increasing energy efficiency in comminution operations globally is considered a significant challenge involving several Sustainable Development Goals (SDGs). In particular, the Bond work index (w_i) is considered a critical parameter at an industrial scale, provided that power consumption in comminution operations accounts for up to 40% of operational costs. Despite this, the variability of w_i when performing the ball mill Bond’s standard test is not always understood enough. This study shows the results of a variability analysis (a 3³ factorial design) performed to elucidate the influence on w_i of several parameters obtained from the particle size distribution (PSD) in feed and product. Results showed a clear variability in the work and grindability indexes with some of the variables considered. Full article

Over the years, alternative procedures to the Bond grindability test have been proposed aiming to avoid the need for the standard mill or to reduce and simplify the grinding procedure. Some of them use the standard mill, while others are based on a non-standard mill or computation techniques. Therefore, papers targeting to propose a better alternative claim to improve validity, to reduce test duration, or to propose simpler and faster alternative methods for determining the Bond work index (w_i). In this review paper, a compilation and critical analysis of selected proposals is performed, concluding that some of the short procedures could be useful for control purposes, while the simulation-based procedures could be interesting within a process digitalisation strategy. Full article