Comminution Methods Research Articles

An experimental study of the long-term bioleaching of large sphalerite ore particles in a circulating fluid fixed-bed reactor

Although the bioleaching of sulphide ores is well studied, the relatively coarse particle size typical of heap and dump leach operations, presents unique challenges. Leaching from such large particles, especially over long-term process, is poorly understood. In this study, three large particle size classes (+23/−25, +14/−16, +5.25/−6.75mm) were prepared from a sphalerite ore from the Northern Cape, South Africa, by two different methods of comminution (HPGR and cone crusher) and packed into leach reactors, which were operated continuously and well mixed through internal circulation of leach solution. Each reactor was inoculated by a mixed culture of mesophilic acidophilic chemolithotrophs (1.86×1010cell/kg ore) in which L. ferriphilum was predominant. This culture had been adapted to the sphalerite ore sample previously. Media containing 1g/L ferrous iron were used as continuous feed to the reactors. The pH, redox potential, Fe+3 and Fe+2 concentration as well as total Fe, Zn, Mg, Al and planktonic cell concentrations in the effluent solution were measured regularly. The reactors were stopped from time to time to investigate the progress of leaching and also the colonisation of the surface of the ore particles by sessile cells was investigated. Planktonic and sessile microbial populations were monitored by quantitative real time polymerase chain reaction (qRT PCR). A comparison of the effect of the different comminution devices on metal extraction indicated that HPGR crushed ore leached more rapidly in all particle size classes and showed 10 to 15% additional zinc leach extraction. On average, larger particles showed a greater difference in the cell population densities (HPGR crushed ore has more cell population) than the finer particles, and L. ferriphilum continued to dominate the microbial population over the course of leaching.

Effect of Tree Species and Comminution Method on Comminution Energy of Woody Biomass

In order to reduce the emission of greenhouse gases, much attention has been focused on energy utilization of biomass in recent years. The promotion of the utilization of domestic woody biomass contributes not only to the improvement of energy selfsufficiency, but also to the environmental protection of forests and undeveloped woodlands near populated areas or satoyamas in Japan. Typical woody biomass derived from Japanese forests and satoyamas are Japanese Cedar and Konara. When woody biomass is utilized as biomass fuel, it is important to examine the energy consumptions for pretreatments such as comminution and reforming. In this study, using Konara, Japanese Cedar, and Balsa, the effects of tree species, comminution methods, and semicarbonization of the woody biomass on comminution energy are investigated. The results obtained in this study are as follows. (1) In the case that water content is less than a fiber saturation point, the comminution energy for three species is expressed as a function of water content. In the case that water content exceeds a fiber saturation point, comminution energy for three species is expressed as a function of density. The comminution energy can be estimated by using the present empirical equations within ±50% accuracy. (2) Regarding the comminution property of semi-carbonized woody biomass, for the wood region, the empirical equations of work index depend on the comminution methods regardless of tree species and sieve of screen. For the semi-carbonized and carbonized regions, the empirical equation of work index is presented regardless of tree species, comminution methods, and sieve of screen. The comminution energy can be estimated by using the present empirical equations within ±60% accuracy.

Variations in the composition and origin of hydrocarbon gases from inclusions in minerals of the Khibiny and Lovozero plutons, Kola Peninsula, Russia

Relationships between methane and its homologues mainly contained in fluid microinclusions have been studied in 332 monomineralic fractions from the Khibiny and Lovozero alkaline plutons. Hydrocarbon gases (HCG) were extracted for subsequent chromatographic analysis using the bulk method of sample comminution. The molecular weight distribution (MWD) of gaseous alkanes in the same and associated minerals is different depending on geological setting of the samples. The molecular mass of HCG increases (i) with decrease in temperature and capture of fluid inclusions in the course of transformation of primary magmatic minerals and the formation of late minerals as products of intensified postmagmatic processes; (ii) in the direction from khibinite at the margin and foyaite in the core of the Khibiny pluton to the central ring structure; and (iii) from the bottom to top of the differentiated complex in the Lovozero pluton. The results obtained coupled with other geochemical data suggest multistage generation and transformation of hydrocarbons from the magmatic to the final low-temperature hydrothermal stage. The MWD of hydrocarbon components in gases occluded by minerals can serve as an indicator of conditions characteristic of rock and ore formation, as well as of the consecutive formation and transformation of associated minerals revealing ambiguous and controversial relationships.

Compactibility of granules prepared by a novel method of granulation and their dissolution

Increasing particle size during prolonged grinding by a ballmill has been used as a novel means of producing a pharmaceutical granulation. The compactibility properties of granules of sodium chloride and of paracetamol produced by this method have been elucidated and compared with those produced by conventional granulation techniques. Force-displacement diagrams and double compactions were used to measure the net energy input on tableting. When compared with conventional granulation methods, the agglomerative phase of comminution (APOC) method produced mechanically stronger tablets with a higher dissolution rate than those compacted from granules made by a conventional wet granulation method irrespective of the compaction energy used. Tablet tensile strength is related to the elasticity and yield strength of the substance used. It is suggested that binderless tablets may be prepared using this method, thus simplifying tablet formulation and enhancing stability. A possible mechanism for the increased dissolution rate is the increased internal surfaces area of the granules produced by the prolonged grinding method.

Pre-weakening of mineral ores by high voltage pulses

A new comminution method has been developed by applying high voltage pulses at specific energy 1–3kWh/t to pre-weaken mineral particles, leading to reduction in energy consumption in the downstream grinding process. Four ore samples were tested using high voltage pulses and conventional crushing in parallel for comparison. Evidence of cracks and microcracks measured with X-ray tomography and mercury porosimetry supported the principle of high voltage pulses induced damage on rocks in the electro-comminution process, which resulted in energy saving up to 24% found in this study. Ore surface texture and mineral properties affected the efficiency of high voltage pulse breakage. The feasibility of the electro-comminution and its benefits need to be investigated case by case.

木質系粉砕物燃料の前処理工程(粉砕・乾燥・半炭化改質)および輸送におけるエネルギー消費量の低減

In recent years, much attention has been focused on the energy utilization of biomass to reduce the emission of greenhouse gas. Especially, woody biomass such as the forestry biomass derived from logging and thinning operations in forests is one of the most promising domestic resources in Japan. Woody biomass contributes not only to the improvement of energy self-sufficiency in Japan, but also to the environmental protection of Japanese forests. When the woody biomass is utilized, it is necessary to examine the energy consumption for collection of resources, pretreatment, transportation and after-treatment. In the present study, woody biomass is assumed to be utilized as pulverized wood fuel in local area. The pretreatment of pulverized wood fuel is consisted of three procedures; drying, semi-carbonizaion and fine comminution. The main purpose of the study is to investigate the comminution characteristic of the Japanese cedar thinning and the reduction in energy consumption for pretreatment process and transportation of pulverized wood fuel. The results obtained in the present study are as follows. (1) Comminution energy increases as the water content increases and the sieve of screen becomes small. The comminution energy of hammer mill is largely affected by the water content. Difference in comminution energy between the hammer and cutter mills is large. The ratio of comminution energy of the hammer mill to that of the cutter mill exceeds 10 for the water content of 40% and sieve of screen of 3mm. (2) To estimate the comminution energy of woody biomass, empirical equations of work index in Bond's Law are presented. In woody biomass region, the empirical equations of work index depend on the comminution method. In semi-carbonization and carbonization regions, the empirical equation of work index is presented regardless of comminution method and sieve of screen. The comminution energy can be estimated by using the present empirical equations within accuracy ±50 percent. (3) Analysis of energy consumption for the pretreatment process and transportation is conducted by using the present empirical equations of work index. From the result of analysis, it is found that the semi-carbonization at a temperature of 250 degree C is effective to the reduction in total energy consumption, when the pulverized wood fuel of 300 microns or less in particle size is utilized.

Experimental study of coal liberation: Electrical disintegration versus roll-crusher comminution

Preferential breakage, where the boundary of mineral particles and coal substances are selectively broken up, is an effective comminution method for poor liberation coals such as middling coal subjected to jig treatment. A comparison of electrical disintegration (ED) product and roll crusher product of Nantun (China) clean coal was carried out in this study. Coal particles of 4 to 8 mm diameter with specific gravities of 1.35 to 1.45 were used as the feed and the crushed product was classified into 12 fractions by size and specific gravity and analyzed for ash and mineral content using a norm calculation method. The generation ratios of light clean coal and heavy waste fractions in the ED product were higher than in the roll crusher product and this indicates that ED improved the mineral liberation. The microscopic observations supported this. The norm calculation results showed that calcite, dolomite, and pyrite were concentrated in the heavy and fine fractions, a behavior that is different from that of kaolinite.

X-Ray diffraction line-broadening study on two vibrating, dry-milling procedures in kaolinites

AbstractDue to the great technological importance of the microstructure of kaolinite, characterizing its evolution during dry milling of kaolin and analyzing the microstructural information obtained from different methods were the main aims of this work. The microstructural alteration of kaolinite is evaluated by X-ray diffraction and electron microscopy methods, comparing the results obtained and analyzing the correlations between them. The Warren-Averbach and Voigt-function methods of X-ray diffraction microstructural analysis have been applied successfully to the study of the effects of two different, vibrating-cup dry-milling configurations in the microstructure of kaolinite from the reflections corresponding to (001) diffracting planes. The crystallite-size estimates obtained from the two methods correlate well. Field emission scanning electron microscopy measurements of kaolinite particle thickness are in good agreement with the crystallite size estimated by the two methods. The Warren-Averbach method also provided estimates of the contribution to line broadening. Vibrating-cup milling has been proved to be a more efficient method of strain comminution of kaolinites than other milling techniques, reaching extensive microstructural degradation within seconds.

Study of native gold from the Luopensulo deposit (Kostomuksha area, Karelia, Russia) using a combination of electric pulse disaggregation (EPD) and hydroseparation (HS)

The mineralogy of a gold–sulphide–arsenopyrite ore from the Kostomuksha iron deposit region was studied by scanning electron microscopy (SEM) in hydroseparation (HS) products from various non-magnetic fractions (40–300 μm) after EPD crushing. The computer controlled hydroseparator CNT HS-11 produced a 100× concentration of native gold grains together with other ore minerals. Selection of >150 native gold grains from HS concentrates shows a grain size distribution of 1–154 μm (average 33 μm). Measured, upgraded gold reports as liberated grains (46.0%), as intergrowths with arsenopyrite (14.2%), löllingite (19.7%), native bismuth (17.1%), and in association with pyrrhotite (0.9%) and chlorite/apatite (2.0%). High recoveries of native gold are explained in terms of the combined effects of selective grain-boundary fracture induced by EPD crushing, resulting in preservation of metallic mineral aggregates and grain boundaries, even within large native Au/Bi particles (such soft particles would otherwise show significant changes during normal comminution methods). High gold recoveries should thus be possible using traditional gravity and flotation followed by cyanidation. A combined EPD/HS protocol demonstrates the unique possibilities of this technology for laboratory-scale gravity recoverable gold (GRG) testing.

Investigation of gemini cationic water based pigment dispersion

The water based ultra fine pigments red 22 are prepared with gemini cationic dispersant by microfluidiser comminution methods. The ultra fine pigments with different sizes are obtained through the change of the amount of the dispersant, the treatment time and the treatment pressure of the system. The stabilisation properties of gemini cationic water based pigment dispersion for the temperature, pH value, electrolyte, centrifugal treatment and deposition time are discussed in detail. The results reveal that the ultra fine pigments of the size of 211·9 nm, the Zeta potential of 32·4 mV and the viscosity of 1·33 × 10−3 Pa s are prepared with the amount of pigment at 5%, the amount of the dispersant at 2%, the dispersion pressure at 172 368 kPa for 30 min. The added electrolytes decreased the Zeta potential. Compared with traditional pigment, the fabric dyed with the gemini cationic water based pigment dispersions has a high K/S value and good dyeing capability.

REVIEW OF APPLIED PARTICLE SHAPE DESCRIPTORS AND PRODUCED PARTICLE SHAPES IN GRINDING ENVIRONMENTS. PART II: THE INFLUENCE OF COMMINUTION ON THE PARTICLE SHAPE

In this article the literature on the shape of particles produced by comminution methods and the grinding condition is reviewed and presented. Some agreement and disagreement among workers for the shapes that are produced by comminution are presented. In addition, the important factors affecting the shape of particles in different comminution methods are also described.

Investigation of the Effect of Different Comminution Methods on the Quality of Chilli Powder

AbstractThe quality degradation of chilli during comminution was investigated through modelling. Two different comminution methods were studied, namely grinding and high‐speed cutting. The colour of the chilli powders, the concentration of two major capsaicinoid compounds, and moisture loss in the powders were taken as the quality indicators. The kinetics of quality degradation was modelled. It was found that although the quality indicators of chilli powder produced by grinding were generally inferior to those by high‐speed cutting, the rate of quality degradation by the former was much lower than that by the later. The mechanism behind this finding is also discussed in this paper.

異相境界面優先破壊を考慮した単体分離モデルおよびその実験的検証―マテリアルリサイクル促進のための定量的指標の確立を目指して―

This paper describes a new liberation model considering preferential breakage at phase boundaries to make a predicted degree of liberation to be feasible. This model is a modification of the Wiegel model, which is one of the most popular and widely acceptable models, introducing an index of Preferential Breakage Probability, e at phase boundaries. Concept, structure, simulation results, and validation of the model were shown in this paper, including the results of applicability for various kinds of natural and synthetic composite materials. This index of Preferential Breakage Probability, e is considered useful to quantify the facility with liberation for various comminution methods, and this index could also become a good measure to evaluate product design for materials recycling when applying disassembly and solid/solid separation technologies. One of the problems of these kinds of models was the determination of a reasonable unit grain size for materials which have grain size distribution. This paper also describes a solution for such cases.

Functional stability of frozen normal and high pH beef

The functional properties of whole, diced or minced high and normal pH beef were determined after 0, 1, 2, 3 and 7 month’s storage. There was no interaction between pH, degree of comminution and storage time for most of the attributes measured. Regardless of storage time or comminution method, high pH meat had significantly ( P < 0.001) higher sarcoplasmic protein solubility, water holding capacity, cooked batter torsion stress and strain, yield and emulsion stability than normal pH meat. Normal pH meat had significantly ( P < 0.01) higher myofibrillar protein solubility and hue angle than high pH meat. Water holding capacity significantly ( P < 0.01) decreased and hue angle increased with the increase in the degree of comminution. Protein solubility in raw meat and the cooked batter stress, strain, yield and emulsion stability of both high and normal pH meat deteriorated with time. However, this deterioration was faster in the normal pH meat compared to high pH meat except for total and myofibrillar protein solubility. Within the parameters of the present study, it is concluded that frozen high pH meat possesses superior functional attributes compared to normal pH meat regardless of the degree of comminution or storage time.

The Role of Particle Shape in Size Analysis and the Evaluation of Comminution Processes

The shape of the particles produced by comminution is affected by the kind of breakage action employed. Furthermore, the procedures used to determine product particle size are themselves influenced by shape. Illustrative examples of the effects of shape on particle size analysis and of shape variations in comminuted material are presented. Light scattering size measurements on narrow sieve fractions were found to indicate size distributions that were significantly broader than the sieve size range, especially for irregularly shaped particles. The distributions were also shifted to coarser sizes for the irregular particles but not for spheres. The apparent size shift is attributed to differences in the definition of size, while it is proposed that the apparent broadening of the distribution is a result of orientation effects. It is shown that broadening is relatively insignificant for broad, continuous distributions due to compensation effects. Applications to the determination of composite distributions by combining sieving and light scattering data are described. Distributions of particle shape descriptors, obtained by image analysis of comminution products, are shown to depend on the comminution method used. A slight variation with size was observed for coal particles but not for quartz. The implications of the size/shape interaction on the evaluation of comminution process performance are discussed.

The energy efficiency of ball milling in comminution

Comminution efficiency is a technical term that relates some measure of the output from a comminution machine to the energy input into it. The term has usually been encompassed in controversial arguments. The conflict in reporting comminution efficiencies has arisen from ill definition of the reference for the output energy. Surface area and surface energy have been widely used in the assessment of comminution efficiency. Review of the energy to produce new surface of quartz shows comminution efficiency ranging from about 0.1% to 1.0%, for various comminution methods, when expressed in terms of the surface free energy of quartz. However, in this paper, comminution efficiencies are based on the comparison of ball milling with single-particle comminution, either in terms of the energy to produce new surface or in terms of some size distribution parameter. If the energy to produce new surface by single-particle breakage is used as the basis for evaluating efficiency, then the efficiency of ball milling has a more realistic value of about 15% for the comminution of quartz and soda-lime glass. In a second approach, comminution efficiency is based on comparing the energy to produce some size distribution parameter of the product from ball milling with that by single-particle breakage. For both materials, dry ball milling efficiency was found to be in the range of 25%.

Mechanical milling of metal sulfide particles and their catalytic activity—hydrogenation of 1-methylnaphthalene with molybdenum sulfide

The comminution of molybdenum sulfide particles with a vibrating mill and with a media-agitating mill was investigated. For equivalent milling times, the media-agitating mill prepared smaller molybdenum sulfide particles than the vibrating mill. Median particle diameters were approximately 40 nm for molybdenum sulfide particles comminuted for 50 h with the media-agitating mill. The specific surface area of these particles was about 120 m 2/g. In comparison, the surface area of the starting material was 5.8 m 2/g. The layered structure of molybdenum sulfide was sustained after the milling, although the crystal stacking height relative to the edge surface area decreased. Catalytic activities of the raw and comminuted molybdenum sulfide were measured using the hydrogenation of 1-methylnaphthalene as a model reaction. The hydrogenation rate constants per weight of comminuted catalyst were much higher than those of the raw material and increased with the specific surface area. Conversely, the rate constants per surface area were almost the same irrespective of both the comminution time and the comminution method. The increased catalytic activity is believed to be caused by a change in crystal structure and morphology.

Effect of comminution method and raw binder system in restructured beef

The effect of particle size, method of particle size reduction (grinding, flaking, slicing) and alginate or Fibrimex ™ binding systems on processing properties of restructured beef were investigated. The size of semimembranosus muscles was reduced with a meat slicer, grinder or flaker (Comitrol) through machine openings that were 2, 4 and 8 mm in size. Bind of meat pieces in raw and cooked beef steakettes were measured. Sensory evaluation to determine the effect of method of size reduction on texture of beef steakettes was done only on steakettes manufactured with alginate. Beef steakettes manufactured with the alginate binding system had significantly ( p < 0.05) higher raw bind values than did the beef steakettes manufactured with Fibrimex. Slicing meat for the manufacture of restructured beef steakettes resulted in a higher raw bind than did either grinding or flaking the meat. Significant ( p < 0.05) interactions were observed for the bind of cooked steakettes between binder and method of size reduction and binder and opening size. When alginates were used to make restructured steakettes the bind of the cooked product was less ( p < 0.05) when meat was sliced than when it was ground or flaked. However, when Fibrimex was used, bind was stronger when sliced meat was used. The alginate system resulted in higher binds for cooked product when particle size was smaller but with the Fibrimex system bind was higher when particle sizes were larger. A consumer panel on alginate restructured steakettes showed no preference for the texture produced by the different methods of particle size reduction.

Development of a method for the determination of low contents of asbestos fibres in bulk material.

Asbestos is a category 1 carcinogen under the EU classification, but in the absence of a method to quantify asbestos in a matrix at the 0.1% level, there has been a delay in implementing relevant directives to asbestos. An analytical scheme for identification and quantification of asbestos using polarised light microscopy (PLM) and phase contrast optical microscopy (PCM) has now been developed. When used on artificial mixtures by an experienced laboratory, it achieved the required target performance, at 0.1% asbestos concentration by mass in a bulk sample, to obtain a result, which with 90% probability, is correct within a factor of two. The method of identification by PLM and quantification by PCM has been assessed by interlaboratory comparisons. The method begins with an initial identification using PLM, and depending on asbestos type and matrix a combination of preparation procedures are used to produce the analytical filter. A gentle comminution method was used which reduces the risk of overmilling. The asbestos mass percentage on the filter is quantified using PCM in combination with a PLM attachment for identification of possible non-asbestos fibres. The final method is supported by efficient methods for fibre identification for size determination and calculation of total fibre volume. A statistical analysis of mass concentration estimates was made and the effect of preferred orientation of fibres on the analytical filter was quantified.

97/02599 Scanning electron microscopy analysis of coal products from different comminution methods

This study provides coal-quality, organic-petrographic and organic-geochemical data on Tertiary subbituminous coal of the Hafik area, northwestern part of the Sivas Basin, Turkey. Coal-petrological studies along with proximate and ultimate analyses were undertaken to determine the organic-petrographic characteristics of the Hafik coals. Huminite reflectances were found to be between 0.38 and 0.48% (corresponding to an organic-material-rich and coal layers), values characteristic of low maturity. This parameter shows a good correlation with calorific values (average 21,060 kJ/kg) and average Tmax (422 °C) mineral-matter diagenesis, indicating immaturity. The studied coals and organic material underwent only low-grade transformation, a consequence of low lithostatic pressure. Therefore, the Hafik coals are actually subbituminous in rank. Rock-Eval analysis results show types II/III and III kerogens. The organic fraction of the coals is mostly comprised of humic-group macerals (gelinites), with small percentages derived from the inertinite and liptinite groups. In this study, organic-petrographic, organic-geochemical and coal quality data were compared. The Hafik deposit is a high-ash, high-sulfur coal. The mineral matter of the coals is comprised mainly of calcite and clay minerals.