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By PEILIN LAN, LEONARD HILL, SIMON TIMBILLAH, BERNARD FOSU, CESAR SOSA-BLANCO

The use of sodium hydrosulfide (NaHS) in most of the operations in byproduct molybdenum flotation comes with safety concerns and, in some instances, a high reagent cost. Engineered solutions at the various operations where NaHS is used have immensely reduced the possibility of hydrogen sulfide (H2S) gas evolution. However, the threat of exposure remains, and this, coupled with the high dosages of NaHS consumed, supports the continued search for alternative depressants. This paper focuses on efforts to study the applicability of disodium carboxymethyl trithiocarbonate (DCMT), an organic depressant, as an alternative to NaHS. Bench-scale rougher flotation results for samples from the Sierrita copper–molybdenum (Cu–Mo) plant showed the best DCMT performance at 8 kg/t of DCMT, pH 10.5, 30 min of shear conditioning and 10 min of flotation conditioning. The Aminpro plant model simulation confirmed that 4 to 8 kg/t DCMT under certain shearing and conditioning times achieved superior or equivalent Mo–Cu separation efficiencies when compared\ to NaHS.

By LUIS ALBERTO TORRES-CRUZ

The Plewes method is relatively well known among geotechnical engineers interested in assessing the liquefaction potential of soil deposits. Furthermore, it was one of the four methods considered in the post-failure investigation report of the Feijao Dam I, also known as the Brumadinho Dam, in Brazil. The inclusion of the method in that report is likely to increase its visibility among geotechnical practitioners tasked with assessing the liquefaction potential of tailings. While the authors of the method duly presented it as a screening method, more recent technical literature contains conflicting views on its reliability. Considering the popularity of the method and that the safety record of tailings dams is a cause of great concern, this study assessed the uncertainty of results from the Plewes method. The study concludes that, even under optimistic assumptions, the results of the method are too uncertain for detailed characterization of tailings deposits.

By Mark C. Williams, Shunsuke Managi, Noriko Hikosaka Behling

Particle processing is a key to using solid particles in fuel cell applications. Selectivity with regard to reactivity, impurities, etc. is an important feature and the treatment of particle surfaces could greatly impact the performance of direct carbon fuel cells. Solid fuel particles will become increasingly important in the future. Present energy conversion systems for solid fuels are too inefficient. New energy conversion systems for solid fuels with higher energy conversion efficiencies are possible. Fuel cell technology is a key technology in these new conversion systems. The direct carbon fuel cell (DCFC) operates on carbon particles obtained from a variety of solid fuel feedstocks. The DCFC is the only fuel cell designed to directly oxidize carbon particles in a special anode chamber. The particles are generally graphite structure with high purity. The electrolyte used is the high temperature solid oxide, molten carbonate, or hydroxide electrolyte. Since a pure stream of CO2 is produced, the stream can easily be sequestered and disposed. Pure carbon dioxide produced as a by-product would also have a market in many industries. A well-defined technology roadmap identifying key research and development (R&D) issues is necessary to provide a framework for the development of these systems and to prevent entrenchment in inherently inefficient technologies. This review paper describes the direct carbon fuel cell and its system, how it works, the developmental status, the characteristics of the carbon particles needed, and the research and development issues for the technology

By Weijie Wei, Jinwang Zhang, Shengli Yang

In longwall top-coal caving (LTCC) mining with an inclined seam, the recovery rate is low and equipment stability is poor due to the unbalanced top-coal drawing process. To address these problems, this paper proposes the dynamic group caving method (DGCM), whose basic premise is that when the drawn volume of top coal from a support reaches about half, the next support begins drawing top coal, and the drawing process between the two supports is half done. Using particle flow code (PFC), the caving mechanism of top coal under DGCM was investigated. The results are of significance to realize high efficiency and precise caving in LTCC mining with an inclined seam.

By Yi Luo, Jian Yang, Hua Jiang

Surface subsidence induced by underground coal mining activities, especially longwall mining operations, can cause various problems to interstate highways ranging from structural integrity to drivability to safety. Accurate subsidence prediction, correct influence assessments and effective mitigation measures are the keys to ensuring the safety of highway traffic. The surface subsidence prediction program, called comprehensive and integrated subsidence prediction model (CISPM), was developed based on the principle of influence function method and has been validated with a large number of subsidence measurements. In this paper, the techniques to use the predicted final surface movements and deformations for assessing their influence on the integrity and functionality of highway structures — such as road surface pavements, concrete slabs and transverse joints — vehicle dynamics, comfort level and drivability are presented. A number of mitigation measures to protect the highway structures and to ensure traffic safety are proposed, along with an application case.

By Leandro Augusto Viana Teixeira, Angela Avelar, Ruberlan Gomes Silva, Virginia S. T. Ciminelli, Daniel Majuste

Rare earth elements are essential for modern life products and green technologies. Recent supply constraints have boosted the development of rare earth projects after the price peak of 2011. The feasibility of a project depends on the definition of a processing route, which in turn depends primarily on the rare earth mineral, with monazite and bastnaesite representing the two most relevant minerals. Monazite-type ores usually contain high acid consumption impurities, such as iron, aluminum, calcium, magnesium and phosphates, and may also contain prohibitive levels of radioactive thorium in its composition. Based on thermodynamic analysis, the present work discusses the fundamentals of a selective process route for rare earth extraction from monazite ores with high iron content. This process involves sulfation by means of concentrated sulfuric acid and roasting at a high temperature. The route yields high rare earth extraction with low iron and thorium extraction and low acid consumption. Rare earth extractions as high as 80 percent were achieved, while iron and thorium extractions were lower than 1 percent, and acid consumption was lower than 0.34 kg of sulfuric acid per kg of ore. The operational window was compared to the one predicted by thermodynamic modeling, with 700 °C representing the optimal roasting temperature.

By Liming Yuan, Isaac Zlochower, RICHARD THOMAS, Thomas H. Dubaniewicz, Teresa Barone

Mining vehicle manufacturers are developing lithium-ion (Li-ion) battery electric vehicles as an alternative to diesel-powered vehicles. In gassy underground mines, explosion-proof enclosures are commonly used to enclose electrical ignition sources to prevent propagation of an internal methane (CH4)-air explosion to a surrounding explosive atmosphere. Li-ion batteries can create pressurized explosions within sealed enclosures due to thermal runaway. Researchers at the U.S. National Institute for Occupational Safety and Health (NIOSH) measured thermal-runaway pressures of lithium iron phosphate (LFP) cells as a function of free space within sealed enclosures and observed an inverse power relationship. A well-confined cell produced 4260 psia (294 bar) of pressure during a thermal runaway, far exceeding minimum pressure containment specifications for conventional explosion-proof enclosures. Results indicate that adding enough free space surrounding LFP cells can reduce thermal-runaway pressures to levels below that expected for CH4-air ignitions. Measured thermal-runaway temperatures were below the minimum autoignition temperature of CH4-air.

By Leandro Augusto Viana Teixeira, Angela Avelar, Ruberlan Gomes Silva, Virginia S. T. Ciminelli, Daniel Majuste

Rare earth elements are essential for modern life products and green technologies. Recent supply constraints have boosted the development of rare earth projects after the price peak of 2011. The feasibility of a project depends on the definition of a processing route, which in turn depends primarily on the rare earth mineral, with monazite and bastnaesite representing the two most relevant minerals. Monazite-type ores usually contain high acid consumption impurities, such as iron, aluminum, calcium, magnesium, and phosphates, and may also contain prohibitive levels of radioactive thorium in its composition. This work presents a thermodynamic analysis of a monazite system and discusses the fundamentals of a selective process route for rare earth extraction from monazite ores with high iron content. This process involves sulfation by means of concentrated sulfuric acid and roasting at a high temperature. The route yields high rare earth extraction with low iron and thorium extractions and low acid consumption. Rare earth extractions as high as 80% were achieved, while iron and thorium extractions were lower than 1%, and acid consumption was lower than 0.34 kg of sulfuric acid per kg of ore. The operational window was compared to the one predicted by thermodynamic modeling, with 700 °C representing the optimal roasting temperature

By Andre Vien, SANDRO DAVID DI, Frank Laroche

In 1994, Claude Bazin presented a novel method for linking size data from milling models to the feed input of flotation models. It was achieved with the simple addition of a metal/mineral distribution–size distribution relationship. This allows grade and recovery predictions from a varying mine plan through product size distribution predictions. 

Dr Hanekom I would like to thank Dr Hanekom for a very valuable -contribution; it summarizes careful statistical test work which was an omission from the original paper. Minor manipulative details, the application of a finer measuring graticule and the reproducibility of the procedure are described and the author accepts with gratitude this ready-made answer to the first and second points of Dr Finkelstein's comments. Mr Williamson The author is indebted to Mr Williamson for historical background to early experiments with captive bubbles and it is conceded that the original paper described another avenue to an old flotation goal. The field of application is restricted and we would not work with all the material illustrated by Klassen and Mokrousov.1 The particles in Figure 74(a) are far too large and irregular; material in Figures (b) through (d) could be employed for semi-quantitative work in spite of obvious disadvantages; Figure 74(f) represents ideal conditions. We have studied this mineral-collector association in the size range given and results were satisfactory. For larger pick-up values than that illustrated an induction period of more than 0.01 second was required (actually 90 seconds for a maximum bubble load at pH 7.2 with 25 g/t oleic acid!). REFERENCE 1. KLASSEN,V. I. ANDMOKROUSOV,V. A., 'An Introduction to the Theory of Flotation,' Butterworths, London, 128, Figure 74, (1963). Mr Slander and Mr Kooij Researchworkers in a practical mineral development laboratory may well ask what contribution yet another micro-technique can make to the problems of large scale ore flotation. The obvious answer is that there can be little or no direct translation of results obtained with a static system comprising air bubble and pure mineral concentrate to a dynamic multicomponent operation. However, for the rapid study of one mineral or variable some small scale apparatus must be employed. In the Anglo American Research Laboratory, the described semi-quantitative pick-up technique has filled a niche and requirement. For ourselves, the system represents a definite advance over the contact angle approach in that samples of minerals conventionally prepared in laboratory or plant may be used, which is a desired step nearer flotation. We bracket this pick-up apparatus with the Hallimond tube1,2 and evidence is now to hand that pick-up curves may often be related to flotation recoveries obtained from this tube with pure mineral samples and from the Fuerstenau glass cell3 with the total ore at low pulp densities. We would not wish to push the comparison of pick-up results past this stage for there is much published development work relating the Hallimond and Fuerstenau equipment to flotation on a larger scale. At the Anglo American Research Laboratory for example, a test in a Fuerstenau cell is often the final integrated step in laboratory investigations into the TORCO process. As these contributors rightly point out, pick-up tests can offer nothing towards the determination of optimum reagent dosage for large scale flotation. This is the function of bench-type flotation cells with up to 2 kg batches of ore. At this level, collector performance and consumption and physical properties of the froth are more comparable with large scale operation. The pick-up cell, Hallimond tube and Fuerstenau cell are essentially equipment from which the effect of control parameters can be derived. For the assessment of collector behaviour, the pick-up approach is rapid and economic and we offer here a pick-up contribution towards the flotation of Witwatersrand uraninite with anionic sulphonate collectors (Fig. 1). A large crystal of the local mineral was not available for contact angle measurements and owing to its low concentration in Witwatersrand gold-bearing reef, a small sample was laboriously obtained by tabling, superpanning and heavy medium separation. The pick-up values of a sized portion were determined by the described procedure in the presence of nine petroleum sulphonate collectors. Responses fell into two categories; "normal" curves (dotted lines) and a group of collectors which were very active at low concentration but showed depression of pick-up at the higher levels. The similarity in form of curves for collectors 1 and 3 was apparent and reagent 3 was found to be simply a diluent of 1. Otherwise, collector performance could not be related to either sulphonate content or molecular weight of the active constituent. However, reagent 2 gave the best performance in a bench flotation cell with regard to overall uranium distribution but, as predicted, reagent 1 yielded the best grades. Later pick-up tests with a similar class of collector have suggested that depression at high reagent concentrations may be due to "bubble armouring" whereby an hydrophilic air-liquid interface is produced which rejects mineral attachment. Prolonged investigations with the same mineral sample have not been required except for the study of uraninite which lasted for more than a year. Variation in pick-up response could not be detected over this period during which the mineral was stored under distilled water. The only visible change was a small efflorescence of lead sulphate, readily removed and decanted off after stirring with a glass rod in the sample tube. In its main role as a "trouble-shooter", the pick-up method is applied to fresh mineral samples taken from a flotation plant and soon discarded or from a current run in the ore-dressing laboratory. After production of a concentrate, a solvent cycle, as described in the original paper, may be required to remove heavy organics or other contaminants as when a sample has been taken from circuits containing detergents, grease or return flotation solutions. This solvent cycle will not remove chemisorbed collectors and we prefer not to work with minerals from flotation tailings or with pick-up cell discards. It has been thought preferable to answer the contributors' other apprehensions with regard to sample preparation, activators, depressants and the physical properties of reagents in another paper on offer to this Journal. It covers pick-up investigations relating to the flotation of nickeliferous pyrrhotite at two Anglo American Corporation Mines, which approach seemed the correct orientation for a reply to another contributor to this paper.

By Kwangmin Kim, Junnhyeok Park, Taehee Lee, Minkyu Kim

Mine tailings storage facilities (TSFs) can be a significant source of fine, respirable dust. This dust poses concerns, especially for nearby communities, because of its detrimental impact on respiratory health. To address these concerns, this study examined the effectiveness of commercially available polymers, known for their biocompatible and environmentally friendly features, to prevent dust generation from upstream-type TSFs in active mining operations. It focused on two areas in TSFs: the tailings beach and slope/dike surfaces. Two types of polymers—polyethylene glycol and poloxamer—were selected, and their effectiveness was evaluated in a series of phased laboratory and field tests. The lab tests investigated the moisture-retention capacity of the tailings after treatment with the polymer solutions as well as the ability of these solutions to reduce dust emissions. Polymers were applied to a tailings bed surface in the lab and dust was generated from this surface using a wind tunnel. PM10 and PM2.5 concentrations were measured using laser-diffraction dust sensors, and the polymers were found to have reduced dust emissions up to 95%. Small-scale wind-blowing tests were conducted in the field (specifically, in a controlled environment at a TSF) to evaluate polymer effectiveness on the tailings beach and slope/dike areas. The tests revealed that the AP could efficiently suppress approximately 80% of PM10 and PM2.5 dust emissions at both types of areas. Finally, 1000 gallons of AP solution were discharged at the top of tailings beach and slope/dike areas, respectively, and found to be effective. The results of these tests showed the high potential of the biocompatible polymers to be a feasible solution for reducing the respirable dust emissions from upstream TSFs in arid and semi-arid regions.

By Paul F. Ziemkiewicz, Aaron Noble, Christopher R. Vass

The conventional rare earth element (REE) industry has historically sought to develop ore deposits where geologic processes have produced mineralized zones with commercially attractive REE concentrations. These deposits are extremely uncommon, particularly in the USA. Given the criticality of these materials and the need for sustainable domestic supply, the current research seeks to leverage other autogenous processes that lead to concentrated REE resources. One such process is the generation of acid mine drainage (AMD). AMD is very common in many coal mining districts and results from the exposure and oxidation of pyrite during mining. During the generation and migration of AMD, liberated sulfuric acid mobilizes several metal ions including REEs. Treatment of AMD is required under U.S.C §1251, the Clean Water Act, and often consists of neutralization, oxidation, and metal hydroxide precipitation. To investigate the deportment of REEs during this process, a field sampling campaign was undertaken, whereby the concentration of REEs in AMD and AMD precipitates was measured directly. In the nine sites evaluated in this study, the REE concentrations of the precipitates varied from 29 to 1286 ppm with an average of 517 ppm among the sampled sites. The individual elements were enriched compared with the associated bulk Northern Appalachian (NAPP) coal material by factors ranging from 3 to 15. Furthermore, the distribution of REEs in all precipitate samples favored the heavy REEs (HREEs) when compared with traditional REE ores. This research represents the first part of multi-part research endeavor to characterize, classify, and determine the practicality of refining REEs from AMD and its by-products.

By Murat Erdemoğlu, Turan Uysal, Thierno Saidou Barry, Mustafa Birinci

The rapid development of the global alumina and aluminum industry is straight coupled with the demands and the needs of these materials. Nowadays, the only well-known accessible resources to produce alumina and aluminum are bauxite ores. But bauxite ores are limited, and the remaining exploitable reserves do not have high contents in alumina. In countries where there is little or no bauxite reserves or where the recovery of existing bauxite ores to produce alumina with the Bayer process are not economic, alternative resources for alumina have been explored. The most attractive resources for replacing bauxites are aluminosilicate clay minerals and coal fly ash. The important processes developed for the recovery of alumina from these sources are acid leaching and alkaline leaching processes. The acid leaching is known as the most efficient in which thermal and mechanical activation are included for improving the performance of the process. The objective of this review is to give a comprehensive insight on the production of the alumina from thermally or mechanically activated clays and coal fly ash by hydrochloric, sulfuric, and nitric acid leaching processes.

By A. Noble, R. Q. Honaker, J. Werner

Recovery of rare earth elements (REE) from coal-related resources has recently received significant interest due to supply concerns and their key roles in critical industries and defense-related technologies. An integrated flowsheet consisting of sorting, crushing/grinding, physical separation, acid leaching, solvent extraction, and selective precipitation was designed to achieve continuous production of rare earth products from various coal-related resources such as coarse refuse and acid mine drainage. A pilot plant was constructed that enabled continuous testing of the circuitry on a range of different coal-based feedstocks. Despite achieving significant success in producing high-grade rare earth oxide products, low REE recovery values and high operational costs necessitated a re-evaluation of the process flowsheet. This article describes the circuitry improvements that were based on both laboratory and pilot plant test results. Roasting as a pre-leach treatment was found to significantly improve the leaching rate and overall REE recovery values. After roasting West Kentucky No. 13 and Fire Clay coal refuse materials at 600 °C, REE recovery increased by 60 and 40 absolute percentage points, respectively. Rare earth concentration in the pregnant leachate solution (PLS) was increased to around 700 ppm prior to solvent extraction using a staged precipitation method. REEs in the precipitate were re-dissolved, purified, and extracted from the PLS using solvent extraction and selective precipitation to values of around 80%. As a result of the improvements, chemical consumption in the acid leaching and solvent extraction processes was significantly reduced. A techno-economical assessment of the improved flowsheet indicated significant commercialization potential.

By Diler Katircioglu-Bayel, Oner Yusuf Toraman, Safak Gokhan Ozkan

One of the most energy-intensive processes for producing submicron range calcite is stirred media mill. In the present work, numerous operating parameters such as solid mass fraction, grinding media size, media filling ratio, and grinding time have been investigated using a vertical type stirred media mill. The results are evaluated on the basis of mean particle size, specific surface area, and specific energy consumption. After conducting this study, optimum experimental conditions found to be as 70% media filling ratio, 25% solid mass fraction, 1 mm grinding media size, and 120 min grinding time. Besides, energy savings up to 22% were achieved with the choice of proper media size.

By H. Y. Yang, L. L. Tong

For gold recovery, a Chinese refractory, high-sulfur gold concentrate was subjected to biooxidation with high pulp density in a single stirred-tank reactor. The flotation concentrate contained 36.9 percent sulfur (S) and 33.9 percent iron (Fe). Different experimental regimes for biooxidation were applied. With a mixed culture and by controlling the amount of addition of the gold ores and the pH of the biooxidation system, maximum iron oxidation of 82.6 percent and sulfur oxidation of 79.3 percent were achieved. The experimental results indicate that the pH control was beneficial to the biooxidation of this concentrate. Approximately 28.4 percent of elemental sulfur (S8) was found in the oxidizing slags. Two dissolution mechanisms of elemental sulfur are proposed: (1) FeS2 → S80 → S2O32− → SO42− and (2) FeS2 → S80 → SO42−. The high pH had a positive effect on the reduction of the S8. The results of thermodynamic analysis indicate that as an oxidant the dissolved oxygen can effectively reduce the Gibbs free energy of the pyrite oxidation process and, compared with the reaction of ferric iron as the single oxidant, the oxidation of pyrite is easier. The efficiency of the gold recovery was related to the iron oxidation as well as the sulfur oxidation. Gold and silver recoveries of 92.4 percent and 66.4 percent, respectively, were achieved.

By Walid M. Abdellah, Soliman Abu Elatta A. Mahmoud, Hanaa A. Abu Khoziem

The high-grade Th-U-Y zone is one of the numerous mineralized zones found in the El Garra El Hamra hydrothermally altered syenites in southwestern Egypt. It is characterized by the thorium minerals thorite and thorogummite, which are closely associated with xenotime-(Y). This zone of mineralization is localized in the eastern part of the El Garra El Hamra hydrothermally altered syenites. This zone does not relate to the first phase of syenites that appeared on the surface but is linked to the other, hidden phase of the syenitic body. Additionally, the fluids responsible for the mineralization of this zone belong to the late-stage hydrothermal event as well as the fault action due to the fact that it had continued reactivations for a long period of time. The studied mineralized zone also contains ceriopyrochlore-(Ce),(Ce,Ca,)2 (Nb,Ta)2O6 (OH), fluorite (CaF2) and barite (BaSO4), which are found in considerable amounts, whereas apatite (Ca5(PO4)3F) and chromite (FeCr2O4) are rarely found together with Fe-oxi-hydroxides (hematite and goethite) with a minor amount of jarosite (KFe33+(OH)6(SO4)2). Finally, the main constituent mineral in the zone is the pseudomorph perthite in addition to quartz, which is found as deformed crystals. A technological sample was collected from this zone and was found to assay 4.62 weight percent thorium (Th), 0.37 weight percent uranium (U) and 3.12 weight percent rare earth elements (REEs). From the chemical and mineralogical composition of the studied technological sample, the leachabilities of Th, U and REEs were investigated using sulfuric acid (H2SO4) agitation leaching and pug leaching methods. The latter was found to be preferred under the conditions of 0.54 ton H2SO4 per ton of altered syenite at 110 °C for two hours.

By J. Casado

This paper presents the results of an analysis and summary of relevant literature on the mechanism of cementation of metals in acidic aqueous media, with the aim of reconsidering the conventional assumptions. The simplicity of the process as a mere galvanic metal displacement is discussed, and the real effects of pH and hydrogen pressure in different cases assessed. Finally, an alternative mechanism scheme with respect to the role of hydrogen species, in agreement with reported data, is proposed.

By J. D. Miller, C. L. Lin

From mine to mill, the 3D characterization of particles ranging in size from meters to micrometers is now possible. A brief review of X-ray tomography for mineral processing is given with recent advances considered, such as high-speed scanning and image analysis procedures to describe important particle properties, including size, shape and composition. Considering these new 3D characterization tools, applications in mineral processing are discussed for high-resolution X-ray microtomography (HRXMT) laboratory analysis of particles ranging from 20 mm to 5 μm, with a voxel resolution of about 1 μm, including (1) multiphase particle characterization by HRXMT and comparison with scanning electron microscopy (SEM), (2) particle damage state as a result of blasting/comminution, (3) liberation characterization to describe expected separation efficiency, (4) exposed grain surface area analysis to explain the flotation of locked particles, and (5) floc size, shape and water content for polymer-induced flocculation. Finally, applications in mineral processing for plant-site analysis using high-speed X-ray computed tomography (HSXCT) are examined, including, for example, coal washability analysis, the analysis of crusher plant products, and the analysis of pebble phosphate products from central Florida. Scanning rates on the order of 1 kg/min for particle sizes ranging from 150 mm to 1 mm are possible, with a voxel resolution of about 100 μm. For coarse particles smaller than 5 to 10 mm, high scanning rates of more than 300 t/h may be possible at a voxel resolution of about 1 mm.

By H. Y. Yang, L. L. Tong

Semicontinuous-flow, multistage biooxidation experiments of a Chinese refractory, high-sulfur gold concentrate were conducted with different pulp densities for gold recovery. The maximum iron, sulfur and arsenic oxidation rates of 90.0, 88.8 and 96.4 percent, respectively, were obtained in the experiments with 5 percent pulp density. The highest gold and silver recoveries of 96.1 and 68.9 percent, respectively, were achieved by cyanidation. The negative effect of high pulp density on biooxidation was related to the decrease of free and adsorbed cell concentrations with increasing pulp density. The data of iron oxidation from the semicontinuous biooxidation experiments were best fitted by a shrinking core model in which the chemical reaction controlled the rate. The dissolution kinetics of sulfur and arsenic were therefore analyzed by a shrinking core model in which the internal diffusion controlled the bioleaching rates. For the quantitative description of biooxidation efficiency, two parameters — mass dissolution rate and volume dissolution rate — were proposed. In the first stage, the mass dissolution rates of minerals were negatively correlated while the volume dissolution rates were positively correlated with the actual pulp density. The iron and sulfur mass dissolution rates decreased with increasing actual pulp densities in the third and fourth stage, while linear increasing relationships between the volume dissolution rates of minerals and the actual pulp density were observed from the second to fourth stage. The highest mass dissolution rates of minerals were obtained in the first stage with 5 percent pulp density. The highest volume dissolution rates of minerals were obtained in the first stage with 15 percent pulp density. Compared to the volume dissolution rate, the mass dissolution rate was more intuitive to reflect the negative effect of high pulp density on biooxidation efficiency.