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By S. M. Marr

"Water availability and water-related environmental impacts are now one of the most significant challenges facing primary production within the global minerals industry. Whereas the industry has, to a large degree, been able to demonstrate a collective response to greenhouse gas emissions and global energy demand, no such strategy exists for water. In part, this is because water quality and availability are regional issues, but also too because water quality cannot be defined by a single attribute, and extrapolation of any set of water quality indices to their associated environmental impact is no trivial matter. In design situations specifically, the situation is exacerbated by the fact that process engineers typically focus on site water management, and consent authorities are primarily in catchment level issues. As a result, an integrated approach to water management is difficult. This does not stem from an unwillingness by members of the professional team to engage with the total picture of water quality and availability, but principally from the fact that there is no common language through which to approach the problem.It is imperative for process engineers to extend their design system boundary, to reflect the geographic scales over which water impacts need to be quantified. It is not suggested that chemical engineers and metallurgists should become experts in geochemistry, hydrology and limnology. Rather, the challenge is to develop tools through which better communication of the relevant environmental impacts can be achieved.It has been estimated that 50% of the capital for new plants is devoted to handling wastes. The integration of mass exchange processes, adopting a life cycle analysis framework for considering environmental impacts and shifting the emphasis from effluent concentration to environmental impacts should be adopted in the framing of the design problem have been suggested as techniques of Environmentally Conscious Design. Shifting the focus from effluent concentrations and legislative requirements to evaluating the environmental impact is an important step towards improving the overall environmental performance of a process facility."

Jan 1, 2003

By Hristo Stanchev, Veselin Mehandzhiyski, Sashka Kozhuharova, Stefan Stamenov, Alexandar Penchev, Nikolay Nestorov, Velika Stamatova, Ekaterina Todorova

"This article presents the results of comprehensive research on the quantitative distribution of gold content in the raw ore and tailings from the flotation enrichment process at the Ellatzite Med plant. The study is a quantitative and qualitative determination of the presence of gold in the ore processed by Ellatzite Med AD, as well as its behavior and distribution in the various metallurgical products of the flotation process. The representativeness of the samples taken is ensured by the frequency of sampling: four work shifts of sampling on different days within a period of four consecutive weeks. The form of gold present is determined both in the analyzed samples and in separate fractions - granulometric, magnetic, electromagnetic, heavy and light. A summarized diagram presents the phase distribution of gold in the final products of the dressing process. The results obtained are used for further analysis and evaluation of the actual technological parameters of the gold. It was established that an increase in the initial gold content, respectively in the content of native gold in the raw ore, with the current process, leads to an increase in gold losses, mostly in the native gold phase. The conducted analysis of the results from the comprehensive tests on determining the form of gold present in the various enrichment products gave rise to further research with the use of a Knelson centrifugal concentrator."

Jan 1, 2014

By Y. F. Li

Fengning ilmenite ore is a magnetic deposit in gabbro containing high phosphorus and low titanium, the main minerals in which are ilmenite, magnetite and apatite. The dissemination size of magnetite is so fine that even the percentage of -0.010mm level is up to 36.50%. The fine and vein magnetite are distributed in gangue and ilmenite, so the majority of the magnetite is difficult to be separated from the gangue. Ilmenite is difficult to be recovered by low-intensity magnetic separation even through fine grinding. In high-intensity magnetic separation of ilmenite, the gangue inter-growth with the magnetite and the Fe-containing silicates may be enriched in the concentrate, and the ilmenite of the concentrate will be reduced. Based on the processing mineralogy research, combined gravity-flotation process is suggested to recover the ilmenite. The method is also good to reduce phosphorus in the ilmenite concentrate.

Jan 1, 2014

By John A. Rumball, Martin R. Houchin

"For gold leaching of oxide ores, the optimum cyanide : oxygen ratio is approximately 106 mg/L NaCN : 10 mg/L O2 (6.9:1 by mole). In sulphide ores, galvanic coupling of the gold with the electrically conductive sulphides significantly increases this ratio such that leaching may occur in a relatively low dissolved oxygen (DO) environment.RESULTS AND DISCUSSIONGold leaching in a carbon in pulp (CIP) and carbon in leach (CIL) circuit is driven by the supply of cyanide and oxygen, as described by Elsner’s equation (1):• 4Au + 8CN- + O2 + 2H2O ? 4Au(CN)2 - + 4OH- (1)Equation 1 suggests that the ideal molar cyanide : oxygen ratio should be 8:1, or 122.5 mg/L NaCN to 10 mg/L of DO. It is generally accepted however, that oxygen is not completely reduced to hydroxide at the gold surface, and that equation (2) better represents the gold leaching reaction (Marsden and House, 1992):• 4Au + 8CN- + 2O2 + H2O ? 4Au(CN)2 - + 2OH- + H2O2 (2)Additionally, since gold leaching is limited by either the diffusion of cyanide or oxygen to the gold surface (Habashi, 1993), then the relative diffusion rates of cyanide and oxygen must also be taken into account. Marsden and House (1992) suggest that the ideal molar cyanide : oxygen ratio is 6:1, while a more recent investigation using laboratory and plant observations (Heath and Rumball, 1998) suggested a molar ratio of 6.9:1.In practice, although a cyanide : oxygen mole ratio of 6.9:1 applies to some circuits, there are many instances when this is not the case.In sulphide ores, galvanic coupling of the gold with the electrically conductive sulphides significantly increases this ratio. Galvanically connected sulphides, and possibly carbon, provide a large surface area for oxygen reduction. As the cathode surface area increases, the oxygen concentration required to sustain the same rate of gold oxidation decreases proportionately.Galvanically connected particles may be composite particles, however they may simply be liberated sulphides in the same suspension as the gold. Particle collisions within a slurry are sufficient to provide momentary galvanic connection (Greet, 1995)."

Jan 1, 2003

By Zhou Junwu, Sun Chuanyao, Wang Fuli

"In this present paper, the authors introduce the artificial neural networks into the modeling of the industrial flotation process, integrating information technology, control theory and intelligent optimizing method to flotation technology. The new idea gives a new way to solve the difficulty in this field, and therefore brings the study on the automatic control of flotation process in China into a new start.The Radial Basis Function (RBF) network, featuring a quick learning speed, is one of the feedforward neural networks. It has attracted much attention from automatic control recently for its implementing the nonlinearity mapping through adjusting the parameters of the nonlinearity transfer function. One of the online adaptive learning algorithm—the nearest neighbor-clustering algorithm, which can automatically determine the number of hidden units, has been implemented in the MATLAB programming language in this paper, laying the foundation for the flotation models.The relation model between ore pulp characteristics and reagents consumption has been proposed using the RBF networks based on the industrial lead rougher flotation of lead & zinc ore, and the simulation has been conducted in the laboratory with the results matching the samples data very well. The Xilin Lead & Zinc Mine Flotation Process Intelligent Consultation System of Reagents Consumption, which suitable for industrial process, has been developed. The reagents consumption advised by this system would stabilize the flotation process, and increase the recoveries. It could be used for providing the technological consultation to flotation operators in site, and for training new operators."

Jan 1, 2003

By Ming’an Wei, Chuanyao Sun, Yangge Zhu, Fayu He, Yanbo Shang, Xingrong Zhang

In order to discuss the separation mechanism of copper-molybdenum ore, surface electronic structures of chalcopyrite and molybdenite were studied in the paper, by using First Principles method of quantum chemistry. So, the separation mechanism of thioglycolic acid (TGA) with chalcopyrite and molybdenite was revealed better. The results showed that differences of the electronic structure of chalcopyrite and molybdenite could directly affect their interactions with TGA, such as band structure, density of states, Mulliken populations, and so on. And the frontier orbitals of chalcopyrite and molybdenite were also calculated by Dmol3 after the optimization by CASTEP, from which the interaction energies between minerals and TGA were obtained and compared. So, the essence of flotation separation of copper and molybdenum were well revealed.

Jan 1, 2014

By E. D. Gálvez, L. A. Cisternas, R. Acosta-Flores, F. A. Lucay

The optimal design of flotation circuits is a complex task as the mathematical model is nonconvex and includes binary variables, making it difficult to obtain the global optimum solution. Furthermore, there are epistemic uncertainties in the evaluation of the performance of flotation and grinding units. This epistemic uncertainty is generated because semi-empirical models are used with parameters that are a function of the circuit design. Therefore, it is not possible to adjust these models based on experimental data as the experimental conditions are not known at the design stage. This paper analyzed the effect of the uncertainties in flotation units, grinding units, and both units simultaneously. As a result, this paper demonstrated that, for a specific mineral, few structures exist that are optimal for a wide range of values in flotation stage recoveries and liberation fractions in the grinding units. A remarkable aspect of this work is that it introduces grinding, one of the operations that most influences energy consumption in mining and has not been studied in depth in the design of flotation circuits. To demonstrate that there are few optimal structures for a specific mineral when there is high uncertainty in the process units, an a priori approach or first principles was used. Two methods of proof were used: proof by construction and proof by exhaustion. Proof by construction is the construction of a concrete example with a property to demonstrate that something having that property exists. In this work, two examples were considered in the proof by construction. In proof by exhaustion, the conclusion was established by dividing it into a finite number of cases and proving each one separately. Here, 30,000 cases were included for each example. This knowledge can be useful in circuit design including grinding, e.g., after selecting the circuit (or the most promising circuits), and the equipment design parameters and operating conditions can be defined based on simulation and laboratory tests.

Jan 1, 2018

By D. Izerdem, S. L. Ergun

"Beneficiation of the finely disseminated valuable minerals has been an important issue in the mineral processing field for decades. Treatment of the fine materials becomes difficult with using traditional gravity concentration equipment. To investigate particles behavior in a commonly used conventional gravity concentration equipment, a comprehensive study was undertaken in a plant, which only consists spiral concentrators as concentration units. Spiral concentrators require relatively coarse material to effectively concentrate valuables as well as offering greater simplicity for especially higher grade feeds. In the current work, chromite ore (d80 = 290 µm) was treated using spiral concentrators and the performance of spiral concentrators was examined. The design of the separation circuit comprised of rougher, cleaner and scavenger stages. The resultant fractions produced by each separation unit and feed samples were analyzed to identify the particle sizes, mineral liberations and chromite content. Grade and recovery comparisons were presented in size-by-size manner and the separation tendency of the particles were determined in varying feed rate conditions. The overall results indicated valuable mineral loss of the plant and alternative suggestions were pointed to reach the target values.INTRODUCTION Spiral concentrators are simple low energy consuming devices, which are generally used for pre-concentration of the minerals. They are cost efficient equipment separating minerals mainly based on density differences of the minerals. The adjustable splitters remove the concentrate as the remaining stream continues to move down the spiral. Separation on a spiral is achieved through a combination of forces that act on particles as they move down the trough of the spiral. The main forces known to act on the particle on a spiral are the gravitational force, centrifugal force, hydrodynamic drag and Bagnold force (Atasoy and Spottiswood, 1995; Burt, 1984). Since the classification in a spiral concentrator depends on particle specific gravity and size, the operation of spirals can be analyzed using size recovery or partition curves (Bazin et al., 2014). Spiral concentrators possess multiple design parameters for a variety of applications. The design parameters that govern the performance of the spiral can be identified as the diameter, number of turns, slope, pitch and the profile of the trough. For an efficient separation on a spiral concentrator, the properties of the slurry flowing on a spiral, ore texture, percent solids and flow rate play important roles."

Jan 1, 2018

By X. Y. Zeng

Most Chinese titanium bearing minerals are the composition of magnetite vanadium and ilmenite. All of such mineral processing plants use low intensity magnetic separators to recover magnetite and vanadium goes with magnetite. In the past years most of the plant tails containing about 10% TiO2 were abandoned. Now many of these plants use SLon magnetic separators to recover ilmenite in the roughing stage, which can throw away most of the gangs and slimes with very low cost. The new development of applications of SLon magnetic separators in Chinese ilmenite processing industry is introduced in the paper.

Jan 1, 2014

By N. Nehoroshev, P. Solozhenkin, N. Voyloshnikova, A. Pshennikov

"Molecular modeling of clusters of major bismuth minerals, Bi2S3, was carried out whereby molecular models of minerals and reagents clusters were created. Their HOMO and LUMO energy levels were calculated and using known modelling equations, the absolute hardness ?, eV and electronegativity were calculated. The charges of separate atoms of clusters and the change of properties of the minerals were determined which allowed predictions of the flotation properties of raw ores containing rare bismuth minerals. Modeled complexes containing the clusters of minerals and various collectors were constructed, consisting of atoms and bonds within clusters of minerals. Major physical and chemical parameters were determined for the complexes created, including the total and electronic energy. Based on the energy calculations, predictions of the collector efficiency were proposed. The efficiency of collector was established for various thiolic reagents, the compounds of phosphorus (III) and mixtures of reagents. Theoretical results were checked and confirmed against laboratory ore flotation tests. A gold-bismuth-magnetite ore type was studied where gold, bismuth and iron (magnetite) are of industrial interest. The ore contains 2.8 g/t Au, 1.0 g/t Ag, 0.26% Bi, 45% Fe and 1.25% As. Sulphide mineralization can be mainly found in the form of pyrrhotite, pyrite and arsenopyrite. Bismuth can be mainly found in the form of bismuthite and native bismuth. Gold is fine. A flow sheet for Zhelezny Kryazh ore treatment was proposed. This flow sheet consists of grinding to 95-98% -74 µm, sulfide flotation with two cleaner with xanthate addition, cyanidation of flotation concentrate and flotation tailings included treatment with with CaO (6 kg, 6 hours), cyanidation (8 hours) and CIL (8+24 hours). Saleable products are gold doré, bismuth and iron concentrate."

Jan 1, 2014

By J. Quinteros-Riquelme

Despite increasing demand, the supply of silver is limited by its inadequate recovery from ores. Due to its scarcity in nature, its high ore variability and complex mineralogy of current silver deposits, its recovery by mineral froth flotation presents a real challenge for process engineers. A silver ore often contains significant amounts of five to ten different silver minerals and knowledge of the mineralogy is a necessary precursor to flotation testing. In this work, a complex silver ore was treated by using batch laboratory flotation, in an effort to find the best experimental conditions to obtain the optimal silver recovery. Mineralogical characterization of feed samples was conducted using a combination of tools, namely the mineral liberation analyzer (MLA) and inductively-coupled plasma mass spectrometry (LA-ICP-MS), which indicated that most of the silver occurred as ?invisible? silver in pyrite. The pyrite assay of the ore was approximately 4%. The ore was processed in two flotation stages. The first stage, sulphide flotation, aimed to collect a sulphide mineral rich concentrate; then a non-sulphide flotation stage was performed by adding sodium sulphide and collectors to the remaining material in the cell, with the objective of obtaining a pyrite rich concentrate. To reach the target recovery of silver from this ore, various variables were altered. In the first stage: mixed collectors, activators, dispersants, and mainstream inert grinding were assessed. In the second stage, the conditions for sulphidization and subsequent flotation were both investigated. From the grade recovery curves for silver and sulphur it was possible to observe a similar metallurgical behavior for both elements, supporting the results given by the mineralogical characterization. Keywords: silver oxide, froth flotation, sulphidization, mig

Sep 1, 2012

By P. Huang

Chitosan was tested as a depressant in the differential flotation separation of chalcopyrite and galena. The micro-flotation results showed that chitosan selectively depressed chalcopyrite while galena was floated by potassium ethyl xanthate in acidic solutions. With the addition of 0.67 mg/L chitosan (CT) in the slurry of chalcopyrite-galena mixtures at pH 4, the recovery of galena was 95% while that of chalcopyrite was 30%, indicating that chitosan could potentially be used in differential Cu-Pb sulfide separation. Furthermore, the study of chitosan with either low (LCT) or high molecular weight (HCT) in the differential flotation indicated that better separation was achieved by the chitosan with lower molecular weight (LCT). ToF-SIMS was employed to study the distribution of CT on the surface of chalcopyrite-galena mixtures by ion mass spectra analysis and surface imaging, which showed that CT adsorbed heavily on chalcopyrite but barely adsorbed on galena. The positive ion ToF-SIMS spectra provided information on the surface composition of chalcopyrite-galena mixtures after CT treatment. It appears that the selective adsorption of CT on chalcopyrite was originated from the strong interaction between NH3+ and Cu. Keywords: differential flotation, micro-flotation

Sep 1, 2012

By John A. Herbst

Professor A.M. Gaudin and his students at MIT were dedicated to understanding the fundamentals of mineral processing and as a consequence were constantly searching for better quantatative descriptions of size reduction, liberation and mineral separations. I have had the good fortune of meeting Professor Gaudin and working with many the modeling pioneers who followed him. I have observed first hand the refinement of mineral processing models as they increased in realisticness moving up the steps of the pyramid (see figure below) from pure empiricism to the current pinacle of physics based models. During this journey our industry benefited significanbtly as model prediction errors were reduced from ± 20% to ± 1%. Unit operation and plant simulations improved in accuracy and speed of calculations.

Sep 1, 2012

By Reuter M. A., R. D. van der Weijden, W. F. C. van Wageningen

"Copper(II) can be recovered or removed from acidic copper sulfate solutions as cuprite or metallic copper powder by reduction with carbohydrates. The copper powder characteristics, such as size and shape of particles, determine the tendency to adhere to reactor walls and to agglomerate. In order to make this process suitable for a commercial scale pipe reactor, process conditions and the reactor configuration were varied in order to influence the copper characteristics in a positive way. The aim was to achieve proper particle throughput in the pipe reactor and to obtain a well defined copper powder.In this paper the effect of both, chemical and physical parameters on the shape and size of particles were systematically studied in a number of autoclave experiments. These parameters include mixing, Cu(II) concentration, pH, temperature, seeding, use of additives and reactor materials. Additionally, Monte Carlo simulations of copper growth inside a Kenics static mixer were made. Results show that the use of additives and the use of static mixers influence particle characteristics the most."

Jan 1, 2003

By Y. G. Zhu, G. B. Zheng, Z. B. Qian, X. R. Zhang, A. J. Ren

"Based on PMA polymer, two kinds of novel macromolecular depressants, PMTA and PMA-PDTC, were designed and synthesized. PMTA was used for desilication in hematite reverse flotation. PMA-PDTC was used in the separation of Cu-Pb concentrate as galena depressant. The micro-flotation results showed that PMTA exhibited a good depression performance compared to starch. We found that 98.29% of hematite was depressed with a grade of 65.24% at pH 11 with 12 mg/L dosage. The flotation separation results of Cu-Pb concentrate demonstrated that PMA-PDTC was an effective depressant for galena in separating galena from chalcopyrite. When IPETC was used as collector, at pH 8.5, the flotation separation tests demonstrated that Cu concentrate was obtained with a grade of 28.89% containing 12.12% Pb.INTRODUCTIONThe role of depressants is crucial in the separation of oxide or sulfide minerals, for example, the desilication in hematite concentrate and the separation of Cu-Pb concentrate.It is well known that, in current reverse flotation processing of hematite, starch is a traditional depressant for hematite. Most research focus on the modification of starch [1-3]. Although its depressing ability is enhanced in some extent, its own shortcomings is still existed. So, it is important to develop a new hematite depressant instead of starch.In the separation of chalcopyrite and galena, because of their extremely similar floatability, it is difficult to realize the separation of these two minerals. Traditionally, there are two methods widely used in the separation of Cu-Pb concentrate by depressing chalcopyrite with cyanide [4] or depressing galena with dichromate [5] in most cases. However, these two inorganic depressants are toxic and hazardous. Their use could cause heavy pollution problems and a large loss of precious metals. In order to adapt to the requirements of sustainable economic development and environmental protection, the research and development of green and environmental depressant has gained more and more significance."

Jan 1, 2018

By A. V. Faiberg

Currently, the interest to conditioning of cyanide-bearing recycled solutions with high-grade of base metals, in particular, copper has significantly grown. This can be explained by two major factors. Firstly, there are strict regulations on cyanides amount in tails and higher cost of detoxification processes. This problem can be easily solved during the ore treatment using the conditioning of solutions and water recycling. Secondly, the presence of other metals minerals which react with cyanide during gold leaching resulting in high cyanide consumption. The presence of copper is a major problem. Many copper minerals react with cyanide with the formation of cyanide complexes-Cu(CN)2-, Cu(CN)32- and Cu(CN)43-. One mole of copper consumes 2-4 moles of free cyanide. Availability of cyanide-soluble copper minerals has deleterious effect on gold leaching (gold recovery, cyanide consumption, tails detoxification, efficiency of gold elution and electrowinning). The precipitation of copper from the solutions improves gold recovery by CIL. The removal and recycling of cyanide allowed the reduction of cyanide addition to the process. The recycling of spent cyanide-bearing solutions based on the removal of copper and the return of cyanide bound in complex compounds for leaching process is an optimal way of solving the problem of gold-bearing copper ores treatment. By using the technology, an adverse impact onto gold recovery process is eliminated and at the same time reducing the cyanide consumption. Today, processes and methods of high-grade copper leaching solutions conditioning before and after gold recovery have been developed, which combine two ways of copper recovery: as a saleable product and cyanide to recover gold and reduce total operating costs. They are Cutech, MNR, SART, Cyanomet, AuGment, Vitrokele, Hannah and Cyanisorb. At the same time, these technologies have not been studied enough and described in literature. Data on parameters and operating conditions as well as introduction is not available. The conditioning technology of recycled solutions developed by IRGIREDMET JSC allows copper to be recovered as high quality concentrate and at the same time free cyanide regeneration in the recycled solution which is amenable to gold leaching. This technology was commercialized at a mine in Kazakhstan in 2008. The removal and recycling of cyanide does not require additional cyanide and is cost-effective. More cost-efficiency is achievable through selling copper concentrates, closed water cycle without the detoxification of effluents and enhanced gold recovery by CIL and cathode quality.

Sep 1, 2012

By Graeme Lane, Yuqing Feng, Kaixi Jiang, Junwu Zhou, Zhengchang Shen, Tao Song

"Airlift reactors are used in a wide range of industries, such as hydrometallurgy, biochemical processes, chemical process industry and waste water treatment. With increasing superficial gas velocity three circulation regimes can be defined: no gas bubbles in the downcomer, gas bubbles remain stationary in the downcomer and gas bubbles in the circulating regime. In this paper a numerical modelling method was presented for gas-liquid flow in airlift reactors under different bubble recirculation regimes. Gas-liquid flow was modelled using the Eulerian two-fluid equations, and extra user defined subroutines were incorporated to consider the complex physics, such as bubble induced turbulence and turbulent dispersion force. Some alternative correlations of drag coefficient were used to capture the bubble distributions in the riser and downcomer of the airlift reactor, with consideration of the interaction between bubbles. As using constant bubble size is hard to describe global characteristics of the flow in airlift reactors for three circulation regimes, a model including multiple bubble sizes was presented to get more accurate simulation results of gas holdup and water velocity. Also, the inhomogeneous MUSIG model was used, as an exploration, to compute the complex flow regimes. The MUSIG model is a population balance method to predict the bubble sizes, taking break-up and coalescence into account. The modelling method was applied to a laboratory internal loop airlift reactor, and the simulation results were compared with the experimental measurements of Simcik et al. (2011) for gas holdup and water velocity. The three bubble circulation regimes were observed from simulation figures. Reasonable agreement was obtained over a range of operating conditions, and an improvement was demonstrated using the proposed methods."

Jan 1, 2014

By Kal Sastry, Anshuman Prasad

"Agglomeration of fine iron ore concentrates is carried out in two steps:Balling, which refers to the production of green pellets by tumbling moist fines powders in drums, discs, or cones, and Induration, which refers to the subsequent thermal treatment of the green pellets in straight grate or grate-kiln systems.This paper addresses computer simulation of balling or green pelletization step. The process of agglomeration from a mechanistic point of view can be described as the transformation of moist feed to well-formed species or pellets. The moist feed is composed of fines of infinitesimal size while well-formed species are of finite size and number. These well-formed species undergo changes in their size and number through different mechanisms of agglomerate formation and growth. Nucleation, coalescence and layering are the three main mechanisms that describe the formation and growth of granules during an agglomeration process. A population balance equation enables quantitative description of the evolution of agglomerate size distribution due to the occurrence of each of the mechanisms.A numerical solution for the population balance model is necessary and is obtained by the use of a sizediscretization approach. The numerical solutions provide a suitable basis for the analysis of the agglomeration process. Also a coalescence kernel has been introduced that is capable of describing the simultaneous occurrence of nucleation, coalescence and layering mechanisms. The effect of feed moisture has been described using a moisture factor with an exponential functional dependence on the moisture content. The effect of the feed to seed ratio is modelled by the introduction of a crowding factor. It was assumed that only the feed particles which are much more in number experience a crowding or restricted in space interactions effect. A computer simulation program has been developed with MATLAB as the simulation language."

Jan 1, 2003

By Kang N. Zhong, Hui H. Luo, Yunan Phosphate Chemical Co., Yi H. Wei, Yao J. Li, Yu L. Wang

"The three kinds of phosphate ores (igneous, metasedimentary and sedimentary) found in China have great differences in flotation flowsheets and reagents suite because of their crystal structure and mineral composition. The igneous and metasedimentary apatites have good floatability with fatty acid as collector and waterglass, sodium hydroxide or sodium carbonate as conditioners. The sedimentary phosphate is very difficult to beneficiate by direct flotation because of their poor floatabilities and relatively high content of MgO and SiO2, even though the dolomite depressants are used sometimes.The differences in floatability of apatites in China are closely related to their differences in specific surface area. The amount of collector to float apatite increases with the specific surface area. Apatite with lower specific surface area showed good floatability at lower collector concentration. Apatite with a higher specific surface area needed a higher concentration of collector. The content of CO3 2- will affect the specific surface area of apatite by distortion of its crystal structure and consequently affect its floatability.Dolomite can be easily rejected from apatite in a weak acidic medium (pH=5), especially in phosphoric acid medium by reverse flotation. Quartz and siliceous gangue in sedimentary apatite can be removed by direct flotation using fatty acid or by reverse flotation using amine. Amine is not practically applied because sedimentary apatite in China is usually very fine and needs fine grinding, which always results in excessive, very fine, stable and non-flowable foam.Based on the floatability of phosphate ore in China, a two-stage flotation process, direct and reverse flotation (D+R), was developed to beneficiate sedimentary ore. For the Haikou phosphate ore containing 25.11% P2O5, 3.46% MgO and 16.5% SiO2, a concentrate containing 31.84% P2O5, 0.48% MgO and 14.8% SiO2 can be obtained through a continuous D+R test at a recovery of 89%."

Jan 1, 2003

By Richard K. Komarek, Antonios Zavaliangos, Roman T. Dec

"The work in the paper introduces a 2-dimensional finite element model for analyzing particular material processing in a roller press. Two basic roller geometries are considered: (a) smooth rolls (used for milling and compaction) and (b) rolls with cavities, commonly used for briquetting. A model is presented that is suitable to analyze material behavior through all stages of the rolling process: feeding zone, nip region, neutral plane and release section. It can predict pressure, shear stress, slip of the material over the roller surface, material velocity field, failure of the compact during release and the course of other important process variables.MODEL, RESULTS AND CONCLUSIONSAn associated Gurson model was employed as a constitutive model for the material. The calibration of the model was based on experimental results from an instrumented compaction die. Coulomb friction law was used to describe phenomena on the material/roller surface interface. Powder River Basin sub bituminous coal fines with moisture content 9% was used as a model material.Two finite element models have been set up, one for the briquetting roll and one for the “equivalent” flat roll. Approximately 3200 plain strain continuum elements with reduced integration (CPE4R) were used. Lagrangian-Eulerian (ALE) approach in conjunction with judiciously applied remeshing was employed with the commercially-available, dynamic explicit version of ABAQUS finite element code.Comparison of model predictions with experiment shows that there is an agreement in terms of the general trends of experimental values recorded on laboratory roller presses. Gurson model overpredicts stresses at low densities and, as a consequence, overpredicts roll force and roll torque."

Jan 1, 2003