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By William Skinner, Jennifer MacCarthy, Jonas Addai-Mensah, Ataollah Nosrati

"Acid leaching in agitated tanks is central to hydrometallurgical processing for valuable metals’ (e.g., copper, gold, nickel and cobalt) recovery from low grade (e.g., < 2 wt.%) ores. In this study, atmospheric leaching behaviour of Australian saprolitic nickel (Ni) laterite ore using sulfuric acid was investigated under isothermal, batch conditions at pH 1. The effect of primary process variables comprising time (4 h) and temperature (70 and 95 oC) on the leaching mechanisms and kinetics was established for -2 mm, low grade (~1 % Ni) saprolitic ore dispersions at 40 wt.% solid loading. Leaching proceeded incongruently, reflecting the proliferation of gangue minerals’ constituent elements (e.g., Mg, Al, Fe) alongside Ni and Co in the pregnant leach solutions (PLS). Subsequent analysis showed that 89% Ni and 78% Co were extracted after 4 h at 95 oC whilst at 70 oC the recoveries of these metals were markedly low (< 25 %). Overall, 177 and 644 kg H2SO4 /t dry ore were consumed at 70 and 95 oC, respectively. Activation energy of 79.0 ±1.0 kJ/mol was estimated for the mechanism of Ni and Co leaching and associated kinetics. Particles size analyses indicated that when the breakage of frail laterite particles due to shear is taken into consideration, differences in feed and leached product particle size distributions were insignificant , despite a remarkable increase in BET specific surface area of the product. Mineralogical analyses of the feed ore and leached solid products revealed a sub-crystalline silica phase enrichment of the latter. The overall results suggest that the mechanism of acid leaching of saprolitic Ni laterite may be described by a chemical reaction-controlled, shrinking core model."

Jan 1, 2014

By Leopoldo Gutierrez

Eight oil sand ores with the bitumen content ranging between 3.6 and 15 wt.% and the fines content (-44 micrometers size fraction) between 9 and 69 vol.% were subjected to the standard alkali extraction test used to measure the degree of oxidation of metallurgical coals. The results showed that there is a strong correlation between the absorbance of extracted solutions at a wavelength of 520 nm and the ratio of the fines content to the bitumen content. The latter factor is directly relevant to assessing the extractability of bitumen from oil sand ores. Bitumen extraction tests showed that the bitumen recovery decreased from 90 % to 30 % when the absorbance at 520 nm increased from 0.23 to 0.64. A comparison of the UV/visible spectra of solutions obtained from the alkali extraction tests with solutions of Aldrich Humic Acids suggest that low bitumen/high fines oil sand ores release substantial amounts of organic matter very similar, if not identical, to humic acids. In contrast, high-bitumen and low-fines ores do not release as much of the organic matter, and UV spectra of these leached substances are quite different from those of humic acids. Overall, the results show that chemical composition of bitumen in the tested ores varies greatly with ore type and oxidation, and that the alkali extraction test is a promising technique to quickly assess the extractability of bitumen from a given ore type.

Sep 1, 2012

By D. Saramak

The comminution technology based on High-Pressure Grinding Rolls presses (HPGR) application is currently one of the most efficient methods of hard ore comminution from the scope of the energy consumption and the development of industrial HPGR applications in ore preparation circuits is presently the world trend. However, even though the technology is already in use in many countries, which are the leaders in application of modern mining technology, there is still lack of base investigations over the HPGR performance. Throughput and energetic models of HPGR performance are quite well developed, but technological models predicting the comminution effects still needs an in-depth research. In the paper authors present the method of modeling of HPGR products? particle size distribution with using of suitable mathematical models. A basis of the HPGR performance assessment and HPGR-based crushing circuits design is a product?s particle size distribution. In order to precisely determine the particle size distribution of a HPGR product, parameters of product?s particle size distributions should be conditional on the main technical parameters of the roller press like operating pressure and the speed of rolls. The most accurate approximation of a distribution of size particle d appeared the Weibull?s truncated distribution and it is possible to obtain significant relationships between the approximation formula and the value of operating pressure, or feed characteristics. It makes possible a determination of mass recoveries of the product?s respective size fractions and the productivity planning. Instead of pressure (P), the other HPGR operating parameters can be applied, but the P value appears to produce the most relevant relationship. Keywords: HPGR, comminution, particle size distribution, ore processing

Sep 1, 2012

By H. X. Yan, J. X. Zhang, F. S. Niu

"The analysis on influencing factors of hydraulic conditions in fine hematite flocculation, such as stirring speed, stirring time and axial distance of particle size and fractal dimension of floc was investigated. Furthermore, response surface methodology(RSM) has been applied according to the Box-Benhnken center-united experimental design principle to optimize parameters of hydraulic conditions as a response index to indicate the fractal dimension of floc. The results show that when the agitation speed is 900r/min, the axial distance is 2.0cm, and the stirring time is 3.0min, the particle size reaches the maximum value of 35.44µm and the fractal dimension is 1.6594. The interaction between the axial distance and the stirring speed is highly significant, but the interaction with the stirring time is not obvious. The experimental data and model predications match well, which indicates that the established model has high accuracy and practicability. INTRODUCTION With the exhaustion of iron ore resources that are easy to be mined and the vigorous demand for iron and steel, the exploitation and utilization of fine-grained embedded iron ore resources have drawn attention from the industry and the government [1~2]. Flocculation flotation is one of the effective methods for separation and recovery of fine granular minerals. In 1975, the method was first applied and succeeded in Tilden Concentrator, USA. Flocculation and desliming became the key technology of the Tilden to raise its annual treatment capacity from 4 million tons to 8 million tons at that time [3 ~ 4]. In 2008, the selective flocculation and desliming-reverse flotation technology was successfully used to treat 2.8 million tons of Qidong iron ore. Under the conditions of 28.36% raw iron grade and 98% grinding fineness -0.038 mm, the ideal index of 62.5% iron concentrate grade and 68% recovery was obtained [5]. Dr Kitchenner of the Royal College of Mining and the Ore Processing Research Group of Wallenstein Laboratory first proposed the use of flocculation to separate minerals. After that, many scholars conducted a great deal of theoretical and practical researches, but mostly they focused on chemical theories, mathematical models and selectivity differences in the flocculation process, while the research on the influence of the pulp flow state on the separation effect in the flocculation process started later [6~9]. The results show that the motion of the agitated flow field has a significant influence on the formation of flocs. The fluid morphology will change with the change of hydraulic conditions. The change of fluid morphology will not only affect the movement behavior of particles, but also change the action of chemical agents on the surface of mineral particles[10~12]."

Jan 1, 2018

By Z. Y. Lan

Bioleaching of marmatite with various mixed cultures of microorganisms was investigated. The experiments were carried out in shaking flasks with iron-free nutrient and the pulp density of 10% wt/vol at the temperature of 30?. The results show that zinc is preferentially leached before iron. The leaching rate of zinc with the mixed culture of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans is 62% in 18 days. The leaching rate of zinc with the mixed culture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans is nearly the same as that with the mixed culture of Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans (45% versus 50%). SEM and EDX analysis of the leaching residues indicate that a solid product layer composed of iron sulfide, elemental sulfur and jarosite accumulates in the mineral surface and becomes a barrier to the dissolution of marmatite. The bioleaching of marmatite follows the shrinking core product layer model. When the product layer increases and becomes insoluble, the leaching rate is controlled by the diffusion through the product layer and slows down. When the product layer decreases or becomes a porous layer, the leaching rate is controlled by chemical reaction and enhanced dramatically.

Jan 1, 2014

By Sanja Miskovic, Manjunath Basavarajappa

In this study, a coupled CFD-DEM (Computational Fluid Dynamics-Discrete Element Method) approach is used to simulate two-phase, solid-liquid flow within the flotation cell. Turbulence plays a key role in flotation cells and level of turbulence is affected locally by the presence of particles. Turbulence in the flow is modelled using Reynolds Averaged Navier-Stokes (RANS) based k-e model. Using particle transport and spatial distribution, mixing mechanism for differed sized particles are analysed. By including the effects of particle-particle collision, particle rotation, and particle translation, as well as the volume occupied by the particles in the fluid, CFD-DEM approach can be used to accurately predict the motion of particles in the turbulent solid-liquid flows with strong coupling. Electrical resistance tomography (ERT) is used to investigate the effect of impeller size, shape, off-bottom clearance and impeller speed on mixing and suspension behaviour inside flotation cell. The effect of flotation impeller design, impeller size, and off-bottom clearance on flow hydrodynamics is investigated. In the case of moderate and high solids loading (> 10 %w/w), energy is dissipated through inter-particle interactions and four-way coupling becomes important (Derksen 2003). The main goal of this study is to understand the effect of particle size and concentration on flow dynamics at high Re in highly turbulent systems using advanced modelling and measurement techniques. Experimental measurements obtained by ERT) system allowed detailed mapping of temporal hold-up profiles of the dispersed phase. Impeller size and off-bottom clearance are found have significant effect on the particle suspension characteristics.

Jan 1, 2014

By M. Ito

Cobalt-rich ferromanganese crust and nodule ores from seamount areas contain volcanic and sedimentary rocks as substrate or nuclei and these ores require mineral processing to remove the substrate/nuclei rock before smelting. This paper reviews the results of jig separation and air table treatment for the coarse fraction and flotation and hybrid jigging for the fine fraction. Using these techniques substrate/nuclei rock was removed from the cobalt-rich ferromanganese oxide components. The mineralogical properties and metallurgical treatment methods including hydrometallurgical treatment of low grade ore is also reviewed.

Sep 1, 2012

By B. Y. M. Bueno

Biosorption of heavy metals can be an effective process for the removal of heavy metals ions from aqueous solutions. In this study, the adsorption properties of Rhodococcus opacus biomass for Pb(II) and Cu(II) ions was investigated. The effects of initial pH, initial metal concentration and biomass concentration on biosorption efficiency were studied in a batch system. Results showed that the initial pH would play an important role in the Pb(II) and Cu(II) ions removal by R. opacus and affected the zeta potential of R. opacus. The equilibrium adsorption was reached with 60 min. The Langmuir and Freundlich models were used for describing of adsorption isotherm data. The maxi-mum adsorption capacities of biomass were determined as 94.3mgg-1 and 32.2 mgg-1 for the Pb(II) and Cu(II) ions, respectively. The experimental data fitted to pseudo second order kinetic model. Adsorption capacity of Pb(II) ions was found to be reduced by the presence of the other competing metal ions in the system. The FT-IR results of R. opacus biomass showed that biomass has different functional groups and these groups are able to react with metal ions in aqueous solution.

Jan 1, 2014

By M. Ghiani, R. Peretti, S. di Giovanni, G. Zonnedda, A. Serci, A. Zucca

"Beneficiation of the epithermal gold mineralizations associated with an extensive alteration zone in the Serrenti-Furtei region on the island of Sardinia, is proving a complex issue. Experimental investigations have in fact demonstrated that while the ores contained in the upper parts of the deposit are amenable to conventional cyanidation, the gold contained in the refractory ores in the lower portions needs to be recovered by means of flotation, combined with leaching where necessary.The results of commercial heap leaching, carbon-in-leach (CIL) processing and flotation, designed on the basis of the experimental findings and applied to the oxidized portions and transition zones of the deep sulphide mineralizations, confirmed the expectations emerging from the laboratory tests."

Jan 1, 2003

By Ghislain Bournival, Cagri Emer, Seher Ata

"It is well known among flotation practitioners that the contact angle can be correlated with the amount of material recovered from feed by flotation. The contact angle of solids can easily be modified by the addition of a collector. However, some collectors also have frothing properties thus altering the solid and bubble surface properties simultaneously. To avoid this problem, a technique has previously been used in which silanol groups are attached to the surfaces of the particles, but this method has its own problems. In this work, silica particles with various surface hydrophobicities were prepared using an esterification process. By using alcohols with different hydrocarbon chain lengths, from 4 to 12 carbon atoms, surfaces with a wide range of contact angles could be prepared. The technique was used in the modification of silica particles that were tested in a fluidized bed flotation column, and a laboratory mechanical flotation cell. In parallel experiments, dodecylamine (DDA) was used as a collector. It was found that irrespective of the type of flotation machine and surface preparation method, there was a close correspondence between flotation recovery and the contact angle of the particles. The silanation process has known drawbacks relating to the presence of moisture during the reaction, and the stability of the silane coating after it is been prepared. Esterification does not suffer from these disadvantages. This work has shown that the esterification technique is a robust alternative method for preparing hydrophobic quartz surfaces."

Jan 1, 2014

By Paolo Bevilacqua, Paolo Antonini, Lorenzo De Lorenzi

"Ceramic production requires large quantities of K-feldspar, which is commonly sourced from granites, alkali-granites, and feldspathic sands. These rocks contain other minerals, such as quartz and plagioclase, which are undesirable for ceramic production. Due to the coarse mineral grains that constitute these rocks, a reasonable liberation is achieved at a relatively coarse particle size.The feasibility of feldspar-quartz separation using a dynamic dense medium separation system has been investigated as an alternative to flotation techniques. The use of a two stages cylindrical vessel (Tri-Flo) was preferred to a conical vessel, due to the improved separation efficiency.In a full-scale processing plant, a dense medium separation process can be used as a K-feldspar preconcentration step. This reduces the amount of material to be treated in the more expensive processes, such as finer comminution, flotation or magnetic separation.A comparison between commercial raw materials for the ceramic industry and the “rich in feldspar” products of the Tri-Flo process is reported, and the validity of the process is demonstrated."

Jan 1, 2003

By Rogerio de Oliveira Baldoino

The sedimentary phosphate deposit of Bayovar is located in a very dry area of Peru (desert of Sechura) which is close to the Pacific coast. It consists of seven superposed layers (beds) which call for different strategy of concentration. The ore is composed predominantly by apatite (84% in weight basis) plus silicates (16%). In order to treat the ore from beds 1-5, a suitable standard mineral processing circuit (composed of scrubbing, screening, attrition and desliming) started its operation in 2010, yielding 3.9 Mt/y of concentrate assaying 30% of P2O5. To concentrate phosphate from beds 6-7, however, it is necessary to carry out further cationic reverse flotation of silicates, at neutral pH, to yield a concentrate, which meets market specification. The new process was developed in laboratory scale by a collaborative program conducted between Vale S.A. and the University of Sao Paulo-Brazil. A pilot plant has currently been running in order to confirm the very good results yielded in laboratory scale. The successful accomplishment of flotation in the current beneficiation flow sheet will enable a capacity expansion of 1.9 Mt/y of concentrate assaying 30% of P2O5. As water resources are very limited at Bayovar region, all the steps of concentration, including flotation, must be performed with seawater, which must be continuously recycled. This work addresses some relevant topics related to the use of seawater in the reverse cationic flotation of silicates: influence of temperature, water quality (ageing and chemical composition) and collector type (ether amine versus condensate). The results indicate that condensate amine works better than ether amine. If flotation is conducted with the former collector, the separation process is able to tolerate changes in temperature (25-40oC) and water quality caused by either evaporation or ageing. Keywords: phosphate, flotation, seawater, temperature, ageing, concentration, salt

Sep 1, 2012

By Heiko Schiemann, Christoph Beyer, Thomas Pretz

"Due to multiple experiences in the field of planning and engineering of processing plants for secondary materials the Chair for Processing and Recycling of Solid Waste Materials decided to develop a software tool that supports the engineering and the planning of the basic layout of processing plants for secondary material flows. The detailed description of the material flow and its characteristic parameters is one of the main tasks to be worked out and should be considered as the basis for representative simulation results.The description of the material flow and its characteristic parameters is based on a fraction vector containing 12 material fractions. This is a compromise between a detailed material flow description and a compact and therefore time-extensive calculation model. Each material fraction is characterized by 15 parameters, which can be edited with the help of an easily accessible user-interface. In addition to basic parameters like ignition loss, water content and calorific value more parameters like the material fraction-specific particle-size distribution are contained. Using the model library SimuRec, the processing success and the recovery of complex processing plants for secondary materials can be predicted."

Jan 1, 2003

By Yury V. Kulikov, Rakan Rahbani, Arkady Y. Senchenko

"The relevancy of complex minerals treatment is constantly increasing taking into account mineral resources depletion. Different refractory ores and concentrates, oxidized and polymetallic ores, as well as metallurgical products (slags) can be assigned to such mineral type. The treatment of such products via conventional flowsheets requires considerable capital and operational costs and does not always provide high recovery level of valuable components into a saleable product. Therefore, considerable amount of ores and metallurgical products are not treated, or treated inefficiently. One of the most promising approaches that allows economic treatment of refractory products is their ultrafine grinding down to 5-20 µm with subsequent processing or hydrometallurgy. Horizontal bead mills - the IsaMillTM, developed by Xstrata Technology, received their wide application in mining industry. Standard testing is performed under laboratory conditions in an M4 IsaMillTM (volume - 4 liters) to define the parameters of fine grinding. This mill completely simulates the operation of full scale industrial mills up to 50 m3 in volume (up to 8000 kW motor). The paper describes fine grinding technology performed in bead mills, and the importance of testing according to a certified method for industrial equipment selection. The paper contains description of promising directions of fine grinding technology application for several projects in Russia and Kazakhstan."

Jan 1, 2014

The introduction and subsequent ascendancy of autogenous and semi-autogenous milling for comminution circuits has undoubtedly lead to many economic advantages. From a process viewpoint, however, at least one downside has been the sensitivity of these machines to process input variations. Foremost among these is ore competence, though feed size comes a close second. This sensitivity is due to the reliance of ag/sag mills on the feed ore for their grinding media competence and size. Autogenous (ag) mills are the most sensitive in this respect with semi-autogenous (sag) mills being increasingly less so as the ball charge is increased. Increasingly designers and operators are recognising the importance of feed size and the benefits of manipulating it to improve performance. This has been achieved by installing additional crushing/screening capacity ahead of the ag/sag, better operation of the primary crusher, better control of segregation cased by stockpiles and bins and by changing blast design/practices to modify the ROM size distribution. This paper describes the influence of feed size distribution on ag/sag mill performance with reference to a range of plant data. It particularly concentrates on how changing blasting practice to modify ag/sag feed size can have a considerable overall benefit.

Jan 1, 2003

By S. Gaydardzhiev

Initial experiments towards preparation of hollow ceramic microtubes by dip-coating of fibrous plants with water based alumina gel-casting slurries using hemp and coconut fibres as templates have been done. It has been found that the wettability of fibres and accordingly the stability of the developed ceramic layer on their surface during slurry gelation varied significantly within the different fibre types. Good correlation between the diameters of the template fibres and the resulting channels has been found at the level of solids loadings used, 31 %. Hemp fibres used as bundles have led to formation of multi channel patterns while the coconut fibres-templated process resulted in uniform monochannel materials. The micro tubes have show good mechanical handling.

Jan 1, 2014

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 Kang N. Zhong, Hui H. Luo, Yi H. Wei, Yu L. Wang

"More than 85% of phosphorous reserves in China occur as middle-low grade phosphate of sedimentary origin. The main gangues are dolomite, quartz, silicates, and clays. The characteristics of minerals are finely disseminated. Flotation results have shown that the floatability of apatite of this kind of ore is much worse than that of igneous and metasedimentary origin because of its high specific surface area. Although some effective depressants, such as naphthalene sulfonate and phenanthrene sulfonate, are used to decrease the MgO content in the P2O5 concentrate, its presence is still high (about 2%) in the Chinese concentrates. Meanwhile, the wastewater may cause some environmental problems. Batch flotation results and measurements of specific surface area and CO3 2- have revealed that there is a relationship between the floatability of apatite and the surface area.A two-stage flotation flowsheet, which includes a combination of direct and reverse flotation, was developed for beneficiating sedimentary phosphate ores. The direct flotation was conducted in an alkaline medium and most of the apatite and carbonate minerals floated leaving quartz and siliceous gangue in the sink. In the reverse flotation circuit, the floated product was further beneficiated in an acidic medium to eliminate the carbonate as a float product. Apart from the high quality of concentrate, the two-stage flotation also facilitated the treatment and the recycling of wastewater. A wastewater recycling procedure was developed and tested in a continuous flotation process. The key factor was the careful selection of effective and non-toxic reagents."

Jan 1, 2003

By Matthew Thurley

Optimisation and control of comminution, pelletization, and agglomeration processes is a complex task with large potential for gains in productivity, energy efficiency, and particle size distribution quality. One factor in realising these gains is the requirement for fully-automated online particle size distribution measurement. Moreover, online particle size distribution measurement that is based on the particles on the visible surface and can avoid or mitigate substantial errors that result from under-sizing overlapped particles and over-sizing areas of fines particles. Literature review indicates a body of substantially 2D photographic based particle size measurement systems that suffer from a large number of significant errors except in the simplest case of a monolayer of particles under good illumination with limited color variation in the material. In order to measure the visible particles on a pile there are a number of requirements including; avoiding particle delineation errors due to variation in material color and shadows, detect overlapping versus non-overlapping particles, and identify areas of fine particles as fines and not large rocks. Results are presented using a fully-automated online measurement system of crushed rock on conveyor belt using a 3D surface laser profile. The system provides continuous online measurement and results are shown on over four hours of production after the primary crusher. Size distribution results are calculated using volumetric estimation of the particles on the surface of the pile. The results show a strong capability to discriminate size variation especially in the 10% and 20% passing values. Furthermore results show that if areas of fines are misclassified as large rocks, and overlapped particles misclassified as small rocks, then a near complete loss of discrimination occurs for the P10 and P20 values which become largely constant values.

Jan 1, 2014

By Arkady Senchenko, Yevgeny Zhagun, Yury Kulikov, John Starkey

"The paper contains description of a new project in Russia - gold-processing plant at Aleksandrovskoye deposit (start up in September, 2013). The paper includes a brief description of plant flowsheet, data for material composition and technological properties of ore, as well as information about the achieved parameters of ore processing over the first months of plant operation. The project is interesting because a new semiautogenous mill and a ball mill were purchased on the basis of SAGDesign Consulting Group recommendations after the testing of ore samples characterizing the deposit according to specific years of operation. The plant has relatively small design capacity - 750 000 tpa, but nevertheless is the biggest gold-processing plant in the territory of Zabaikalsky region. Major valuable component in the ore is gold, silver is recovered as a by-product. The ores are very hard to grind. The design grinding flowsheet includes a semiautogenous mill operating in closed circuit with a screen, and a ball mill operating in a closed circuit with hydrocyclones (SAB). Process technology includes gravity processing and flotation with subsequent cyanide leaching of concentrates. Mill operation analysis and conclusions about the compliance of the achieved values to target ones are shown, as well as the accuracy of SAGDesign method when applied to very hard ores of Aleksandrovkoye deposit are presented in this paper. Basic directions of technological flowsheet optimization are also given."

Jan 1, 2014