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By S. Dwarapudi

Pelletizing of Indian chromite ores is more challenging due to their high refractory nature. High Cr/Fe ratio and high MgO content in these ores demand high firing temperatures and longer firing cycles but often result in low strength fired pellets. Aim of this study was to develop cold bonded chromite pellets for smelting in submerged arc furnace (SAF) from chromite fines using suitable binder that induce less gangue into the pellets but cures quickly. Different binders were studied through laboratory pelletizing experiments for their suitability for cold bonding the pellets. As result, a composite binder comprising organic and inorganic binding agents was found to be suitable and pellets made from the same were tested for their low and high temperature behavior. High temperature reduction studies revealed that pellets were resistant to disintegration up to 1200 °C.

Sep 1, 2012

With rapid development of Chinese iron & steel industry, it is of significance to intensify the utilization of domestic complex iron ore resources. The tin, zinc-bearing complex iron ores are typical polymetallic and intractable ones because of the complicated intergrowth relations among the multi-elements, and they have not been efficiently utilized, presently. Based on the thermodynamic analysis of iron, tin and zinc oxides reduction by CO, the technological conditions of tin and zinc recovery and pellets preparation from tin, zinc-containing iron concentrates by selective reduction roasting are studied and a new comprehensive utilization process is developed in this investigation. Under the optimum conditions, the tin and zinc volatilization is respectively in excess of 80% and 70%, and the compression strength of roasted pellet is more than 2500 N/P. Moreover, the residual tin and zinc in the finished pellets is below 0.06%. The finished pellets can be used as high quality iron-making burdens for large-scale blast furnace.

Jan 1, 2014

By X. Tan

In this paper, the application of the metallurgical residue produced from oceanic cobalt-rich crusts leaching process is studied in the area of wastewater treatment. The modification of the sulfuric acid leached residue and the adsorption behavior behaviour of heavy metal ions such as (Pb(II), Cu(II), Zn(II), Cd(II), Ni(II), Mn(II), Co(II), As(III)) in the waste-water on the surface of the residue are investigated. The rate of adsorption efficiency of heavy metal ions in the wastewater on the modified sulfuric acid leached residue is investigated. It is showed that when the initial pH value of wastewater containing heavy metal ions including Pb(II), Cu(II), Co(II), Ni(II), Mn(II), Zn(II), Cd(II) and As(III) range from 1.4 to 1.9, with the use of the modified leached residue, As(III) ion can be selectively separated from wastewater, and the separation efficiency can reach 90%~100%. The adsorption efficiency is affected by pH, reaction time, amount of adsorbent and the initial concentration of heavy metal ions in wastewater. The results showed that the optimum pH was natural pH value and the absorption equilibrium time was 2 hours. The adsorption efficiency of heavy metal ions increases with the addition of adsorbent and de- creases with the increase of the initial concentrations of heavy metal ions in wastewater. The heavy metal ions polluted wastewater, of which concentration is about 22.5~793.6 mg/L, can meet the national disposal standard for industrial wastewaters in China very well, after 2 hours treated by 3.75~7.50 g/L modified adsorbent at room temperature. Standard methods were used to investaged investigate the absorption behaviour between abosorbentabsorbent and metal ions in the wastewater. It is concluded that the adsorption behaviour of Co(II), Mn(II) and As(III) ion fits Freundlich iso-therm, while the adsorption behaviour of Pb(II), Cu(II), Zn(II), Cd(II) and Ni(II) ions fits Langmuir isotherm, and the saturated adsorption amount of the modified adsorbent is about 54.0~336.7mg metal/g?adsorbentabsorbent. It is suggested that the modified sulfuric acid leached residue produced from oceanic cobalt-rich crusts is environmentally attractive and meaningful as absorbent used in heavy metal ions polluted wastewater.

Jan 1, 2014

By Peng Qian, Xiao Li, Guoyan Fu, Peiwei Han, Yongliang Wang, Shufeng Ye

"Arsenic removal from high arsenic gold concentrate is conducive to increase the mineral value and realize the mineral comprehensive utilization. This study investigated the alkaline pressure oxidation leaching (APOL) of an arsenical gold concentrate in lower temperature to separate the arsenic into filtrate. The effects of temperature, NaOH concentration, solid-liquid ratio, reaction pressure and stirring speed on the leaching efficiency were investigated, and the characteristics of the gold concentrate and leaching residues were evaluated using XRD and SEM analysis methods. The obtained results showed that by using lower temperature (<60?) it is possible to avoid the production of elemental sulfur during the leaching process, which is benefit for the oxidation of arsenopyrite; When the reaction was carried out under appropriate conditions, more than 98% of the arsenic will be extracted into the filtrate as the form of arsenate or thioarsenate. INTRODUCTION In recent years, there has been considerable interest in the recovery of gold from refractory arsenical gold ore. The arsenic in this kind of ore usually exists as the form of arsenopyrite, and the gold surrounded by arsenopyrite exists as the form of fine particles, which will give many difficulties to metallurgical work. When the content of arsenic in the gold ore is more than 0.5%, it will seriously penalize the smelting efficiency (Ruiz et al., 2014). So pretreatment of the refractory gold ore is necessary to obtain the largest economic value and environmental benefits (Balaz et al., 2000). The oxidation pretreatment processes mainly include roasting oxidation, pressure oxidation, chemical treatment and biological treatment (Ann et al., 1992; Kou and Chen, 2012; Tongamp et al., 2010; Fernandez et al., 1995; Lin and Zheng, 1996). Among them, the roasting oxidation and pressure oxidation are the more ordinary processes in industry. The roasting oxidation process is the mature and adaptable technology, but the production of waste gas containing sulfur and arsenic will pollute the environment. The pressure oxidation method possesses certain metallurgical and environmental advantages, and can efficiently decompose the mineral. According to the different solution media, the pretreatment can be divided into alkaline and acidic pressure leaching pretreatments (Papangelakis and Demopoulos, 1990; Hiskey and Sanchez, 1995). The acidic pressure oxidation method has been used in most smelting plants for high arsenic gold ore pretreatment, while the alkaline pressure oxidation is still not widely applied. Compared with the acidic pressure oxidation, the alkaline pressure oxidation can be realized under lower temperatures."

Jan 1, 2018

By G. C. Li

Gold extraction using iodide leaching from refractory carbonaceous gold ores was studied. Thermodynamic analysis of iodide leaching chemistry had been carried out. Eh-pH diagram of Au-I2-I--H2O leaching system showed that the coordinating active forms from iodides were I3- and I-, while the major coordinate compound formed during iodide leaching was AuI-. For leaching parameters optimization, technological parameters such as I2 concentration, I2 :I- ratio, oxidation assisting agents, liquid/solid ratio, and leaching duration were studied. The leaching results showed that the average Au leaching rate reached 91% and 92% for oxidized ore and roasted primary ore respectively. Leaching process proceeded in weekly acidic or neutral slurry at ambient temperature; the leaching duration was 4 hours. After that gold was extracted from the pregnant liquor by activated carbon adsorption ? desorption ? electrowinning process. Gold recovery was over 93% in the adsorption process, while the gold recovery in electrowinning process was about 95%, provided that the initial gold concentration is 40mg/L or larger. For iodine regeneration it is enough to add hydrogen peroxide in excess into the filtrate after gold electrowinning, all the iodides existing in the solution in any forms would be precipitated in the form of elemental iodine.

Jan 1, 2014

By G. Zaitsev

In mining and mineral processing, ammonium and nitrate from residues of explosives and other sources are discharged to the aquatic environment. Nitrogenous compounds in mine water can adversely affect the aquatic environment. The aim of this work was to study the biological removal of nitrate from cold inorganic mine water at the pilot-scale in an operating underground mine. Seven-months pilot testing on biological removal of nitrate from inorganic mine water was successfully performed in denitrifying fixed-bed biofilm reactors. The feed to denitrification bioreactors contained 11 mg NO3--N/L. Methanol was added as an external carbon source to the denitrifying bio-reactor since the inorganic mine water contained only traces of organic compounds (<CODCr (50 mgO2/L). Nitrate removal reached 75 g NO3--N/m3/d with removal efficiencies above 95% at temperature below 4°C. Thus, removal of explosives-residues from cold inorganic mine water was shown in pilot-scale biofilm reactors.

Jan 1, 2014

By W. Rubarth

The kaolin losses in hydrocyclone classification are determined by the fines, which are discharged together with the water to the underflow. This paper presents an improved technique of water injection to the conical part of the cyclone applied especially for small cyclones in kaolin preparation. In small hydrocyclones water, injection is a sensitive process. Therefore, the process was stabilized by controlled water injection dependent on the measurement of the underflow shape. Three applications of this innovation are presented. In the first case, the water injection is applied for the separation stage in dilute suspension where the final product is produced in the overflow of a 50mm hydrocyclone. The underflow contains sand and residual kaolin. For a higher kaolin recovery, the underflow is usually treated downstream in washing cyclones. The wash water injection results in a 45 ? 50% - reduction of the kaolin fraction <25µm in the underflow. Thus, water injection to the classifying cyclone leads to a separation comparable with a downstream washing stage. An additional hydrocyclone stage can be deleted. The second application refers to a classification in dense suspension. Here, the underflow of the last hydrocyclone stage was directed to a washing in a 50mm hydrocyclone. The additional injection of 3L/min water in to the conical part of the cyclone reduced the kaolin losses by half.The third application was executed in the washing stage equipped with 75mm hydrocyclones where the underflow is directed to flotation. Using the water injection the kaolin recovery in this stage was increased by approximately 20%. Keywords: hydrocyclone, classification, kaolin beneficiation, water injection, underflow washing

Sep 1, 2012

By M. K. Aydogan

Today, arsenic has become a much greater problem than before because of the limitations introduced by WHO and USEPA that are lowered from 0.05 ppm to 0.01 ppm. In the nature Arsenic is mostly found as inorganic compounds in the forms of arsenite (As+3) and arsenate (As+5) in aqueous solutions. Arsenic contamination in ground and surface waters has been encountered in almost every country. This element has a carcinogenic effect and can occur in natural sources and anthropogenic sources such as metal mining, groundwater usage and industrial activities. In this study adsorbing colloid flotation was applied in the presence of aluminum sulfates. In the experiments SDS and K-Oleate were used as collectors while MIBC was the frother employed. The effects of collectors and aluminum/arsenic ratios on the removal of arsenic were examined under various pH values. It was found that arsenic removal enhanced with increasing aluminum concentration. Furthermore, it was observed that pH was a very critical parameter in all experiments. The best results were obtained when initial As: SDS: Al concentrations were 10:40:40 ppm at pH 5.5. At this concentration, the efficiency of arsenic removal found to be 99.9%. Keywords: arsenic, adsorbing colloid flotation, aluminum sulfate

Sep 1, 2012

By B. Friedrich, A. Weyhe, H. Heegn

"Nickel-metal hydride batteries (Ni-MH) are storers of electrochemical energy, which have a higher specific storage capacity than lead or nickel-cadmium batteries. The demand for Nickel-metal hydride batteries is increasing rapidly since their market launch in the early 1990’s. Today there is no suitable and sustainable recycling process to recover nickel, cobalt and rare-earth metals. The discarded batteries are used today in the steel industry as alloy material because they contain nickel. Cobalt and rare-earth metals (RE) are lost; they are non-recycleable.In a German governmental funded research project, IME Aachen, ACCUREC Mühlheim and UVR-FIA Freiberg are cooperating in processing as well as in creating a feasibility study. The target of this project is the development of a new recycling process for metal recovery from Ni-MH-batteries. The proposed process described in this paper consists of a combination of mechanical, pyrometallurgical and hydrometallurgical processing steps. This process is capable of treating all types of Ni-MH-batteries. After comminution steel and organics are separated. The separated Ni-MH is smelted in an electric arc furnace. The products are a nickel-cobalt alloy and a slag phase enriched with rare-earth oxides for further treatment to ‘mischmetal’. Both the Nickel-Cobalt alloy and the ‘mischmetal’ will be directly used in battery production."

Jan 1, 2003

By A. Erdem

In this study, approximately 3 tons of coal sample taken from thickener entrance was prepared by mineral processing techniques and cleaned by gravity methods. The samples were classified to 5 size fractions by wet screening. The size fractions of +1mm and -1 +0.500 mm were chosen for direct consumption or cleaning by spirals. The studies by Multi Gravity Separator (MGS) were carried out with the -0.500 +0.280 mm and -0.280 +0.020 mm size fractions where the -0.020 mm fraction does not used in the experiments. The clean coal fractions of +1 mm and -1 +0.500 mm obtained by classification were subjected to lower calorific value (LCV), ash and total sulphur analyses. The results were 4168-4946 kcal/kg (on dry basis), 31.01-38.54 % ash and 4-4.27 % total sulphur content respectively. The results of the clean coal concentrated by MGS experiments in -0.500 +0.280 mm fraction was found 5918 kcal/kg LCV, 19.82 % ash content and 80.47 % combustible recovery. The results for the -0.280 +0.020mm fraction were 6004 kcal/kg LCV, 19.19 % ash content, 80.47 % combustible recovery respectively. With reference to the above experimental results, pre-economic evaluation studies were completed and decided to construct an additional unit to the plant. Capacity of the constructed unit is 75.000 t/y which corresponds $ 2.600.000 income in a year. General Directorate of Turkish Coal Enterprises concluded to apply this project to the other coal washing plants in the country due to the successful results of this study and laboratory studies has been going on by MTA currently. Keywords: coal tailings, mgs, recovery, washery, pre-economic evaluation

Sep 1, 2012

This investigation addressed two products from Samarco?s desliming circuit, namely underflow of cleaning cyclones and underflow of desliming cyclones. The roughing cyclones receive the product of the grinding circuit. The underflow of the roughing cyclones feeds the cleaning cyclones and the overflow feeds the desliming cyclones. The underflows of cleaning and roughing cyclones are combined to constitute the feed of the flotation circuit. These fractions were characterized and a new process route was proposed. The size distributions of the two fractions are quite different. The desliming cyclones underflow presents higher amount of material passing 37 µm and of ultrafines as compared with the cleaning cyclones underflow. Laboratory scale flotation tests were performed in a mechanical machine aiming at comparing the performances of these products in the presence of the reagents employed in the concentrator. Pi-lot scale column flotation yielded enhanced iron recoveries for both products in comparison with those achieved in laboratory mechanical cells, without impairing the concentrate quality. The in-crease in recovery was more significant in the case of the cleaning cyclones underflow. These results suggest the use of columns in the flotation of this product aiming at increasing the overall iron recovery. Nevertheless the results also showed that the use of columns to float the cleaning cyclones underflow should also be taken into consideration. Despite the fact that this product requires a longer residence time in order that the required silica content in the concentrate is achieved, the indication is that higher levels of iron recoveries might be reached. The conclusion is that, due to the different behaviors of the two products, they should be processed in distinct circuits to maximize the iron recovery.

Jan 1, 2014

Nowadays, the more successful plants are those who have adopted effective and efficient strategies to optimise their plant operation. As the ?heart of the plant? could be viewed as the mil-ling/grinding area, one of the key steps in plant optimisation is, therefore, ensuring the mill is operating properly. In the past, when primary, secondary and tertiary crushers fed material directly to large ball mills, the energy efficiency of the concentrator was determined for the most part by the ball mill operation, whereas now the energy efficiency of a plant often rests largely on the semiau-togenous grinding (SAG) mill operation. As a result, mines have shifted their emphasis in optimization from ball mills to SAG mills. The grinding mill?s energy efficiency essentially depends on ore characteristics and the discharge rate of broken particles, which in turn depends on how efficiently the discharge pump (grate and pulp lifters) operates. The essential function of pulp lifter being to transport the broken material and slurry out of the mill, its design optimization therefore affects the discharge capacity (or mill throughput) of AG and SAG grinding mills. This paper will discuss how the optimised design of the pulp lifter/ discharger has helped to eliminate material transport issues such as flow-back and carry-over of slurry and pebbles to in-crease the energy efficiency of SAG mill using the actual operational data.

Jan 1, 2014

By S. H. Morar

Froth flotation is a physico-chemical separation process that takes place in two phases; pulp and froth phase. It is widely recognised as a complex process, due to the range of interactions present within the system. Of critical importance is the role of the froth phase within the system. The pulp kinetics governs the maximum potential recovery within a flotation cell, while the froth phase governs the selectivity via the froth?s stability. Higher froth stability improves recovery at the expense of grade, and lower froth stability improves selectivity. It is well known that the two major factors affecting froth stability are attached particles and solution chemistry. This paper looks at a flotation bank at different froth depth and frother concentrations. The air recovery to the concentrate is determined at each condition and relates the effect of the operating conditions on froth stability and transport to the amount of solids that are recovered to the froth and concentrate by true flotation. The results presented show that, for a given process objective, which in this case was a consistent mass pull profile, depending on the operating conditions, solids recovery in the pulp is affected by the air rate required to maintain the target mass pull. To a smaller extent, the changes in the pulp composition affect down-stream pulp recovery. The variation in solids recovered into the froth drives the froth stability at the start of the flotation bank, while the frother drives the froth stability at the end of the bank. The performance in between these two extreme conditions arises from an interaction of these two effects. The consequences of these interactions can give rise to counter-intuitive responses that can confound efforts to optimise the performance of the bank.

Jan 1, 2014

By Neill Bartie, Jacques Eksteen, Sharif Jahanshahi, Shouyi Sun

The gradual increase in Cr2O3 levels of UG-2 ores has become a matter of concern for platinum producers in South Africa due to the formation of chromite spinels in melters. The effect of bulk FeOx/MgO ratio, Cr2O3, temperature and oxygen partial pressure on phase stability and composition in the system FeOx-MgOSiO2- Cr2O3-Al2O3-CaO has been studied between 1400°C and 1600°C using the drop-quench technique. An increase in temperature was found to result in a decrease in [Fe/Cr]spinel. An increase in bulk FeOx/MgO caused Mg, Al and Cr in spinel to decrease, forming more magnetite relative to other spinels. [Fe]spinel decreased and [Cr]glass increased with a decrease in oxygen partial pressure.

Jan 1, 2003

By Ari Kokko

Metso has a long history supplying boilers for high ash coal firing. These boilers are based on circulating fluidized bed (CFB) technology. CFB?s biggest benefit is fuel flexibility ? it can burn fuels from high moisture content to high ash content. Metso has delivered tens of CFB boilers burning waste or high ash coal starting on 80?s. Some of the boilers have been in operation twenty years meaning that there is a long term experience from these plants available. This feedback includes boiler performance and maintenance issues of the boiler. Metso is also delivering coal washing plants to improve coal quality, i.e. reducing ash content of the coal. The idea to combine coal washing plant and CFB boiler was made up two years ago in Metso. Up-coming legislation of coal washing and restrictions for washery reject land-filling in India are good drivers for this kind of concept. Pre-study of this kind of concept led to the conclusion that coal washing process can be fine-tuned so that reject?s calorific value is only 1100 kcal/kg and that was set as a target for boiler design. Metso shipped 200 tons of washery reject to its own research center located in Tampere Finland. First a wide range of fuel characterization tests were done in lab-scale and after that one week test run in 4 MW CFB pilot boiler was done. Test run proved that 1100 kcal/kg can be fired without any support fuel with special boiler design. Test run results gave a good set of data regarding combustion efficiency, emission performance and boiler dynamic behaviour when burning this kind of fuel. These results are introduced in this paper. This paper introduces also the CFB boiler concept for washery reject firing including boiler plant, fuel and ash handling systems and flue gas cleaning system. Power plant can be integrated with coal washing plant so that boiler size matches with washing plants c

Sep 1, 2012

By Georges Delemontex, Nigel Grigg

"Pre-concentration of precious metal and base metal ore types is becoming more relevant with the discovery, development and operation of many lower grade deposits around the world. The fluctuations in metal prices and currencies expose many mines to risks especially dealing with low and variable ore grades. Pre-concentration, the process of concentrating the valuable metal into a smaller mass yield, effectively results in the introduction of higher feed grades to milling circuits. Gangue rejection, the removal of lower S.G. waste rock from the circuit, not only results in higher downstream grades but also potentially removes harder, non-valuable mineral, providing significant power savings within the circuit. The pre-concentration or ‘gangue rejection’ process offers a number of benefits when considering the treatment of marginal ore deposits, especially if it can be performed at a coarse crush size; these benefits include a reduction of the operating costs and the feed of more metal units to the mill. Gekko Systems has effectively utilized the Inline Pressure Jig (IPJ) to pre-concentrate the valuable metal, achieving high primary recoveries into a range of mass yields resulting in upgrade ratios between 2 and 10 times. This paper explores: the benefits of pre-concentrating ‘marginal’ ore deposits prior to the milling circuit; the selective rejection of ore types that may affect either the recovery or comminution process; and also looks into the potential to effectively reduce the ‘cut-off’ grade when considering the mine planning process. Case studies of projects using the IPJ to pre-concentrate and reject gangue are also included. Pre-concentration and gangue rejection provide the potential to develop marginal ore deposits, thus providing higher grades, less gangue and more metal at a lower operating cost to producers."

Jan 1, 2014

The flotation behavior of kaolinite and diaspore using N, N-diethyl dodecyl amine (DEN12) and N, N-dimethyl dodecyl amine (DRN12) as collector have been investigated through flotation experiments. The mechanism of adsorption of two tertiary amine collectors on surface of kaolinite and diaspore were investigated by FTIR spectral, Zeta potentials measurements and calculation of molecular orbital energy. It has been found that DEN12 and DRN12 have stronger collecting power to kaolinite and weaker collecting abilityto diaspore than DDA. Kaolinite and diaspore in bauxite ores can be separated by using DEN12 and DRN12 as collectors at pulp pH below 8 and 6, respectively. The results of zeta potentials and calculation of molecular orbital energy indicated that the adsorption strength on kaolinite surface is in the order DEN12>DRN12>DDA and the adsorption strength on diaspore surface is in the order DDA>DEN12>DRN12. FTIR spectral analysis and Zeta potentials approve that the action between kaolinite and tertiary amine collector is strong electrostatic adsorption and that of diaspore is weak electrostatic adsorption in the range of pH 5~6.

Jan 1, 2014

By K. C. Corin, M. S. Manono, R. M. Manenzhe, J. G. Wiese

"Environmental concerns necessitate the recycling of process water within mining operations. Given that recycled water is chemically different from fresh water, and collectors are added such that they adsorb at the liquid-particle interface, changes in the aqueous phase are expected to affect collector adsorption. A Finnish nickel-copper ore was floated in synthetic plant waters of varying ionic strengths and plant waters obtained at Boliden Kevitsa Mine, with aerophine and sodium isopropyl xanthate as collectors. Of the tested waters, the copper thickener overflow was the least conducive to xanthate adsorption and valuable mineral recovery. The nickel thickener overflow, standard process water, and raw water were the most conducive to xanthate adsorption. For the raw water and nickel thickener overflow, increased adsorption correlated with increased valuable mineral recovery. Further, recycling xanthate retained in water affected the selectivity of the collector and hence the concentrate grades.INTRODUCTIONFlotation is a separation process that exploits the differences in the surface properties of the particles being separated. The efficiency of separation is dependent on the degree of hydrophobicity achieved by the particles meant to be floated, which are, in most cases, valuable minerals. The hydrophobicity is in turn dependent on the adsorption of the chosen collector onto the surfaces of the floated particles (Fuerstenau, 1984; Taggart and Hassialis, 1946). Empirical findings suggest that species dissolved in solution strongly influence collector adsorption and overall flotation response (Fuerstenau and Chander, 1986). Due to environmental concerns, it is becoming more pertinent for mining plants to recycle process water and hence limit the usage of potable water. There is an interest to ensure minimal discharge of plant water into the environment, as this water is typically polluted with process reagents that may render it toxic (Levay et al., 2001)."

Jan 1, 2018

By L. Tong

Stirred milling of laterites offers possibilities for improving liberation and selective size reduction of soft nickel-bearing minerals in laterites. Batch grinding tests were performed in a Netzsch LME4 stirred mill on a siliceous goethitic (SG) nickel laterite sample (-2000 µm particle size) to evaluate the effect of operating conditions such as stirrer speed, grinding time, pH, solid content, water salinity and charge volume. The target was to produce a -38 µm fraction in the milling product with high nickel recovery and grade. Addition of dispersant (sodium hexametaphosphate) was also optimized with respect to the rheology of the slurry. In terms of stress intensity, the optimum grinding conditions for selective size reduction were: 1000 rpm, 50 per cent charge volume. At higher stress intensity (2000 rpm), Ni recovery in the -38 µm product was higher, but Ni grade was low, due to the breakage of the harder siliceous particles. Decreasing the yield stress by modifying slurry pH or adding dispersant improved the rheological properties of the pulp, but had no great influence on Ni upgrade in the fine product. Modifying water salinity by adding 2 M NaCl had also little effect. The breakage of the +38 µm particles in the feed determined Ni upgrade greatly. Ni grade in the -38 µm product decreased with grinding time, suggesting that the Ni-bearing minerals break first, while the harder siliceous minerals have a lower breakage rate. The breakage rates with respect to sample mass for Ni, Mg and Si indicate that: Mg > Ni > Mass > Si. The optimum grinding time for the highest Ni upgrade was 0.25 min. The Ni grade increased from 0.88 per cent to 1.35 per cent (upgrade 54 per cent), with 24 per cent Ni recovery. Keywords: fine grinding, stirred media mill, nickel laterite, slurry rheology

Sep 1, 2012

By Y. X. Yang

Porous silica was obtained by acid leaching of chrysotile. The porous silica had been characterized by chemical analysis, powder X-ray diffraction (XRD), Fourier transform infrared spectros-copy (FT-IR), and N2 adsorption-desorption techniques. It is shown in this study that the porous silica retains the nanofibrous morphology of the original chrysotile, and produces a high specific surface area (SBET) of 391. 8 m2/g and total pore volume of 1. 05 mL/g. The increase in SBET and the total pore volume of the porous silica reflect the formation of micropores of 1.2~1.5nm and meso-pores of 3.2~3.8nm in diameter inside the porous structure. The hysteresis loop of N2 adsorption-desorption curve indicates mainly slit-shaped pores. The porous silica is amorphous, but its structure is regular to some extent. The structural unit of silica from chrysotile is a SiO4 tetrahedron and six-member silicon-oxygen rings with the tetrahedral positioned alternately up and down in the six-member rings.

Jan 1, 2014