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By Ting Liu, Qian Li, Peng Deng

The wastewater containing Hg2+ and Pb2+ does great harm to the environment and human bodies. Traditional wastewater treatment cannot fundamentally put a stop to heavy metals pollution for producing secondary pollution. In this paper, Hg2+ and Pb2+ in wastewater were removed and recovered by sulfide precipitation- flotation. Sodium sulfide was used as precipitant and butyl ammonium aerofloat was used as collector. Results indicated that Hg2+ and Pb2+ could be reduce to less than 0.03mg/L and 0.16mg/L respectively by both coprecipitation- floatation and fractional precipitation- floatation. In these two methods, fractional precipitation flotation could not only remove Hg2+ and Pb2+ from wastewater, but also could recover mercury and lead effectively. The infrared spectrograms showed that the adsorption between butyl ammonium aerofloat and mercury precipitate or lead precipitate is chemisorption.

Jan 1, 2015

By Petrus Christiaan Pistorius, Ming Tang

Magnetite concentrate is pelletized and then hardened by elevated-temperature oxidation to hematite, to produce pellets for ironmaking. Previous work showed that the rate of oxidation is under mixed control of gaseous mass transfer of molecular oxygen through the pellet pores, and solid-state diffusion into the oxidizing grains. Because of the partially limiting role of solid-state diffusion, concentrate size distribution strongly affects pellet oxidation. Previously, a simple mixed-control model was formulated to describe isothermal oxidation. In that model, the main effect of concentrate size distribution was on the plateau level of oxidation which is reached at a given temperature. However, the extent of plateau oxidation increases with increased temperature, requiring a more complex model for non-isothermal oxidation. In this paper, predictions of the non-isothermal model confirm the strong effects of concentrate size distribution and oxygen enrichment. In particular, a greater fraction of coarse magnetite particles would be beneficial, decreasing the size of the macroscopic unoxidized pellet core.

Jan 1, 2015

By Jr. Napolitano, Jr. Sanders

"Morphological evolution of a dendritic growth front in a binary alloy is simulated using a cellular automaton approach to establish the feasibility of modeling such growth with a local rule-based scheme. The motivation for this work is derived from the need to predict the development of solidification structures within real components of complex geometry, where significant constraint of the thermal and solutal fields may exist. Such cases present complex boundaries and large domain sizes, which may preclude the effective use of more conventional methods. In this work, a model is presented which couples a two-dimensional alternate-direction-implicit finite-difference diffusion solution with a cellular automaton growth algorithm to simulate morphological evolution in alloys solidifying under directional growth conditions. Temperature, composition, and interface curvature are incorporated into a local growth potential which is used by the automaton, allowing the interface to evolve. Alloy solidification is simulated over a range of experimental conditions, producing various structures. Issues addressed include morphological instability, primary spacing selection, interface curvature, microsegregation, and tip conditions.IntroductionThe development of dendritic structure plays an essential role in alloy solidification. Virtually every microstructural feature, within a cast alloy component, is related to the interface morphology present during solidification. Conventional solidification theory, describing dendrite tip kinetics and mushy zone phenomena, provides a means for estimating overall microstructural parameters for an alloy solidified under steady-state conditions. Microstructural prediction for actual components, which are finite in size and complex in geometry, requires a description of the evolution of the interface morphology under transient conditions and geometrical constraint and an understanding of how the structure propagates through the mold. Any useful simulation tool must be equipped to handle these circumstances within the limits of computational feasibility."

Jan 1, 1998

By Wang Jia, Chai Li-yuan, Zhang Jin-Long, Peng Bing, Zhang Qiang

"Electrolytic manganese dioxide (EMD) residue was mixed with shale and fly ash as the main materials to make solidification/sintering brick for the utilization of the residue from EMD production. The effects of sintering temperature, sintering time, solid waste content and cooling process on its mechanical properties and toxic elements solidification were investigated according to compressive strength and leaching toxicity. The results showed that the calcined residue had capability of solidifying toxic metals and exhibited perfect strength after treated in the optimal parameters of EMD residue below 50%, temperature at 1000-1100°C, time3-5h, and semi-quenched at 600°C1 InstructionSolid clay-brick holds the leading position among building materials for a very long time in China. The traditional technique of making clay-brick has the drawbacks of backward process, simple facilities and single product. Since Chinese Reform and Opening-up, urban-rural construction and real estate have been booming with the rapidly development of national economy and science technology. The problems of ruining fertile land, environment contamination and high energy consumption in the traditional technique of clay-brick making have not been solved yet. On the other hand, more than 7 billion tons of industrial wastes are accumulated over years which occupies over 6.7 million hectares filed and causes serious environmental problems[1-31. Strategy present in ""The Chinese Agenda of the 21st Century"" required the production of wall materials less energy conservation, land saving and waste recycling.Coal gangue[4-9l, fly ash[I0- 13l, sludge from waste water treatment and tailings of gypsum, pyrite, copper mine, high silicon containing iron, asbestos and ects [l4-lSJ are the solid wastes used for brick making around the world. There are two kinds of process for brick making, high temperature sintering and low temperature steam curing[19•201. Although the technology of two brick making made great progress and got widely application in construction field, no precedent for preparing sintering-bricks with EMD residue as materials occurred in China because of its complicated processing technics and lack of sufficient practical experience to guarantee the bricks' quality.In this study, EMD residue was mixed with shale and fly ash as the main materials to make solidification/sintering brick. The effects of sintering temperature, sintering time, solid waste content and cooling process on its mechanical properties and toxic elements solidification were investigated according to compressive strength and leaching toxicity."

Jan 1, 2011

By Dean David

The evaluation of a new mineral sands prospect with unusual characteristics is described, The heavy minerals are very fine grained, have comparatively low average specific gravity (3.6) and are altered. Poor performance by conventional processing techniques made it necessary to trace the response of the major minerals during the separation processes, QEM*SEM® was used to quantify mineral volumetric abundances and mineral locking in magnetic and gravity separation products.

Jan 1, 1989

By Bhagyadhar Bhoi, Chitta Ranjan Mishra, Hara Prasanna Mishra

"In the Sukinda Valley of Orissa, India, the total quantity of nickel ore reserves comprising of both lateritic and chromite over burden(COB) have been estimated at around 231 million tonnes containing 0.3 to 0.9% Ni. While mining of one tonne of Chromite ore, around 6-7 tonnes of chromite over burden are removed. These overburden materials are disposed as waste materials, which causes lot of environmental hazards and ecological imbalance. India imports a large amount of nickel and ferro-nickel to meet its growing demands in various sectors. For import substitutions, efforts have been made to produced ferro-nickel from the lean deposits of nickel bearing lateritic ores/ chromite over burden materials by reduction roasting followed by magnetic separation and then the nickel rich magnetic fraction is smelted to produce ferro-nickel. It has been possible to produce ferro-nickel of grade varying from 4-25% nickel.IntroductionDuring mining of chromite ore, large quantities of overburden materials are being generated. The materials amount to approximately 10 million tones per year contain around 0.3-0.9% Ni, 0.02-0.06% Co, 20-50% Fe and 4-9% Cr2O3 depending upon the location and the depth of the mine. These materials presently do not find any application for the extraction of nickel due to lack of a suitable technology. The materials are also unsuitable for ferro-nickel making because of their very high iron to nickel ratio. The country is seriously looking for a suitable technology to utilize these resources as its entire domestic requirements of nickel is met though imports. In this connection, a systematic approach has been made at the Institute of Minerals and Materials Technology, Bhubaneswar to develop a process for ferro-nickel making from this indigenous resource."

Jan 1, 2011

By Yuanyuan Wang, Hong Li, Xueting Liu, Hao Bai, Kang Zhou

"Phase change materials are widely used in efficient utilization of energy and new energy technology. Especially, more attention has been paid to composite phase material, which is applied on architectural energy-saving and efficient working fluid. In this paper, stearic acid-silicon dioxide composite material was prepared by sol-gel process from tetraethyl orthosilicate (TEOS) and stearic acid (SA). The material was investigated by Field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR) and Differential scanning calorimeter (DSC). The FE-SEM results show that 3D-grids of silicon dioxide were formed clearly and SA was encapsulated in the silicon dioxide shell. The FT-IR results show that there were no chemical reactions between silicon dioxide and SA, which is the chemical property of the composite material, is stable. The DSC results show that the composite phase change material has favorable heat capacity. This material is expected to be used to make a cooling working fluid.1. IntroductionEnergy thermal storage becomes increasingly prominent issue in recent years, because thermal storage has been used in many aspects, for example, it can be added into building materials to improve heat conditioning. Another potential application of thermal storage materials is that the intermittent waste heat can be collected and recycled effectively by using the thermal storage facility. Thus, energy thermal storage plays a significant role in conserving available energy and improving its utilization [1]. Energy thermal storage includes sensible heat storage and latent heat storage. The latent heat storage has great heat density with a constant temperature during the phase change process [2-5]. Large quantities of latent heat storage will be absorbed and released when phase change takes place. Based on the former researches, some phase change material (PCM), such as fatty acid and paraffin waxes, has been proved to have high latent heat storage capacity and appropriate thermal properties [5-6]. However, using the PCM in energy storage systems directly is restricted, e.g. some properties of organic PCM, like form-stability and thermal conductivity, are not good enough to use. Meanwhile, almost all the inorganic PCMs are corrosive and most materials may cause sub cooling and segregation [7-9].The other problem is that the leakage when the temperature reaches the phase change point. Therefore, encapsulated composite phase change material (CPCM) emerged in order to solve the problem of leaking out, minimize the sub cooling and prevent phase segregation. [10-13] However, the easy flammability of fatty acid also has hindered the development of PCM. Accordingly, it has been found out that silicon compounds are environmentally friendly promising substitutes for halogen-containing flame retardants. Especially, silsesquioxanes are excellent in the flame retardancy. So CPCM can be encapsulated with SiO2 acting supporting material."

Jan 1, 2014

By Lin Li, Xiang Li, Yifang Zheng, Jilai Xue, Jun Zhu

"Al drops and gas bubbles in the anode-cathode space of aluminum electrolysis cell are of great importance for cell operation improvement in metal loss, current efficiency and energy consumption. A direct observation on the Al drop, gas bubble and ultrasound was carried out through a see-through cell. The Al drop immersed into the cryolitic melt was found moving up and down irregularly in the anode-cathode space without electrolysis, which was then completely dissolved into the melt. During electrolysis, the Al drop came to the anode area and reacted with the gas bubbles generated on the anode. Under ultrasound, the gas bubbles were removed from the anode surface while the Al drop was kept on the side of anode. The observed phenomena were useful for technology improvement in reducing the anode-cathode distance or lowering the energy consumption in aluminum electrolysis.IntroductionDuring aluminum electrolysis, aluminum metal drop and anodic gas bubble are in close contact each other within the anode-cathode space, and the interaction between them can produce significant impact on metal loss, current efficiency and energy consumption. The motions of the Al drop and the gas bubble are also related to the dissolution of aluminum metal into cryolitic melt and the cell voltage drop due to the bubble layer covering the anode surface.A number of studies have been carried out using different types of see-through cells, where the dissolving process of metal Al into cryolitic melts (metal fog) in the anode-cathode space was directly observed and photographed [1, 2]. With the similar method, some direct observations on the anodic bubble behaviors with and without ultrasound were performed during aluminum electrolysis [3-6]. However, to our best knowledge, there is no published work on direct observation on the behavior of Al drops and anodic gas bubbles staying together within the same anode-cathode space, as well as the motion and interaction of them in cryolite-alumina melts."

Jan 1, 2011

By M. L. Cunha

The lack of control of As and Sb compounds from copper smelters and converters has rendered some chalcopyrite containing arsenopyrite, stibnite and tetrahedrite minerals unusable for metal extraction. In the present investigation, we have studied the carbothennic reduction of Portuguese chalcopyrite mineral concentrate in the presence of lime/CaS04 and CaS04/Si02. Thermodynamic equilibrium calculations were performed to study the distribution of As and Sb between metal and the CaO-Si02-FeO slag phase. The phase equilibrium calculations also show the effect of oxygen partial pressure on the increase in the volume of the slag phase, which helps in lowering the copper metal formation temperature and facilitates a better separation between metal, matte and slag. The reduction reaction kinetics was studied between 850°C and 1100 °C, and the phases formed were identified by X-ray powder diffraction and scanning electron microscopy techniques. The importance of this research for using recycled matte, lean and rich minerals with As and Sb is also explained.

Jan 1, 2001

By J. Pesl, U. Kemey, F. Sauert

"The CONTOP® smelting cyclone is a water-cooled, upright, high-intensity smelting reactor. The technology for the reactor was initially developed and brought into industrial-scale operation in the area of non-ferrous metallurgy. The two largest smelting cyclones were built with a capacity of 32 tons per hour of copper concentrate mix.The newest industrial CONTOP® plant treats up to five tons per hour of zinc-bearing residues including EAF dust. The highly concentrated zinc-lead oxide produced is sold to the zinc industry. The slag fulfills the leaching criteria and is used in waterway construction. The heat transferred to the cyclone cooling system and the off-gas boiler produces steam from which power is generated in a turbine.V AI has erected a new CONTOP® demonstration plant at MEFOS, Lulea, Sweden. A zinc volatilization rate of 90% was achieved during hot commissioning with Swedish EAF dust.Treatment costs in the range of 85 to 100 EUR per ton were estimated in a feasibility study on the treatment of 73,000 and 57 ,000 tons EAF dust for a group of steelmaking mills in Southern Europe."

Jan 1, 2000

By Ronald C. Askin

Dredging is a common method of remediating ponds containing contaminated wastes. However, dewatering of the dredged solids is usually not well integrated with the dredging phase. As a result, overall project efficiency can be poor. Specifically, since dredges deliver material in a widely varying slurry form and since dewatering presses require the delivered material to be uniform, union of the two systems often results in inconsistent operation of the overall process. In an effort to enhance overall dredging and dewatering process production rates as well as minimize the return of suspended solids in the decant water, a new process was developed to provide a consistent dredged sludge for delivery to the press. This paper discusses modifications made to a conventional dredging and dewatering process to improve production rates and dewatering capabilities. These modifications are applicable to any project where efficient solids dewatering is required and where returning decant water must be visually free of suspended solids.

Jan 1, 1996

By Laszlo Kadar, J. D. Lavers

"In the continuous casting of aluminum killed steel, the tundish nozzle often experiences clogging problems. Water model studies have shown that the clogging problem is dependent on the flow pattern in the nozzle entry region. In particular, the flow can separate at the entrance to the nozzle, leading to the development of a recirculation region. Although a nozzle can be designed such that no recirculation develops, even a small misalignment from the vertical positioning of the nozzle may render the design ineffective.To reduce the possibility of nozzle clogging, the recirculation zone must be reduced or eliminated. This may be achieved by moving the fluid downwards or raising the turbulence level in the separation region. In the case of a tundish nozzle, it is proposed that this can be achieved by using electromagnetic forces.To generate the required electromagnetic force, two systems are considered. The first is based on injecting a DC current; the second by using electromagnetic induction. Both methods are described in this paper. Order of magnitude calculations are provided to illustrate that both methods are essentially feasible. The performance of each method in terms of modifying the turbulent flow characteristics in the nozzle entry region is then examined using a numerical model. It is shown that both methods can greatly reduce the recirculation zone. A cylindrical nozzle was chosen for the model studies since it represents a worst case situation.On the basis of the model studies, it can be concluded that whereas both of the proposed methods have the potential to reduce the troublesome recirculation zone, the induction method appears to be simpler in terms of practical implementation."

Jan 1, 1999

By Hong Yong Sohn, Miguel Olivas-Martinez

"Different approaches are used for calculating the ‘energy requirement’ of a process. The determination of energy requirement becomes confusing for a process in which a fuel is also a reactant. The key issue is which heat of chemical reaction should be included in the ‘energy requirement’ value. We will use the example of ironmaking processes to illustrate the problem. The different approaches essentially boil down to the question: does one include the combustion heat of the reductant used in the reduction reaction or just the heat of the reduction reaction? Depending on the viewpoint, either approach can be accepted; it is a matter of convention. There is a need, however, to select a standard approach because the absolute value of ‘energy requirement’ of a process depends on the choice. The energy requirement of a novel flash ironmaking process will be compared with that of an average blast furnace operation.IntroductionDifferent approaches are used for performing energy balance calculations and perhaps more significantly in presenting the ‘energy requirement’ of a process. The question becomes more involved for a process in which one or more reactants are also used to generate the process heat by combustion. Often the key issue is which heat of chemical reaction to include in presenting the ‘energy requirement’ of the process.It is worthwhile to note at the outset that the difference in energy requirements between different processes for converting similar raw materials to the same desired product is largely unaffected by the choice of chemical reactions to be included. However, the absolute value presented as the ‘energy requirement’ of a process can be different by a large amount depending on the approach. We use the example of ironmaking processes to illustrate the problem. In these processes, as currently practiced or under development, carbon and/or hydrocarbons (including hydrogen) are used as the fuel as well as the reactant for reducing the iron oxide mineral.The different approaches in this case essentially boil down to the following question: does one include the combustion heat of the reductant used in the reduction reaction or treat the reductant portion as just a reactant? Depending on the viewpoint, either approach can be considered acceptable. It is a matter of convention. There is a need, however, to select a standard approach because the absolute value of ‘energy requirement’ of an ironmaking process (e.g., the currently dominant blast furnace process) depends on such a choice. It is particularly important to clearly state the specific approach used when the energy requirement of ironmaking is compared with those of other industrial processes such as petrochemicals production."

Jan 1, 2014

By C. M. Iheagwara

An overview of the scope and ramifications of scrap recycling in the Nigerian metallurgical industries has been presented in this paper. The modern state-of-the-art processing techniques and the operational strategies employed in the recycling plants are discussed. Optimization techniques for cost effective recycling operations are highlighted. As new units within existing metallurgical plants and new metal working plants approach commercial operations, expansion of existing recycling plants and the emergence of new ones have been showing to hold the key to their profitability from the raw material standpoint. The present economic predicament of the entire industrial sub-sector, lack of sufficient foreign exchange to procure new machineries and the emergence of a maintenance culture have triggered a phenomenal increase in the number of spin-off industries which depend on metal recycling activities. This, it is argued, widens the horizon for scrap processing/recycling.

Jan 1, 1992

By N. Panagiotopoulos

A low-grade (1.06% Ni, 0.06% Co) hematitic type lateritic ore from Triada, Euboea Island, Greece, has been leached with sulfuric acid at atmospheric pressure for the extraction of the contained Ni and Co values. The effect of various parameters, including reaction time and leaching temperature, acid strength, pulp density, etc., on Ni, Co extraction and Fe dissolution was determined. By leaching at 95°C for 4h with a 3N sulfuric acid solution at 25% pulp density, Ni and Co extractions were 82 and 75% respectively, and Fe co-dissolution 28%, yielding a pregnant solution containing 2.7 g/l Ni, 0.16 g/l Co, and 33 g/l Fe. Overall acid consumption was 850 kg/t ore (or 100 kg/kg Nil. Preheating of the laterites at 600°C before leaching resulted in much faster leaching kinetics for Ni, but the final extraction and acid consumption remained unaffected; Fe extraction was not influenced. Three-stage counter-current leaching at 9S°C, using 2N acid strength at each stage and 35% pulp density, reduced acid consumption to 350 kg/t ore (41 kg/kg Nil, and yielded 81% Ni recovery. Percolation leaching of -10 mm laterite at ambient temperature with 3N acid for 7 days resulted in 58% Ni extraction.

Jan 1, 1988

By T. B. Braun

Cathode contamination is the principal factor affecting the quality of electrorefined copper. It is commonly accepted that annealability is unfavorably affected by the following elements, in decreasing order of adverse effect: tellurium, selenium, bismuth, antimony, and arsenic. Silver in cathodes has importance as it represents a nonrecoverable loss of silver to the refinery. Mechanisms for the contamination of cathodes by these elements are examined and the effect of operating variables on contamination, including anode composition, electrolyte composition, electrolyte temperature, addition agent practice, and electrolyte discard rate, are discussed.

Jan 1, 1976

By Lichao Ding, Jingbiao Fan, Yunnen Chen

"With the development of industrial production, more and more wastewater containing high concentration ammonia nitrogen was discharge into the environmemt, which caused serious harm to the environmemt. Treating the wastewater has great significance to protect water resources. Using air-stripping combined with oxidation to uptake high concentration of ammonia nitrogen wastewater. The influence of operating parameters was investigated. Experimental results revealed that pH of solution, aeration time and aeration strength showed heavy influence on ammonia nitrogen removal. Air-stripping combined with oxidation can be considered as an alternative approach for the removal of high concentration of ammonia nitrogen from practical metallurgical wastewater. When pH was 11, aeration time 20 min, aeration strength 1040 Lh-1, and oxidation with 10 % NaClO solution 10 min, the initial ammonia nitrogen 2130 mgr1 could reduce to 12 mgr1. Other items could also be removed to meet the ""Integrated wastewater discharge standard (GB8978-88)"".1. IntroductionThe rapid development of human activities has caused a worldwide increase of nitrogen in rivers, lakes and coastal waters. It leads to considerable eutrophication and an increase in the frequency of toxic algae blooms [1,2]. The concentrations of nitrogen in the water of China are pervading high [3]. The discharge of wastewater containing high concentration of ammonia nitrogen is one of the most important factors. Great efforts have been devoted to the removal of ammonia nitrogen from wastewater. Traditional methods include biological denitrication [ 4 ], chemical precipitation with magnesium ammonium phosphate [5], electrochemical conversion [6], air-stripping [7] and so on. Biological denitrication is the most common process in the treatment of ammonia nitrogen wastewater. But the process is only suitable for the removal of relatively low ammonia concentration due to the requirement of appropriate C/N ratio [8]. Chemical precipitation needs additional reagents, which may introduce new pollutants to water body. Electrochemical method often uses expensive metal or metal oxide as electrodes, and also consumes large quantity of energy [6].Although air-stripping makes use of stripping tower and consumes energy, it is very suitable for the removal of relatively high ammonia concentration. Different air-stripping conditions would appear different removal efficiency. And only air-stripping the effluent can not be attained the ""Integrated wastewater discharge standard (GB8978-88)"". In this study, we use air-stripping and oxidation to removal high concentration of ammonia nitrogen from simulated and real ammonia nitrogen wastewater."

Jan 1, 2011

By Bernd-Arno Behrens, Klaus-Georg Kosch

"In times of increasing energy costs automotive lightweight construction is gaining in importance. This paper deals with the production of hybrid steel-aluminum compounds by forging. The compound forging process is a promising method to successfully manufacture functional parts by applying resource-saving process steps. Nevertheless, challenges resulting from different material properties must be solved.The heating of hybrid material work pieces made of steel and aluminum is a great challenge. Steel is forged at a temperature of at least TSt =900 °C, while aluminum should not exceed a temperature of TA1= 500 °C. For achieving the required temperature gradient extensive experimental investigations have been carried out. Intermetallic phases form during the manufacturing process and can influence the bonding and the global part quality. In addition, methods for the characterization of the joining zone between the materials steel and aluminum are analyzed and the factors influencing the formation of intermetallic phases are determined experimentally.IntroductionIn times of increasing energy costs and stricter conditions relating to environmental protection, automotive lightweight construction is gaining in importance. The production of hybrid compounds by forging is a promising method to manufacture functional parts by applying resource-saving process steps. In compound forging a hybrid raw part consisting of a solid core, which is enclosed by a hollow casing, is joint in the forming process. This results in a graded material structure in the part in which the mechanical properties can be specifically adapted to the requirements. Compound forging is the form joining and/or firmly bonded joining of at least two different materials while plastic shape forming occurs (Figure 1)."

Jan 1, 2012

By Ann M. Hagni

Microscopic and sub-microscopic gold commonly occurs in the sulfides pyrite (FeS2) and arsenopyrite (FeAsS). To recover refractory gold from pyrite and arsenopyrite, these sulfides are roasted to create porosity and permeability prior to cyanide leaching. A new technique of adding Ca(OH)2 and roasting, lime roasting, is being tested fro retention of contaminant sulfur and arsenic and effectiveness of gold extraction. The lime roasting of pyrite at 500°C contains anhydrite (CaS04), oldhamite (CaS), calcium sulfite (CaS03), hematite (FenOs), magnetite (Fe304), and minor amoupts of pyrrhotite (Fel.,S) and pyrite. At 600°C, 650°C and 700°C the main constituents are anhydrite, oldhamite, and hematite. At 750°C, 800°C, and 850°C anhydrite and hematite are the predominant phases with minor oldhamite. The roasted arsenopyrite at 450°C contains arsenic sulfides, calcium sulfite, hematite, and minor oldhamite, magnetite, and pyrrhotite. At 650°C 700°C 750°C and 800°C, anhydrite, oldhamite, arsenic sulfides, and hematite are present. At 850°C, the same minerals are present with only minor oldhamite. The textures indicate excellent porosity and permeability at high temperatures. At lower temperatures, rims of low porosity and permeability surround many of the pyrite and arsenopyrite particles, and the complete oxidation process from pyrite to pyrrhotite to magnetite to hematite can be observed in individual particles. Additional process mineralogy techniques employed in this study are electron spectroscopy for chemical analysis (ESCA) and cathodoluminescence microscopy (CLM) in the determination of the calcium-sulfur- oxygen phases. Automated scanning electron microscopy-energy dispersive spectroscopy was utilized to analyze particles for gold content. Reflected light microscopy (RLM) revealed arsenopyrite and pyrite encapsulated in quartz particles of the gold-bearing concentrate, gold roast calcine, and cyanide leach residue.

Jan 1, 1993

By Carvalho A. Felipe de

The search for environmentally friendly and cost-effective methods for gold extraction has been undertaken in order to provide alternatives to the use of cyanide leaching in the gold industry. Among such alternative reagents is the combination of chloride and hypochlorite ions due to their oxidation of metallic gold and its complexation. Therefore, the current work aims at investigating gold leaching from an oxidized material by means of a solution comprising calcium hypochlorite and sodium chlorite. The sample used in the current research contained 66.1% Fe2O3, 20.4%SiO2, and 35.7 g/t of Au. In addition, XRD and SEM-EDS analysis revealed iron oxide, quartz and muscovite as the main crystalline phases in the sample. For comparison purposes, cyanidation of the oxidized material resulted in 90% gold extraction in 24 h. The reference conditions for the leaching tests with the chlorite-hypochlorite system were: particle size −37 μm, solid/liquid ratio of 10% (w/v), 10 g/L NaCl, 10 g/L Ca (OCl)2, pH 5–6, 3 h of leaching. The effects of the: (i) Ca(OCl)2 concentration, (ii) NaCl concentration, (iii) pHrange and (iv) the effect of pulp density in the extraction of gold were assessed. In addition, the stability of the hypochlorite solutions (OCl−) was investigated. The ideal concentrations of Ca(OCl)2 and NaCl were determined as 25 g/L and 15 g/L, respectively, whereas the optimal pH range was 4–6. Under these conditions, the final gold extraction reached approximately 84%. By varying the solids content of the pulp (10%, 20% and 30%), it was observed that the lower solids value resulted in greater gold extraction (84%). The degradation of the hypochlorite solution and the possible catalytic effect of the presence of the solid were evidenced. To sumup, in the experiment, high gold extractions were achieved in shorter periods of time (3 h), as compared to the cyanidation of the same sample. On the other hand, itwas necessary to use significant amounts of the reagent due to hypochlorite instability at the pH conditions recommended for high gold extractions.