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By Kirsi M. Riihilahti

The oxidation characteristics of solid copper matte particles under simulated Kennecott-Outokumpu Flash Converting conditions are presented. This project is concerned with the determination of the effects of operating variables on the reaction of the particles. Experiments were carried out in a large laboratory-scale flash furnace with 72 wt-% Cu matte by varying initial particle size, temperature, oxygen partial pressure, oxygen-to-matte mass ratio and residence time. Chemical analysis was used to study the oxidation extent and copper volatilization. Particle fragmentation was examined. Fractional conversion and sulfur removal slightly decreased with initial particle size, while a higher oxygen-to-matte mass ratio mainly resulted in higher fractional conversion and more efficient sulfur removal. The fractional conversion values represented the overall extent of oxidation more closely than degree of sulfur removal.

Jan 1, 1997

By Roger N. Kust

Removal of heavy metals from industrial process streams is becoming increasingly important for _the recovery and reuse of values in process tails. Technology has been available for several years which removes heavy metals, from dilute (0.1-3.0 g/L) streams, as hydroxide or hydrated oxide sludges, allowing discharge of washed cakes with up to 60% solids. This paper reports on improvements to this technology which now allows treatment of streams with metal concentrations in excess of 60 g/L while eliminating the need for thickeners. Streams containing copper, iron, aluminum, chromium, nickel, zinc, cobalt and lead have been successfully treated.

Jan 1, 1992

By Wei Gao, Qing-cai Liu, Cun-fang Lu, Jian Yang, Hinmi Zheng

"The mode of occurrence of sulfur and mercury in 57 Chinese bituminous coals have been examined using X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), and Zeeman atomic absorption mercury spectrometer. Mercury levels in coal are related to the geographic location of the coals and types of the coals. A synthesis of result indicated that most likely occurrence modes of mercury in high-sulfur and high-mercury coals are in solid solution in pyrite. Our study from 57 coal samples showed that most values of mercury concentration in coal varied from 100 to 1000 ng/g with an average of approximately 500ng/g, and mathematical model about correlation between mercury and sulfur was gained by mathematical statistics. This is apparent that mercury and sulfur vary concomitantly from coal data (table 3) , the high correlation between them in all coals at confidence of 95% ( a=0.05 ) .1. INTRODUCTIONThere contained about one trillion ton abundant coal resources in China. As a leading level of proven coal reserves in the world, the coals mainly distributed in north China and northwest China, especially in Shanxi, Guizhou, Shanxi provinces and Inner-Mongolia autonomous region. At the same time, China has the largest production and consumption of coal, and has the output of coal nearly accounted for 37 percent of the world's production. Coal-fired power plants are the major source of energy generation in China, and the proportion of coal combustion is up to 75 percent in the total energy configuration. Therefore, the mercury pollution caused by coal-fired has become a topic of wide-spread discussions since 1990. The contamination of mercury of human activities accounted for 10 to 30 percent [1], and the mercury emissions of coal-fired flue gas has made the greatest contribution to the pollution of atmosphere[2] In the past 30 years, the global increasing concentration of mercury pollutant in atmosphere maybe result from coal combustion[2]. The mercury emissions caused by coal-burning has become the main reason of China's mercury pollution, and the characteristics of mercury pollution is closely related to China's energy configuration, additionally, the features of mercury pollution have changed from the point pollution in 1970's to diffused pollution today[3]. Mercury can be found in various types of coals, and it is evaporated into gas phase during the combustion process."

Jan 1, 2011

By John M. Gaines

Lead concentrates from the Viburnum Trend in the Southeast Missouri Lead district are sintered prior to smelting to bind the particles together homogenize the feed, and reduce the sulfur content. Good sinter forms competent masses about 4 to 6 inches across, that hal!e about 15% porosity and good mechanical strength to withstand transport and the weight of the overlying load in the smelter. Bad sinter has poor mechanical strength and forms fine fragments that retard the circulation of reducing gases in the furnace and lengthen the time required for reduction. The productivity of the lead smelter depends on good sinter feed. Because some lead sinter plants produce bad sinter about 20% of the time, this applied mineralogy study has been undertaken to determine the mineralogical and microtextural differences between good and bad sinter. A reflected light microscopic study of 130 polished sections has shown that good and bad sinters differ distinctly in their mineralogy, tex1ure. and character of, porosity. Good sinter consists of hardystonite, franklinite. lead-zinc-bearing magnesium-calcium silicate, lead silicate matrix, and large crystals of calcium-magnesium-iron silicate, together with minor amounts of lead oxides, lead-zinc silicate, metallic lead, specular hematite, magnetite, lead-iron-bearing zincite and zinc-Iead-magnesium-bearing wustite in a tightly intergrown mesh of crystals and with an evenly distributed porosity of 15% to 20%. Electron microprobe analyses show that the principal phases contain lead (or zinc): hardystonite (4-20% Pb) franklinite (2-14% Pb) and lead silicate matrix (65-74% Pb). Bad sinter differs from good sinter in the greater abundance of lead silicate matrix, galena metallic lead, and lead oxides and the lesser abundance of hardystonite, franklinite and calcium-magnesium-iron silicate. Bad Sinter is characterized by a lack of an intimate intergrowth of the constituent phases. Its porosity is much lower commonly 0 to 5% and those pores are concentrated in local areas rather than distributed evenly throughout the sinter.

Jan 1, 1991

By Dirk Verhulst

The Altair Hydrochloride Pigment Process is a new ?third route?, besides the established high-temperature chloride process and the older sulfate process, to manufacture TiO2 pigment from ilmenite ore. It has been tested at a scale of 5 t/day feed. The ore concentrate is digested in high-acid, high total chloride solution (+/- 39% Cl). Titanium and iron both go into solution. Iron is separated as FeCl2 crystals after reduction and cooling. Titanium is transferred by solvent extraction into a purified, high-Ti stream. It is spray-hydrolyzed to produce a TiO2 hydrate and further calcined with additives into high-quality pigment. HCl solutions generated by pyrohydrolysis and spray hydrolysis are treated by pressure-swing distillation to regenerate HCl gas for re-injection into the digestion reactor. All chloride streams are recycled. Recent work has concentrated on optimization, particularly in 3 areas: - Solvent extraction: a new organic mixture, including a new diluent, makes it possible to work at room temperature, to avoid TiO2 hydrolysis problems and to improve phase disengagement and impurity separation. - Pigment finishing: a systematic study of the parameters involved, followed by long runs in the best conditions confirm pigment quality. - Flow sheet optimization: innovative modifications of the conditions of spray hydrolysis and pyrohydrolysis, combined with re-routing of streams achieve significant energy savings. A 100 t/year pilot plant including these features as well as other process improvements is under construction.

Jan 1, 2006

By Fabiola Alvarez, Ana E. Bote, Daniel Pasquevich

"The oxidation of aluminum and its alloys was extensively studied for improving the corrosion resistance in structural materials having high specific strengths. But this reaction involves the formation of a very thin barrier layer on the metallic pieces. Furthermore, the ·recent development of the directed melt oxidation process for producing metal-ceramic; composites has renewed the interest in the study of interaction between gases and metals. Oxidation experiments in the presence of different chlorine partial pressures and at different temperatures were performed in ·a thermogravimetric balance, and microstructures were analyzed by electronic microscopy and X-ray diffraction. The oxy-chlorination kinetics was determined and the oxide formed W(IS amorphous at temperatures below 600 °C and crystalline .at higher temperatures. The appropriate experimental conditions for the fastest completed oxidation was further determined.IntroductionThe use of fine powders for the manufacture of ceramic components has significant advantages. They include excellent sinterability; low sintering temperature and better microstructure leading to improved mechanical properties. The conventional method of producing fine oxide powders involves controlled precipitation and pirolysis of suitable salts. The main limitation of the high temperature decomposition route is the evolution of environmentally unacceptable and corrosive gases. Controlled precipitation of hydroxides from solutions of salts, followed by thermal treatment involves large volumes of solutions and the calcination step that can induce grain growth (1).Direct oxidation of aluminum metal for producing alumina powder requires high temperatures for the direct oxidation of molten Al alloys by a vapor phase oxidant process (2, 3) or high technological process like thermal plasma reactor ( 4).Oxidation of high purity aluminum (5, 6) below the melting temperature· is initially characterized by a nearly linear reaction rate, followed by a rate which decreases rapidly with further weight gain. However, the oxidation rate of an aluminummagnesium alloy is much faster and it does not conform to any common oxidation law, but it is nearly parabolic at temperatures between 200 and 400 °C, an nearly linear· above 400 °C."

Jan 1, 2000

By Manfred K. Walther

"Tests were conducted on instrumented plates cast in the Abex Experimental Foundry to compare recorded solidification histories with results computed for corresponding models simulated with the C.A.S.T. program. The first plate was cast of low alloy steel and the second of carbon steel with a graphite chill at one end. Both were cast in molds of bonded silica sand. Temperature histories were recorded in the castings, molds and chill. Exceptionally good agreement was achieved between computed and experimental data. Other investigators will find the results useful as a benchmark against which they can compare the results of their own calculations.IntroductionSince the early 1970's our foundry engineers have used both two- and three-dimensional versions of the G.A.S.T. program to gain knowledge of the solidification process [1,2,3]. Study of the computed data gave insight as to how the rigging and risering of specific castings might be changed or adjusted to improve quality and yield. New schemes based on such analyses were then recommended for implementation on the foundry floor. The degree of success of the new practice was subsequently evaluated after the part had been poured, shaken out and examined. Similar conditions were noted in the sectioned castings whenever porosity and voids had been predicted by the computations. Appropriate modifications, when found successful in the model, were applied to the process. This led to a reduction, if not complete elimination, of the defects. Such results gave credence to the use of these programs as an aid in the production of better castings.Earlier investigations on simple shapes revealed excellent correlation between output derived with the G.A.S.T. program and exact solutions. Results also compared favorably with data calculated using other codes as reported in the literature [4] and summarized in the Appendix. However, since the computer program had not been verified by direct experiment, it was decided to run instrumented tests to check the theoretical predictions with actual measurements."

Jan 1, 1986

By John J. Mazza

Treatability studies were performed to determine the effectiveness of two commercially available treatment methods (solvent extraction and thermal desorption) for the removal of PCBs and PAHs from contaminated dredged riverbed sediments. The solvent extraction method evaluated was the B.E.S.T. process which extracts the contaminants with triethylamine. The thermal desorption method utilized was the ATP process which desorbs the contaminants at elevated temperature in an anaerobic atmosphere. A description of both methods and. an evaluation of the treatability study results is provided. Each treatment method was used to treat two separate samples (high and low concentration) from the site. Overall, both methods proved to be very effective with solvent extraction achieving 98% removal of both PCBs and PAHs and thermal desorption achieving better than 99% removal of both the PCBs and PAHs from the high concentration sample. Both solvent extraction and thermal desorption achieved greater than 99% removals of PCBs and PAHs from the low concentration sample. Vendor cost estimates for full scale treatment were roughly equivalent. The primary differences between the two methods lies in the realm of permitting, operational requirements, and emission concerns.

Jan 1, 1994

A comprehensive numerical capability for the analysis of Thermal Spray (TS) systems consisting of a three-dimensional compressible, turbulent flow Navier-Stokes model and a multi-phase particle flow model in Lagrangian formulation, was developed. This capability is validated for a set of flow conditions typical for TS. The developed methodology is used for analysis of the JP-5000 TS gun gas and coating powder flow conditions. Modeling and analysis of particle/turbulent eddies interaction is performed. Details of gas flow field, particle temperature, and particle velocity histories, and particle temperature, velocity profiles in the system are presented. For the validation of numerical analysis, the computed results are compared with available experimental measurements. The flow phenomena for different flow parameters are analyzed and explained as the results of gas dynamics and heat and momentum transfer between the gas and particle phases. This methodology can be used for process control and reliability improvement, and has the potential to significantly improve TS gun performance through control of its parameters.

Jan 1, 1996

By Edward Peters

Scandium (Sc) has unique properties and is one of the more valuable elements in the periodic table. Scandium can be used in solid oxide fuel cells and to produce high strength aluminium alloys of value, for example, in the aerospace industry. Scandium is often grouped together with the rare earth elements (REE). Amongst others, scandium can be found in bauxite residues, so called red mud. It is possible to extract and enrich scandium from red mud by leaching and solvent extraction. Scandium can then be recovered from the pregnant strip liquor by crystallization. The strip liquor will however still contain certain impurity elements. In the present work, a method for obtaining a pure scandium solid phase by direct crystallization from the strip liquor is evaluated. It was found that Fe and Ti co-precipitate with Sc under the conditions employed.

By F. F. Aplan, G. Simkovich

"A review is given of the effects of solid state point imperfections upon a number of mineral benefication processes and a metal extraction process. It has been found in numerous flotation studies that small amounts of aliovalent impurities (dopants) in binary compounds may show major effects upon flotation behavior. Both semiconducting and ionic conducting compounds are affected. These effects are also seen in hydrometallurgical studies as well as in electrostatic operations. Additionally, de-copperization of lead melts appears to be strongly influenced by similar defects. It is hypothesized that the effects observed in these studies are present in actual operations and should be considered in designing processes. A few speculations concerning future efforts are advanced. IntroductionImperfections [point (e.g., vacancies, interstials, quasi-free electrons, electron holes, impurity ions), line (e.g., dislocations), two dimensional (e.g., grain boundaries) and three dimensional (e.g., 2nd phases) defects] are generally present in solid materials and these imperfections may, and often do, have important effects upon a variety of properties and processes. In general, one may, in most cases, attain elimination of three dimensional defects by a separation process of one type or another (e.g., gravity, electrostatic, magnetic, flotation, hydrometallurgical etc.,). Thus, this type of defect has rarely been investigated in a systematic fashion. Two dimensional defects are always present in non-single crystal materials but have also escaped systematic studies in processes primarily because the control of such defects is not easily attained. Line defects are non-equilibrium entities which are present in ill-defined quantities so that they present a variable that cannot be easily controlled although through careful systematic experiments one can attain some reproducible relations pertaining to this type of defect.Contrary to the lack of studies concerned with the effects of 1, 2 and 3 dimensional types of defects there has been some activity concerned with point defects and their effects upon a number of mineral/metallurgical processes, especially flotation processes. Thus, this article will present a review primarily of point defects in relation to their effects upon flotation although other processes and defects will also be mentioned."

Jan 1, 1988

By Sung-Joo Lee, Gi-Chon Han, Nam-Il Um, Hee-Chan Cho

"In Korea, almost all of bottom ash produced by coal power plants is disposed of in ash ponds. Ash storage areas comprise more than 80% of most coal power plant sites. This disposal method is causing environmental problems and a managerial burden for plant operators. In this study, investigations to develop a beneficiation process for separating coal pond ash into various products were undertaken. To improve efficiency of the separation, coal ash was separated by sizes and each size fraction was subject to various beneficiation processes. The separation process used were flotation (-200 mesh size), hindered settling (16x200) and tabling (16x200 and 8x16 mesh). The results showed that various marketable products, such as lightweight aggregate, sand, high-carbon fuel, could be recovered from coal pond ash using simple physical separation techniques.IntroductionDue to the increased use of coals every year, about fifty million ton of coals were used in 2007 alone. As a result, about 6 million tons of coal ash were generated. In Korea, the coal bottom ash is classified as a general industrial waste and is usually disposed of in ash ponds. The costs for this disposal method continue to increase due to rising costs of site management and development and more strict environmental regulation. Therefore, utilities are constantly looking for ways to increase utilization of coal ash. In this study, various beneficiation processes were evaluated to examine the possibility of separating coal pond ash into various products which can be used as aggregates and high-carbon fuel."

Jan 1, 2008

By F. J. J. van Loo, J. K. Kivilahti, M. Paulasto

"Activation mechanism and interfacial reactions in brazing of ShN4 with different AgCuTi filler alloys has been investigated thermodynamically and experimentally. During brazing the AgCuTi filler alloy is divided into two liquids Ll and L2, where the (Cu,Ti)-rich liquid L2 gathers at the ShN4 interface and reacts with it. The concentration of Ti in L2 is high, but due to the strong attractive interaction between Cu and Ti, the activity of Ti in L2 is considerably low. In reaction between ShN4 and Cu-containing brazes a Ti-Cu-Si-N compound is typically formed at the interface. In absence of Cu, in joints brazed with AgTi based filler alloys, extremely Ti-rich solution reacts with ShN4 and as reaction products TiN and TisSh[N] are formed. IntroductionAdvanced ceramics like silicon nitride are increasingly used as structural components in demanding applications as well as in electronics industry. Complex, multicomponent structures for engineering applications generally require interconnections and therefore joinability of ceramics largely determines the possibilities of metal-ceramic structures to enable demanding functions. Brazing with active filler metals, most of which are based on the Ag-Cu-Ti system, has been commonly employed for joining of ShN4 to other ceramics and metals. The interfacial microstructures formed when ShN4 is brazed with Ag-Cu-Ti braze alloys have been discussed in several recent studies [1-7]. However, some inconsistencies exist in the reported results. The formation of layers of TiN and titanium silicides, possibly TisSh, next to the ShN4 has been reported in several studies [1-5], while in another investigation, a layer of an orthorhombic TiSi- Cu-N phase was found beyond the TiN layer [6]. In few investigations the thermodynamics of the ShN4-Ti system has been considered, but no detailed thermodynamic analysis of the chemical interactions between the braze and ShN4 has been provided. In order to resolve which chemical reactions are possible under various joining conditions and thereby to be able to control the brazing of ShN4 the reactions in brazing has to be studied using both microstructural and thermodynamic analysis."

Jan 1, 1996

By Martin E. Nelson

Several heavy metal separation techniques are currently being developed for soil remediation at various Department of Defense and Department of Energy (DOE) Facilities. The majority of these techniques involve a wet process using water, PH modifiers or other compounds. The United States Naval Academy (USNA) has developed a dry process for heavy metal separation. The process uses air classification technology to concentrate the metal contaminant into a fraction of the soil. The advantages of this dry process are that it creates no contaminated by product and uses commercially available technology. The USNA process is based on using a Gayco-Reliance air classifier. Tests have been conducted with the system at the Naval Academy and the University of Nevada-Reno (UNR). The USNA tests used soil from the Nevada Test Site mixed with bismuth at a concentration of 500-1000 ppm. The UNR tests used soil from four DOE sites mixed with uranium oxides and plutonium at an activity level of 100-700 pCi per gram. Concentration of activities and volume reduction percentages are presented for the various soils and contaminants tested.

Jan 1, 1995

By Pekka Taskinen

The converter-less nickel matte smelting technology (DON) adopted more than 20 years ago in Boliden Harjavalta smelter has been since that applied successfully to the processing of large number of nickel sulphide concentrates of various Ni-to-Cu ratios and MgO contents. The operational point of the technology is far from the conventional primary nickel smelting in the smelting-converting route. Therefore, a careful scouting of distribution equilibria of the base and trace elements in the smelting conditions of DON process has been conducted, in order to obtain quantitative information about the equilibria and thermodynamic properties of the nickel mattes at low iron concentrations, less than 10 wt% [Fe] in matte. The series of investigations has included novel experimental and analytical techniques for increasing the reliability and sensitivity of the phase equilibria as well as the element distribution observations carried out in typical high-grade nickel matte smelting conditions.

By Hiroyuki Matsuura, Fumitaka Tsukihashi

"Emission of CO2 gas from steelmaking industry covers more than 12 % of total CO2 emission in Japan. Though many efforts have been made to curtail energy consumption and high energy efficiency of Japanese steel production process has been achieved so far, further reduction of CO2 emission is strongly requested to develop sustainable steel production process and produce “green material”. Recently, authors have proposed the innovative hydrogen production process, in which water vapor is reacted with discharged steelmaking slag to produce hydrogen gas. This reaction can be achieved without any external energy source and operated by huge thermal energy associated with steelmaking slag and FeO or unrecovered Fe droplets that are relatively rich in the slag. In this paper, thermodynamic calculation results with various initial conditions in terms of hydrogen productivity were presented. Laboratory-scale experiments were also conducted to clarify the validity of thermodynamic calculation and the reaction rate in realistic conditions.IntroductionIronmaking and steelmaking process from iron ore through blast furnace and BOF is an essential steel production route for Japanese steel industries to supply high quality steel products in large quantity to society stably. Blast furnace – BOF process requires huge amount of fossil fuels such as mainly coal, resulting the emission of considerable amount of CO2 gas. Since the emission of CO2 gas from steel industries, about 147 Mt (FY2011), accounts for approximately 12 % of domestic CO2 gas emission in Japan (FY2011),[1] it is an urgent issue for steel industries to develop environmental-friendly ironmaking and steelmaking process and reduce CO2 emission. Various kinds of gases and by-products generated from ironmaking and steelmaking processes have been recycled as much as possible at present. Enormous thermal energy is also generated from processes and released to surrounding atmosphere as various forms such as sensible heats of gases, molten steels or by-products, and as heat losses. However, these energies are not utilized before final dissipation to atmosphere. Although various technologies to utilize thermal energy from ironmaking and steelmaking processes have been attempted to develop, practical application of these technologies has not been achieved because the thermal energy is not always useful as an energy source. In steelmaking process by BOF, fluxing agent such as CaO is added during reefing and thus about 100 kg/t-steel of steelmaking slag are generated. Since the steelmaking slag is discharged at temperature range between 1873 and 1923 K after discharge of refined molten steel, it also has large thermal energy. Amount of generated BOF slag is 11.0 Mt/y (FY2012) in Japan.[2] Assuming the amount of steelmaking slag is 10 Mt/y and its average heat capacity from room temperature to 1923 K is 1 kJ/kg·K,[3] unutilized heat is estimated to be 16 PJ/y, which is equal to annual energy consumption of 420 thousand families in Japan.[4]"

Jan 1, 2014

By Chidchai Loyprasert, R. A. Stoehr

"A computer model has been developed to predict grain structures in alloys solidified under unidirectional flow using a combination of three techniques -- solution of the equations for flow of an incompressible fluid bounded by curved surfaces by the SOLA-SURF algorithm, calculation of heat flow by a finite difference method, and simulation of grain formation by a two-dimensional cellular automaton (CA) model. The changing rigid surface has been taken into account. Heterogeneous and homogeneous nucleation are considered, and the growth kinetics of a dendrite tip are evaluated by the Kurz-Giovanola-Trivedi (KGT) model. These calculations were applied to solidification of an Al-4.5% Cu alloy flowing over a chill on the bottom of a channel, a system for which experimental results were available. Using a variety of flow rates and superheats, agreement between the computed and experimental results were very good including transitions between columnar and equiaxed grains, the aspect ratio of the grains, and the inclination of the grains to the flow.IntroductionModeling of casting and solidification processes has developed over the years along two distinct tracks: (1.) modeling of macroscopic heat transfer and fluid flow for design purposes, and (2.) modeling of microscopic processes such as nucleation and growth in order to improve the scientific understanding of the phenomena involved. The present work is an attempt to combine the macroscopic and microscopic approaches for the solidification of an alloy flowing over a chill. The specific case chosen is that of an aluminum-4.5 % copper alloy flowing linearly over a water-cooled copper chill for which experimental results were available over a range of flow rates and superheats. For the macroscopic calculations, the SOLA-SURF algorithm for solution of the twodimensional fluid flow equations was combined with the finite difference method (FDM) for calculating heat transfer. For the microscopic calculations, heterogeneous and homogeneous nucleation were considered, and the growth kinetics at the dendrite tips were evaluated. The cellular automaton (CA) technique was used to apply the microscopic kinetics to the temperature and .flow conditions."

Jan 1, 1999

By Bora Derin

This work deals with the recovery of valuable metals from the ancient copper smelting slags located in Küre-Turkey. In this process, copper and cobalt were recovered in metallic form and/or as their compounds, whereas iron was recovered as magnetic oxide or pigment. Abrasive grit material was produced using reduced final slag. The process stages involved carbothermal reduction in a DC arc furnace, granulation, leaching, chemical precipitation, selective sulfidizing roasting and product preparations. In this paper, the process stages were described as theoretically and experimentally whereas slag and products were characterized in detail.

Jan 1, 2003

By Achilles J. B. Dutra, Carlos M. Juarez

"The use of thiourea as a gold leaching reagent has been extensively studied by many researchers, and it has proved to be promising for some cases as refractory ores. Otherwise, the recovery of gold from these solutions did not receive so much attention. In this paper the electrowinning of gold in acidic thiourea solutions was studied by voltarnmetry and chronopotentiometry. An adsorption step was detected prior to Au(I) reduction and the diffusion coefficients at 25°C for Au-TU complex and FD were found to be 1.00 x 10.5 cm2 S-I and 1.98 x 10-5 cm2 S-I respectively. At -0.350 V (SCE) a passivation probably due to TU adsorption was observed. For higher overpotentials hydrogen evolution was the main reaction.IntroductionThe use of acidic thiourea solutions for the extraction of gold and silver has shown to be a promising alternative to the traditional process of cyanidation, specially for certain refractory ores (1-3) and electronic scrap (4). In some cases, the industrial scale was reached (1,5). The thiourea leaching of precious metals presents advantages over cyanidation, as faster kinetics, lower toxicity and lower sensibility to base metals; however the costs due to high thiourea consumption impairs its use.The majority of the publications on thiourea processing of gold is on leaching. Many are review papers (5-7). Recently, the adsorption and desorption of the gold-thiourea complex on activated carbon and ion exchange resins have been studied (8-11).Little research has been done on the electrowinning of gold from acidic thiourea solutions, most of it has been carried on the seventies and beginning of the eighties in the former USSR (12-17) and concerned the eletrolytic extraction of gold in tridimensional cathode cells.The present paper concerns the cathodic behavior of the gold-thiourea complex in the presence of formamidine disulfide in order to provide information on the electrowinning of gold from solutions obtained directly from leaching or from an elution process."

Jan 1, 1997

By B. J. Vorster

AngloGold South Africa region currently consists of 12 Gold Plants. These plants use a combined total of $20 million of cyanide per annum. Of this, the .major portion (60%) is consumed at two Ergo dump retreatment plants. Historically the primary motivation for cyanide control at Ergo has been one of leachlcost optimisation. However, more recently, with the increased public awareness of cyanide in the environment, a secondary but increasingly important motivation for control has been to ensure that only the minimum amount of cyanide is added to the process whilst not compromising leach performance. Following a brief overview of the Ergo process, the methodology in detennining the amount of cyanide to be added is described. The paper then traces the developments in cyanide control from very basic? manual systems to the current automated control system. In line with the increasingly sophisticated control systems, developments also took place in regards to the method of cyanide analysis. The development of these analysers is also discussed. Whilst cyanide is one of the major drivers, if not the major driver of gold dissolution, it cannot be viewed in. isolation particularly with respect to the relationship between cyanide and oxygen as ascertained from the Elsner's well known equation. Consequently, in order to control cyanide addition, knowledge of the relative cyanide/oxygen profiles is necessary. Various means investigated at Ergo for pulp oxygenation have therefore been included for the sake of completeness. Finally a comparison is made of the control achieved from the current system compared to the? original manual system. The knowledge and experience gained at Ergo is now being used to draw up guidelines for the installation and optimisation work at the other AngloGold plants. The net effect of this will be reduced cyanide consumption for the region, which also, apart from the obvious economic benefit, translates into a reduced environmental; risk.

Jan 1, 1998