Sponsored by: EPD Aqueous Processing Committee
Program Organizer: Professor David Dreisinger, The University of British Columbia, Department of Metals and Materials Engineering, 309-6350 Stores Road, Vancouver, B.C., Canada V6T 1Z4
Monday, PM Room: A14-15
February 5, 1996 Location: Anaheim Convention Center
Session Chairperson: Professor David Dreisinger, The University of British Columbia, Department of Metals and Materials Engineering, 309-6350 Stores Road, Vancouver, B.C., Canada V6T 1Z4
NEW EVALUATION OF NON-CYANIDE LIXIVIANTS FOR GOLD EXTRACTION FROM COMPLEX AND REFRACTORY GOLD ORES:
L.M. Abrantes and Y.Z. Zhang, University of Lisbon, ICAT, Faculty of Science, 1700 Lisbon, Portugal
Cyanide has generated environmental concerns because of its toxicity, and it may not respond to the treatment of complex gold ores and refractory gold ores. Non-cyanide lixiviants thiourea and thiosulphate are the most promising substitutes of cyanide. However, the commercial adoption of the non-cyanide process has been hindered by three factors: more expensive and higher consumption than cyanide, and the gold recovery step still requires more development. The consumption of gold lixiviants include the stoichiometric usage for gold dissolution, the degradation loss, and the loss due to the impurity interference (forming complexes, precipitates and adsorption). The degradation processes of cyanide, thiourea and thiosulphate systems are discussed on thermodynamics, kinetics and electrochemistry basis. The influences of various factors on the degradation reactions of gold lixiviants are analysed and illustrated for gold leaching from different refractory gold ores. New progress on decreasing the consumption of non-cyanide and avoiding gold passivation are summarized. Finally, progresses on gold recovery from the non-cyanide pregnant solutions by various techniques such as cementation, CIP, RIP, solvent extraction, hydrogen reduction and electrowinning are reviewed. The potential of non-cyanide leaching as a replacement for cyanidation is discussed.
THE LEACHING BEHAVIOR OF PLATINUM POWDER IN IODIDE SOLUTIONS WITH OXYGEN: X. Meng and K.N. Han, South Dakota School of Mines and Technology, Department of Metallurgical Engineering, 501 East Saint Joseph Street, Rapid City, SD 7701-3995
The leaching behavior of platinum powder in iodide solutions under oxygen pressure in an autoclave was investigated. Ammonium-halogen salts were used at neutral pH as the key lixiviants for the dissolution study of platinum. The effect of temperature, partial pressure of oxygen, concentration of iodide and ammonium salts on the dissolution of platinum was examined. Under experimental conditions, the leaching behavior of platinum powder exhibited a complex reaction mechanism. A precipitate was found during the leaching and identified to be platinum ammine iodide, Pt(NH3)2I4. The dissolution rate was found to be controlled by a chemical reaction and limited by the equilibrium concentration of the platinum ammine iodide. A series of chemical reactions are believed to take place.
FERRIC CHLORIDE LEACHING AND METALS RECOVERY OF POLYMETALLIC GOLD ORE: X.J. Guo, Beijing General Research Institute for Nonferrous Metals, Beijing, 100088, China; J.L. Hendrix, University of Nevada, Reno, Mackay School of Mines, Reno, NV
In this paper, an alternative process to recover the value metals from polymetallic gold ore by FeCl3 leaching was proposed. In the process, gold was recovered by direct cyanidation from the leaching residue, the isolative electrolyte in chloride solution was selected to recover lead, the cementation with copper powder was used to recover silver and the solvent extracting was applied to recover copper and zinc. The total recovery of gold, lead, copper, silver and zinc in the process is 90.8%, 96.05% , 84.3%, 81.98% and 54% to the bullion of gold, lead and silver and sulfate of copper and zinc, respectively. The process conditions selected for FeCl3 leaching are the temperature of 104deg.C, leaching time of 6 hours, Fe3+ content of 140 g/l and stoichiometry of FeCl3.
PRETREATMENT USING ALKALINE SULFIDE LEACHING AND NITRGOEN SPECIES CATALYZED PRESSURE OXIDATION ON A REFRACTORY GOLD CONCENTRATE: Corby G. Anderson, Suzzann M. Nordwick, Sunshine Mining & Refining Company, PO Box 1080, Kellogg, ID 83837
Hydrometallurgical technology for the pretreatment of refractory gold concentrates has been developed at Sunshine. It utilizes the patented nitrous-sulfuric acid pressure leaching process which has been industrially proven at the Sunshine refinery. Additionally, antimony and some other impurities can be removed by also employing alkaline sulfide leaching. This paper will discuss the successful application of these two technologies for pretreatment prior to CIL gold recovery. A complex gold concentrate composed of pyrite, arsenopyrite and stibnite was tested. Results of antimony leaching in alkaline sulfide media will be discussed including some details of a novel and selective recovery method for gold leachined by polysulfide or thiosulfate. Also, the factors important in and the results of the application of nitrogen species catalyzed pressure leaching to refractory gold concentrates will be detailed.
AN OXIDATIVE CHLORIDE LEACHING OF PALLADIUM POWDER: H. Zhang, X. Meng and K.N. Han, South Dakota School of Mines and Technology, Department of Metallurgical Engineering, Rapid City, SD 57701-3995
The leaching behavior of palladium powder in aqueous solutions containing NaCl or NH4Cl was investigated. Cupric iron was used as an oxidant for the dissolution reaction. The effect of a number of leaching parameters such as temperature, concentration, stirring speed and surface area on the leaching rate was investigated. The leaching system containing chloride and cupric ion was found to be very effective for the dissolution of metallic palladium. Based on the experimental results, the overall leaching rate was believed to be controlled by a chemical reaction step. The dissolution rate of palladium was found to be a first order with respect to the concentration of cupric ion and a second order with respect to the concentration of chloride.
APPLICATION OF FACTORIAL OPTIMIZATION TECHNIQUE FOR GENERATING KINETIC DATA FOR HYDROMETALLURGICAL PROCESSES: K. Sanjay, S. Anand, R.P. Das, Regional Research Laboratory, Bhubaneswar, 751 013, Orissa, India
The statistical optimization technique using full factorial design of experiments is generally applied to determine the boundary conditions for maximum yields of desired products. The response surfaces are generated to provide flexibility of operating parameters without affecting the yield. The regression equations developed from these set of experiments will show the dependence of yield on individual parameters as well on interactions for simultaneous variations of parameters. These experiments do not give an insight into the kinetics or mechanism of various reactions taking place in the process. In the present work, kinetic data is generated from the factorial optimization results for dissolution of manganese from manganese oxide using Sulphuric acid as a leachant and carbon as a reductant. The boundary conditions for a 23 full factorial design were fixed to achieve variations in the yield in the wider range (30 to 90%). The results obtained are discussed both for process optimization and kinetics of leaching reactions.
THE QUANTITATIVE DETERMINATION OF SUB-PPM QUANTITIES OF Au AND Pt IN SULFIDE MINERALS: L.J. Cabri, G. McMahon, CANMET, 555 Booth Street, K1A 0G1 Canada
The ion microprobe (SIMS technique) is a very sensitive instrument for the
quantitative determination of trace quantities of precious metals (often at the
ppb level) occurring in common sulfide minerals, either chemically-bound or as
discrete particles too small for resolution by SEM. The technique typically
involves sputtering the surface of sulfide grains to a depth of one um and
analysis of an area of 62.5 um. The combination of quantitative mineral-specifc
sub-ppm analyses together with depth-profiling and the ability to produce
secondary ion maps of trace precious metals makes this a very powerful
technique in quantifying the precious metal distribution in refractory and
other sulfide ores and process products. Applications of the technique to gold
and platinum ores and process products will be discussed.
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