Sponsored by: Jt. EPD/MDMD Synthesis, Control, and Analysis in Materials Processing Committee, EPD Process Fundamentals, Aqueous Processing, Copper, Nickel-Cobalt, Pyrometallurgy, Lead, Zinc, Tin Committees, MSD Thermodynamic & Phase Equilibria Committee
Program Organizers: R. G. Reddy, Department of Chemical and Metallurgical Engineering, University of Nevada, Reno NV 89557; S. Viswanathan, Oak Ridge National Lab., Oak Ridge, TN 37831-6083; J.C. Malas, Wright-Patterson AFB, OH 45433-6533
Tuesday, AM Room: A16-17
February 6, 1995 Location: Anaheim Convention Center
Session Chairpersons: G.W. Warren, Department of Metallurgical and Materials Engineering, University of Alabama, Tuscaloosa, AL 35487; Y.B. Hahn, Department of Chemical Engineering & Technology, Chonbuk National University, Duckjin-Dong 1Ga, Chonju, Korea
8:30 am
KINETICS OF MILLERITE DISSOLUTION IN CUPRIC CHLORIDE SOLUTIONS: R.C. Hubli, T. K. Mukherjee, C. K. Ghupta, Bhabha Atomic Research Centre, Trombay, Bombay, India; S. Venkatachalam, Department of Metallurgical Engineering, and Materials Science, Indian Institute of Technology-Bombay, Bombay, India. R.G. Bautista, Department of Chemical and Metallurgical Engineering, University of Nevada, Reno, NV 89557
A kinetic study of the dissolution of millerite in cupric chloride media has been conducted to determine the effect of different variables in the rate expression. Experimental data were obtained on naturally available millerite in a laboratory scale stirred pressure reactor under inert atmosphere. The variables evaluated include acid strength, initital copper (II) concentration, total chloride concentration, and temperature. The rate equation is expressed in amount of mineral dissolved per unit area of mineral surface per unit time.
8:55 am
EVALUATION OF THIOUREA CONSUMPTION FOR GOLD EXTRACTION FROM COMPLEX AND REFRACTORY GOLD ORES: Dr. Yongzhu Zhang, ICAT, Faculty of Sciences, University of Lisbon, Campo Grande, 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 absorption). The degradation processes of cyanide, thiorea and thiosulphate systems are discussed on thermodynamics, kinetics and electrochemistry basis. The influences of various factors on the degradation reactions of gold lixiviants are analyzed and illustrated for gold leaching from different refractory gold ores. New progress on decreasing the consumption of non-cyanide and avoiding gold 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.
9:20 am
A MODEL TO DESCRIBE THE CHEMICAL SPECIES CONCENTRATION CHANGES IN THE DISSOLUTION OF MILLERITE IN CUPRIC CHLORIDE SOLUTIONS: R.C. Hubli, T.K. Mukherjee, C.K. Gupta, Bhabha Atomic Research Centre, Trombay, Bombay, India; S. Venkatachalam, Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology-Bombay, Bombay, India; R. G. Bautista, Department of Chemical and Metallurgical Engineering, University of Nevada, Reno, NV 89557
The model computes the initial concentrations of the chemical species present in the lixiviant and leach solutions and the subsequent changes in their concentrations with small increments of dissolution of the mineral for the specified amount or period of dissolution. The dissolution step is simulated under initial cupric and acid concentrations. The initial analytical concentrations of the components are specified. The initial concentrations of all the species are obtained by solving a set of simultaneous non-linear equations for the independent mass action expressions, mass and charge balance equations and the dissolution rate equation.
9:55 am BREAK
10:05 am
THE GAS COMPOSITIONS CALCULATIONS ON THE SYSTEM OF FeS-H2O AT ELEVATED TEMPERATURE: GUO Xian Jian, Beijing General Research Institute for Nonferrous Metals, Beijing, 100088, China; James L. Hendrix, Mackay School of Mines, University of Nevada, Reno, NV
In this paper, the gas compositions calculations on the FeS-H2O system at elevated temperature were performed. The results show that the gas constituents are H2O, SO2, H2S, Sj, H2, and O2 and the order of the compositions partial pressure is PH2O > PH2 > PSO2 > PSj > PH2S > PO2 when FeS is oxidized into Fe3O4 and FeO by steam in the temperature range of 700 to 960[[ring]]C, the Claus process occurs with the decrease of gas temperature in the off-gas and the SO2 and H2S in the gas are transformed into Sj, the critical temperature for the transformation is 600[[ring]]C, and conversion percent of Sj is 97% at 330[[ring]]C.
10:30 am
OXIDATION MECHANISM OF ARSENOPYRITE IN ACIDIC FERRIC SULPHATE MEDIA IN THE ABSENCE AND PRESENCE OF BACTERIA T. FERROOXIDNAS: Y. Z. Zhang, Y.Y. Lu, T.C. Zhao, Department of Metallurgy, Central South University of Technology, Changsha 410083, Hunan, China
The mechanism of arsenopyrite oxidation by ferric ion and bacteria has been investigated. Rest potential, polarization resistance measurements, polarization curve, cyclic voltammetry experiments are conducted in a ferric sulphate medium of 10g/L Fe3+, temperature 25-35[[ring]]C, pH 1.5-2.5 in the absence and presence of bacteria T.ferrooxidans, respectively. The anodic oxcidation process of arsenopyrite is expressed as: at low potential: FeAsS + 3H2O = Fe3+ + H3AsO3 +S0 +3H+ + 4e; and at high potential: FeAsS + 8H2O = Fe3+ + H3AsO4 +SO42- + 14H+ + 14e. The cathodic process is the reduction of oxygen. The oxidation behavior of arsenopyrite in sterile and inoculated media are compared. The preferential attachment of bacteria onto the surface of arsenopyrite decreases the rest potential of arsenopyrite from 455 (sterile) to 402 (inoculated) mV(SCE) and the charge transfer resistance from 206 (sterile) to 80 (inoculated) [[Omega]]/cm2. The absorption of oxygen by bacteria increases the transfer of electrons from anode to cathode pots, and accelerates the dissolution rate of arsenopyrite.
10:55 am
MATHEMATICAL MODELING OF THE SEPARATION OF LIQUID-LIQUID DISPERSIONS IN A DEEP-LAYER GRAVITY SETTLER: M.C. Ruiz, R. Padilla, Department of Metallurgical Engineering, University of Concepción, Casilla 53-C, Concepción, Chile
An experimental study has been carried out on the separation of phases in a laboratory scale mixer-settler, for a system consisting of 10% Acorga M5640 in Escaid 103-0.25 M Na2SO4 solution. The thickness of the dispersion band, the local dispersed phase holdup and the size distribution of the dispersed phase droplets were determined for various operational conditions. Based on the experimental findings, a mathematical model for the steady state operation of a deep-layer gravity settler has been developed by using a population balance approach. This model takes into account the size distribution of drops within the dispersion band and it uses rate expressions for the description of drop-drop and drop-interface coalescence phenomena. The model predicts very well the thickness of the dispersion band as well as the growth of the dispersed phase drops occurring by drop-drop coalescence within the dispersion band.
11:20
PAPER STABILITY DIAGRAMS FOR THE GOLD-THIOUREA-WATER AND SILVER-THIOUREA-WATER SYSTEMS: T. Xue, K. Osseo-Assare, Dept of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802
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