1997 TMS Annual Meeting: Thursday Abstracts

MATERIALS PROCESSING FUNDAMENTALS: Session V

Session Chairpersons: R.G. Reddy, Department of Metallurgical and Materials Engineering, University of Alabama, Tuscaloosa, AL 35487-0202; J. Hryn, Blvd. 362, Argonne National Labs, 9700 S. Cass Ave., Argonne, IL 60439

8:30 am

A MATHEMATICAL MODEL TO CHARACTERIZE, THE DISSOLUTION OF SULFIDES IN CuCl2-CuCl-FeCl3-FeCl2-NaCl-HCl- H2O SYSTEM: CUPRIC CHLORIDE LEACHING OF SYNTHETIC NiS: R.C. Hubli, T.K Mukherjee, C.K. Gupta, Bhabha Atomic Research Centre, Trombay, Bombay 400085, India, S. Venkatachalam, Department of Met. Eng. and Matls. Sci., I.I.T. Bombay, India; R.G. Bautista, Mackay School of Mines, University of Nevada, Reno, NV 89557

Simulation of sulfide dissolution in cupric chloride media using the partial equilibrium approach has been investigated under different process conditions. The following observations may have a significant bearing on the dissolution behavior: The amount of cupric-chloro-hydroxy complexes is low, <1% of total Cu(II), when the pH of the lixiviant is around 1.5 but increases at lower H+ concentrations. Under aerated conditions the hydrolysis is higher and control of pH during the dissolution process is necessary, the total initial Cu(II) concentration higher than 0.50 M does little to enhance dissolution but may entail a higher loss of "free" copper, the optimum temperature for cupric chloride leaching is around 373-378K (100-105°C) and the presence of small amounts of ferric ion results in increasing the initial rate of dissolution as well as suppressing the hydrolysis of copper.

*Acknowledgments: This investigation forms a part of the INDO-US collaborative research programme supported by the Department of Science and Technology, Government of India and the NSF, USA under NSF Grant No. INT-9103106.

8:55 am

LEACHING OF A CHALCOCITE CONCENTRATE WITH CUPRIC CHLORIDE-OXYGEN: M.C. Ruiz, S. Honores, R. Padilla, Department of Metallurgical Engineering, University of Concepcion, Casilla 53-C, Concepcion, Chile

This work outlines the results of leaching studies on a copper concentrate containing chalcocite (CU2S) and digenite (Cu9S5) with an acid saline solution of cupric chloride oxygenated at ambient pressure. The variables studied included the stirring speed, concentration of cupric ions, concentration of HCl, concentration of chloride ions, oxygen flow rate, temperature and time. The leaching system was found to be very effective for the dissolution of the concentrate. Over 95% of the copper was dissolved in 30 minutes with negligible dissolution of iron. The dissolution of copper increased with the stirring speed up to about 400 rpm and depended little on the total chloride concentration. The oxygen flowrate affected the dissolution of copper only below 0.09 l/min. The concentration of HCl did not influence tile dissolution providing its was sufficient to avoid the precipitation of copper oxychloride. The study of the effect of the temperature showed a maximum in copper dissolution around 90°C.

9:20 am

ELECTROCHEMICAL STUDY OF PYRITE OXIDATION IN CHLORIDE SOLUTION: H.K. Lin, Mineral Industry Research Laboratory, 212 O'Neill Building, University of Alaska Fairbanks, Fairbanks, AK 99775-7240; W.C. Say, Department of Material Science, National Taipei Institute of Technology, Taipei, Taiwan

Pyrite oxidation in chloride solution was investigated with cyclic voltammetry, ac impedance and potential step techniques. The pyrite oxidation in quiescent electrolytes is irreversible and controlled by diffusion. Depression of the semi-circle in the complex plane plot has been explained mathematically based on the concept of the equivalent circuit. When the semicircle is depressed, the mathematical formula indicates that the reaction resistance should be obtained from the intersection of the semi-circle with Z'-axis instead of the semi-circle diameter. The peak charging current densities at 1.10 and 0.90 V vs. SHE obtained from the equivalent circuit coupled with the ac impedance measurements match the peak current densities obtained with the potential step measurements.

9:45 am

LEACHING OF CHALCOPYRITE IN CuCl-NaCl-O2 SYSTEM: R. Padilla, D. Lovera, M.C. Ruiz, Department of Metallurgical Engineering, University of Concepcion, Casilla 53-C, Concepcion, Chile

The leaching behavior of chalcopyrite concentrate in acidic CUCl2-NaCl-O2 solutions was investigated. Experiments were conducted under continuous flow of oxygen at atmospheric pressures. The results indicated that among the variables temperature has the largest influence on the dissolution of chalcopyrite in this medium, and high dissolution can only be obtained at temperatures near the boiling point of the solution. It was also found that the stirring speed did not influence appreciably the dissolution of chalcopyrite and that an increase in the oxygen flow rate in the leaching reactor increased the dissolution of chalcopyrite. The total chloride concentration affects markedly the dissolution of chalcopyrite up to about 4 M. Copper dissolutions of about 85% were obtained in leaching chalcopyrite of size fraction -65+100# Tyler at 100°C in 2 hours.

10:10 am BREAK

REACTIVE METALS (GENERAL ABSTRACT SESSION)

10:20 am

VAPOR PRESSURE STUDIES OF THE SALT FLUX PHASES: S. Wang, ASARCO Inc., Technical Services Center, 3422 South 700 West, Salt Lake City, UT 84119; R.G. Reddy, Department of Metallurgical and Materials Engineering , The University of Alabama, Tuscaloosa, AL 35487

Physical and chemical properties of the salt flux phase play a significant role in the recycling of UBC and aluminum melting processes. Particularly, the knowledge of several properties such as salt vapor pressure, melting temperature, loss of aluminum, corrosion of refractories are useful for the performance improvements in aluminum industry. In this paper, vapor pressure of sodium and potassium salt fluxes were studied in the pure, binary and ternary systems. The experimental results of vapor pressure studies are presented and the potential application I the industry to the efficiency and the operating advances are discussed.

10:45 am

COMPLEXES OF NIOBIUM (IV,V) IN LiF-NaF-KF MELTS WITH VARYING O2- CONCENTRATIONS: Flemming Matthiesen and Pia Tolstrup, Jensen Kernisk Lab. A, DTU, 2800, Lyngby, Denmark; Terje Ostvold, Institutt for Uorganisk Kjemi, NTNU, Gloshaugen, 7034, Trondheim

The ternary eutectic LiF-NaF-KF (FLINAK) melt at 700°C was used as a solvent for a study of Nb(IV,V)-O-F complexing. The motivation for this study is the electroplating mechanism of Nb from such melts. A 1.8 mol% Nb2O5 solubility is observed in this melt. The dissolution mechanism is K+ +Nb2O5=NbO2Fx1-x+KNbO3(s)+xF-. When Na2O or SrO is added to FLINAK containing 1 mol% Nb(V), a constant concentration of Nb and a concentration of O2- given by the added oxide up to nO/nNb=2 is observed. For 2 < nO/nNb < 3, the NbO2Fx1-x complex reacts to form KNbO3(s). The solubility data of this compound is matched by literature data. By further additions of O2-, this solid reacts to form NbO43- type complexes. When Na2O is added to FLINAK containing 1 mol% Nb(IV), a constant concentration of Nb and a concentration of O2- given by the added oxide up to nO/nNb=1 is observed. Above this ratio some Na2O still dissolves, but an unknown compound precipitates. At nO/nNb=2 the O2- and Nb(IV) concentrations decrease with increasing oxide additions and reaches a minimum at NO/nNb=3 and probably K2NbO3(s) is formed. Up to nO/nNb=3 the melts are coloured, but changes to colourless (white solids when cooled) at nO/nNb>3. A melt containing a complex of the type NbO42- is probably formed at these high oxide concentrations. Na2O is now completely soluble in the melt.

11:10 am

KINETICS OF ERBIUM OXIDE CORROSION IN MOLTEN CERIUM: C. Lensing, D.L. Olson, B. Mishra, Center for Welding, Joining and Coatings Research, Department of Metallurgical & Materials Engineering, Colorado School of Mines, Golden, CO 80401

The compatibility between erbium oxide and molten cerium was investigated to understand the high temperature corrosion mechanisms and to provide kinetic data. High and low density erbium oxide samples were immersed into molten cerium at temperatures ranging from 850 to 975°C for 16 to 128 hours. A parabolic rate dependence for corrosion scale formation was observed as well as an intergranular penetration of cerium into erbium oxide was noted. Activation energy for the complete corrosion process is 38.5 kCal/mole. Two reaction layers formed for the cerium system, viz. cerium oxide particle layer and a layer of erbium oxide-cerium oxide solid solution.

11:35 am

DEVELOPMENT OF PROCESSING METHODS FOR STAINLESS STEEL-ZIRCONIUM NUCLEAR WASTE FORMS ALLOYS: S.M. McDeavitt, D.P. Abraham, Argonne National Laboratory, Chemical Technology Division, 9700 South. Cass Avenue, Argonne, IL 60439

Stainless steel-zirconium waste form alloys are being developed at Argonne National Laboratory for the immobilization of metallic materials left behind following the electrometallurgical treatment of spent nuclear fuel. The metal waste form comprises fuel cladding, noble metal fission products (e.g., Ru, Rh, Pd, Zr, and Tc), and other metallic constituents. These metallic wastes are not generated in the electrorefiner; they are present with the spent fuel before treatment. The nominal compositions stainless steel- 15 wt% zirconium and zirconium-8 wt% stainless steel are the baseline alloys for stainless steel-clad and Zircaloy-clad fuels, respectively. The selection process for the baseline compositions will be described and the subsequent development of basic alloying procedures will be reviewed (e.g., alloying temperatures, molten metal containment, and heating method). Other process-related issues still under development include microstructural refinement through annealing and molten salt fluxing for surface purity and composition control.