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., C V6T 1Z4
Tuesday, AM Room: A14-15
February 6, 1996 Location: Anaheim Convention Center
Session Chairperson: Professor Manoranjan Misra, University of Nevada-Reno, Department of Metallurgical Engineering, MacKay School of Mines, Reno, NV 89557-0136
8:30 am
ENERGY AND VOLUME REQUIREMENTS FOR OXYGEN TRANSFER TO SAND SLURRIES IN THE DIP (DELFT INCLINED PLATE) AERATOR: G. Van Weert and A. Borleffs, Delft University of Technology, Faculty of Mining and Petroleum Engineering, Department of Raw Materials Technology, Mijnbouwstraat 120, 2628 RX Delft, The Netherlands
Hydrometallurgical oxidation of sulphides is capital and energy intensive, with autoclave and bio-technology competing for lowest overall cost status. The use of surface aerators instead of stirred tank reactors could provide lower costs for bio-oxidation of concentrates. With this in mind, the Delft Inclined Plate reactor was designed with inclined plates above a settler shaped reactor to return slurry to the surface of the liquid. The multiplate superstructure overcomes the scale up restriction of the standard circular aeration patterns. DIP aerator energy and volume requirements for oxygen transfer from air will be presented in terms of kg O2/kWh and kg O2/m3/h transferred as a function of wt % sand in the slurry and compared to stirred tank performance. Scale up from the 4 m3 pilot unit will be discussed.
9:00 am
BACTERIA OXIDATION OF SULFIDES DURING ACID MINE DRAINAGE FORMATION: A MECHANISTIC STUDY: K. Nyavor and N.O. Egiebor, University of Alberta Department of Mining, Metallurgical & Petroleum Engineering, Edmonton, Alberta, Canada T6G 2G6; P. Fedorak, University of Alberta, Department of Biological Sciences, Edmonton, Alberta, Canada T6G 2G6
The indirect, and the direct contact mechanisms of bacteria oxidation of sulfides were studied using Thiobacillus(T) ferrooxidans and pyrite. The aim was to determine which of the two generally accepted mechanisms played a dominant role, if any, during acid mine drainage (AMD) formation from the oxidation of sulfide minerals. The results show that at a pH of 4.5 and Eh of 0.1 volts where T. ferrooxidans are quite active, but where initial chemical oxidation of pyrite to Fe2+ is limited, the bacteria were unable to directly oxidize pyrite to any significant extent. Whereas, in the presence of Fe2+, T. ferrooxidans assisted oxidation of pyrite by the indirect mechanism was observed and sustained over the pH and Eh range where the bacteria is active. The results lead to the conclusion that the direct contact mechanism of pyrite oxidation by T. ferrooxidans is insignificant. The predominant, and possibly the only, pathway involves the indirect bacteria oxidation of available Fe2+ to Fe3+, which in turn oxidizes FeS2 to generate additonal Fe2+ and acidity in a cyclic process.
9:30 am
AMBIENT PRESSURE PRODUCTION OF CRYSTALLINE SCORODITE FROM ARSENIC-RICH METALLURGICAL EFFLUENT SOLUTIONS: D.J. Droppert and G.P. Demopoulos, McGill University, Department of Metallurgical Engineering, Montreal, Quebec, Canada, H3A 2A7. B. Harris, 3670 St-Famille, Montreal, Quebec, Canada
This paper describes the precipitation-production of crystalline scorodite (FeAsO4.2H2O) from arsenic-rich sulphate-based metallurgical solutions at ambient pressure (95deg.C). Arsenic is precipitated by means of a controlled precipitation technique in which the supersaturation of the solution is carefully controlled. By controlling the supersaturation in the presence of seed material the formation of amorphous ferric arsenate is prevented. Scorodite is known to be the most stable As(V) compound and is therefore preferred as host mineral for arsenic immobilization. The effect of the following paramters on the precipitation behavior and kinetics of scorodite will be discussed: type of base, seed concentration, initial [AS], Fe/As ratio, sulphate concentration, neutralization rate, seed recycling and method of Fe(lll) addition to Fe-deficient arsenic solutions.
10:00 am
METAL RECOVERY FROM A COMPLEX SULPHIDE CONCENTRATE USING A FERRIC CHLORIDE LEACH PROCESS: C.J. Ferron, R.G. Williamson and A.D. Zunkel, Lakefield Research, Lakefield, Ontario, Canada
A modified Cuprex chloride leach process was used to extract Cu, Ni and Co from a complex sulphide concentrate. The standard leach was modified to a two-stage countercurrent leach process which provided emf control of the copper SX feed and minimized iron dissolution. A flowsheet was developed to recover the base metals and silver from the leach solution and gold and platinum group metals from the leach residue, which was predominantly elemental sulphur. Techniques required to maintain an iron balance in the system including pressure oxidation and solvent extraction are described.
10:30 am
ACID RECOVERY FROM SPENT ACIDS & ELECTROLYTES VIA CONTINUOUS ION EXCHANGE: R.S. Dennis, Tetra Technologies, Inc., 25025 I-45 North, The Woodlands, Texas 77380
Acid recovery employs ion exchange resin as separation media for inorganic acids from dissolved metallic salts by physical adsorption and without the use of chemicals. This technology has been used for years on spent etching and plating liquors to recover acid for reuse in the bath and to reduce waste acid neutralization costs. It is also used for electrolyte treatment to facilitate valuable metal recovery. Tetra's CCIX(TM) continuous I-X contactor has been used successfully in a simple, continuous operating mode for acid separation from its metallic salt counterpart. Efficient separation is enhanced by acid reconcentration to its original strength or as high as 14-20%. Continuous treatment also recovers heat to the tankhouse or bath and improves metal quality due to consistent acid quality. Conventional fixed bed ion exchange (I-X) systems are impractical for acid recovery because of complex control design and large resin inventories needed to process very low liquid-to-resin treatment ratios associated with strong acid concentrations.
11:00 am
THE DESTRUCTION OF FREE AND METAL-COMPLEXED CYANIDE BY PHOTOLYSIS: T. Valentine, S.P. Cashin, C.A. Young, Montana Tech., Dept of Metallurgical Engrg., Butte, MT 59701-8997
Cyanide is a strong lixivant for metals making it favorable for finishing and treatment, flotation control, and leaching. As a result, industrial effluents vary considerably in volume and conentration of free and metal-complexed cyanide. In this study, photolytic techniques are described and experimentally compared for the destruction of free and metal-complexed cyanides. Several weak-acid dissociables (WADs) and strong-acid dissociables (SADs) are examined. Various reaction mechanisms are determined by ion chromatography (IC) and inductively-coupled plasma (ICP) emission spectrography.
11:30 am
THE REMOVAL OF METAL CATIONS FROM ACID-MINE DRAINAGE USING RHIZOPUS JAVANICUS: J.J. Ballard, D. Dysinger, Ctr for Advanced Mineral Processing, Montana Tech, Butte, MT 59701; P.P. Wood, C.A. Bradley, Mycotech Corp., Butte, MT 59701; C.A. Young, Montana Tech Dept of Met Engrg, Butte, MT 59701-8997
Biosorption is a proven technology for the extraction of metal cations from
industrial waste waters; however, most research activity has been conducted
with algae, moss, and bacteria. By comparison, little research has involved
filamentous fungi. In this regard, an inexpensive and easily cultivated fungus,
Rhizopus favanicus, was investigated using acid-mine water from the Berkeley
Pit, Butte, Montana. Various operating parameters such as temperature, pH,
fungus concentration, fungus size, fungus age, and fungus pretreatment method
were studied. Results indicate that extraordinary loading capacities can be
achieved.
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