The recovery of molybdenum from leach solutions by reduction
- PDF / 507,283 Bytes
- 6 Pages / 597.28 x 785 pts Page_size
- 97 Downloads / 229 Views
I.
II.
INTRODUCTION
W A R R E N et al 1.2 and workers at the United States Bureau of Mines 3-8 have proposed a sodium hypochlorite leach for selective dissolution of molybdenum from copper sulfidemolybdenum sulfide concentrates. The USBM process has been piloted on off-grade MoS2 concentrates containing 16 to 35 pct molybdenum and 6 to 15 pct copper. Warren et al have designed their process to treat rougher concentrates containing 0.3 pct molybdenum and 12 pct copper. The basic flow sheets for both processes are shown in Figure 1, and Table ] gives the compositions of the leach liquors produced. In the USBM process, molybdenum is recovered by solvent extraction using a tertiary amine after acidification to pH = 2. 4 This method could be applied to solutions produced by the Warren et al process, but a technique capable of recovering molybdenum from alkaline solutions would be preferable for a hypochlorite leach operating at pH = 9. Alternative means of molybdenum recovery have been suggested. These include reduction of molybdate solutions with hydrogen at elevated temperature and pressure to produce MOO2,9-14 and reduction with iron followed by neutralization to precipitate Mo(OH)3. ~s As described in the literature, however, both of these processes operate in acid solution. The potential pH diagram for the molybdenum-water system published by Pourbaix 16indicates that reductive precipitation of MoO2 could be possible over a wide range of pH (Figure 2). Despite the simplicity of the diagram, however, the aqueous chemistry of molybdenum is complex. It is now recognized that MoV, MoIV, and MoIII ionic species can be prepared and are stable in aqueous solution. 17Hydrated oxides of each of these valence states can be precipitated in appropriate pH intervals. 18-21In addition, molybdenum aquo ions show a tendency toward polymerization and formation of mixed valent species such as the well-known molybdenum blues. The present work was undertaken to investigate the use of hydrogen gas and hydrazine for reductive precipitation of molybdenum oxides. These reagents are attractive because they offer the possibility of obtaining a high purity oxide product.
A. Materials
Molybdate solutions were made up using Mallinckrodt analytical reagent grade sodium molybdate (Na2MoO4 9 2H20). Hydrazine solutions were prepared by dilution of BDH 99 to 100 pct hydrazine hydrate or Eastman Kodak 64 pet hydrazine in distilled water. Commercial tank hydrogen was used for hydrogen reduction. B. Apparatus
Hydrogen reduction Was performed in a Parr 2-liter autoclave enclosed in a resistance heater. The resistance heater was controlled by a Yellowsprings Instrument Company Thermistemp Temperature Controller Model 71. The Table I.
Comparison of Leach Liquor Solutions for Molybdenum Recovery
H20 NaC1 Na2SO4 Na2MoO4 Cu NaOCI3 NaC104 Re pH
METALLURGICALTRANSACTIONS B
Warren et al
USBM
1100 kg 170 kg 68 kg 10 kg variable nil 5 to 8 kg -9
900 kg 100 kg 37 kg 4 to 43 kg -5 to 13 kg 0.14 to 0.72 kg 0.001 to 0.050 kg 5 to 7
Cu-Mo ROUGHER CONCEN
Data Loading...
