Circular 81—Hydrometallurgical recovery of molybdenum from the Questa mine

By R. B. Bhappu, D. H. Reynolds, R. J. Roman, and D. A. Schwab, 1965, 24 pp., 4 tables, 12 figs.

The dissolution of molybdenite (MoS2) was studied using various oxidizing agents including hypochlorite, ozone, oxygen-alkali, acid-permanganate, persulfate, acid-ferric chloride, nitric acid, chlorine dioxide, acid-chlorate, maganese dioxide-sulfuric acid, and bacterial oxidation. Hypochlorite in basic solution offers a fast and selective method for dissolving molybdenite. It has the disadvantage of being an expensive and unstable reagent, difficult to handle, and troublesome to regenerate. Acid-chlorate leaching is not so rapid nor so selective as hypochlorite but presents less of a handling problem, provides for easy extraction of molybdenum from solution, and is more efficiently regenerated. The manganese dioxide-sulfuric acid oxidation of molybdenite was studied in detail and was also found effective. Its only application, however, appears to be in dissolving molybdenum from high-grade ores or concentrates. Preliminary tests on bacterial oxidation of molybdenite indicate a favorable response of the specific species Thiobacillus thiooxidans and Thiobacillus ferrooxidans, which have been tentatively identified in the Questa mine water.

The molybdenum from the primary oxide-molybdenum minerals such as ferrimolybdite and molybdenum-bearing limonite may be extracted either by leaching with acid solution or decomposing with carbonate solution. If acid leaching is used, provisions should be made to prevent complexing of molybdenum with iron, calcium, and aluminum ions. The extraction of molybdenum from leach solutions was studied employing anion exchange resins, organic solvents, and activated carbon. The adsorption characteristics shown by all three for Mo (VI) are alike, with highest D values obtained at pH 1.5–2.5 for the processes. The observed similarities indicate that the ionic species adsorbed may be the same for the processes. Efforts are made to explain the irregular variation of D with pH and to establish optimum conditions for loading and elution. Studies of the recovery of molybdenum as a marketables product were directed toward its precipitation as the ferric-molybdenum complexes. Stable dehydrated compounds containing 70–80% MoO3 and 20–30% Fe2O3 were produced under optimum concentration and pH conditions. Efforts have been made to elucidate the scheme of precipitation and composition of the precipitated iron-molybdenum compound and to compare it with the naturally occurring mineral, ferrimolybdite, in the oxidized zones of the molybdenum deposits.