Recovery of Tin and Tungsten from Various Zones of the Van Roois Vley Deposit, Including Settling and Filtration

摘要

Eight samples of tin-tungsten concentrates from various zones of the Van Roois Vley deposit were tested, by a standard leach, in 10 M hydrochloric acid at 95 degree C under atmospheric pressure for 4 hours. The samples were milled to smaller than 106 micrometers before being leached. Some samples were of a more refractory nature than the others, and gave poor recoveries of tungsten (one as low as 34 per cent). However, when the samples were milled to finer than 38 micrometers, all except sample VRC-2 gave optimum recoveries. An extended leach of up to 10 hours brought the recovery from VRC-2 to 99.9 per cent. Larger composite samples (of 1.5 kg each) were leached under a pressure of 200 to 300kPa at 120 degrees C for 5 hours. The object was to produce some design parameters with regard to leaching, settling, filtration, and precipitation of synthetic scheelite. Leaching yielded extractions of 99 per cent. Leaching under pressure caused dissolution of the calcium fluoride impurity in the concentrate and severe attack of the glass lining of the leaching vessel by the hydrofluoric acid thus formed. The overall recovery of tungsten as calcium tungstate was 98.6 per cent at a grade of 94 to 97 per cent calcium tungstate, with impurity levels well below the limits set by industry.