Abstract
The pressure leaching of tungsten ores with ammoniacal ammonium phosphate solution was investigated at 160-220 C.The experimental results are summarized as follows(1) The tungsten extraction from scheelite and wolframite ores is 90 and 80%, respectively, under the optimum conditions viz. reaction temperature 200 C, reaction time 2hr, molar ratio of ammonium phosphate to tungsten in the ores: 8 and pulp density: 2g-ores per 8ml concentrated ammonia solution.(2) As the solubility of phosphate in concentrated ammonia solution containing several %of ammonium tungstate is less than 200 mg-P205/l, most of the phosphate in the leachate can be removed by merely blowing gaseous ammonia into it.(3) The ammonium phosphate method is inferior to the sodium carbonate one in the degree of the tungsten extraction, but has advantages that both ammonia and ammonium phosphate, which are decomposing agents, can be used circularly, and that the dissoiution, of silica can be suppressed.
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