Chemical treatment of low-grade wolframite concentrate having high Mo/WO.sub.3 ratio

A process for recovering tungsten and molybdenum values from wolframite concentrates containing about 3% to 40% WO.sub.3 and about 0.1% to 10% by weight of molybdenum which comprises:

• subjecting said concentrate to atmospheric leaching at a temperature ranging from about 40.degree. C. to 130.degree. C. in a sodium hydroxide solution of concentration ranging from about 50 gpl to 350 gpl for a time sufficient to effect dissolution of at least about 75% WO.sub.3 and molybdenum contained in said concentrate and provide a pregnant liquor of said WO.sub.3 and molybdenum,
• subjecting said pregnant liquor to evaporative crystallization to convert the contained tungsten and molybdenum to crystals of Na.sub.2 WO.sub.4 -Na.sub.2 MoO.sub.4 and provide a residual sodium hydroxide solution for recycle to said atmospheric leach,
• producing a solution of said tungsten and molybdenum values by the aqueous dissolution of said crystals,
• said solution being thereafter filtered of insolubles to provide a filtrate of said tungsten and molybdenum values,
• adding to the solution a stoichiometric excess of a sulfide precipitating agent relative to the amount of molybdenum present and adjusting the pH in a first sulfide precipitation step to precipitate substantially all of said molybdenum and some tungsten as a sulfide and produce a filtrate containing a major portion of said tungsten for the subsequent recovery thereof,
• dissolving said sulfide precipitate in a dilute sodium hydroxide solution,
• and adding a stoichiometric deficient amount of a sulfide precipitating agent relative to the amount of molybdenum present and adjusting the pH in a second sulfide precipitation step to precipitate a major portion of said molybdenum and provide a filtrate containing residual tungsten and molybdenum for recycle into the process.

A process for recovering tungsten and molybdenum values from wolframite concentrates containing about 3% to 40% WO.sub.3 and about 0.1% to 10% by weight of molybdenum which comprises:

• subjecting said concentrate to atmospheric leaching at an elevated temperature ranging from about 40.degree. C. to 130.degree. C. in a sodium hydroxide solution of concentration ranging from about 50 gpl to 350 gpl for a time sufficient to effect dissolution of at least about 75% WO.sub.3 and molybdenum contained in said concentrate and provide a pregnant liquor of said WO.sub.3 and Mo,
• subjecting said pregnant liquor to evaporative crystallization to convert the contained tungsten and molybdenum to crystals of Na.sub.2 WO.sub.4 -Na.sub.2 MoO.sub.4 and provide a residual sodium hydroxide solution for recycle to said atmospheric leach,
• producing a solution of said tungsten and molybdenum values by the aqueous dissolution of said crystals,
• said solution being thereafter filtered of insolubles to provide a filtrate of said tungsten and molybdenum values,
• and adding a stoichiometric excess of a sulfide precipitating agent and adjusting the pH in a first sulfide precipitation step to precipitate
• substantially all of said molybdenum and some tungsten as a sulfide and produce a filtrate containing a major portion of said tungsten for the subsequent recovery thereof,
• the stoichiometric excess of the sulfide precipitation agent ranging from about 25% to 100%,
• dissolving said sulfide precipitate in a dilute sodium hydroxide solution,
• and adding a stoichiometric deficient amount of a sulfide precipitating agent and adjusting the pH in a second sulfide precipitation step to precipitate a major portion of said molybdenum and provide a filtrate containing residual tungsten and molybdenum for recycle into the process,
• the stoichiometric deficient amount of sulfide precipitating agent ranging from about 5% to 25%.