Selective precipitation of nickel and cobalt sulfides from acidic sulfate solution

A method of efficiently precipitating nickel as nickel sulfide from an acidic nickel sulfate solution containing up to 15 gpl nickel which comprises:

• neutralizing said solution to a pH in the range of about 1.5 to 4 by adding a neutralizing agent that forms a soluble inert sulfate salt by reaction with free acid in said solution, the inert sulfate salt providing sulfate ions in said solution in an amount ranging from about 30 to 400 gpl,
• the sulfate ion formed behaving as an acid buffer by combining with hydrogen ions formed during precipitation of nickel sulfide to form HSO.sub.4.sup.-1,
• adding a slurry of finely divided nickel sulfide to said solution to provide a seed concentration of at least about 75 gpl,
• and then subjecting said solution to sulfide precipitation with H.sub.2 S under pressure at a temperature of about 65.degree. C to less than 100.degree. C while vigorously agitating said solution until substantially complete sulfide precipitation of nickel obtains.

A method of efficiency precipitating nickel as nickel sulfide from an acidic nickel sulfate solution containing up to 15 gpl nickel which comprises:

• neutralizing said solution to a pH of about 2 to 3.5 by adding a neutralizing agent that forms a soluble inert sulfate salt by reaction with free acid in said solution, the inert sulfate salt providing sulfate ions in said solution ranging from about 30 to 400 gpl, the amount being substantially directly related to the nickel concentration,
• the sulfate ion formed behaving as an acid buffer by combining with hydrogen ions formed during precipitation of nickel sulfide to form HSO.sub.4.sup.-1,
• adding a slurry of finely divided nickel sulfide to said solution to provide a seed concentration of about 75 to 300 gpl,
• and then subjecting said solution to sulfide precipitation with H.sub.2 S at a pressure of about 5 to 50 psig at a temperature of about 65.degree. C to less than 100.degree. C while vigorously agitating said solution until substantially complete sulfide precipitation of nickel obtains.

A continuous process for efficiently precipitating nickel as nickel sulfide from an acidic nickel sulfate solution having a pH below 1.5 containing up to 15 gpl nickel and up to 5 gpl cobalt which comprises:

• neutralizing said solution to a pH in the range of about 1.5 to 4 by adding a neutralizing agent that forms a soluble inert sulfate salt by reaction with free acid in said solution, the inert sulfate salt providing sulfate ions in an amount ranging from about 30 to 400 gpl in said solution,
• the sulfate ion formed behaving as an acid buffer by combining with hydrogen ions formed during precipitation of nickel sulfide to form HSO.sub.4.sup.-1,
• adding a slurry of finely divided nickel sulfide seed to said solution to provide a seed concentration of at least about 75 gpl,
• feeding said solution through a group of series-connected precipitation tanks starting with the first tank and feeding under pressure H.sub.2 S to said tanks starting with the last tank and causing said H.sub.2 S to flow from said last tank through said series-connected tanks to the first tank to effect precipitation of nickel sulfide in said tanks at a temperature ranging from about 65.degree. C to less than 100.degree. C while vigorously stirring said solution in each of the precipitation tanks and while said solution, together with said seed, is passed from the last tank to a flash drum,
• continuously removing H.sub.2 S from said flash drum and passing it to an ejector and condenser system for recycle to the precipitation tanks,
• continuously passing precipitated nickel sulfide from the flash drum to a thickener,
• continuously elutriating the nickel sulfide collected in said thickener,
• recycling a portion of said elutriated nickel sulfide to fresh nickel solution as seed material to provide a seed concentration of at least about 75 gpl, and then recovering the remainder of said precipitated nickel sulfide as the end product.