Abstract According to the invention, substantially pure, particulate elemental nickel is recovered from nickel compounds and particularly from basic nickel carbonate, which are soluble in aqueous ammoniacal ammonium sulphate solution and which contain impurities including particularly zinc, manganese and/or magnesium by first extracting substantially all the nickel content from the impure nickel compound by dissolving it in an aqueous ammoniacal ammonium sulphate solution containing ammonium sulphate in excess of the stoichiometric amount required to react with the nickel to form nickel diammine sulphate. The resulting nickel diammine sulphate solution is separated from undissolved residue and is reacted with hydrogen at elevated temperature and pressure to reduce dissolved nickel to elemental form and to precipitate it in powder form. Nickel-depleted solution, referred to as ''''reduction end solution,'''' containing zinc, manganese and/or magnesium as well as small amounts of other impurities as dissolved sulphates is recycled to the nickel compound dissolution step and the quantity of such solution recycled is controlled such that the impurities'' level in the reduction end solution is maintained at a predetermined level above the level that would result if no solution were recycled but below that level at which zinc, manganese and/or magnesium report in the nickel powder product in sufficient quantity to contaminate the product. The portion of the reduction end solution which is not recycled is bled from the process circuit.
The process according to claim 1 wherein the material treated is wet basic nickel carbonate precipitated from an ammoniacal ammonium carbonate leach liquor and the dissolution step is conducted to produce a nickel diammine sulphate solution containing from about 40 to about 70 g.p.l. of dissolved nickel and from about 100 to about 145 g.p.l. sulphur in sulphate form.
Claim 2
Dependent Claim
33 words
The process according to claim 1 wherein the ammonia content of the solution reacted with hydrogen is adjusted to provide between 1.8 and 3.0 moles of ammonia per mole of elemental nickel produced.
Claim 3
Dependent Claim
61 words
The process according to claim 1 wherein the reduction operation is conducted on a batch basis with successive batches of fresh feed solution being reacted with hydrogen in a closed reaction vessel and with the nickel powder product of each such reduction being left in the reaction vessel for each subsequent reduction until a plurality of such reductions have been completed.
Claim 4
Dependent Claim
35 words
The process according to claim 4 wherein from about 0.1 to about 1 millilitre per litre of 2.5 percent aqueous polyacrylic acid solution is added to each batch of solution treated in said reduction operation.
Claim 5
Dependent Claim
33 words
The process according to claim 2 wherein the ammonium sulphate concentration of the ammoniacal ammonium sulphate solution used in the nickel dissolution step is adjusted to within the range of about 500-550 g.p.l.
Claim 6
Dependent Claim
35 words
The process according to claim 2 wherein the water balance within the process circuit is maintained by evaporating from the recycled reduction end solution any excess water not removed from the circuit with the bleed.
Claim 7
Dependent Claim
67 words
The process according to claim 1 wherein the nickel compound also contains cobalt which is dissolved along with the nickel and wherein the level of dissolved cobalt in the process circuit is maintained substantially constant by stripping cobalt from a sufficient portion of the reduction end solution to remove from the process circuit a quantity of cobalt equivalent to that coming into the circuit with the nickel.
Claim 8
Dependent Claim
64 words
The process according to claim 2 wherein said basic nickel carbonate contains sulphur and said nickel diammine solution from said dissolution step is reacted with a free oxygen bearing oxidizing gas at a partial pressure of oxygen above about 5 p.s.i. at a temperature within the range of about 200*F. to about 500*F. to convert substantially all contained sulphur values to the sulphate form.
Claim 9
Dependent Claim
51 words
The process according to claim 9 wherein the quantity of reduction end solution bled from the process circuit and the level of zinc, manganese and/or magnesium in said solution are controlled to maintain the sulphur balance in the process circuit whilst simultaneously maintaining the balance of said impurities in the circuit.