Separation and Precipitation of Nickel from Acidic Sulfate Leaching Solution of Molybdenum-Nickel Black Shale by Potassium Nickel Sulfate Hexahydrate Crystallization

Nickel was separated and precipitated with potassium nickel sulfate hexahydrate [K2Ni(SO4)2·6H2O] from acidic sulfate solution, a leach solution from molybdenum-nickel black shale. The effects of the potassium sulfate (K2SO4) concentration, crystallization temperature, solution pH, and crystallization time on nickel(II) recovery and iron(III) precipitation were investigated, revealing that nickel and iron were separated effectively. The optimum parameters were K2SO4 concentration of 200 g/L, crystallization temperature of 10°C, solution pH of 0.5, and crystallization time of 24 h. Under these conditions, 97.6% nickel(II) was recovered as K2Ni(SO4)2·6H2O crystals while only 2.0% of the total iron(III) was precipitated. After recrystallization, 98.4% pure K2Ni(SO4)2·6H2O crystals were obtained in the solids. The mother liquor was purified by hydrolysis-precipitation followed by cooling, and more than 99.0% K2SO4 could be crystallized. A process flowsheet was developed to separate iron(III) and nickel(II) from acidic-sulfate solution.