The leaching behaviour of nickeliferous pyrrhotite concentrate in hot nitric acid

Abstract

This paper describes the leaching behaviour of nickeliferous pyrrhotite concentrates in hot nitric acid. The effect of the following parameters was investigated by applying a conventional leach procedure, where pyrrhotite was leached in a solution containing excess HNO 3 temperature, solids content, [HNO 3] and particle size. The reaction products were, Fe(NO 3) 3 Ni(NO 3) 2 elemental sulphur, SO 4 2− and NO gas. Sulphate formation has a strong negative effect on the efficiency and economics of any nitric acid based leach process and special attention has been given, therefore, to the mechanism of formation of SO 4 2− Sulphate formation can be minimized by applying a so-called controlled leach technique. This technique involves activation of the dissolution reaction of pyrrhotite by addition of a small excess of HNO 3 followed by slow addition of HNO 3 keeping the acid concentration at a constant low level. By applying this technique the efficiency and kinetics of the leach are improved as well. Finally a method for recovery of Ni as a Ni-sulphide concentrate is discussed and a conceptual flowsheet is proposed, in which Fe will be produced as well grown and clean hematite, sulphur as elemental sulphur and Ni as a Ni-sulphide concentrate.