Final neutralization method in hydrometallurgical process of nickel oxide ore

Abstract

A final neutralization method is aimed at removing metals dissolved in a waste liquor, preferably with a pH of 1.0 to 3.0, discharged during recovery of nickel sulfide from a leachate produced in high temperature and pressure acid leaching of nickel oxide ore, the method including: subjecting the waste liquor, having an adjusted iron ion concentration ranging from 1.0 to 4.0 g / 1, to a first neutralization treatment at pH 5.0 to 5.4 by adding a limestone slurry preferably having an average grain size of 5 to 15 um and has a concentration of 20 to 30% by mass; and subjecting the waste liquor to a second neutralization treatment at higher pH as compared with the first neutralization treatment by adding a slaked lime slurry preferably having an average grain size of 15 to 30 um and has a concentration of 20 to 30% by mass.