Process for enrichment of a ferronickel alloy to 90 Pct Ni

Abstract

The nickel of most lateritic ores is extracted as a FeNi alloy containing a certain amount of cobalt. The utilization of this ferroalloy is effectively limited to the fabrication of stainless steels, which absorbs about 40 pct of the total nickel consumption. The production of electrolytic nickel from ferronickel is feasible, but it requires anodes made of alloy enriched to at least 80 pct Ni. Such enrichment is complicated by the simultaneous oxidation of nickel during the slagging of iron, which accelerates as the iron is depleted and becomes prohibitive for an alloy with more than 60 pct Ni. A simple and economical upgrading of ferronickel up to 90 pct Ni is proposed by a two-stage converting with oxygen, under simultaneous addition of nickeliferous laterite. Nickel losses are effectively restricted by the two-stage operation. The rich slags of the second stage, produced in contact with an alloy of more than 60 pct Ni, are recycled in liquid state into the empty first stage converter. The subsequent addition of the low grade liquid metal into the first stage converter “washes” the rich slags and reduces their nickel content. The slags of the first stage, produced in contact with low grade alloys, contain little nickel and are discarded. The overall nickel loss is considerably reduced by blowing in short blows with intermediate slag skimmings. The addition of the lateritic ore, during converting, achieves a very satisfactory and inexpensive temperature control, substitutes as a flux, and introduces nickel and oxygen to the process at a very minimal cost. The heat evolved during the oxidation of the iron in the molten alloy is effectively utilized for the smelting of the laterite added.