Oxidation and alkaline treatment of New Zealand ironsand

Abstract

For over a hundred years now the Taranaki ironsands have proved to be a lure to people as a source of iron. The history of attempts to extract the approximately 60% iron present in the magnetic fraction is one of successive hopes and failures, expectations and disappointments. Several blast furnaces have been built and operators have produced pig iron, often of good quality.(1) However no process has yet survived more than a few years, and indeed the most successful plant to operate found that it could do so only on limonite, available in relatively small quantities in comparison with the amounts of ironsand available. This plant was initially built to process ironsand, but the difficulties involved, caused by the presence of approximately 8 per cent titanium dioxide, enforced its removal to Onekaka where the non-titaniferous ore was available. This brings to the fore one of the main causes of past failures, the presence of titanium dioxide. Recent work(2) has shown that when a blast furnace is operating at its maximum efficiency, titanium is converted by nitrogen in the air to a cyano-nitrade, an infusable substance, immiscible with iron or slag at furnace temperatures. This material will not flow from the furnace and its build up finally chokes the furnace. A development which has taken place where electric power is relatively inexpensive, has been that of the electric are furnace. This furnace, because its heat is derived electrically and not by combustion of air, avoids the production of the cyano-nitride with its associated difficulties, thus opening up new possibilities in the smelting of titaniferous ores such as the ironsands.