Seabed Mining

At BHP New Zealand Steel’s Glenbrook steel mill (Fig. 1), ironsand from the Waikato North Head mine is blended with Huntly sub-bituminous coal in the ratio of about 1.8:1, preheated in multiple hearth furnaces to about 650oC, and then fed into sloping rotary kilns 65 m long and 4.6 m in diameter. The kilns operate at a temperature of 1100oC and, during the flow-through time of about 12 hours, reduce the iron oxide to form sponge iron containing 70% Fe.

The sponge iron, known as reduced primary concentrate, is melted in an electric arc furnace to produce molten pig iron plus a vanadium-rich slag, which is separated as a valuable by-product. Steel is made using both the basic oxygen process and the electric arc furnace process. Molten pig iron is converted to steel in a KOBM oxygen steel making furnace, whereas an electric arc furnace is used for producing steel from scrap steel. The steel is continuously cast as slabs up to 1.55 m wide x 0.21 m thick x 10 m long and then later processed by hot and cold rolling into pipe, rectangular hollow section and flat products.

Glenbrook Steel Mill, Waiuku
Glenbrook Steel Mill, Waiuku