REFINING OF ILMENITE BY REMOVAL OF EXCESS CHROMITE

摘要

The presence of chromite in significant amount in ilmenite downgrades the market value of the ilmenite. A substantial amount of the chromite may be removed, firstly by a reduction step, secondly by a leaching, aeration or oxidation roasting step and finally by a physical separation step. An optional preoxidation may precede the reduction step and an optional physical separation step may be inserted between the first and second steps. The first step is one of solid state reduction above 1000 DEG C in the range 1000-1300 DEG C with coke, coal, gaseous fuels, such as natural/petroleum gas or liquid fuels, such as oils or their products. Various additives such as alkali metal salts, chlorides, magnesium or manganese compounds may be added to promote segregation of the reduced metallics, (Fe, Cr). The reduction may be carried out in fluidised bed or rotary kiln furnaces. The second step consists preferably of oxidising or aerated dilute acid/ferrous-ferric salt attack, aqueous aeration in the presence of an activator or thermal oxidation roasting. The aqueous aeration, which has been used in this specification consists of bubbling air for 5 to 16 hours, depending on the finished requirement, with strong agitation in the presence of low concentrations (e.g., 0.5 - 1.0 %) of ammonium chloride. Activating agents are selected from sodium or iron chlorides, organic acids and salts. The final physical separation step is usually a magnetic separation, which effectively removes the chromium from the titanium. A magnetic separation may also be inserted after the solid state reduction step, prior to the aeration step. The procedure results in a better than 80 % recovery of the TiO2 content and the removal of about two thirds of the Cr2O3 content.