Лако-красочные материалы — производство

In contrast to ilmenite, only a small number of rutile deposits can be mined econom­ically, and the price of natural rutile is therefore high. Consequently, many different processes have been developed to remove the iron from ilmenite concentrates without changing the grain size of the mineral because this is highly suitable for the subse­quent fluidized-bed chlorination process. All industrial processes involve reduction of Fe3+ with carbon or hydrogen, sometimes after preliminary activation of the il — menite by oxidation. Depending on the reducing conditions, either Fe2+ is formed in an activated ilmenite lattice, or metallic iron is produced.

The activated Fe2+-containing ilmenite can be treated with hydrochloric or dilute sulfuric acid (preferably under pressure), and a “synthetic rutile” with a TiO2 content of85-96% is obtained [2.13]. The solutions containing iron(II) salts are concentrated and then thermally decomposed to form iron oxide and hydrochloric acid, which can be used again in the digestion process [2.14].

Metallic iron can be removed in various ways. The following processes are de­scribed in the patent literature:

1. Size reduction followed by physical processes such as magnetic separation of flotation.

2. Dissolution in iron(III) chloride solutions [2.15], the resulting iron(II) salt is oxidized with air to give iron oxide hydroxides and iron(III) salts.

3. Dissolution in acid.

4. Oxidation with air in the presence of electrolytes. Various iron oxide or iron oxide hydroxide phases are formed depending on the electrolyte used. Possi­ble electrolytes include iron(II) chloride solutions [2.16], ammonium chloride [2.17], or ammonium carbonate-carbonic acid [2.18].

5. Oxidation with the iron(III) sulfate from ilmenite digestion, followed by crys­tallization of the iron(II) sulfate (see Section 2.1.3.1) [2.19].

6. Chlorination to form iron(III) chloride [2.20].

7. Reaction with carbon monoxide to form iron carbonyls [2.21] which can be decomposed to give high-purity iron.

Another possible method of increasing the TiO2 content of ilmenite is by partial chlorination of the iron in the presence of carbon. This is operated on a large scale by several companies [2.22, 2.23]. The most important

companies producing synthetic rutile are located in Australia (Renison Goldfields Consolidated, Tiwest, Westralien Sands), India (Kerala Minerals and Metals, DCW, Bene-Chlor Chemicals), and Malaysia (Hitox). In 2000 production of synthetic rutile was ca. 0.8 x106 t (as TiO2).

2.1.3