APPLIED MINERALOGY
Leaching of ilmenite in sediments

Stefan Bernstein, Dirk Frei, Christian Knudsen, Henrik Stendal, with Roger McLimans (DuPont Ltd.)

Ilmenite and its alteration products form important sources for titanium production. Ilmenite has a stoichiometric TiO2 content of about 52 wt.%, but the value of a given resource increases with increasing TiO2 content of the ilmenite. In some modern beach sand deposits, mainly in the belt between 30°S and 30°N, ilmenite occurs in a highly altered state. This altered ilmenite has been subjected to a process whereby iron has been leached from the crystal structure and the mineral grains, known as leucoxene, have elevated TiO2 contents with values up to 80 wt.%. The projects aims at describing the occurrence of leucoxene and the variation in ilmenite-leucoxene chemistry in mainly beach deposits. Ultimately, this should lead to a better understanding of the nature of the leaching process and place constraints on where such processes occur at present and in the past. The study is based on CCSEM and microprobe analyses of heavy mineral separates of the sand coupled with whole-rock XRF analyses.

Figure texts
1. Backscatter image of an ilmenite grain (ca 60 microns across) from high-grade metasediment, Kerala State, South India. Dark patches in the grain represent altered ilmenite with elevated Ti contents and decreased contents of Fe. The line represents the analytical traverse in the figure below.

2. Elemental variation along the traverse in the ilmenite grain presented above, showing the increase in TiO2 from about 52 wt.% in the central portion of the grain to nearly 70 wt.% in the altered patches. This increase in TiO2 is followed by a strong dissolution of Fe and increase in the concentration of other elements such as Al, Mn, Si, Mg, and Ca which are normally excluded from the ilmenite structure.