A New Approach on the Egyptian Black Sand Ilmenite Alteration Processes

Several studies have investigated the process of alteration of ilmenite, especially in black sand. To predict the mechanisms of ilmenite alteration and the role of some minor element oxides in the alteration process, separated non-magnetic altered ilmenite grains were examined using a binocular microscope and a Cameca SX-100 microprobe instrument. Twenty intergrown phases of alteration products were concluded in three postulated scenarios for the following alteration processes, carried out after forming the most stable lowest Leached pseudorutile (LPSR) phase FeTi3O6(OH)3. Most of the alteration phases of pseudorutile (PSR) and LPSR have real Ti/(Ti+Fe) ratios between 0.6 and 0.75. Some misleading calculations of definite analyzed ilmenite alteration spots showed that the analyzed TiO2 percentage is contained within the chemical formula of the analyzed LPSR phase. In these cases, the false Ti/(Ti+Fe) ratios attain up to 0.9, the false included total number of anions (O, OH) ranges between 7 and 8.5, and the associated molecular water ranged between half and two water molecules (0.5-2 H2O). In these cases, the structure of the remaining LPSR phase may be intergrown with a separated individual triple rutile phase, which appears to have the same X-Ray Diffraction (XRD) pattern as the single PSR phase, or intergrown with a cryptocrystalline TiO2 phase. Some molecular formulas of PSR or Hydroxylian PSR (HPSR) from previous studies were discussed and explained following the proposed approach.