Phase Transformation of Minerals in Bauxite

Bauxite comprises five major elements viz. Al2O3, SiO2, Fe2O2, TiO2 and LOI. Major aluminium bearing mineral phase present in the bauxite are gibbsite, boehmite and diaspore however however Iron minerals are mainly in the form of alumo-goethite, hematite and some accessory minerals like magnetite, Illmenite etc. The alumo goethite and hematite are structurally and characteristically different from each other. In general, Indian bauxite contains alumo-goethite is a dominant mineral as compared to hematite. In the beneficiation of bauxite process, an iron mineral plays an important role in magnetic separation study. Hema-tite being a paramagnetic mineral gets easily separated via magnetic separation process while alumo-goethite is feebly magnetic in nature and requires high intensity

Thin layer chromatographic study of Indian bauxites

65-73Thin layer chromatography (TLC) has been used for the detection and separation of Al³⁺, Fe²⁺, Si⁴⁺ and Ti⁴⁺ in bauxite. Thirty bauxite samples of different geological origin have been studied to identify the optimized chromatographic systems capable of selective separations of the constituents. Binary and ternary separations of Al³⁺, Fe²⁺, Ti⁴⁺ and Si⁴⁺ in bauxite were realized with chromatographic systems comprising various combinations of silica gel G, silica gel H and microcrystalline cellulose coated plates and aqueous mobile phases consisting alkali salt solutions, formic acid and hydrochloric acid etc. The chromatographic system consisting of silica gel H and mixture of 10% aqueous solutions of sodium chloride and formic acid in 8:2 (v/v) ratio was found to be the ideal combination for the analogous separation of Al³⁺, Fe²⁺ and Ti⁴⁺ in bauxites. The efficacy of optimized chromatographic system has been investigated by monitoring reproducibility of RF values and spot compactness with respect to change in bauxite geology, sample concentration and change of mobile phase composition. Chromatograms of the cations were quantitatively evaluated by scanning densitometry in comparison with wet analysis method

<span style="font-size:11.0pt;font-family: "Times New Roman";mso-fareast-font-family:"Times New Roman";mso-bidi-font-family: Mangal;mso-ansi-language:EN-GB;mso-fareast-language:EN-US;mso-bidi-language: HI" lang="EN-GB">Quantitative thin layer chromatographic study of Al³⁺ in geological samples</span>

146-154A facile and sensitive quantitative visual analytical method has been developed for the determination of Al3+ in geological samples. The alumina (Al2O3) content in gibbsitic bauxite and related samples of geological origin is extracted in triple acidic medium. The sample solutions are purified and then subjected to quantitative thin layer chromatography (TLC) analysis. Combination of plain silica gel H and dilute aqueous solution of aluminon (0.005-0.50%) has been identified as the best chromatographic systems for the selective detection of Al3+. The important chromatographic parameters such as sample composition, pH effect, nature of adsorbent and mobile phase composition as well as detection limit are optimized in terms of spot size, colour stability and resolution of Al3+. The TLC chromatograms of Al3+ are quantitatively assessed by scanning densitometry and digital image analysis. Analytical potential of the optical quantitative methods have been verified for the quantitative TLC assessment of Al3+ in bauxite, soil, rock and aluminium spent potlining (SPL) samples with respect to the analogous wet analysis. Repeatability and reproducibility of the method are also evaluated under the optimized experimental conditions such as sample concentration, components and pH, slurry volume and layer thickness