Mechanism and kinetics of iron extraction from high silica boehmite-kaolinite bauxite by hydrochloric acid leaching

The chemical and mineral compositions of bauxite recovered from the Severoonezhsk Bauxite Mine (Arkhangelsk region, Russia) were studied by XRD, ICP-OES, TG/DSC, SEM, TEM, and Mossbauer spectroscopy. The iron-containing minerals of the bauxites were found to comprise alumogoethite (alpha-Fe1-xAlxOOH), alumohematite (alpha-(Fe1-xAlx)(2)O-3), alumoakaganeite (beta-Fe1-xAlxO(OH,Cl)), and chromite (FeCr2O4). The efficiency of Fe extraction from the bauxite by HCl leaching was 82.5% at 100 degrees C, HCl concentration of 10%, solid/liquid ratio of 1:10, and the process duration of 60 min, with aluminum loss from the bauxites below 4.5% of the total Al contents in the bauxite. Analysis of the kinetics of the iron leaching process proved diffusion to be the limiting stage of the process at 90-100 degrees C. Bauxite residue after leaching presented traces of alpha-Fe1-xAlxOOH and beta-Fe1-xAlxO(OH,Cl), and most of the iron content was in the FeCr2O4. In bauxite residue after HCl leaching, in addition to iron oxide, the contents of chromium and calcium oxides significantly decreased. The iron chloride liquor after leaching contained the rare earth elements (REE) of 6.8 mg/L Sc, 4.1 mg/L Ce and 2.3 mg/L Ga.