Acid-assisted leaching of iron and manganese from Sri Lankan laterite: a potential source of alumina production

Laterites are of great interest for industrial applications. This study is focussed on determining optimum conditions (i.e. pH, temperature, and sonication time) for leaching Fe and Mn from Sri Lankan laterite. Physicochemical parameters, atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectroscopic analyses were performed. Different solutions were prepared for a pH range from 1 to 10, temperature from 40 ºC to 100 ºC, and sonication time from 10 min to 60 min. Elemental concentrations of the filtrates were used to determine the optimum conditions. Fe and Mn leaching efficiencies decreased with increasing pH from 1 to 5. The solution of pH 1 indicated the maximum leaching capacities of Fe (17.69 ppm) and Mn (2.05 ppm). Fe and Mn leaching efficiencies almost exhibited a positive correlation with temperature. The maximum leaching concentrations were observed after 15 min of sonication. Therefore, the optimum conditions for leaching both Fe and Mn were determined as pH 1 at 60 ºC temperature after 15 minutes of sonication. Precipitates of treated samples were characterised using XRD and FTIR to determine changes compared to the raw sample. XRD results identified the crystalline phases, and thereby chemical composition of raw laterite can be discovered by the software as goethite and hematite as main Fe-rich minerals. The raw laterite was also associated with gibbsite, kaolinite, and quartz. However, weak reflections of hematite were observed in the XRD spectra of treated samples. FTIR observations suggested alteration of functional groups (e.g. the disappearance of Fe―O bond) in acid leached and sonicated samples. Consequently, FTIR and XRD results also confirmed the acid-leaching capacity of Sri Lankan laterite.