Eco-friendly leaching of rubidium from biotite-containing minerals with oxalic acid and effective removal of Hg2+ from aqueous solution using the leaching residues

Abstract

Efficient leaching of valuable metal resources from minerals and comprehensive utilizations of the leaching residues are extremely important for the sustainable use of mineral resources and reducing the environmental pollution. In this study, rubidium was leached from biotie-containing minerals with oxalic acid and the leaching residues were used to remove Hg2+ from aqueous solution. Results showed that the leaching efficiency of rubidium was 96.54% at 90 °C when oxalic acid concentration was 3 mol/L after reaction of 120 min. More than 75% iron were reserved in the leaching residues, which was favorable for the subsequent extraction of rubidium from leachate. It was found that the leaching residues could efficiently remove Hg2+, and the Hg2+ removal efficiency reached to 97.59% at initial concentration of 100 mg/L and pH of 2. The maximal Hg2+ removal capacity of the leaching residues was identified as 357.14 mg/g, and kinetics and thermodynamics results showed that the removal of Hg2+ was mainly depended on chemi-sorption and monolayer adsorption. XRD and SEM results of these residues suggested that a large number of 10 nm FeC2O4•2H2O particles were formed on the layered silica, and mesoporous structure was observed from the BET analysis. HAADF-STEM results indicated that a new rod-like morphology was formed and most of the adsorbed mercury existed in this structure after reaction with Hg2+ solution, which was identified as HgC2O4. The Hg2+ removal involved in ion exchange, reducing-oxidation and adsorption. It was concluded that this new method can efficiently realize the comprehensive utilization of Rb-bearing minerals.