Desorption of La3+ and Ce3+ from Treated ‘Chert’ a Siliceous Byproduct of the Phosphate Mining Industry of Gafsa-Metlaoui Basin (Southwestern Tunisia)

Abstract

Chert, the most abundantby-product of the phosphate mining industry, collected from the Metlaoui Gafsa basin underwent purification treatments and was characterized by various analytical methods (XRD, XRF, SEM, FTIR, laser granulometry). The obtained treated chert is a siliceous phase SiO2 (~ 98%) mainly composed of opal-CT (trydimite phase and cristobalite) and traces of quartz. The chert morphology is granular. Treated chert has been successfully tested and proved to be an effective sorbent of rare earths. In this study, the desorption of La3+ and Ce3+ from ion-loaded chert was investigated and the reversibility of sorption reaction was verified. Several eluting agents at different concentrations were tested to desorb those lanthanides such as mineral acids (HCl and HNO3), chloride salt (CaCl2) and ultra pure water. Results show that, HCl and CaCl2 are efficient eluents and the adsorbed Ce3+and La3+ can be easily eluted by them. However, the highest desorption percentages were achieved using calcium chloride as eluting agent (Ce3+, 93.651%; La3+, 96.446%). Kinetics of desorption of La3+ and Ce3+ from treated chert were studied. The rate of desorption was initially fast in the first 30 min, but gradually declined with time. Among all tested kinetic models, the pseudo-second-order model fits the kinetic data best with a better correlation coefficient (R2 > 0.9) and the desorption isotherms fitted better to freundlich, which means that lanthanum and cerium release was dominated by multilayer desorption process from heterogeneous and independent surfaces.