Recovery of rare earth elements from aqueous solution obtained from Vietnamese clay minerals using dried and carbonized parachlorella

• Dried and carbonized parachlorella are used for biosorption–desorption of rare earth elements.
• Rapid adsorption within the first 5 min characterized the sorption process.
• Combination of four kinds of reactions explained the biosorption mechanism.
• The reversible process is less temperature and pH dependent, high recovery rate.
• Parachlorella is a good and low-cost adsorbent to recover rare earth from solution.

The ongoing development of new advanced technologies, created increasing demands for rare earth elements (REEs) in the international market. The available conventional technologies for concentration and recovery of REEs are expensive making biosorption an efficient and low-cost technology for the recovery of REEs from aqueous solution. Thus, the biosorption and desorption of multi-component solution containing Y(III), La(III), Sm(III), Dy(III), Pr(III), Nd(III), Gd(III) were investigated using dried or 250 °C and 350 °C carbonized parachlorella. Evaluating the effect of pH with respect to contact time indicated a dependency of the system with those parameters. The optimum pH for dried and 250 °C carbonized parachlorella was 7 whereas 350 °C reaches it maximum uptake at pH 4. Rapid adsorption within the first 5 min of contact followed by a slight variation in the following 20 min characterized the sorption processes onto parachlorella by-products. The mechanism of the biosorption is explained by a combination of complex reactions occurring simultaneously in the biosorption process.In addition, desorption process has been investigated using various concentrations of HCl, HNO3, and H2SO4 at different temperatures. It was found that the reversible process is rapid, less temperature and pH dependent with high desorption percentage. Moreover, only light REEs were desorbed regardless of the kind of acid and the solution temperature. Parachlorella is found to be good and low-cost biosorbent for the recovery of above REEs from aqueous solutions.