Desorption of lanthanum, europium and ytterbium from Sargassum

Abstract

The desorption of La, Eu and Yb was studied in this work. The purpose of this work was to verify the reversibility of the sorption reaction, and thus the possibility of the desorption process for simultaneous metal recovery and regeneration of the biomass. The desorption of calcium ions at different levels of pH using mineral acid was also verified and the Ca release increased with decreasing pH, achieving 2.5 mequiv. g −1 at pH 2 and 2.8 mequiv. g −1 using 0.1 mol L −1 HNO 3. Several eluting agents at different concentrations were tested to desorb the lanthanides including nitric and hydrochloric acids, calcium nitrate and chloride salts, EDTA, oxalic and diglycolic acids. 95–100% desorption for all metals was obtained with 0.3 mol L −1 HCl. La desorption with the other eluting agents was 70% with 2 mol L −1 CaCl 2, 83.7%, with 0.5 mol L −1 EDTA and 88.4% with 0.023 mol L −1 diglycolic acid. A plateau was reached when a liquid to solid ratio (L/S) of 2 L g −1 was used with 0.1 mol L −1 HNO 3. Desorption levels ranged between 85 and 95%. At the same (L/S) ratio, 0.2 mol L −1 HCl was able to elute all the metals from the individual metal loaded biomass, although it could not remove the metals completely from the mixed-metal loaded biomass. The desorption levels decreased with increasing metal sorption affinity as follows, 94.0, 86.3 and 75.2% for Yb, La and Eu, respectively when the eluting agent was 0.1N HCl. There was no difference between not washing the biomass at all and washing it either once or twice after the sorption process.