The enrichment and separation of lanthanides ions from wastewater using solvent sublation coupled with high speed countercurrent chromatography

Rare earth elements are non-renewable resources. During their processing, a lot of wastewater are produced, which poses a danger to human beings and the environment. Herein, the enrichment method of solvent sublation for La (III), Ce (III), Gd (III) and Er (III) was designed and established. Enrichment parameters pH, flotation time, extractant concentration and air flow rate were optimized. The result showed that the highest recovery of La (III) reached up to 92.33 % under the optimized conditions of pH 8, 10 min of flotation time, 0.15 mol L^-1 of the extractant 2-ethylhexyl phosphate acid-2-ethylhexyl ester and 30 mL min⁻¹ of air flow rate. The light rare earth element Ce (III) and heavy rare earth elements Gd (III) and Er (III) were also examined and obtained with maximum recovery. The stability of the extractant complexation with rare earth ions and the mechanism of competitive extraction were studied by density functional theory calculations. The extraction ability was following sequence of La (III) < Ce (III) < Gd (III) < Er (III). The enrichment of rare earth elements from real water samples was investigated and obtained result was consistent with the experiment result of synthetic solutions. The established high speed countercurrent chromatography method was used to successfully separate La (III), Ce (III), Gd (III) and Er (III) from the solution of rare earth ions enriched by solvent sublation.