Rare-earth metals adsorption on a novel bisphosphonate separation material

摘要

Rare earth metals are irreplaceable in many technological applications. In Europe, rare earths can be found in waste materials. Methods developed for rare earth metal separation and pre-concentration are not cost-effective. Adsorption is considered a simple and eco-nomical method for rare earth metals recovery. In this work, a novel bisphosponate-based adsorbent N10O was tested. The research objectives were to investigate performance of the adsorbent and to establish optimal conditions for recovery of Nd(III), Eu(III), Tb(III) from aqueous solutions.Theoretical part of the work includes information on rare earth metals supply, demand and separation methods, as well as on properties of bisphosphonates and their use in metal che-lation. In experimental part, batch adsorption in test-tube scale was used. The influence of pH, temperature, ionic strength, initial metal concentration and contact time on adsorption process were investigated from HCl, HNO3 and H2SO4 media. Metal concentrations were subsequently analyzed by ICP-MS.The experiments revealed that adsorption process was highly pH dependent. Optimal metal uptake in all three media was achieved after pH 2. The results also showed that the capaci-ty of N10O was comparable to that of common ion exchange resins (>200 mg/g). Temper-ature proved to enhance the adsorption process. Selectivity coefficients for pairs of Nd, Eu and Tb turned out to be 1.2-2. Adsorption models were fitted to experimental data points. Langmuir-Freundlich isotherm shows the best fit. Empiric kinetic models suggest that ad-sorption process is controlled by film and intra-particle diffusion.On the basis of the results of this research, it can be concluded that the adsorbent N10O is applicable for selective recovery of rare earth metals. Metal uptake is high in wide pH range and the capacity is similar to existing low-cost materials, or even higher. More experimental work is to be done for investigating kinetics and solubility of the adsorbent. For pilot-scale application, it would be beneficial to impregnate the N10O into carrier material.