Comparison of extraction abilities of deep eutectic solvents and aqueous acid solutions for extraction of rare earths and transition metals

Abstract

In recent years, deep eutectic solvents have attracted increasing interest as effective extractants for the separation of both organic substances and metals from various objects. Acid-based deep eutectic solvents are most often used as extractants for the extraction of metals. In this work, for the first time, the extraction efficiency of transition metals and rare earth elements (Y, Zr, Nb, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf and Ta) from mining tailings and Na, K, Ca, Mg, Cu, Fe, Mn, Pb, Ba, Ni and Sr from biodiesel samples using acidic deep eutectic solvents and saturated aqueous solutions of the same acids (malonic, malic, tartaric and citric) is compared. For this, deep eutectic solvents based on acids and their aqueous saturated solutions were prepared and studied. The prepared mixtures were analyzed by IR spectroscopy to confirm the formation of eutectic solvents. Properties such as the density and viscosity of the resulting mixtures were also investigated, as this can be of key importance for the efficiency of metal extraction. The extraction of rare earth metals from mining tailings took a long time (up to several days), while the extraction of metals from fuel took no more than 30 min. Atomic emission spectral methods were used as an analysis method. It is shown that the extraction efficiency with aqueous solutions is better than that with eutectic solvents, which casts doubt on the need for deep eutectic solvents use in this area.