Applicability of new sustainable and efficient alginate-based composites for critical raw materials recovery: General composites fabrication optimization and adsorption performance evaluation

Based on the 2020 list of raw materials for the EU, there are 30 critical minerals on the critical raw materials list, among which the rare earth elements group is placed. This study demonstrates a viable approach to the increasing possibility of the critical materials recovery through biosorption. The environmentally friendly biosorbents were prepared modifying calcium alginate with biochar and clinoptilolite. Firstly, the optimization procedure was applied for obtaining new biocomposites. After that the adsorption studies of La(III), Ce(III), Pr(III), and Nd(III) ions as a function of solution pH, biosorbent mass, interaction time, initial metal concentration, temperature, and competing ions presence were carried out using the batch mode. The kinetic studies were analyzed using the pseudo-first order, pseudo-second order, Weber and Morris intraparticle diffusion, Boyd as well as Dumwald-Wagner kinetic models. The experimental equilibrium data were fitted using the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models. The thermodynamic functions, i.e. ΔG°, ΔH°, and ΔS° were also determined. Importantly, the biocomposite beads were readily regenerated using diluted mineral acids (exemplary 0.1 mol/dm3 HNO3) and moreover, the adsorption effectiveness was very satisfactory even after six adsorption–desorption cycles (97%). New biocomposites as potential sorbents were characterized with ATR/FT-IR and XPS spectroscopy, SEM, EDX, OM and AFM microscopy, nitrogen adsorption, TG/DTG, CHNS, XRD as well as the sieve analysis and pHpzc measurements. After the interactions of the alginate composites with La(III) ions, a possible sorption mechanism was analyzed by ATR/FT-IR, XPS, and EDX spectroscopy.