Purification of saturated LiNO3 solution using titanium phosphate ion-exchanger: Equilibrium study
(Tananaev Institute of Chemistry and Technology of Federal Research Centre, Kola Science Centre of the Russian Academy of Sciences, Apatity, Russia)
Abstract: Sorption properties of titanium phosphate ion-exchanger (Li-TiOP) towards Cu2+, Co2+, Mn2+, Ni2+ and Cr3+ ions in saturated LiNO3 solution were investigated. Solid samples were characterized by XRD, SEM, TG, DSC, NGSP and elemental analysis. Concentrations of elements in the solutions were determined by AAS and ICP MS methods. The adsorption isotherms for studied metal ions were calculated using the Langmuir, Freundlich, Temkin and Nikolsky models. Necessity for allowing for the solvated state of the sorbate is shown in studying the sorption of metal ions. Selectivity of Li-TiOP towards studied ions is found to be described in the following order of Cr3+ > Cu2+ > Mn2+ > Co2+ > Ni2+ for all models. The change in the thermodynamic parameters of the sorption process is associated with that in the ionic potential of the sorbent. Titanium phosphate effectively removes trace concentrations of metal ions from multi-component solutions, resulting in achievement of LiNO3 purity level of >99.999 wt.%.
Key words: lithium nitrate; titanium phosphate; purification; transition metal elements; sorption; adsorption isotherm; thermodynamics