Adsorption of platinum by thiosemicarbazide/quaternary ammonium lignin

Lignin and its derivatives have broad application prospects in the fields of extraction of valuable metals and removal of toxic metal ions because of the characteristics of economical, efficient and friendly. Platinum was adsorbed by thiosemicarbazide/quaternary ammonium lignin in this study. The mechanism of adsorption was revealed by FTIR and the influence factors such as initial concentration of Pt(IV), hydrochloric acid concentration, adsorption time and adsorbent dosage on adsorption were optimized. The results show that the modified lignin contains a large number of phenolic hydroxyl, amino and quaternary ammonium functional groups. PtCl₆²⁻ is reduced to PtCl₄²⁻ by phenolic hydroxyl and then reacts with amino group by coordination reaction and chloride by ion exchange reaction. Using the optimum conditions, which include hydrochloric acid of 0.5 mol·L⁻¹, Pt(IV) of 1 170 mg·L⁻¹, adsorption time of 120 min and thiosemicarbazide/quaternary ammonium lignin addition of 1 g·L⁻¹, the maximum adsorption capacity is 267.80 mg·g⁻¹. Under the same conditions besides 7 g·L⁻¹ thiosemicarbazide/quaternary ammonium lignin, the maximum adsorption ratio is 88.50%. The adsorption process can be simulated by Freundlich model and quasi-second-order kinetic model, which indicates that adsorption is chemisorptions of monolayer heterogeneous.