Optimization of Pt(II) and Pt(IV) Adsorption from a Water Solution on Biochar Originating from Honeycomb Biomass.

Novel CO 2 - and H 3 PO 4 -modified biochars were successfully synthesized from raw honeycomb biomass. They were characterized via several instrumental techniques. The optimal Pt(II) and Pt(IV) adsorption onto the studied biochars was reached for the initial pH of 1.5 and a contact time of 5 min (Pt(II)) and 24-48 h (Pt(IV)). The highest static adsorption capacities for Pt(II) and Pt(IV) were obtained for the H 3 PO 4 -modified biochar: 47 mg g -1 and 35 mg g -1 , respectively. The Freundlich model described the Pt(II) adsorption isotherms onto both materials and the Pt(IV) adsorption isotherm onto the CO 2 -activated material, and the Langmuir model was the best fitted to the Pt(IV) adsorption isotherm onto the H 3 PO 4 -activated biochar. The best medium for the quantitative desorption of the Pt form from the H 3 PO 4 -modified biochar was 1 mol L -1 thiourea in 1 mol L -1 HCl. The adsorption mechanism of both the studied ions onto the synthesized H 3 PO 4 -modified biochar was complex and should be further investigated. The H 3 PO 4 -modified biochar was successfully applied for the first time for Pt(IV) removal from a spent automotive catalyst leaching solution.