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

Novel CO₂- and H₃PO₄-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 H₃PO₄-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 CO₂-activated material, and the Langmuir model was the best fitted to the Pt(IV) adsorption isotherm onto the H₃PO₄-activated biochar. The best medium for the quantitative desorption of the Pt form from the H₃PO₄-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 H₃PO₄-modified biochar was complex and should be further investigated. The H₃PO₄-modified biochar was successfully applied for the first time for Pt(IV) removal from a spent automotive catalyst leaching solution.