Basic Study On Desorption Of PtCl₄^2- Loaded On Quaternary Ammonium Rice Straw Lignin And Reduction Of Pt（Ⅱ）

Platinum is widely used in the fields of national economy,national defense construction,advanced technology and other fields for its excellent physical and chemical properties.The extraction and separation of platinum has attracted much attention with the expansion of the application field and the demand.As Platinum resources composition is complicated,pyrometallurgy and hydrometallurgy are of the disadvantages of long process,low recovery rate and serious pollution because raw materials need to be pretreated to make platinum enriched and then through a complex and long process to recover platinum.Ion exchange,by which ion exchange resin can directly extract platinum from its multiple metal ions solution,has the advantages of short process,high recovery rate and good selectivity.But ion exchange resin,which is extracted and synthesized from petroleum,is expensive,high-energy consuming and has pernicious products like tar and benzene when burned at the end of life cycle.The quaternary ammonium rice straw lignin adsorption metal ions method has obvious advantages in cost reduction,metal recovery and pollution abatement.But problems such as the desorption process,the morphology and distribution characteristics of the desorption products,the desorption behavior and the reduction of Pt（II）after the desorption of PtCl₄^2-loaded quaternary ammonium straw lignin have not been resolved.In this study,the adsorption capacity of 31.71 mg/g loaded PtCl₄^2-quaternary ammonium rice straw lignin was used as raw material and the mixture of hydrochloric acid and thiourea was used as the desorption agent.The desorption steps is analyzed through the desorption reaction.The morphology and distribution characteristics of the desorption products were ascertained by thermomechanical analysis.The effects of composition of desorption agent,desorption time,hydrochloric acid concentration,thiourea concentration,liquid solid ratio and desorption times on the desorption were investigated.The regeneration performance of the quaternary ammonium rice straw lignin was also explored.The feasibility of the reduction of both zinc powder and iron powder were clarified by thermodynamic analysis,and the reduction abilities were compared.Furthermore,the effect of zinc powder reduction time and dosage on reduction rate was investigated.（1）The effects of desorption agent such as EDTA,oxalic acid,sodium carbonate,sodium thiosulfate,ammonium chloride and the mixture of hydrochloric acid and thiourea were compared.The result showed that the mixture of hydrochloric acid and thiourea has the best desorption effect.（2）The desorption process is that the PtCl₄^2-loaded on the quaternary ammonium rice straw into the solution by the ion exchange reaction with Cl^-in the solution.Then it formed Platino-chloridiurea complexes with thiourea,which reduced the PtCl₄^2-concentration in the solution and motivated the ion exchange reaction with Cl^-.The desorption rate of PtCl₄^2-is improved.（3）The thermodynamic analysis of the desorption process showed that the primary desorption product is[PtCl₃SC（NH₂）₂]^-,and its mole percentage increase with the concentration of hydrochloric acid and thiourea.（4）The experiment result conducted with the hydrochloric acid and thiourea solution showed that the desorption equilibrium time is 60 min and the maximum desorption rate is 60.72%on condition that hydrochloric acid and thiourea concentration is 1.0 mol/L and liguid-solid ratio is 3:1,respectively.The total desorption rate of loaded PtCl₄^2-quaternary ammonium rice straw is 98.78%after two desorption processes.The FTIR analysis showed that the quaternary ammonium rice straw lignin is reproducible.（5）The potential-pH diagram of Zn/Fe-[PtCl₃SC（NH₂）₂]^--HCl-H₂O system showed that both iron powder and zinc powder have a reduction ability of[PtCl₃SC（NH₂）₂]^-in solution after adsorbed,and the reduction ability of zinc powder is stronger.The ammonium hydrogen carbonate is used to reduce the amount of zinc powder before reduction.Under the condition of 25℃,20.75mg/L Platinum concentration,ten times the amount of theory and 300 rpm oscillation speed,the reduction equilibrium time of zinc powder is 60 min and the reduction rate of Platinum（II）is 98.91%.The reduction process follows the diffusion mass transfer equation,and the reduction reaction is controlled by the diffusion mass transfer process.