In the production of platinum-based anticancer drugs (cisplatin and carboplatin), silver iodide residue containing 5-8% Pt is generated, with Pt dispersed in the silver iodide as fine particles. The nitric acid dissolution method was previously used to separate and recover platinum and palladium. However, this method leads to platinum dispersion; specifically, during nitric acid dissolution, 20% of Pt co-dissolves with Ag. When AgCl is precipitated from the nitric acid solution with HCl or NaCl, some Pt co-precipitates with AgCl in the Ag₂PtCl₆ state. The process of dispersing Pt and repeatedly separating Ag and Pt is lengthy, resulting in low Pt yield.
Hydrazine hydrate reduction is carried out at 90℃ with stirring to convert the Pt-Ag complex into a metallic state. The reactions are:
2Pt(NH3)I2 + N2H4·H2O + 4NaOH = 2Pt + 4NaI + N2 + 5H2O + 2NH3
4AgI + N2H4·H2O + 4NaOH = 4Ag + 4NaI + N2 + 5H2O
After washing and drying, a powdered metal mixture is obtained, containing 8.16% Pt, 83.1% Ag, and the remainder Ag. Experiments show that the Ag-Pt mixed powder is not easily dissolved by concentrated sulfuric acid.
If the mixed powder is smelted at 1300℃ with a small amount of soda ash and borax to form an Ag-Pt alloy (containing 9.14% Pt and 90.64% Ag), and the sheet alloy is directly dissolved in concentrated sulfuric acid at 150℃ for 3 hours, the Ag dissolution rate reaches 99.51%. The Ag-containing solution is precipitated with NaCl to form AgCl, and then reduced to silver powder in suspension with formaldehyde. Because the formaldehyde reduction process is highly exothermic and can cause explosive spraying, special attention must be paid to controlling the reduction rate. Ag recovery rate >99%. The insoluble residue contains 93.88% Pt and 4.57% Ag. After dissolving in aqua regia, it is refined to pure platinum product through denitrification. Pt recovery rate reaches 99.5%. This process can be applied to the treatment of other silver and platinum waste.
