Recycling and reuse of waste electroplating solution

Plating platinum group metals (PGMs) onto other metal substrates to replace monolithic PGM components can significantly reduce material usage. Pt, Pd, and Rh plating are particularly common. Platinum plating was initially used in jewelry, tableware, medical devices, and scientific instruments; it is now widely used in chemical engineering, cathodic protection (platinum-titanium anodes), electronics, aerospace, and other fields. Palladium plating is mainly used for electrical contacts, jewelry, watches, and eyeglass frames. Rhodium plating is primarily used in scientific instruments, microscopes, searchlight reflectors, and electrical contact devices.

Composition and Properties of Electroplating Solutions: Preparing electroplating solutions and electroplating itself are fundamental concepts in electrochemistry and electrical engineering. This section only provides a brief overview of the chemical properties and applications of PGMs.

I. Platinum plating solutions include:

1. Chloroplatinic acid plating solution: Contains 15-25 g/L H₂PtCl₆, [HCl] > 1 mol/L;
2. Alkaline plating solution: Contains approximately 18 g/L Na₂Pt(OH)₆, approximately 30 g/L Na₂SO₄, approximately 5 g/L NaOH, and approximately 5 g/L sodium oxalate Na₂C₂O₄;

II. Palladium plating solutions include:

1. Acidic palladium plating solution: Contains approximately 50 g/L Pd(PdCl₂), approximately 50 g/L NH₄Cl, pH 0.1-0.5;
2. Weakly alkaline palladium plating solution: Contains 10-40 g/L Pd [added as Pd(NH₃)₂Cl₂ salt], approximately 10 g/L NH₄Cl, approximately 25 g/L (NH₄)₂SO₄, pH 8.5-9; III. Ruthenium electroplating solutions include:
3. Ruthenium chloride plating solution: Contains approximately 2 g/L Ru (added as ruthenium nitrosyl chloride RuNOCl3 compound) and 2 mol/L H2SO4;
4. Ammonium sulfamate plating solution: Contains approximately 10 g/L Ru [added as (NH4)3N(Ru2Cl4H2O)2 compound] and 10 g/L ammonium sulfamate, pH 1.3;

IV. Cyanide molten salt electroplating solution: Pt 3 g/L or Ir 5-6 g/L are electrolyzed in a NaCN+KCN mixture molten salt (550-600℃) under argon protection, used as an electroplating solution for platinum and iridium.