Metal refining process using mixed electrolyte
View Patent ↗An electrorefining process is disclosed for producing high purity tin having reduced short-term and long-term alpha particle emissions and reduced lead levels. The process may use a mixed acidic electrolytic solution including at least a first electrolyte that provides sulfate ions in the mixed electrolytic solution, such as sulfuric acid, and a second electrolyte that provides halide ions in the mixed electrolytic solution, such as hydrochloric acid.
1. A method for electrorefining tin, the method comprising:
providing an acidic electrolytic solution comprising:
a first concentration of sulfate ions;
a second concentration of halide ions of about 100 ppm to about 1000 ppm; and
a third concentration of stannous ions, wherein the third concentration of stannous ions exceeds 50 g/L; and
electrodepositing the stannous ions from the electrolytic solution onto a substrate to produce a refined tin.
2. The method of claim 1 , wherein the third concentration of stannous ions is about 55 g/L to about 75 g/L.
3. The method of claim 2 , wherein the third concentration of stannous ions is about 60 g/L to about 70 g/L.
4. The method of claim 1 , wherein the first concentration of sulfate ions is about 54 g/L to about 72 g/L.
5. The method of claim 1 , wherein the second concentration of halide ions is about 500 ppm to about 1000 ppm.
6. The method of claim 1 , wherein the electrodepositing step is performed with a current density of about 10 A/ft 2 to about 70 A/ft 2 at the substrate.
7. The method of claim 1 , wherein the refined tin that is electrodeposited onto the substrate has a lead content of less than about 1 ppm.
8. The method of claim 1 , wherein the refined tin that is electrodeposited onto the substrate has alpha particle emissions of less than about 0.001 counts/hour/cm 2 measured at least one of 0, 30, 60, or 90 days after the electrodepositing step.
9. The method of claim 1 , wherein the first concentration of sulfate ions is at least about 50 times greater than the second concentration of halide ions.
10. The method of claim 1 , wherein the halide ions are selected from the group consisting of chloride, bromide, and iodide.