Ⅰ. Background Technology
During PCB production, outer panel need about 5-8μm tin on the surface before micro-etching. Until now, nitric acid type tin stripping agent is one kind of main agents in PCB production, containing nitric acid, nitric acid stabilizer, nitrogen oxides inhibitor, sulfonate, ferric nitrate and so on， which function is selectively dissolving surface tin and avoiding erode copper layer. During tin stripping process, when the tin content reach to above 100g/L, the ability of tin stripping will decrease. So it is very imperative to recovery the tin from tin stripping waste.
But tin stripping waste contain high content of acid as well as large content of tin, copper, iron and stabilizer. Usually in tin waste, there are 20-30g/L tin, 1-3mol/L acid, 20-30g/L copper ion. So recovering tin need to adjust PH level and neutralize precipitation to get deposit.
Ⅱ. Recovery Methods
1. Precipitation Method
By precipitation method, add chemicals to precipitating tin deposit. Get tin panel after press and filtration.There is no pollution and air during reaction. The waste after processing could be discharged to sewage station.
2. Electrolysis Method
We also could use electrolysis method to recovery the new type tin liquid. And tin recovery rate could reach to 98% and purity of tin is about 98%. This method has many great characteristics, like no nitric acid inside, low cost, auto-operation, high economic value and recycle of tin liquid.