Finishers' Think Tank Revisited-VI

摘要

Freshly precipitated nickel hydroxide, rather than nickel carbonate, may be used to raise the pH of a nickel solution. Nickel sulfate is dissolved in water and sufficient sodium hydroxide (50 percent solution) is added to precipitate the nickel as a hydroxide. The nickel hydroxide precipitate is thoroughly washed free of sodium hydroxide by repeatedly stilling, settling, decanting and adding fresh water to the nickel hydroxide. As you may realize, using nickel carbonate is the standard means of raising pH and, all things considered, may still be the best if you do it properly. When operating a nickel solution, the nickel carbonate should be slurried and picked up in the nickel filter, where it will be neutralized slowly as nickel solution is pumped through the filter. Under no circumstances should sodium hydroxide or ammonium hydroxide be used for pH adjustment. Many bright nickel solutions have a low tolerance for sodium ion and the ammonium ion will cause brittle deposits. Normally, the pH of a nickel solution should always be increasing. If your pH is continuously decreasing, you probably have a problem with passive anodes.