Since Ni is a valuable resources and its plating solution is costly, improvements in recycling technique from waste solution and slurry in the Ni plating process have been an necessity. In this paper, the retrieval of Ni from the electroless plating waste waters, especially worn-out ones with high concentration of Ni is considered. The compound precipitation method which retrieves Ni from waste waters as carbonate form or oxalate form is examined.
The results show that higher solution temperature is preferable, and that Fe can be removed by neutralization precipitation. Among carbonate, Na
2CO
3 turns out to be the more effective precipitator than NaHCO
3. When the double dose or more of the theoretical equivalent of Na
2CO
3 were added, and the initial pH was larger than 2, precipitation took the form of weak crystalline whose composition was Ni(CO)
3(OH)
4 · 4H
2O. When NaHCO
3 was used as precipitator, together with CO
2 bubbling, globular particles precipitated.
For oxalate, crystalline particles of NiC
2O
4 · 2H
2O precipitated. The method was tested for waste water from an actual plant and followings were suggested: Ni-B solution should be precipitated with carbonate, while Ni-P solution with oxalates.
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