A study on nickel hydroxide crystallization characteristics

The precipitation characteristics of nickel hydroxide as well as carbonate and sulfide were studied to determine the proper treatment condition of the wastewater induced from nickel-plating industry. When the pH value was maintained higher than 10, the nickel concentrations in the effluent could be kept lower than 5 mg/l. The precipitation of nickel salts in the model wastewater was conducted by alkaline addition, such as the uses of sodium hydroxide, sodium carbonate, sodium bicarbonate and sodium sulfide. In case of sulfide treatment, the nickel concentration of treated wastewater showed the lowest value after the removal of precipitates. The change of particle size of the crystal precipitates by the precipitation conditions and precipitants was also investigated. In spite of the various precipitation conditions that were adopted, the change of particle size of the crystal precipitates showed no great differences. The settling rates of the precipitated particles were observed and the free settling period was terminated within 20 minutes. Although the hindered settling as well as bed compaction progressed subsequently, the bed heights were maintained almost the same level after few hours later