Treatment of Spent Bath

Hydroxide precipitation with sodium or calcium hydroxide is the standard method used for treating heavy metal wastes. Sodium hydroxide was used in this study because it forms an insoluble oxide, mercuric oxide, when added to the spent plating bath. The pH should be increased to between 10 and 12. The filtrate still contained a high level of mercuric chloride in solution and had to be treated before disposal. 

The cost of the Duolite GT-73 is much higher than the other resins selected in the Navy study. The volume of waste generated at our facility is a thousand times less than the volume generated in the Navy study and the local discharge limit is not as low. Therefore one of the other three resins may be more cost-effective. 

Alternative hazardous waste management practices for the treatment of heavy metal wastes are necessary in order to comply with the current landfill ban requirements. In Washington State the priorities for managing hazardous waste are 1) reducing the volume or toxicity at the generation source 2) recycling recovery and reuse practices 3) treatment alternatives and 4) landfill. 

The electrolysis of the mercuric chloride waste solution in this study resulted in the recovery of significant amounts of mercury metal. The recovery was sufficient to reduce the average volume of mercuric chloride waste disposed of off-site 8 fold. The estimated reduction in annual disposal costs is 1500. Furthermore, no liability costs for the transportation and disposal of the recovered mercury are 

The methods and apparatus used in this investigation must be improved in order to increase the recovery efficiency and to automate the process. Design modification of the cathode and anodes is one obvious approach to enhancing the recovery capability of the process. 

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