Electrochemical Concentration and Purification of Spent Sodium Bicarbonate Blasting Media

Abrasive blasting with sodium bicarbonate media is a choice replacement for degreasing with ozone-depleting 1,1,1 trichloroethane, but produces relatively large amounts of contaminated waste. The bulk of the waste consists of valuable resources, namely sodium bicarbonate with needs to be recystallized for reuse, as well as water. Removal of insoluable contaminations by flotation and settling is readily accomplished following dissolution of the spent media, but recovery of the sodium bicarbonate from dilute solution by conventional means is energy intensive. An electrochemical concentrating step is proposed which recovers the bicarbonate as a five-times more concentrated solution of sodium hydroxide and leaves behind a depleted bicarbonate effluent containing 220 ppm bicarbonate that is suitable for recycle. The sodium hydroxide may be sold as a by product, or precipitated out as sodium bicarbonate crytals by reaction with the carbon dioxide which is evolved in the electrochemical cell. Preliminary cost estimates suggest the cost of electrical energy for processing the spent media is less that $.15/lb of sodium bicarbonate. The objective of the Phase I program is to assess the potential for membrane fouling and electrode degradation, and to establish design and cost parameters for the process.