Treatment and Recovery of Fluoride and Nitrate Industrial Wastes:Phase II.

摘要

Laboratory and pilot-scale techniques to treat selected metal-finishing solutions and rinse waters containing fluorides and nitrates were developed and successfully demonstrated. Lime-treatment parameters were optimized for various fluoride and nitrate influent levels. Ion-exchange techniques reduced the fluoride and nitrate concentrations of rinse waters to three and ten parts per million,respectively. Pilot-scale centrifugal techniques to separate precipitated calcium fluoride and metal hydroxide sludges were developed. The nitrate concentration of centrifuged effluents was reduced from 28,000to less than five parts per million by passing the effluents through a thin-film,mechanically aided evaporator. Fluoride concentration was reduced from 117,000to less than one part per million. The potential feasibility of using calcium fluoride sludge as a strength-maintaining additive for concrete was shown. Greenhouse tests indicated that concentrated calcium nitrate recovered from mechanically aided evaporation is a beneficial and practical plant fertilizer. Economic and production scale-up plans for process solution and rinse water treatment are also presented.