Treatment of industrial acid wastewaters containing metals, especially from pickling and electroplating, concentrates fluid to remove at least some components in solid form

摘要

The waste water is concentrated. At least some of the components in the concentrate, are recovered in solid form. Freeze-crystallization is employed for recovery, with at least partial separation of the solvent (especially water). Single- or multiple-effect crystallization is employed. One or more of the following processes may be used: crystallization with direct cooling, cyclone-crystallization, vacuum cooling crystallization, freeze-crystallization, spray-drying or pyrohydrolysis. Freeze crystallization is carried out at -150[deg]C to 0[deg]C. The pressure ratio lies between 0 and 300 bar. Solvent recovered by concentration is used to cool the feed solution supplied to the concentration stage and/or conversely, the feed solution supplied to the concentration stage is used to heat the recovered solvent. Recovered solvent is returned as wash water and/or fluid withdrawn from the second crystallization process is returned to the pickling- or plating process. Feed solution to the concentration stage may also be supplied to a following concentrations stage. During recovery, solvent from several concentration stages is combined. An independent claim is included for the corresponding plant system.