LOW AND NON WASTE TECHNOLOGIES FOR METALS RECOVERY BY REACTIVE POLYMERS

Conservative technologies have been investigated in order to utilize n atural and synthetic reactive polymers for selective metal removal, re covery and reuse. Examples refer to the treatment of industrial wastes containing silver, cadmium, mercury, chromium, iron and aluminum by d ifferent innovative processes. A precipitation process is described, n amely Metals Extraction by Xanthate Insolubilization and Chemical Oxid ation (MEXICO), using agricultural raw materials to prepare starch or cellulose xanthates as precipitating agents for metals. The process re liability has been proven at pilot scale level (15 m(3)/d) by a demons trative campaign treating continuously real chlor-alkali wastewaters f or mercury removal and recovery. Results demonstrated Hg concentration s in the filtered effluent in the range of 5-20 ppb, with an average r emoval efficiency of 99.8%. The metal-xanthate sludge was then detoxif ied by treating with NaClO solution at acidic pHs. Concentrated(> 10 g /l) chlorocomplex Hg(II) solutions were obtained, to be directly recyc led to the electrolytic cell. Other applications deal with the treatme nt of segregated chromium in exhausted spent baths. The patented Ion E xchange REcovery of CHROMium (IERECHROM) process utilizes a weak catio n (carboxylic) ion exchange resin and allows for recovery and reuse of 90% of high purity (> 99%) chromium from other interfering metals suc h as Fe and Al present in the spent tanning baths. A process for the t reatment of tannery sludges has also been studied, particularly for po ssible restoration of contaminated landfilling sites. The process is b ased on the acid leaching of the sludges and on treating the leachate by a weak base anion resin, selective to ferric species, coupled with a strong cation resin (sulphonic) for the separation and recovery of c hromium and aluminum.The economical evaluation of the conservative pro cesses described is favorable, without taking into account the economi c revenues from the recycling operation of the metals recovered and fr om the minimized environmental impact related to these technologies. ( C) 1997 Elsevier Science Ltd.