Low and non waste technologies for metals recovery by reactive polymers

Conservative technologies have been investigated in order to utilize natural and synthetic reactive polymers for selective metal removal, recovery and reuse. Examples refer to the treatment of industrial wastes containing silver, cadmium, mercury, chromium, iron and aluminum by different innovative processes. A precipitation process is described, namely Metals Extraction by Xanthate Insolubilization and Chemical Oxidation (MEXICO), using agricultural raw materials to prepare starch or cellulose xanthates as precipitating agents for metals. The process reliability has been proven at pilot scale level (15 m3/d) by a demonstrative campaign treating continuously real chlor-alkali wastewaters for mercury removal and recovery. Results demonstrated Hg concentrations in the filtered effluent in the range of 5–20ppb, with an average removal efficiency of 99.8%. The metal-xanthate sludge was then detoxified by treating with NaCIO solution at acidic pHs. Concentrated (> 10 g/l) chlorocomplex Hg(II) solutions were obtained, to be directly recycled to the electrolytic cell. Other applications deal with the treatment of segregated chromium in exhausted spent baths. The patented Ion Exchange REcovery of CHROMium (IERECHROM) process utilizes a weak cation (carboxylic) ion exchange resin and allows for recovery and reuse of 90% of high purity (> 99%) chromium from other interfering metals such as Fe and Al present in the spent tanning baths. A process for the treatment of tannery sludges has also been studied, particularly for possible restoration of contaminated landfilling sites. The process is based on the acid leaching of the sludges and on treating the leachate by a weak base anion resin, selective to ferrie species, coupled with a strong cation resin (sulphonic) for the separation and recovery of chromium and aluminum. The economical evaluation of the conservative processes described is favorable, without taking into account the economic revenues from the recycling operation of the metals recovered and from the minimized environmental impact related to these technologies.