ION-EXCHANGE PROCESS FOR CHROMIUM REMOVAL AND RECOVERY FROM TANNERY WASTES

A new process, namely, IERECHROM (Ion Exchange REcovery of CHROMmium), has been developed for removal of Cr(III) ionic complex from segregat ed wastewaters (10% of the overall wastewaters discharged from tanning operations). The process is based on a macroporous carboxylic resin ( i.e., Purolite C106) retaining the metal of reference, together with o ther trace metals, including aluminum and iron. In a first regeneratio n step, alkaline hydrogen peroxide (pH 12) is used. The anionic specie s formed (chromate and aluminate) are quantitatively eluted from the c ation resin and separated. In a second polishing step of the resin, fe rric species are eluted with 1 M sulfuric acid. The resulting ferric a nd aluminum sulfate solutions are recycled as flocculating agents. The residual chromate solution is directly reused in the plating industry or, after reduction to Cr(III), in the same tannery. Before the new e xhaustion cycle, the resin is reactivated by elution of 1 M NaOH follo wed by hydrolysis with softened water. A 10 m(3)/day fully automated p ilot plant was assembled, and process reliability and cost benefits we re demonstrated.