QUALITY IMPROVEMENT OF RECYCLED CHROMIUM IN THE TANNING OPERATION BY MEMBRANE PROCESSES

Use of pressure-driven membrane processes integrated with conventional precipitation/dissolution operations is described in order to reduce chromium content in waste water from the tanning process and simultane ously improve the quality of the recycled chromium by means of elimina tion/reduction of organic lipolytic components, metals and other impur ities that accompany the chromium recovered by traditional processes. The results obtained in the identification of types of membranes and m odules, chemical-physical parameters, pre treatment of fluids, cleanin g procedures and fluid dynamic conditions are reported and discussed. According to the obtained results, it is possible to suggest a process scheme that, starting from the exhausted chromium solution, through a nanofiltration membrane purification/concentration permits to obtain solutions that can be reused in tanning and/or retanning operations. T he concentrate solution seems to guarantee improved characteristics of tanned and retanned skins with respect the skins treated with the tra ditional techniques as showed by chemical and physical essays on leath er samples. The process permits also the reuse of the permeate from th e nanofiltration in the pickling phase, considering the high content o f chlorides in the solution.