Obtaining sodium chromate from ash produced by thermal treatment of leather wastes

Currently, 80–90% of leather production uses chromium tanning; thus, the trimmings and shavings resulting from the manufacturing of leather goods create a waste with a high pollution potential. One alternative for handling this scrap-leather waste is thermal treatment (gasification and combustion). The ashes generated during this process are rich in chromium, containing between 50% and 60% chromium oxide (Cr2O3) by mass, and the ashes can thus potentially be utilized as a source of chromium for the synthesis of sodium chromate (Na2CrO4). With the aim of improving on the results of previous attempts made to recover chromium from these ashes, in this work, the use of sodium nitrate to oxidize the trivalent chromium to the hexavalent form was studied. The resulting conversion of chromium (III) to chromium (VI) achieved was over 94%, and the sodium chromate obtained from the ashes showed physical properties similar to the commercial product.