Dechroming spent tanning liquor using filtration cake from enzymatic hydrolysis of chromium shavings

Abstract

The work presented deals with the treatment of spent tanning liquor using the chromium cake from alkali enzymatic hydrolysis of leather shavings, the scheme is seen as a part of complete recycling of chromium in the leather industry. There is a long-term worldwide effort to keep all chromium under control, ideally in a closed loop, since chromium, especially in its hexavalent form, has a negative impact on the environment and human health. The filtration cake obtained by hydrolysis contains a significant amount of chromium and, due to its alkaline character it could be used for the treatment of spent tanning liquor. The work demonstrates that total dechroming of spent tanning liquor is possible. The efficiency of the process depends on the weight ratio between chromium cake and spent tanning liquor and on the retention time. Using a ratio of 0.3 and a retention time of 1 hour, the dechroming level achieved was 81.6%; for a ratio of 1, the dechroming reached up to 98.3%. Using the former ratio, the dechroming level increased to 94.1% after 6 hours. The treatment process has some limitations - the feed composition plays an important role in the process setup to achieve the high dechroming level.