Closed Loop for Chromium in Tannery Operations

Abstract

Even though the leather industry is environmentally important as a user of a byproduct of the meat industry, it is still perceived as a consumer of resources and a producer of pollutants. When processing one metric ton ofrawhide, 200 kg of a leather-final product is obtained, and only 20% of the raw material weight is converted to leather. The biggest problem, and one that is now under scrutiny, is the disposition of chrome-tanned solid wastes. To keep the chromium from tanned wastes within control limits we have worked out a modified enzymatic dechromation technology and developed it into an industrial scale with a daily capacity of three metric tons of chrome shavings. The chromium-containing sludge, isolated by this technology, contains 10-15% magnesium oxide, and is used (here) as a precipitator for chromium in spent tanning liquor. We treated a spent liquor containing 2294 ppm of chromium with the chromium sludge, obtained from the enzymatic reaction. After the treatment, the content of chromium decreased from the original 2294 ppm to 6 ppm, which means that practically total dechromation of the waste chrome water has occurred. This chrome removal from the spent tanning liquor, using the chrome sludge from digestion of the chrome-tanned solid wastes, effectively provides a closed loop for chromium in tanning operations.