Submitted to: Journal of American Leather Chemists Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2002
Publication Date: 12/1/2003
Citation: KOLOMAZNIK, K., SHELLY, D., TAYLOR, M.M., MLADEK, M., LANGMAIER, F. CLOSED LOOP FOR CHROMIUM IN TANNERY OPERATION. JOURNAL OF AMERICAN LEATHER CHEMISTS ASSOCIATION. 2003. V. 98(12). P. 487-490. Interpretive Summary: The leather industry is environmentally important as the major consumer of hides and skins, a byproduct of the meat industry. However, when processing rawhide only 20% of the raw material weight is converted to leather, while the remainder could be classified as waste. The annual cost of treating this tannery waste in Europe is approximately 700 million Euros. The disposition of chromium-containing solid wastes that result from the tanning process has been one of the biggest concerns. Historically, these chrome-tanned solid wastes had been disposed of in landfills. With the development of new environmentally safe treatment processes, it is now possible to keep the chromium from solid tanned wastes under control. A modified enzymatic treatment process was developed and applied on an industrial scale with a daily capacity of three metric tons of chrome shavings. The chromium sludge isolated by this technology contains an alkali; we found that this alkali-containing sludge could be used to remove residual chromium from spent tanning liquor. As a result of these treatments, both the solid and liquid chromium-containing waste could be treated and ultimately recycled. Thus, no chromium would have to be disposed of in the environment.
Technical 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 of rawhide, 200 kg of a leather-final product is obtained, along with 250 kg of non-tanned waste, 200 kg of tanned waste (3 kg chromium) and 50,000 kg of waste-water (5 kg chromium). Thus, only 20% of the raw material weight is converted to leather. It is estimated that within Europe the annual cost of treating tannery waste is around 5% of the turnover, which equates to nearly 700 million Euros. The biggest problem and one that is now under potential control is the disposition of chrome-tanned solid wastes. The simplest solution for chrome-tanned solid waste has been disposal in landfills, but such a solution is environmentally suspect due to fear of conversion of Cr III into toxic Cr VI. To keep the chromium from tanned wastes under control we have worked out a modified enzymatic dechromation technology and developed it into industrial scale with a daily capacity of three metric tons of chrome shavings. The chromium sludge isolated by this technology contains 10-20% magnesium oxide, and could be used as a precipitator for chromium in spent 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.