Cleaner Chrome Tanning - Technology of Chrome-reduced Tanning Without Salt, Pickling and Short Procedure

摘要

Tannery effluents with high salinity and containing chromium have a serious environmental impact. The traditional chrome tannage that involved the use of sodium chloride, acid and chromium is one of the main origins of salt and chromium pollution. In this study, a non-pickle, chrome-reduced tanning technology was developed. The novel chrome-free agent SL can be directly employed to tan bated bovine hide producing wet-white. The shaved wet-white was pre-treated by a poly-carboxylate auxiliary agent PAA and tanned by chrome powder. It was found that the shrinkage temperature of the wet-white tanned by SL reached over 80 degrees C, the optimal consumption of poly-carboxylate auxiliary agent was 1.5-2wt% based on the weight of the shaved wet-white, the better chrome-reduced tanning conditions were that the wet-white was tanned with 3-4wt% chromium powder for 150-180 minutes at room temperature when the initial pH value was 3.0-3.5. The next processes were same as those of a traditional chrome tannage. Meanwhile, the shrinkage temperature of the leather tanned by the chrome-reduced tannage reached more than 95 degrees C, the absorption of chromium was 96%, the content of Cr2O3 in the effluent was under 200mg/L. For the chrome-reduced tanned leather,the absorption of dyestuff and fat-liquor reached 99.5% and 82.5% respectively. Compared with the traditional chrome tanning process, not only was the conventional pickling process eliminated, the process was shortened and reduced the pollution of sodium chloride. The process can reduce by 50% the consumption of chrome powder, improve the absorption of chromium and reduce the content of Cr2O3 in effluent.