Transposition of chrome tanning in leather making.

To avoid the release of chrome from leather into post tanning effluents and the generation of chrome shavings, an inverse chrome tanning technology based on wet white was investigated. Conventional bated pelt was firstly tanned using an amphoteric organic tanning agent (Tingjiang white tanning agent, TWT) without pickling. Then, the TWT tanned wet white was directly processed with conventional post tanning processes. Chrome tanning was transposed to the end of the post tanning. The wet white had a shrinkage temperature (Ts) around 85 o C that met the needs of shaving operation, and did not generate chrome shavings. The Ts and Cr 2 O 3 content of the leather, by using this inverse chrome tanning technology, were higher than those of the conventional chrome tanned leather. With this inverse technology, the chrome output was reduced by 48%, mainly because no chrome was released from leather in post tanning processes. Meanwhile, the volume of chromium-containing wastewater discharged from the inverse processes was barely 31% of that from the conventional processes, which makes it much easier to collect and recover chromium from the effluents. Additionally, the tensile strength, tear strength and general appearances of the leather produced by the inverse technology were comparable to those of the conventional chrome tanned leather.