Mineral Tanning: Chromium(III)

Abstract

In the international leather industry, the most prevalent tanning process, in perhaps 90% of all leather manufacture, uses basic chromium(III) salts. The reaction is deceptively simple, hence it can be used by tanneries with little technical knowledge or support. That serves to indicate the degree of ignorance that is common in the sector concerning the science that underpins the reaction. Even an explanation of the apparent anomalously high thermal stability conferred by the process was not available a quarter of a century ago. There have been many myths and much incorrect received wisdom associated with chrome tanning, such as the alleged role of crosslinking, the function of the counterion, the purpose and consequences of masking (reactivity modification by complexation) and the mechanism of the heterogeneous fixation. Today, we have a much clearer understanding of the science of the familiar technology, which allows more targeted changes to the parameters of tanning, to make the reaction more efficient and effective, while improving the environmental impact.