Potential Applicability of Mg/Al-Layered Double Hydroxide (LDH) for Environmentally Friendly Chromium-based Leather Tanning

In this work, a highly efficient tanning agent was developed by combining magnesium–aluminum-layered double hydroxide (MgAl-LDH) with different Mg:Al molar ratios and 2% chrome (MgAl-LDH-2%Cr composite). MgAl-LDH-2% Cr (at 1 Mg:1 Al molar ratio for a 4-hour aging period) showed a much higher leather shrinkage temperature (Ts) of up to 93.8 °C upon tanning than a bare 2% chrome tanning agent (74.2 °C). The use of MgAl-LDH-2%Cr in the tanning process was also environmentally friendly, as it helped reduce the leaching amount of chromium ions in the tanning effluent (e.g., from 99.6 to 35.0 mg L–1), accompanied by the reduction of BOD5 and COD-Cr by 67% and 46%, respectively (relative to the conventional chrome tanning process). The improved tanning effects can possibly be accounted for by the adsorption of a positive chromium complex onto MgAl-LDH laminates with hydroxyl groups to obtain a better tanning effect through the penetration of chromium into skin collagen fibers.