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

Abstract

MgAl-LDH fixes the chrome tanning agent by adsorption. Thisdesign greatly reduces the chromium content in the waste liquid, makingthe leather tanning process cleaner and more sustainable. In this work, a highly efficient tanning agent was developedbycombining 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 & DEG;C upon tanning than a bare 2% chrome tanning agent (74.2 & DEG;C).The use of MgAl-LDH-2%Cr in the tanning process was also environmentallyfriendly, as it helped reduce the leaching amount of chromium ionsin the tanning effluent (e.g., from 99.6 to 35.0 mg L-1), accompanied by the reduction of BOD5 and COD-Cr by67% and 46%, respectively (relative to the conventional chrome tanningprocess). The improved tanning effects can possibly be accountedfor by the adsorption of a positive chromium complex onto MgAl-LDHlaminates with hydroxyl groups to obtain a better tanning effect throughthe penetration of chromium into skin collagen fibers.