Effect of Leather Chemicals on Cr(III) Removal from Post Tanning Wastewater

Abstract

The effect of typical leather chemicals on removal of Cr(III)
from tannery post tanning wastewater by PAC coagulation was
investigated. It was found that all the leather chemicals
investigated could form complexes with Cr(III) through their
anionic hydrophilic groups. The determinations of fluorescence
quenching titration indicated that the Cr(III)-complexing ability
of these anionic hydrophilic groups was in the sequence of
phenolic hydroxyl of vegetable tannins and syntans > carboxyl of
acrylic resins > sulfonic acid group of fatliquors and dyes. The
complexes formed had higher hydrophobicity because a part of
anionic hydrophilic groups of leather chemicals were blocked.
The Cr(III) complexes with vegetable tannins, syntans and dyes
were in the form of hydrophobic colloid or particle due to both
the blocking effect of hydrophilic groups and the strong
hydrophobicity of benzene ring, which favored the removal of
Cr(III) from post tanning wastewater by coagulation (removal
extent 82%-99%). But the Cr(III) complexes with acrylic resins
existed as water-soluble pieces, probably because a part of free
carboxyl group still kept on the polymer chain at reaction
equilibrium, and acrylic resins had no structure/group with
hydrophobicity as strong as benzene ring. As a result, Cr(III) was
difficult to be removed from wastewater when acrylic resins
existed (removal extent <60%). That is, the formation of Cr(III)-
acrylic resin complexes is the major obstacle in removing Cr(III)
effectively from post tanning wastewater.