Tanning using trivalent chromium salts underwent an evolution marked by
the need to obtain technical performances for the leathers at first and then to limit the
penetration of chromium in the environment by means of wastewater or solid waste.
The evolution of methods to reduce environmental pollution with trivalent chromium
salts included general environmental principles on advanced absorption of chromium,
partial replacement of chromium, recycling, recovery and total replacement of
chromium. Advanced technologies for exhaustion of chromium from effluents are based
on the development of technological conditions favorable to absorption of chromium
above the accepted level of concentrations by osmotic balance between the two
environments, hide and tanning bath. Partial chromium replacement technologies are
probably the most studied methods of reducing the use of chromium as tanning metal.
The great diversity of variants proves that there is no imposed variant as of yet in the
industry. Recycling and reuse of chromium are methods that require additional
investment in facilities for recycling used tanning solutions or for precipitation and
dissolution of chromium salts. The advantages consist in reducing environmental
pollution and chromium consumption, while disadvantages are related to laborious
analytical control and quality of leathers obtained, which is not at the same level as that
obtained by using basic salts with a consistent quality. The newest way to reduce
environmental pollution by chromium salts is wet-white tanning, which implies a pretanning
with chromium-free materials, mechanical processing by splitting and shaving
followed by tanning and retanning with chromium salts or syntans. The organic nature
of chromium-free wet-white versions is the main advantage, but it also distances itself
from the traditional, mineral character of natural leather. In this respect, the approach of
tanning metallic hetercomplexes provides both classic features of mineral leathers and
reduces environmental pollution.
Keywords: Advanced exhaustion, Chromium replacement, Chromium reuse,
Chromium recovery, Wet-white technologies.
