The main synthesis reaction of metallic heterocomplexes is the oxidationreduction
reaction in acid medium using glucose as a reducing agent. Understanding the
mechanism of synthesis of metallic heterocomplexes with various basicities is related to
the stoichiometric mechanism of sulfuric acid release by the aluminum sulphate present
in the system, to the use of sulfuric acid by the ferrous sulfate which oxidizes to ferric
sulfate. The theoretical study of the synthesis reactions of tanning heterocomplexes
reviews all the basicity values which can be obtained and proposes formulas for
calculating the amount of sulfuric acid required to obtain a quantity of tanning metallic
heterocomplexes containing 100 kg of metal oxides. Monitoring the laboratory scale
synthesis of chromium-iron, chromium-aluminum-iron and iron-chromium-zirconium
metallic heterocomplexes confirms the stoichiometric mechanism for heterocomplexes
with 33% basicity. The influence of aluminum and iron in metallic heterocomplexes
consists in destabilizing the complex so that the chromium-iron and the chromium-ironzirconium
heterocomplexes are more stable than the chromium-aluminum-iron one.
Stability to alkali of the new tanning metallic complexes confirms internal
heterocomplexation and the formation of more stable structures than the monometallic
salts they derive from. Stability of the three types of tanning metallic heterocomplexes
over time is good after 20 days up to 5 months and demonstrates the possibility of using
them in leather tanning and retanning under similar conditions to using basic chromium
salts. Tanning metallic heterocomplexes enable Cr2O3 offer reduction by 30-50% and
therefore reduction of pollution provided that a synergy of interaction with collagen is
achieved. Pilot scale synthesis of chromium-iron, chromium-aluminum-iron and
chromium-iron-zirconium variants of heterocomplexes with the best stability has
validated the theoretic reactions developed and showed the higher stability of tanning
metallic heterocomplecxes. Tanning metallic heterocomplexes can also be developed as
powder by atomization, and the stability to alkali of solutions obtained from powders is
higher in the case of chromium-iron heterocomplexes and remains unchanged for other
types of tanning heterocomplexes.
Keywords: Synthesis of heterocomplexes, Basic chromium salts, Chromiumaluminium
heterocomplexes, Chromium-iron heterocomplexes, Chromiumaluminium-
iron heterocomplexes, Chromium-zirconium heterocomplexes,
Chromium-aluminium-zirconium heterocomplexes, Chromium-iron-zirconium
heterocomplexes.
