Chapter 4

Theory and Experimentation of Synthesis Reactions of Tanning Metallic Heterocomplexes

Carmen Gaidau


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.

Total Pages: 50-94 (45)

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