Dissolution de phases minérales MSiO3 ( M Cu, Co, Ni, Zn, Mg) imparfaitement cristallisées au contact de solutions d'agents complexants organiques (porphyrines, amino-acides, asphaltènes)

Abstract

The kinetic and thermodynamic aspects of the dissolution of ill-organized (“gels”) high surface area silicates of general formula MO- SiO 2- nH 2 O( M = Cu, Co, Ni, Zn, Mg) in the presence of the following organic compounds have been investigated: meso-tetraphenylporphyrin (H 2TPP, water insoluble), mesotetra(N-methylpyridyl)porphyrin (H 3TMPyP, water soluble), glycine, and asphaltenes. Kinetic aspects were emphasised in the case of H 2TMPyP. The initial rate of the gross dissolution complexation process followed almost quantitatively (passing from one metal to another) the complexation rate of M 2+ ions by H 2TMPyP in a purely homogeneous medium, suggesting that the rate limiting step of the overall process is not related to the chemical or physical processes occurring in the solid particles or at the solid-solution interface, but is simply the complexation, in the solution, of the M 2+ ions released by the gel particles. Thermodynamic aspects were emphasised in the case of glycine. The total amount of metal which is extracted at equilibrium can be reasonably well predicted from a simple model which takes into account 1. (i) the stability constant of the metal-glycine complex. 2. (ii) the “solubility product” of the gel particles in water. The results obtained with asphaltones are closer to those obtained with glycine than to those obtained with porphyrins, suggesting that porphyrins represent only a minor population in the complexing functional groups of asphaltenes.