EXPERIMENTAL-STUDY OF MINERAL SURFACE AND AQUEOUS ALUMINUM COMPLEXATION WITH ANILINE AND 2-CHLOROANILINE

The thermodynamic stabilities of the aqueous and surface Al-aniline an d Al-2-chloroaniline complexes were investigated using solubility and adsorption experiments. Aqueous complexation was studied by measuring the solubility of gibbsite (Al(OH)(3)) as a function of aniline and ch loroaniline concentrations. Experiments measuring aniline and chloroan iline adsorption onto corundum (alpha-Al2O3) were conducted as a funct ion of pH, from pH 1.5 to 9.0, at room temperature in .01 molal NaCl s olutions, with starting concentrations of 10(-3.)0 and 10(-3.3) molal aniline, 10(-2.7) molal 2-chloroaniline, and 2.72 X 10(-3) molal total surface sites. The experiments place quantitative constraints on the thermodynamic properties of the aqueous and the surface Al-aniline com plexes. the solubility data indicate that if Al-aniline of Al-2-chlora niline aqueous complexes exist, they are not stable enough to signific antly affect the solubility of gibbsite under the experimental conditi ons. Conversely, the adsorption data provide unequivocal evidence for the presence of two distinct surface Al-aniline and Al-chloroaniline c omplexes according to the following reactions (1) Aniline(0) + = Al(OH )(0) double left right arrow = AlOH(Aniline)(0 )(2) Aniline(0) + = Al( O)(-) double left right arrow = AlO(Aniline)(-) (3) Chloroaniline(0) = Al(OH)(0) double left right arrow = AlOH(Chloroaniline)(0) (4) Chlo roaniline(0) + = Al(OH2)(+) double left right arrow = AlOH2(Chloroanil ine)(+) We use a constant capacitance model to quantify the stability constants for reactions 1-4, and the results yield log equilibrium con stant values of 2.09, 2.67, 2.87, and 2.30, respectively. The experime ntal results indicate that for most contaminated systems, aqueous Al-a niline, and Al-chloroaniline complexation does not have a significant effect on aniline speciation in groundwater, but that mineral surface complexation can significantly affect total aniline and chloroaniline budgets. Copyright (C) 1998 Elsevier Science Ltd.