EFFECTS OF PYROGALLOL ON Al_(13) TRIDECAMER FORMATION AND HUMIFICATION

摘要

The Al_(13) polycation is the predominant hydroxy-Al species in partially neutralized solutions, However, the existence of the Al_(13) species and the factors governing its formation in terrestrial environments still remain obscure. The objective of this study was to investigate the influence of pyrogallol, a common polyphenol in soils, on the formation of Al_(13) tridecamer. Hydroxy-Al solutions with an OH/Al molar ratio of 2.2 (pH 4.53) at pyrogallol/Al molar ratios of 0, 0.01, 0.05, 0.1 and 0.5 were prepared and mixed with 0.5 M sodium sulfate to form aluminum sulfate precipitation products. The solid-state ~(27)Al nuclear magnetic resonance (NMR) spectra of the precipitates show that the pyrogallol perturbed the formation of Al_(13) tridecamer species as indicated by the decrease in the intensity of resonance peak, observed at 62.5 ppm, with increase in the pyrogallol/Al molar ratio. The crystallization of the precipitated Al sulfates was also hampered by pyrogallol, resulting in the formation of X-ray non-crystalline products at a pyrogallol/Al molar ratio of 0.50. The absorbance at 465 and 650 nm of the hydroxy-Al-pyrogallol solutions, the C coprecipitated, the electron spin resonance and ~(13)C CPMAS-NMR spectra of the precipitates indicate the concomitant enhanced abiotic humification of pyrogallol by the X-ray amorphous Al species.