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This article in SSSAJ

  1. Vol. 38 No. 2, p. 235-244
    Received: July 27, 1973
    Accepted: Nov 7, 1973

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Effect of Monosilicic Acid on Hydrolytic Reactions of Aluminum1

  1. G. M. Luciuk and
  2. P. M. Huang2



The mechanisms and products of hydrolytic reactions of Al ions as influenced by Si(OH)4 were studied under the experimental parameters of degere of hydrolysis of Al (OH/Al molar ratios,) Si/Al molar ratios, Al concentrations of 1.39 × 10-3M and 1.39 × 10-4M, and time.

As the degree of hydrolysis of Al increased, the amounts of Si along with Al initially precipitated and removed from the solution phase by ultrafiltration consistently increased. The coprecipitation data, infrared evidence, and stoichiometric considerations of Si(OH)4 removal and proton release strongly indicate that the predominant coprecipitation of Si(OH)4 with hydroxy-Al ions is the condensation reaction involving the hydroxyl groups in hydroxy-Al ions. At the OH/Al molar ratios of 1 and 2 and in the absence of Si(OH)4, precipitation of Al continued with aging; whereas at the Si/Al molar ratios of 0.5 and 1, the reaction products were metastable, and there was formation of a significant portion of nonextractable Al which was not removed by ultrafiltration.

In the absence of Si(OH)4, the product was crystalline Al(OH)3 even at the OH/Al molar ratio of 1. Materials amorphous to X-ray and electron diffraction were the only products at Si/Al molar ratios of 0.5 and 1, OH/Al molar ratios of 2 and 3, and both initial Al concentrations even after prolonged aging. Decreasing degree of hydrolysis of Al resulted in a distinct decrease in particle size for crystalline products, and in a decrease in the extent of aggregation for amorphous products. The thermal stability and Si/Al ratio of the reaction products were influenced by the Si/Al molar ratio of solution and the period of aging. The presence of Si(OH)4 in solutions also resulted in a decreased Cl inclusion in the reaction products.

The results clearly show that the presence of Si(OH)4 affects the hydrolytic reactions of Al at all degrees of hydrolysis of Al. This knowledge is of basic significance for a further understanding of pedogenic processes, and the fate of certain nutrients and environmental pollutants.

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