The solubility of an hydroxyaluminosilicate期刊界 All Journals 搜尽天下杂志传播学术成果专业期刊搜索期刊信息化学术搜索

This unconventional solubility expression was derived to take account of the non-stoichiometric dissolution of HAS_B(s) and included theoretical dissolution products which could then be substituted for the dissolution products which were measured experimentally.

K^*HAS_B=[Al_r][Si(OH)₄]²[OH^-]⁴

The derivation of the solubility expression, though non-standard in approach, was validated by its application to Al(OH)_3(s) and the calculation of a realistic solubility constant.

K^*Al₂O(OH)₄=[Al₂O⁴⁺][OH^-]⁴

K*HAS_B(s) was found to be independent of [Si(OH)₄] and predicted that HAS_B(s) could be the predominant secondary mineral phase controlling the solubility of Al in environments in which the pH > 4.00 and [Si(OH)₄] > 100 μmol/L.

The solubility of an hydroxyaluminosilicate

Authors:	C line Schneider, Fr d ric Doucet, Stanislav Strekopytov,Christopher Exley

Affiliation:	^aChemistry Department, University of British Columbia, 2036 Main Mall, Vancouver, Canada BC V6T 1Y6 ^bDivision of Food Sciences, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, UK ^cBirchall Centre for Inorganic Chemistry and Materials Science, Lennard-Jones Laboratories, School of Chemistry and Physics, Keele University, Staffordshire ST5 5BG, UK

Abstract:	Hydroxyaluminosilicates (HAS) are critical secondary mineral phases in the biogeochemical cycle of aluminium. They are formed from the reaction of silicic acid (Si(OH)₄) with an aluminium hydroxide template and act as a geochemical control of the biological availability of Al. There are two main forms of HAS which we have called HAS_A and HAS_B and which of these will predominate will depend upon the Si(OH)₄ to Al ratio in any one environment. In all but the most heavily weathered environments or those undergoing a progressive acidification Si(OH)₄ will be present in significant excess to Al and HAS_B will be the dominant secondary mineral phase. We have tried to determine the solubility of HAS_B(s) so that its contribution to Al solubility control might be compared with other secondary minerals such as Al(OH)_3(gibbsite). In preliminary experiments, the dissolution of HAS_B(s) was found to be non-congruent with almost no Al being released during 18 months ageing. We then demonstrated that HAS_B(s) was significantly less soluble than Al(OH)_3(s) prepared under identical experimental conditions. We have used this information to describe a solubility expression for HAS_B(s) at a predefined quasi-equibrium and to calculate a solubility constant. K^*Al₂Si₂O₅(OH)₄=[Al₂O⁴⁺][SiO₂]²[OH^-]⁴

Keywords:	Hydroxyaluminosilicate Aluminium Silicic acid Aluminium solubility Aluminium biological availability
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