An assessment of complex formation between aluminium and silicic acid in acidic solutions

• Published in: Geochimica et cosmochimica acta Vol. 58; no. 16; pp. 3331 - 3334
• Main Authors: Farmer, V.C., Lumsdon, D.G.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.08.1994
• Subjects: Freshwater
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/0016-7037(94)90088-4

The extent of the reaction A1 3+ + Si(OH) 4 → AlOSi(OH) 3 2+ + H + has been assessed by measuring the shift in log[H +] between solutions containing A1(ClO 4) 3, HClO 4, and NaClO 4 with and without added silicic acid. The observed shifts of 0.018–0.027 units are about one tenth of those predicted from the formation constant ( pK 110 = 1.07 ± 0.06) proposed for the monomeric aluminosilicate species by Browne and Driscoli (1992). An estimate of this formation constant on the basis of the shifts in log[H +] ( pK 110 = 2.50 ± 0.05) indicates that the concentration of aluminosilicate species can be neglected in many natural waters.