Aluminum Hydroxide's Solubility and the Forms of Dissolved Aluminum's Occurrence in Seawater

The solubility of aluminum hydroxide in seawater of 35% salinity at pH = 7.4-8.2 and 25 degrees C was determined experimentally for three samples synthesized in different ways. The solubilities of two phases subjected to ageing and precipitated (a) from a boiling solution of aluminum sulfate and (b) immediately from seawater at room temperature were a little different and showed the minimum within pH = 8.05-8.10. The solubility of aluminum hydroxide precipitated from a solution of sulfate aluminum at room temperature and not subjected to ageing was about twofold at pH similar to 7.9. The analysis of the pH dependence of the concentration of dissolved aluminum allows one to suppose that an Al(OH)(2)(+) hydroxo complex is the primary form of the aluminum occurrence in seawater at pH < 8.05, whereas the Al(OH)(4)(-) anion is prevailing at pH>8.10. Electrically neutral Al(OH)(3)(0) hydroxocomplexes may be prevailing within the narrow range of pH = 8.05-8.10 and, in general, are of secondary importance.