摘要：

A combination of field and laboratory investigations was conducted in order to gain an understanding of aluminium dynamics in coastal seawater environments. Filterable (0.025 to <0.45μm) aluminium species were generally minimal, apart from one field sample collected close to a river mouth where aluminium was associated with iron-containing colloids. In seawater (pH 8.15, 22°C) spiked with small increments of aluminium so as not to attain supersaturation, the solubility limit was 500μgL-1. However, at higher total aluminium concentrations the solution chemistry became highly dynamic. In the presence of aluminium precipitate it was not possible to measure a solubility limit over the 28-day duration of the experiment because the dissolved aluminium concentration varied with both reaction time and precipitate concentration. For instance, when seawater solutions were spiked with 10000μgL-1 of total aluminium, a pulse of dissolved aluminium up to 1250μgL-1 was sustained for several days before decreasing to below 100μgL-1 after 28 days. The initial precipitate appeared to be solely aluminium hydroxide and transformed over time to contain increasing magnesium, consistent with the formation of hydrotalcite (Mg6Al2CO3(OH)16·4H2O), reaching 21% of the precipitate mass after 28 days. Adsorption studies showed that at anticipated suspended particulate concentrations for coastal waters, natural particulate material has a fairly low affinity for dissolved aluminium. The results of the current study highlight the complex chemistry of aluminium in marine waters and the role of precipitation reactions.

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