Abstract
Seawater with reduced amounts of calcium and magnesium was used for increasing the concentration of sediment solids from a mine tailing. The assays were carried out considering a synthetic tailing, composed of quartz and kaolinite, and utilising an anionic flocculant of high molar weight. Seawater produced an efficient behaviour when working at pH < 9. However, at higher alkalinity the solid concentration of the sediment was substantially reduced. Isolating the effect of the main seawater ions it was found that magnesium, and to lesser extent calcium, are responsible for reducing the flocculation efficiency, caused by the formation of MgOH+ /CaOH+ complexes and Mg(OH)2 precipitates. For this reason, when using seawater with a reduced amount of calcium and magnesium, it was possible to considerably increase the solids content, offering an effective alternative to operate at highly alkaline conditions.
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