The chemical nature of precipitates formed in solutions of partially neutralized aluminum sulfate

This study examined the solid degradation products formed in partially neutralized aluminum sulfate (PNAS) solutions. The PNAS, which has superior properties as a coagulant for treatment of some waters, suffers from instability as is evidenced by a precipitate which forms with age. The precipitate was found to contain aluminum and sulfate, but the ratio of these two species changed over time. It is suggested that the observed increase in sulfate content in the solids is consistent with the view that polymeric aluminum species are preferentially precipitated during the initial stages followed by monomeric species as degradation continues.