Sorption Model for Dissolved Aluminium in Freshwaters

A series of aluminium speciation measurements were madein the freshwaters of the Yare and Great Ouse rivers (England). Samples were analysedfor dissolved and particulate Al, suspended particulate matter (SPM), and other alliedchemical species in order to assess the role of sorption processes on the suspended phasesin controlling dissolved Al levels. Partitioning of Al occurs between solid andsolution phases with a distribution coefficient (K_d) which varies over about one anda half orders of magnitude for suspended particle concentrations of comparablemagnitude. A sorption model is proposed for dissolved Al concentrations in thesefreshwaters with most of the data fitting the model defined by a zone with K_dvalues of 0.316 × 10⁶ and 10⁷. However, a few data points lie outside thiszone, suggesting that other processes may also influence dissolved Al distributions.Nevertheless, the model may serve as a starting point for predicting concentrations ofdissolved Al in rivers where SPM levels are moderate to high (>1 mg l^-1 but< 75 mg l^-1), and indeed, this model works reasonably well for the Conway system(Wales). Further, the empirical distribution coefficient, K_d, decreases withincreasing suspended particle concentration, which may be due in part to colloidal phenomena.