Limnetica 34

The specific adsorption of phosphate (P) on strongly magnetisable carbonyl iron (Fe) particles and their subsequent removal by in-flow High Gradient Magnetic Separation (HGMS) is considered a promising tool for restoring eutrophied waters. A previous study showed the existence of chemical interferences in natural waters without considering the influence of specific major ions on the P removal efficiency (de Vicente et al., 2011). Therefore, in this manuscript, we assess the single-effect of some of the major ions present in natural waters, including sulphate (SO₄^2-), calcium (Ca²⁺), humic acid (HA, as an indicator of Dissolved Organic Carbon, DOC), and reactive silicate (Si), on P adsorption to magnetic Fe particles in artificial lake water. The results showed that HA and Si significantly decreased the effectiveness of P adsorption by magnetic Fe particles. In particular, P removal efficiency decreased to 12 % and 22 % when HA and Si concentrations were 35.5 mg HA L^-1 and 10 mg Si L^-1, respectively. By contrast, SO₄^2- and Ca²⁺ did not significantly reduce P removal. We recommend chemically analysing the lake water and determining the Fe dosage that obtains the highest P removal before using magnetic particles for the restoration of aquatic ecosystems in a whole-lake application.