Extraction and separation of phosphorous and heavy metals from freshwater sediment – influence of experimental variables on the electrodialytic treatment

This study explores the influence of experimental variables on the electrodialytic (ED) treatment of freshwater sediment for extraction and separation of phosphorus (P) and heavy metals (Cd, Cu, Pb, Zn). The overall idea is to extract an uncontaminated P product and an unpolluted sediment fit for recycling. The influence of the experimental variables, current, liquid-to-solid ratio (L/S), duration, stirring rate, suspension liquid (distilled/tap water), was studied in 11 ED experiments with the help of a multivariate analysis tool, projection to latent structures (PLS). In the experimental domain studied, current and L/S had the most influence on P extraction (50%), and the extracted P was uncontaminated with heavy metals. The stirring rate and current had the most influence on the extraction of Zn (90%) > Cd (87%) > Cu (60%) > Pb (48%). The concentration of heavy metals was compared with the limits for soil improvers because that is one of the options for sediment recycling. Cd and Zn in the treated sediment met the standards for soil improvers, whereas optimization is necessary for Cu and Pb. The multivariate analysis revealed that the extracted Cd and Zn were mostly associated with the exchangeable and reducible fractions of the sediment. It was also revealed that the extracted Cu was mostly associated with the oxidizable fraction, whereas for Pb, no clear relationship could be established. The optimization for improving the extraction of Cu and Pb associated with the oxidizable fraction could be done by treating the sediment at a high stirring rate, high current, and long duration.