Sorption as a pre-concentration step for metal ions recovery in multi-elemental systems

Abstract

Sorption is here proposed as a promising approach for metal pre-concentration and recovery from wastewater. A study was carried out on the simultaneous sorption of Co2+, Cu2+, Ni2+ and Zn2+ on macroalgae, microalgae and cyanobacteria. The effect of pH, initial metal concentration, metal competition and time of contact on metal sorption were evaluated. Metal competition hampers sorption at the studied metal concentration ranges. The metal counterion (sulfate, chloride or acetate) did not influence metal sorption. The brown algae Sargassum sp. was the most promising sorbent (qmax = 0.66 ± 0.03 mmol·g−1), followed by the microalgae Phaeodactylum tricornutum (qmax = 0.36 ± 0.02 mmol·g−1) and the cyanobacteria Spirulina sp. (qmax = 0.216 ± 0.007 mmol·g−1). All biomass samples showed preferential sorption of Cu2+. The experimental kinetic data were well described by Ho’s model, showing chemisorption to be the main sorption mechanism. Ion-exchange of Ca2+, K+ and H+ also played a significant role in metal sorption. After sorption, metal recovery was achieved resorting to incineration. The metal content of the obtained biochar was 4639-fold higher when compared to the initial aqueous solution concentration.