Effective adsorption of phosphate from wastewaters by big composite pellets made of reduced steel slag and iron ore concentrate

摘要

In order to remove phosphate from wastewater, a large plastic adsorption column filled with big phosphate-adsorbing pellets with diameters of 10mm, heated by electromagnetic induction coils, was conceived. It was found that the prepared big pellets, which were made of reduced steel slag and iron ore concentrate, contain magnetic Fe and Fe3O4. The thermodynamics and kinetics of adsorption of phosphate from synthetic wastewaters on the pellets were studied in this work. The phosphate adsorption on the pellets followed three models of Freundlich, Langmuir and Dubinin-Kaganer-Radushkevick. The maximum phosphate adsorption capacity Q(max) of the pellets were 2.46, 2.74 and 2.77mg/g for the three temperatures of 20 degrees C, 30 degrees C and 40 degrees C, respectively, based on the Langmuir model. The apparent adsorption energies were -12.9kJ/mol for the three temperatures. It implied that ion exchange was the main mechanism involved in the adsorption processes. The adsorbed phosphate existed on the pellet surface mainly in the form of Fe-3(PO4)(2). A reduction pre-treatment of the pellet precursor with H-2 greatly enhanced pellet adsorption for phosphate. The adsorption kinetics is better represented by a pseudo-first-order model. The adsorbed phosphate amounts were similar for both real and synthetic wastewaters under similar adsorption conditions. The percentage of adsorbed phosphate for a real wastewater increased with increasing pellet concentration and reached 99.2% at a pellet concentration of 64 (g/L). Some specific phosphate adsorption mechanisms for the pellets were revealed and the pellets showed the potential to efficiently adsorb phosphate from a huge amount of real wastewaters in an industrial scale.