Multifunctional use of magnetite-coated tuff grains in water treatment: Removal of arsenates and phosphates

Abstract

Natural filtration material tuff (T) was modified by coating with nano-sized magnetite. The grain fraction of 0.6-1.9 mm was submitted to hydrothermal synthesis of magnetite. Thus formed magnetite modified tuff (MMT) was characterized in terms of Fe-content, N2 adsorption-desorption isotherm, SEM, zeta potential-pH analyses and adsorption behavior towards phosphates/arsenates in batch and column conditions. Elemental analysis showed that 36.54 mg g(-1) of magnetite was attached to the porous tuff grains. This modification changed pore structure and specific surface area. An increase of cca 35% in Sp value was obtained. Batch experiments proved that MMT was 4-5 times more efficient in removal of phosphates/ arsenates than non-modified T. The maximum sorption capacities of phosphates calculated based on Langmuir equation were 0.45 and 1.91 mg g(-1), while those for arsenate were 0.551 m g(-1) and 2.36 mg g(-1) for T and MMT, respectively. The intra-particle diffusion model was the most suited for describing the adsorption process of phosphate and arsenate onto MMT. Fixed-bed column data corroborated batch results, i.e. MMT was 6 times superior in contaminant adsorption than T. Modification with magnetite improved T potential for usage in water treatment applications: its filtration ability remained unchanged, while adsorption capacity for phosphates/arsenates removal was improved.