Adsorption of Phosphates from Aqueous Solutions on Alginate/Goethite Hydrogel Composite

Abstract

The basic process to reduce the phosphate ions in aquatic environments is to move the phosphorus circulation processes on the water–sediment phase boundary towards depositing it in the solid phase through chemical precipitation or adsorption. Modern technologies for removal of phosphorus can be based on cheap and environmentally friendly natural polysaccharides modified with multivalent metals. In this study alginate/goethite hydrogel composite has been investigated for phosphate uptake from aqueous solutions. The composite was produced by a cross-linking reaction between sodium alginate and calcium chloride in six configurations of suspensions, which differed in goethite content. In all cases, spherical and durable capsules of alginate/goethite composite were produced. In laboratory tests, mechanical stability of the capsules at various temperatures and the coexisting ions of lake water were tested. Chemical composition of the aquatic environment had a strong influence on their mechanical stability. Static batch adsorption of phosphate studies were carried out for two adsorbents: goethite and alginate/goethite composite. The goethite gelation resulted in almost double growth of sorption capacity in the case of adsorption from deionized water and, on average, a 50% growth in adsorption from the environmental water compared to raw goethite. The alginate/goethite adsorbent removed phosphate in a wide pH spectrum—from 4 to 10. Results suggest that the proposed adsorbent has potential for the removal of phosphate from contaminated water.