Binding mechanisms of polysaccharides adsorbing onto magnetite concentrate surface

Abstract

Polysaccharides have been widely investigated in past decades as alternative binders in iron ore pelletization. This study aims to further clarify adsorption mechanisms and binding characteristics of three representative polysaccharides: carboxymethyl starch (CMS), carboxymethyl cellulose (CMC) and guar gum (Guar). FTIR analysis and zeta potential measurements indicate that CMS and CMC can adsorb onto magnetite concentrate via carboxymethyl and hydroxyl groups, while guar gum through the hydroxyl group. Chemical interaction and hydrogen bonding are dominant interactions between binders and magnetite. AFM images show that a continuous thick film is generated after the adsorption of CMS. CMC adsorbs onto magnetite surfaces in the shape of fibrous structure, forming a much thinner layer. The adsorption layer of Guar is the thinnest. Chemical interaction force is the main contribution for adhesive force. Equilibrium adsorption data of these binders can be described by the Freundlich isotherm. Chemical adsorption is the dominant mechanism and adsorption capacity can represent adhesive force. Pelletization results verify that wet strengths of pellets produced with Guar are the largest, followed by CMC and CMS. Viscous force rather than adhesive force is the determining contribution to wet strength. Binder cohesive force and adhesive force are significant contributions to dry strength. Solution viscosity and adsorption capacity are primary criteria to evaluate binders. The combination usage of these binders is recommended to reach the required wet and dry strengths at a lower cost.