Effects of nano-CaCO3 on the adsorption of carboxymethyl starch onto magnetite concentrate in pelletizing

Abstract

The carboxylmethyl starch modified with nano-CaCO3 has been identified as an alternative binder in iron ore pelletization. This study aims to further clarify effects of nano-CaCO3 on the adsorption of carboxymethyl starch (CMS) onto magnetite particles. Variables influencing the adsorption capacity of CMS, such as solution pH, initial concentration, the ratio of nano-CaCO3 to CMS and adsorption time, were systematically investigated. Zeta potential and solution pH results verify that nano-CaCO3 can serve as an active site, which reducing the repulsive force between the negatively charged CMS and magnetite surface. Consequently, the adsorption capacity of CMS is promoted by the addition of nano-CaCO3. Besides, both the adsorption capacity of CMS and strengths of green pellets with the addition of nano-CaCO3 decrease by increasing the pH value of binder solution. In other words, there is a positive correction between the adsorption capacity and the strength of green pellet. The equilibrium adsorption data of CMS can be described by the Freundlich isotherm. The addition of nao-CaCO3 does not change the adsorption type of CMS onto magnetite surface. For the adsorption of CMS with or without the addition of nano-CaCO3, the pseudo-second-order kinetics of chemical reaction provides the best correlation. Moreover, the adsorption rate of CMS with nano-CaCO3 is much larger than that of CMS. SEM results indicate that the cross-linked structure built by CMS+nano-CaCO3 is unique and different from that of CMS. The nano-CaCO3 can serve as the active site and skeleton, and promote the cohesion force of neighboring CMS molecules. Consequently, this unique structure gives CMS+nano-CaCO3 a high binding ability.