Binding effects and mechanisms of the carboxymethyl starch modified with nano-CaCO3 in magnetite concentrate pellets

Abstract

This study aimed to identify the carboxymethyl starch modified with nano-CaCO3 (CCMS) as an alternative binder in iron ore pelletization. Pelletization results showed that all wet, dry, preheated and fired pellets produced with CCMS met with the required values of strengths. The total Fe content of pellets also had a 1.04% increase by replacing 2% bentonite with 1% CCMS. FTIR and zeta potential tests verified that CMS interacted with the magnetite mainly through ligand exchange, hydrogen bond and electrostatic interaction. Meanwhile, in addition to above three interactions, CCMS reacted with negative sites of the magnetite by its unique positive charge sites (-Ca(OH)+). CCMS had more active sites and the chemical bonding of CCMS on the magnetite surface was stronger. Besides, nano-CaCO3 interacted strongly with CMS and the cross linked structure between nano-CaCO3 and CMS molecules was built, giving CCMS a higher solution viscosity. Therefore, compared with CMS, the increased strength of green pellets with CCMS was mainly caused by the stronger chemical bonding and higher solution viscosity of CCMS. Porosity and FESEM measurements were also carried out to clarify the developed strengths of preheated and fired pellets with CCMS. In comparison with CMS, the nano-CaCO3 in CCMS resulted in the formation of more melt slags and facilitated the bridging, bonding and recrystallization between hematite particles. Thereby, the developed oxide bonding between hematite grains and the formation of more slags jointly decreased the porosity and improved the compressive strength of heat treated pellets.