Desilication of concentrated alkali solution by novel desilication reagent calcium hydroferrocarbonate: Part III. Standard thermodynamics investigation of desilication reaction using hydroferrite desilication reagents

The property of lower soda and alumina contents of iron hydrogarnet can reduce the loss of soda and alumina in Bayer and Sub-molten salt process. Thus, the economic efficiency of alumina production could be improved. How to solve the effective formation of iron hydrogarnet in concentrated caustic aluminate solution and its cycle in the digestion process has become an important research topic. The base of hydroferrire desilication agents (calcium hydroferrite CHF, calcium hydroferrocarbonate CHFC, calcium hydroferrosulfate CHFS) were synthesized, the desilication experiments and desilication products (DSPs) were characterized, the results show that the hydroandradite and aluminum-hydroandradite are the main components in DSPs. The free energy of synthesis reaction of desilication agents and desilication reaction in concentrated caustic solution was investigated using the complex silicate theory. The investigation shows that CHFC has the better desilication performance for hydroferrite desilication agents. The free energy of desilication reaction in concentrated caustic solution using hydroandradite is affected by the initial silica coefficient, the reacted silica coefficient of DSPs, and the reaction temperature. From the point of view of thermodynamics, the substitution reaction between aluminum to iron that occurred in the concentrated caustic aluminosilicate solution main occurs when the higher initial silica coefficient of hydroandradite and the higher alumina coefficient of reaction product