Abstract
Chemical recycle process of waste gypsum board obtaining synthetic calcium ferrite for steelmaking have been investigated. Thermodynamic estimation and results of small-scale heating tests revealed that decomposition of gypsum promoted in proper range of partial pressure of O2 and in lower partial pressure of SO2 through preventing formation of CaS. Adding Fe2O3 to gypsum contributed a lowering of decomposition temperature of gypsum resulting in formation of calcium ferrite in lower temperature. Decomposition of gypsum was incomplete after heating in air at 1180 °C. In contrast, calcium ferrite was successfully obtained by 2-step heat treatment of gypsum ; firstly forming CaS thorough reduction by composite carbon and subsequently heating mixture fine between Fe2O3 and CaS at 1180 °C. Furthermore a possibility of forming calcium ferrite was found even in a single heat treatment if we adapt proper gas and material conditions. After trial tests with using large-scale rotary kiln, it was confirmed that heating of sample consisting with gypsum, coke fine and Fe2O3 at temperature less than 1200 °C resulted in the formation of calcium ferrite accompanying with high desulfurization degree of gypsum.
