CO2 sequestration by ammonia-enhanced phosphogypsum mineral carbonation: Development and optimization of reaction kinetic model

Comparing of existing kinetic models for direct mineral carbonation by solid waste, an optimized kinetic model was developed to depict the relationship between phosphogypsum carbonation ratio and reaction time. Based on the optimized model, the reaction mechanism of CO2 sequestration by ammonia-enhanced phosphogypsum mineral carbonation was analyzed. The experimental results show that, under specific conditions, including an ammonia ratio of 2.3, room temperature (25 degrees C), a liquid-solid ratio of 5:1, a gas flow rate of 200 mL/min, and a rotational speed of 500 rpm, phosphogypsum achieved its peak carbonation efficiency of 91 % within 30 min. The optimized model fitting curve has a high consistency with the experimental data, and the average R2 value is 0.991. The process of ammonia-enhanced phosphogypsum mineral carbonation comprises three distinct subprocesses. It is consisted of mass transfer in gas-liquid interface and solid-liquid interface, respectively, and product layer diffusion. Among them, the gas-liquid mass transfer is identified as the rate-controlling step in the mineral carbonation process. The present study provides a basis for the operation optimization and large-scale utilization of phosphogypsum mineral carbonation.