Statistical testing of input factors in the carbonation of brine impacted fly ash

Abstract

A D-optimal design was applied in the study of input factors: temperature, pressure, solid/liquid (S/L) ratio and particle size and their influence on the carbonation of brine impacted fly ash (FA) determined. Both temperature and pressure were at two levels (30°C and 90°C; 1 Mpa and 4 Mpa), S/L ratio was at three levels (0.1, 0.5 and 1) while particle size was at 4 levels (bulk ash, <20 μm, 20 μm −150 μm and >150 μm). Pressure was observed to have a slight influence on the % CaCO₃ yield while higher temperatures led to higher percentage CaCO₃ yield. The particle size range of 20 μm – 150 μm enhanced the degree of carbonation of the fly ash/brine slurries. This was closely followed by the bulk ash while the >150 μm particle fraction had the least influence on the % CaCO₃. The effect of S/L ratio was temperature dependent. At low temperature, the S/L ratio of 1 resulted in the highest % CaCO₃ formation while at high temperature, the ratio of 0.5 resulted in the highest percentage CaCO₃ formation. Overall the two most important factors in the carbonation of FA and brine were found to be particle size and temperature.

Keywords:

• Design of experiments
• D-optimal design
• fly ash
• brine
• mineral carbonation
• sequestration
• ANOVA
• chittick test

Acknowledgments

The authors acknowledge Dr. Patrick Ndung’u for his assistance as well as Eskom and Sasol for funding this study.