Ca-based sorbents modified with humic acid for flue gas desulfurization

With humic acid ( HA) as a special additive, modified Ca( OH)(2) sorbents referred to as M-Ca( OH)(2)-iHA, where i is the weight percentage of HA in the dry product and is in the range between 0 to 10, were prepared by hydrating CaO with water in which the expected amount of HA had been dissolved. The physicochemical properties of the sorbents were characterized using SEM, XRD, BET, etc., and the desulfurization activity of the sorbents, expressed as "Ca utilization", was investigated in a differential fixed-bed quartz reactor under isothermal conditions at 65 degrees C and 70% relative humidity. The experimental results indicate that both hydration treatment and HA modification play important roles in improving the microstructure and desulfurization activity of M-Ca( OH)(2)-iHA. In particular, hydration treatment is the key contribution to M-Ca( OH)(2)-0HA, whereas both factors are significant for M-Ca( OH) 2-iHA ( i) 4, 6, 8, 10). It was also found that the microstructure and desulfurization activity of M-Ca( OH)(2)-iHA improves considerably as i increases from 0 to 8 and then levels out when i increases further to 10. That is, M-Ca( OH)(2)-0HA has almost the optimal microstructure among the sorbents prepared in this study, i. e., volume mean diameter of 0.5 Am, BET surface area of 19.29 m(2)/g, and mesopore volume of 0.084 cm(3)/g, as well as the highest desulfurization activity, Ca utilization of 0.52 mol of SO2/mol of Ca. In addition, the mechanism of HA modification might be due to the acceleration effect of HA on the dissolution of lime, as well as the disturbance effect of Ca2+-HA chelates on the nucleation and growth processes of Ca( OH)(2) crystals.