Enhanced PbCl2 adsorption capacity of modified kaolin in the furnace using a combined method of thermal pre-activation and acid impregnation

The emission of semi-volatile heavy metal lead (Pb) is one of the environmental pollution in the solid waste incineration process, and using mineral sorbents such as kaolin for in-situ adsorption of Pb vapor in the furnace is an effective way to control Pb emissions. To reduce the consumption of sorbent, a modification method combining thermal pre-activation and acid impregnation was designed to improve the adsorption performance of kaolin. The PbCl2 vapor capture performance of the as-prepared sorbent was tested in a fixed-bed furnace with dual temperature zones. The experimental results show that the combined modification method can effectively improve the adsorption efficiency of unit-mass kaolin. The presence of O2 and H2O promoted the capture of PbCl2, while the presence of CO2 was not conducive to the capture of PbCl2. Moreover, the influence of combined modification method on the physicochemical properties of kaolin was analyzed, and the enhancement mechanism of PbCl2 adsorption by modified kaolin was proposed. The combined modification process promoted the formation of highly active free silica, improved the specific surface area and pore structure, and induced the conversion of 6-coordinated Al atom (Al(VI)) to unsaturated coordinated Al atom (Al(V)/Al(IV)), all of which contributed to the adsorption of PbCl2 vapor by kaolin in the furnace. According to the multifaceted analysis, the relationship between physicochemical properties of the sorbent and adsorption performance was established, providing a new strategy for the development of high-performance in-furnace sorbents.

Automated summary

The combined modification method of thermal pre-activation and acid impregnation effectively enhances the adsorption efficiency of kaolin for PbCl2 vapor capture. O2 and H2O promote the capture of PbCl2, while CO2 hinders it. By promoting the formation of highly active free silica, improving the specific surface area and pore structure, and inducing the conversion of 6-coordinated Al atom to unsaturated coordinated Al atom, the modification process enhances the adsorption of PbCl2 vapor by kaolin in the furnace.