Experimental and theoretical studies on the adsorption performance of lead by thermal pre-activation and phosphate modified kaolin sorbent
Lead removal from flue gas continues to be an important environmental issue. Adding sorbents in the furnace is a reliable method to control lead emission. Modified kaolin sorbent developed by a combined method of thermal pre-activation and phosphate impregnation was first applied to capture lead from flue gas. Modified kaolin exhibited higher PbCl 2 removal performance than raw kaolin at 800–1100 ℃. The best adsorption performance of raw and modified kaolin was obtained at 1000 ℃ with adsorption efficiencies of 76.72 % and 85.87 %, respectively. The adsorption capacity of modified kaolin was about 283.51 mg/g at 1000 ℃. Lead aluminosilicate and lead phosphate were produced in the adsorption reaction. O 2 was conducive to the conversion of PbCl 2 to PbO, and directly participated in the formation of lead aluminosilicate· H 2 O was in favor of the adsorption reaction, and reduced the energy barrier for dechlorination of PbCl 2 , and promoted the eutectic melting process. SO 2 and NO inhibited PbCl 2 removal due to the competitive adsorption between SO 2 /NO and PbCl 2 at the active sites. High concentration of HCl can obviously suppress the reaction of PbCl 2 and modified kaolin. Quantum chemistry calculations were conducted to identify the active sites, and to uncover the molecular-level interaction of PbCl 2 and modified kaolin. Theoretical results manifested that PbCl 2 adsorption was chemisorbed on kaolin (0 0 1) surface. The adsorption energies of PbCl 2 on raw kaolin and modified kaolin were − 124.60 and − 205.90 kJ/mol, respectively. Al, O and P atoms of modified kaolin were identified as the active sites for PbCl 2 adsorption.
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