Study On The Preparation Of Chemically Modified Lawny Grass Cellulose Adsorbents And Biosorption Of Pb(Ⅱ) And Cd(Ⅱ)

In this paper, lawny grass as solid waste during the process of city beautifying or gardensbuilding was modified with different chemical reagents, a series of adsorbents was gained forremoval of Pb(II) and Cd(II). The reaction mechanism was discussed and followed ionexchange adsorption mechanism. Influences of solution pH, contact time, initial metal ionconcentration, solid/liquid ratio and temperature were also investigated. Experimental resultswere express as follows:1. The optimum pH for all adsorbents was: in the pH range of 5.0-5.8, the order ofadsorption capacities of Pb(II) was: 1CG > 0.6CG≈0.6SCG > CMNG≈0.6PG≈0.1CG≈SG≈ZCG >RG; in the pH range of 5.5-6.5, the order of Cd(II) was 1CG > 0.6CG≈0.6SCG> 0.3CG > 0.6PG > 0.1CG≈CMNG≈SG≈ZCG.2. Biosorption equilibrium was obtained after 60 min when the concentration of metalsolution was 0.001 mol l^-1. Biosorption equilibrium was obtained after 80 min for 0.002 mol l-1 Cd(II). Biosorption process of all adsorbents followed the pseudo-second-order model.3. A comparison of different isotherm models revealed that Langmuir and Freundlich (LF)isotherm model fitted experimental data best. The fitting results showed the order: 1CG >0.6CG > 0.6SCG, The maximum capacities qm for Pb(II) were 1.55, 1.26 and 1.08 mol kg^-1,respectively, and for Cd(II) were 1.29, 1.19 and 1.08 mol kg-1, respectively. The comparisonof adsorption capacities of 1CG and other low-cost adsorbents indicated that 1CG have ahigher adsorption capacity than other adsorbents.4. The optimum s/l ratio of Pb(II) was 3.67 g l^-1 with 1CG, 0.6CG和0.6SCG, that ofCd(II) was 5.67 g l^-1 in 0.004 mol l^-1 solution and 4.33 g l^-1 in 0.002 mol l^-1 solution.5. Thermodynamic parameters indicated that: The negative value ofΔG indicatesadsorption process was spontaneous. The positive value ofΔH indicated adsorption processwas endothermic. With temperature increased, the adsorption for Pb(II) and Cd(II) alsoincreased, this also indicated the adsorption process was endothermic.6. In the column studies, 0.6CG was used to remove Pb(II). The result showed that thebreakthrough point began at 100 BV, and the column bed is completely saturated at 280 BV.The column bed adsorbed Pb(II) can be easily regenerated by a small amount of 0.1 mol l^-1HCl which was about 20 BV. 1CG and 0.6CG were used to remove Cd(II).The breakthroughpoint was around at 100 BV by 0.6 CG and 138 BV by 1CG. Regeneration column of Cd(II)with 1CG was finished by 0.1 mol l^-1 HCl which was about 15 BV. After several cycles ofadsorption-desorption, the adsorption capacity of regenerated column was hardly changed.