Study On The Preparation Of Biosorptions By Garlic Stems&Leaves And Their Heavy Metal Adsorptions Characteristics

In this paper, garlic stem&leaves (one of the valuable biomass wastes) modified with different chemical reagents (H2C2O4and C6H6O7·H2O) as biosorbents were prepared and used to remove Pb(II),Cu(II),Cd(II) and Zn(II) from aqueous solution. New types of sorbents were obtained, Their advantages were environmentally friendly, low cost. The biosorption of Pb(II),Cu(II),Cd(II) and Zn(II) on chemically modified garlic stem&leaves have been investigated. Effects of initial pH, initial metal ion concentration, shaking time and solid/liquid ratio were also investigated. Reaction mechanisms were inferred.Their results were shown as follow.(1) The preparation temperature and concentration of modifier have great effects on the adsorption characters of biosorbents. Adsorption capacities increased initially with the increase of the preparation temperature. The optimal preparation temperature is80°C.Effects of different concentration of citric acid and oxalic acid modified biosorbents on the adsorption of Pb(II),Cu(II),Cd(II),Zn(II) were also investigated and the optimal concentrations were0.6mol.L-1citric acid and oxalic acid0.9 mol.L-1.(2) The adsorption capacity of Pb(II),Cu(II),Cd(II),Zn(II) on different biosorbents has been greatly improved. By analysing of FT-IR garlic stem&leaves after modification were introduced to the surface of a large number of carboxyl.(3) A comparison of different isotherm models revealed that the biosorption data perfectly fitted the Langmuir adsorption isotherms models. The linear correlation coefficient close to1, The adsorption is mainly single molecule layer adsorption.The maximum adsorption capacities of Pb(Ⅱ), Cu(Ⅱ),Cd(Ⅱ) and Zn(Ⅱ) were obtained as122.25,24.94,41.98and37.06mg.g-1, respectively.(4) Biosorption equilibriums were rapidly established in about180min and the adsorption kinectics of Pb(Ⅱ),Cu(Ⅱ),Cd(Ⅱ) and Zn(Ⅱ) followed the Lagergren first-order kinetics model.(5) The adsorption reaction mechanism show that hydroxyl and carboxyl of the modified biosorbents involved in the adsorption of metal ions by ion exchange.the affinity of modified biosorbents on the four kinds of metal is Pb(Ⅱ)>Cd(Ⅱ)>Zn(Ⅱ)>Cu(Ⅱ).