Study On The Preparation Of Chemically Modified Orange Peels Cellulose And Biosorption Of Heavy Metal

In this paper, orange peel (one of the valuable biomass wastes) modified with different chemical reagents as biosorbents were prepared and used to remove toxic and harmful heavy metal from aqueous solution. Different types of alkali (NaOH, Ca(OH)₂ and NH₄OH), or inorganic acid (H₃PO₄) or organic acid (H₂C₂O₄ and C₆H₆O₇·H₂O) were used to modify orange peels. Therefore, nine types of sorbents were abtained. The biosorption of Cd(II), Ni(II), Co(II) and Zn(II) on chemically modified orange peel have been investigated. Effects of initial pH, initial metal ion concentration, shaking time, solid/liquid ratio and desorption on metal ions biosorption were also investigated. Reaction mechanisms were inferred.1. Temperature and concentration have great effects on the adsorption characters of biosorbents. Adsorption capacities increased initially with the increase of temperature, and then decreased when temperature was 80℃, so the optimum prepared temperature was 80℃. Effects of different concentration of citric acid modified biosorbents on the adsorption of Cd(II) were also investigated and could be explained in terms of acidic and basic sites and the points of zero charge (PZC).2. The order of maximum adsorption capacity on different biosorbents was: Zn²⁺: SCA>SNa>SOA>SPA>SAm>SCa>OP; Cd²⁺: SOA>SCA>SPA>SNa>SAm>SCa>OP; Co²⁺ and Ni²⁺: SPA>SCA>SOA> SNa>SAm>SCa>OP.3. A comparison of different isotherm models revealed that the biosorption data perfectly fitted the Langmuir and Freundlich adsorption isotherms models. The maximum adsorption capacities of Ni(II), Co(II), Zn(II) and Cd(II) for SPA, SPA, SCA and SOA were obtained as 1.28, 1.23, 1.21 and 1.13 mol kg-1, respectively.4. The optimum S/L ratio of Zn(II) was 4.3 g l^-1 with SCA, that of Cd(II) was 4.3 g l^-1 with SOA, and that of Ni(II) and Co(II) was 3.0 g l^-1 with SPA, respectively.5. 0.05 mol l^-1 HCl was noted to most effectively desorb 87.23% Zn(II) biosorbed by SCA; The maximum removal percentages of 93.72% of Cd(II) was realized with 0.15 mol l^-1 HCl from the Cd-loaded SCA; Desorption of Co(II) and Ni(II) from the metal-laden SPA with 0.1 mol l^-1 HCl resulted in 81.06% and 80.11% recovery of these metals, respectively.6. Biosorption equilibriums were rapidly established in about 180 min and the adsorption kinectics of Cd(II),Co(II),Ni(II) and Zn(II) followed the Lagergren first-order kinetics model.