Chemically Modified Persimmon Biosorbent And Its Adsorption Of Heavy Metal Ions

With the fast development of modern industry, heavy metal contaminant becomes more severe. How to eliminate the damage and effectively recover heavy metals is the outstanding problem of current environmental protection work. Biosorption as a novel heavy metal removal technology has many advantages, including abundant resource, low cost, high metal binding capacity, environmental friendly and without second pollution, which make biosorption have a wide application prospect.In this paper, persimmon powder was chosen as the raw material to prepare two biosorbents SPP and CPP through chemical modification by using H2SO4 and CaCl2, respectively. These two biosorbents were used to adsorb Cu2+, Pb2+, Zn2+and Cd2+ from aqueous solutions. PSD, SSA, SEM and FTIR were used to characterize the biosorbents. The effects of various parameters, including solution pH, temperature, time and metal ion concentration on the biosorption process were investigated by using batch adsorption techniques. The adsorption thermodynamic, adsorption kinetics and adsorption isotherms of these four individual metals were analyzed systematically. The separation of Pb2+/Zn2+ and Pb2+/Cd2+ under low pH values was conducted by column adsorption experiments. Furthermore, the technology of desorption and reuse for the modified persimmon powder was tested and the adsorption mechanism was also discussed.The results of characterization showed that after chemical modification, SPP and CPP had smaller particle size, larger specific surface area and more closely surface morphology. It indicated that modification allowed molecular interactions to be strengthened to effectively reduce the solubility of persimmon powder.Solution pH had great effect on the adsorption efficiencies of Cu2+, Pb2+, Zn2+ and Cd2+ by biosorbents. Under the temperature range from 30℃to 60℃, the adsorption processes of SPP were exothermic except for Cd2+; the adsorption processes of CPP were all exothermic.It was found that all the adsorption of Cu2+, Pb2+, Zn2+ and Cd2+ on SPP and CPP was a fast adsorption process that could be reached equilibrium within 30 minutes. The adsorption processes could be well described by the pseudo-second-order equation.By analyzing the adsorption isotherms, the adsoprtion of Cu2+, Pb2+, Zn2+ and Cd2+ on SPP and CPP fitted both Langmuir and Freundlich model, but fitted Langmuir model better. The maximum adsorption capacities for Cu2+, Pb2+, Zn2+ and Cd2+ on SPP were 89.2,285.7,75.3 and 106.4mg/g respectively, which of CPP were 93.2,299.4,72.1 and 123.3 mg/g respectively, both higher than that of the unmodified persimmon powder.Metal loaded biosorbents were be regenerated using 0.1 mol/L HC1 solution and could be used repeatedly for five times with little loss of adsorption capacity. The results of column adsorption experiments suggested that effective mutual separation of Pb2+/Zn2+ or Pb2+/Cd2+ and pre-concentration of Pb2+ away from Zn2+ or Cd2+ using modified persimmon powder could be satisfactorily achieved.Based on the analysis of the change of solution pH and movement of typical adsorption peaks in FTIR spectrum before and after heavy metal adsorption, the adsorption mechanism involved both ion exchange and complexation between heavy metal ions and functional groups (Phenolic-OH,-COOH) on the surface of biosorbents.