Sorption Of Heavy Metals From Water By Modified Palm Thread

Three novel biosorbents, palm thread modified with NaOH(NaOH-PT), palm thread modified with SDBS(SDBS-PT), palm thread ash burned at low temperature, were prepared from the cheap natural biomass materials palm thread(PT). And were successfully applied to the adsorption of cationic Ni (Ⅱ), Cd (Ⅱ), Cr (Ⅲ) and anionic Cr (Ⅵ) from water. The influential factors and adsorption mechanism of adsorption process were detailedly discussed.The removal of heavy metals, sorbed by different adsorbents prepared under different conditions, was investigated.The results showed that the optimal modified conditions for NaOH were the concentration of NaOH3%(w/w), modified temperature25℃C, the modified time5h; and the optimal modified conditions for SDBS were the concentration of SDBS5g-L-’, the modified temperature35℃, the modification time5h.The quality of biomaterial is the key factor that affects the sorption potential. The surface characteristics and active groups of adsorbents were identified by using scanning electron microscopy, specific surface area measurements, Fourier transform infrared spectroscopy, X-ray diffraction analysis, Bohem titration and so on. The analysis showed that: the palm thread modified with NaOH and SDBS became more rough and their microtoubule structure expanded; Ash-PT retained the basic framework of the palm thread.Compared to PT, specific surface areas of NaOH-PT, SDBS-PT and Ash-PT were increased by232%,116%and408%. NaOH modification could effectively improve the relative content of cellulose in adsorbent.Relative PT of NaOH-PT, SDBS-PT and Ash-PT specific surface area were increased by232%,116%and408%. NaOH modification can effectively improve the relative content of cellulose adsorbent; SDBS was effectively grafted onto the surface of the palm thread; the active SiO2of Ash-PT was fully exposed. The total acidic groups of the three adsorbents were reduced, while the total basic groups increased.PT and NaOH-PT were successfully appied to sorb Ni (Ⅱ), Cd (Ⅱ), Cr (Ⅲ) and Cr (Ⅵ). Many parameters that affected the sorption were investigated, such as contact time, temperature, initial concentration, solution pH, cation electrolytes, organic ligands and other heavy metal ions.The results showed:at25℃,300min was enough for PT and NaOH-PT to sorb Ni (Ⅱ), Cd (Ⅱ), Cr (Ⅲ) and Cr (Ⅵ) from solution; with the rise of temperature and initial concentration, the adsorption capacities of Ni (Ⅱ), Cd (Ⅱ), Cr (Ⅲ) and Cr (Ⅵ) onto the PT and NaOH-PT gradually increased. The solution pH had a severe influence on the adsorption process. The adsorption kinetics were well fitted the Lagergren pseudo-second order kinetic model; the data of Ni (Ⅱ), Cd (Ⅱ), Cr (Ⅲ) were well fitted both Langmuir isotherm model and Freundlich isotherm model, but the data of Cr (VI) just was well fitted Freundlich isotherm model. Compared to the PT, the adsorption capacities of Ni (Ⅱ), Cd (Ⅱ) and Cr (Ⅲ) onto NaOH-PT increased by190%,96%and104%; but for Cr (Ⅵ) was slightly reduced by1%. About adsorption process,△G<0,△H>0, AS>0,△H values was in the36-188kJ-mol-1range, AS values was in the90-217-(mol·K)-1range, the adsorption process is spontaneous and endothermic reaction.The SDBS-PT were used to sorb Ni (Ⅱ), Cd (Ⅱ), Cr (Ⅲ) and Cr (Ⅵ) from water. The effect of contact time, temperature, initial concentration and solution pH were investigated The results showed:at25℃, the adsorption could reach equilibrium about300min; compared to PT, the adsorption capacities of Ni (Ⅱ), Cd (Ⅱ), Cr (Ⅲ) and Cr (Ⅵ) increased by55%,45%,78%and17%。 The solution pH had different influences on the adsorption process of Ni (Ⅱ), Cd (Ⅱ), Cr (Ⅲ) and Cr (Ⅵ). The adsorption kinetics were well fitted the Lagergren pseudo-second order kinetic model and Langmuir isotherm model, the adsorption process belongs to chemical adsorption.The Ash-PT were applied to adsorb cation, such as Ni (Ⅱ), Cd (Ⅱ) and Cr (Ⅲ), and many parameters and adsorption characteristics were studied. Compared to PT, the capacities of Ni (Ⅱ), Cd (Ⅱ) and Cr (Ⅲ) onto Ash-PT increased by2800%,1500%and1900%. The cationic electrolytes (Na+, Ca2+and Fe3+)of the solution would effect the adsorptions of Ni (Ⅱ), Cd (Ⅱ) and Cr (Ⅲ), and the affected order was Fe3+>Ca2+>Na+; the organic ligand of solution would reduce the adsorption capacity, and the competitive adsorption was existed between the different heavy metal ions. The kinetics of the adsorption process were well fitted the Elovich kinetic model, pseudo-first-order kinetic model and pseudo-second order kinetic model. Langmuir isotherm model could simulate the experimental results very well(R2>0.99). The thermodynamic study showed that, Ash-PT adsorption processes were spontaneous endothermic reaction, and elevated temperatures were conducive to the adsorption process.