Preparation Of Novel Chitosan Hydrogel And Its Adsorption Properties For Heavy Metals

Heavy metal, due to non-degradability, toxicity, secondary pollution, and accumulation nature of heavy metals through a food chain, has become a direct threat to the survival of humanity and all kinds of creatures. In recent years, the events of water pollution by heavy metals occur frequently, which is becoming a severe issue to the environment and human society. Therefore, how to effectively remove heavy metals from wastewater have become an unavoidable environmental and social issues. Up to now, traditional treatment methods, including chemical precipitation, electrolysis, ion exchange, etc.,are applied to remove heavy metals, which have some disadvantages such as poor treatment effect to low concentration wastewater, secondary pollution, etc. Therefore, finding a effective method attracts attention of each researchers. Adsorption has been recognized as one of the most popular methods because of its wide range of application, environmentally friendly, no secondary pollution, etc. Among many adsorbents, hydrogels, as a polymeric material, which have porous three-dimensional network structure, can swell while holding large amounts of water and keeping insolution.A large number of active groups in the molecule that can adsorb metal ions by chelation, ion exchanging and forming ion pairs etc. Above all, hydrogels can effectively remove heavy metal ions in wastewater with great development potential and broad prospects.In this paper, a novel chitosan hydrogel was prepared by chitosan and N, N'-methylene-bis-acrylamide.Characterization the hydrogel surface morphology, thermal stability, and radical elements by SEM, TG, FT-IR and XPS.By examining the adsorption time, initial concentration, temperature, pH and other factors experiments, examine its impact on the three heavy metals adsorption efficiency, Investigate their impact on the adsorption performance of Pb2+,Ni2+and Cr3+.Adsorption mechanism of heavy metals on chitosan hydrogel by EDS. Conclusions are as follows:1)A successful novel hydrogels was prepared with chitosan as raw material, ammonium persulfate as initiator, acrylic as graft monomer, N,N'-methylene-bis-acrylamide as crosslinking agent Temperature oscillation for 3 h at 60 degrees Celsius.Ammonium persulfate and N, N'- methylene-bis-acrylamide dosing volume will affect the chitosan hydrogel for the three heavy metal ions removal, Chitosan Hydrogel has best removal ability when ammonium persulfate and N, N'-methylene-bis-acrylamide is ratio of 5:1.SEM analysis showed that the chitosan hydrogel is a specific surface area macroporous material.2) Through batch experiments examined the influence of dosage, temperature, pH, initial metal ion concentration for removal effect. The study found that under the same conditions, chitosan hydrogel has a low removal rate in a short period of time. As time increases, the removal rate increases, equilibrium is reached at 48 h. Increase the amount of hydrogel, the reaction temperature can improve the efficiency of three kinds of heavy metal ions; When the pH of the solution is acidic, chitosan hydrogel has a better removal capacity of Pb2+, Ni2+, Cr3+.A greater impact on the initial concentration for chitosan hydrogel adsorption of metal ions, Competitive priority is Pb2+>Ni2+>Cr3+, With the increase of initial concentration, chitosan hydrogel for Pb2+, Ni2+, Cr3+ removal rate decreased, the higher the concentration, the lower the removal efficiency.3) By examining the competitive adsorption of three heavy metals, it is turn out when the initial metal concentration was 1 mmol/L,the competitive priority for the heavy metal ions: Pb2+>Ni2+>Cr3+.Competitiveness of Pb2+ is significantly better than Ni2+?Cr3+, Ni2+ similar to Cr3+. Competitive adsorption of heavy metal ions is mainly by the negative impact of metal electrodes, electronegativity greater the competition the greater. Compared single Adsorption and competitive adsorption can be found, removal of different components of heavy metal ions have decreases, indicating there is competition between the three heavy metals. Also shows the same type of active centers on the role of metal ions. When high concentrations of heavy metals, active adsorption sites hydrogel is saturated, heavy metal ions will compete with each other for it. Heavy metal ion at the active site, the stronger the force the removal of the larger, that the stronger competitive.4) By examining the adsorption kinetics and adsorption isotherm can be found, the correlation coefficient of quasi-order kinetic model is less than quasi-second-order kinetic model. And curve fitting pseudo-second adsorption kinetics model showing a good linear relationship(R2>0.99). Showed that chitosan hydrogel for three heavy metals adsorption reaction well described by the pseudo second-order kinetic model. While the adsorption isotherm study can be found, chitosan hydrogel for three heavy metals ions more in line Langmuir adsorption isotherm. Description chitosan hydrogel for adsorption of heavy metal ions belonging monolayer.