Application Of Modified Chitosan In Removal Of Heavy Metals From Water

The heavy metal elements in the aquatic environment are highly toxic and difficult to degrade.The enrichment and accumulation in the human body is difficult to be excreted.Therefore,the removal of heavy metals in the aquatic environment is a hot issue of scholars at home and abroad,but the conventional method is high in cost,high in energy consumption,complicated in operation,poor in removal effect,or inefficient in removal,and has a long duration.Therefore,it is one of the methods to solve the problem to find a new type of heavy metal element adsorbent which is cheap,environmentally friendly and has a good effect on heavy metal treatment.In this thesis,chitosan modified by acrylic acid cross-linking was used as adsorbent,and the effect of the amount of each reagent on the adsorption performance of the material was analyzed by orthogonal experiment with the composite of nano-ferric oxide.Modified chitosan magnetic adsorption material has high adsorption efficiency,good separation performance and recyclability.For studying on the adsorption behavior of simulated wastewater and simulated bottom sediment,we change the pH value of the solution to be adsorbed,the initial concentration of the solution to be adsorbed,the adsorption time,the adsorption temperature and other parameters,calculate the adsorption capacity of the three materials when initial concentration of the lead,cadmium and copper solution is 100 mg/L.When the pH of the solution was 5 and the temperature of 25°C,the adsorption performance of the two materials to the three ions was optimized.For Pb²⁺,the adsorption capacities of unmodified materials,acrylic modified materials and acrylic modified magnetic materials are 103.35 mg/g,197.05 mg/g and 147.13 mg/g,respectively;for Cd²⁺,adsorption of three materials The capacities were 93.75 mg/g,159.88 mg/g,and131.80 mg/g,respectively.For Cu²⁺,the adsorption capacities of the three materials were 71.92 mg/g,147.45 mg/g,and 113.13 mg/g,respectively.The adsorption properties of the modified materials on the three ions are better than those of the unmodified materials.When the adsorption time of the three kinds of ions reaches 2days,the two materials reach saturation,the adsorption amount does not change.By fitting the isothermal adsorption data of the three ions by two materials,it was found that the isotherm adsorption process of the three ions is better for the Langmiur adsorption model,so it can be inferred that the adsorption process is the uniform surface monolayer chemical adsorption.The theoretical saturated adsorption capacity obtained by the Langmiur adsorption model fitting equation is close to the actual saturated adsorption capacity.The adsorption kinetics and thermodynamic behavior of acrylic acid modified chitosan adsorbent and acrylic modified chitosan magnetic adsorbent for Pb²⁺,Cd²⁺and Cu²⁺ions were investigated.It was found that the adsorption of Pb²⁺,Cd²⁺and Cu²⁺ions by the two materials are chemical adsorption,physical adsorption and internal diffusion mainly,which chemical adsorption was dominant.The adsorption of Pb²⁺,Cd²⁺and Cu²⁺ions at 20°C to 40°C is endothermic reaction process.The adsorption process of Pb²⁺,Cd²⁺and Cu²⁺ions in the bottom sediment sample was investigated by using acrylic modified chitosan magnetic adsorption material.0.01 mol/L nitric acid solution,0.1 mol/L acetic acid solution,0.008 mol/L EDTA solution and the chitosan solution were used as extractants to extract Pb²⁺,Cd²⁺and Cu²⁺ions in the sediment samples,compared with the adsorption effect of acrylic acid modified chitosan magnetic adsorption materials,it was found that its adsorption effect was better than other extractants.The extraction efficiency of Pb,Cd and Cu elements in the sediment was 73.18%,71.12% and 69.26%respectively.