Preparation Of Adsorbent Based On Marine Product Wastes And Its Adsorption Property For Heavy Metal Ion

With the development of modern industry and the urbanization, the discharge of heavy metal wastewater is increasing. The problem of heavy metals pollution is getting more and more serious, and it causes great harm to environment and human health. The conventional physicochemical methods for removal of heavy metal from wastewater have many problems, such as great investment, complicated operation, difficult to achieve standard discharge and causing secondary pollution, etc. Some methods were restricted by high cost in the field of water treatment. Therefore, it is urgent to search for a new method which is effective and environment-friendly. In recent years, biological adsorption method is being highly concerned because of its characteristics of highly effective, simple operation, rich sources of raw materials, environment-friendly in heavy metal wastewater treatment, especially for the treatment of lower concentrations heavy metal wastewater. Thus, the biological adsorption method is progressively used to remove heavy metals from the viewpoint of economics and environmental protection.Marine product wastes (including crab shell and fishbone) are nature and low-cost industrial by-products. Those marine product wastes are very hard and difficult to be disposed, but these materials can form stable chelate with heavy metal ions by amino, hydroxyl etc, and some ions on its surface can exerts a concerted effect of ion exchange with heavy metals. If recycle to prepare a new absorbent is a environment-friendly method of changing waste into valuables, which can reduce the cost of sewage treatment.In this topic, crab shell and fishbone were used as raw materials to preparate absorbent. The adsorption property of these bioadsorbents for heavy metal ions studied through the static adsorption test. The adsorption kinetics and adsorption isotherms were studied systematically. The modification mechanism of crab shell and adsorption mechanism of new biological adsorbents absorbing heavy metals were discussed. The main results are as follows:(1) Crab shellThe crab shell were modified by FeCl3, C6H8O7 · H2O and NaCl, respectively. The results indicate that the CSCA modified by C6H8O7 · H2O has good adsorption affinity for Pb2+, and compared with CS, the removal rate can be improved about 27.52%. The CSSC modified by NaCl was most effective for the elimination of Cd2+, the removal rate can be improved about 13.72%.Study on adsorption kinetics, adsorption isotherms, and influencing factors:the analysis of relating impact factors shows that the lower pH and the higher dosage (>2.0 g/L) was, the smaller the adsorption capacity of CSCA, and the lower pH and the higher dosage (>0.3 g/L) was, the lower efficient of CSSC. The adsorption behavior of CSCA and CSSC met the pseudo-second-order model, and the adsorption process is controlled by film diffusion and particle diffusion. The equilibrium data of Pb2+ on CSCA was better fitted by using Langmuir models and the adsorption capacity was 4.989mg/g. The adsorption precess of Cd2+ on CSSC fitted for Freundlich adsorption isotherm, and the maximum Cd2+ adsorption was 2.503mg/g with the original Cd(Ⅱ) concentration of 0.76 mg/L(pH=6, T=40 ℃,0.3 g/L biomass dose).The comparative analysis between CS and CSCA, CSSC in BET, FTIR, SEM-EDX showed that the structural morphology of CSCA and CSSC become rough porous, surface area was inereased. The carboxyl groups and Na+ were introduced onto the surface of CS. These changes were beneficial to absorbing metal ions. The adsorption mechanisms mainly involves physical adsorption, electrostatic attraction present in hydroxyl and metal ions, coordination complexation reaction because of N-H, O-H and C-Cl, and ion exchange reactions of Cd2+ with Na+ in surface of CSSC.(2) FishboneFishbone was degreased by the mixture of NaOH and detergent to prepare effective adsorbent.Study on adsorption kinetics, adsorption isotherms, and influencing factors:fishbone adsorbent (FIBA) has good adsorption effect on Pb2+, Cd2+ and Cu2+. At the initial concentration of Pb2+10 mg/L and Cd2+0.88 mg/L, the highest metal uptake for Pb2+, Cd2+ were 33.389mg/g,1.851mg/g (pH=6, T=40 ℃,0.3 g/L biomass dose). The maximum Cu2+ adsorption was 49.773mg/g with the original Cu(II) concentration of 50 mg/L(pH=5, t=6h, T=40 ℃,1.0 g/L biomass dose). The residual metal ions concentration in treated water was less than the standard of Surface Water Environment Quality Standard (GB3838-2002). The kineties of heavy metal ions adsorption followed pseudo-second-order, and the Intra-particle diffusion was not the only rate-limiting step. The adsorption rate constant increased with temperature increasing, this shows that temperature increasing is conducive to the adsorption reaction. Compared with Langmuir model, Freundhch model is more suitable for describe the adsorption course, which indicate that the adsorption of Pb2+, Cd2+ and Cu2+ on FIBA belongs to multilayer adsorption. All of the values of the characteristic parameters (1/n) are less than 1, the results showed that FIBA exhibited high adsorption capacity for Pb2+, Cd2+ and Cu2+.According to EDX spectra of FIBA before and after the adsorption of Pb2+, Cd2+ and Cu2+, FIBA can effectively adsorb Pb2+, Cd2+ and Cu2+ because of the appearance of characteristic absorption peaks of products and the changes of elemental contents of Na, P, Ca and O. The adsorption mechanisms of Pb2+, Cd2+ and Cu2+ on FIBA are similar to each other, they mainly consist of physical adsorption, ion exchange reactions of Pb2+, Cd2+ and Cu2+ with Na+, Ca2+ in surface of FIBA, and coordination complexation reaction because of N-H, O-H, C-O-C and C-Cl.