Preparation Of Cerium/Crab Chells Adsorbent And Its Adsorption Property For As (?) Ion

Due to its serious environmental harm as well as a variety of sources, arsenic pollution has long been of global concern. It has great practical significance to research arsenic removal technology. At present, the methods of removing arsenic mainly include chemical precipitation, coagulation, oxidation, ion exchange, biochemical, adsorption method and so on.In contrast, the adsorption method has advantages of wide material source, efficient, economical, easy operation.Arsenic adsorbents are mainly divided into two categories:inorganic adsorbents and organic adsorbents, according to the different chemical composition.However, there are many problems in the composition of single adsorbent.For example, activated carbon as an adsorbent for arsenic has the problems of low adsorption capacity, long cycle adsorption and other shortcomings.In recent years, the research of organic/inorganic composites has attracted widespread concern in the field of arsenic removal. Many excellent adsorbents were prepared with different kinds of composite materials.In this paper, a cerium/crab shell composite (CS-Ce) was prepared by a series of procedures, and the optimal conditions of CS-Ce prepared was determined according to arsenic removal efficiency:Particle size<0.2mm (80 mesh), content of hydrochloric acid was 6%, content of cerium nitrate was 8%, soaking time was 4h, drying temperature was 75?. SEM-EDX analysis showed that, compared with the CS, surface voids?specific surface area and pore volume of CS-Ce increased, element components of Ca?Mg?P were decreased, while C?O content increased and the element of Ce was introduced. BET analysis showed that the surface area and pore volume of CS-Ce were increased compared to CS. FTIR and XPS analysis showed that, part of the Ce3+was oxidized to Ce4+, during in the reaction process of CS and Ce, the hydro xy groups of CS molecular chain were deprotonated, Oxygen was bonded with Ce3+?Ce4+ by coordinated reaction, and N atoms was not involved in the reaction.The influence of the dosage, pH, initial concentration, background anions and other factors were studied by batch adsorption experiments. The results showed that the removal rate of CS-Ce for As (?) ions was significantly higher than that of CS, and the removal rate of As (?) ions increased with the increase of the dosage of the two adsorbents.Compared to CS, CS-Ce has a higher arsenic removal rate over a large range of pH (2-9), the pH of solution have varying degrees of increase after adsorption. Under certain conditions, the adsorption capacity increased with the increase of initial concentration.When the initial concentration was 400mg/L, the maximum adsorption capacity reached a maximum value of 71.10 mg/g; Cl-, NO3-, SO42- did little effect on the performance of CS-Ce for arsenic removal while high concentrations of PO4-, HCO3- did large effect on the adsorption.Data analysis showed that the date of CS-Ce exhibited a good fit with Langmuir adsorption isotherm model. According to the Langmuir adsorption isotherm equation, the maximum adsorption capacity were 62.150,67.705,71.788mg/g at 293k,303k,313k, which is similar to the test results.Thermodynamic analysis showed that the adsorption of As (?) ions by CS-Ce was a spontaneous, endothermic and entropy increasing process.Kinetic analysis showed that, at the initial concentration of As (?) ions were 2mg/L,10mg/L,the adsorption capacities of CS-Ce reached 0.988,4.866mg/g at an equilibrium time of 12 and 14h, respectively.The pseudo.second.order rate model could perfectly describe the adsorption of As (?)ions on CS-Ce, with the linear correlation coefficient R2 was larger than 0.99. Regeneration and recycling studies showed that with the increase of the number of cycles, CS-Ce arsenic removal efficiency decreased significantly.The changes of morphology^ element and functional groups before and after the adsorption are measured by scanning electron microscope% Energy Dispersive X-ray Detector and X-ray photoelectron spectroscopy. Research on mechanism of arsenic removal indicated that the interaction between the As (?)ions and CS-Ce was proposed to be depend on electrostatic attraction, and coordinated reaction occurred between As (?)ions and Cerium ions; the pH of solution have varying degrees of increase after adsorption may implied that ligand exchange reactions between surface hydroxyl groups and solution As (?) ions might take place during in the adsorption.