Preparation Of Novel Composite Adsorbents Based On Polymer Matrix And The Research On The Adsorption Of Heavy Metals In Aqueous Solutions

The wastewater containing heavy metals produced from various human activities was discharged into the natural environment and caused soil, surface water and groundwater pollution, which has become the serious threat to the ecological environment, public health and the sustainable development of social economy. How to effectively remove the heavy metals in aqueous solution, various treatment technologies and methods have been attracted great attention by researchers and the governments around the world. Adsorption is one of the most effective and promising technologies used to remove heavy metals due to its simplicity, high efficiency, easy handing and no sludge generation. In recent years, various efforts have been focused on the research and development of novel adsorption materials with excellent properties such as large adsorption capacity and high selectivity, fast adsorption rate, easy separation and reusability, low cost, simple preparation, no secondary pollution.This paper summarized the present situation and the harm of heavy metals pollution, the development of technologies and methods for treatment of heavy metals at home and abroad, the development of adsorption technology for removal of heavy metals from aqueous solutions, and the preparation and application of novel composite adsorption materials. Based on the excellent properties of polymer, poly(vinyl alcohol) and sodium alginate were chosen as the supporter. Seven different kinds of polymer-based composite adsorbents were prepared including PVA/CS foam, PVA/CS beads, PVA/CS/ATMPZ beads, PVA/ZrN beads, PVA/CNTs-NC beads, Fe3O4@SA-Zr beads and Zr-DETA/TA/SA-Ca beads. These new adsorbents were characterized by FTIR, XRD, SEM, TGA, XPS, and so on. Tests were then conducted to study their adsorption performance for heavy metal ions and the effects of experimental parameters such as solution pH, initial metal concentration, contact time, temperature, ionic strength, humic acid and competitive ions on the removal of heavy metal ions were investigated in batch systems. Isotherms, kinetic and thermodynamic models were used to fit the experimental data to understand the adsorption mechanisms and the rate-limiting step. FTIR and XPS were used to analyze the mechanisms involved in the adsorption of heavy metals. Desorption efficiency and regeneration potential of novel adsorbents were studied by using various desorbing agents and several adsorption-desorption cycles were repeated to evaluate the reusability. The ability of novel adsorbents to remove heavy metal ions was further conducted by using the fixed-bed continuous column and breakthrough curves were analyzed at different flow rates and influent metal concentrations. Thomas model was used to analyze the dynamics of the adsorption column.1. A novel composite foam of PVA and CS was prepared by using CaCO3as forming agent and cryogenic-thawed treatment. Batch adsorption experiments were carried out to study the ability of PVA/CS foam to remove heavy metal ions from aqueous solution. The results showed that the introduction of CS not only enhanced mechanical strength, chemical and thermodynamic stability, but also improved the adsorption capacity. Different mass rations of PVA/CaCO3/CS had a significant effect on the adsorption of PVA/CS foam. The maximum adsorption capacity of PVA/CS foam was193.39mg/g, and removal efficiency of Cu2+was higher at lower metal concentration. Equilibrium data of Cu2+onto PVA/CS foam was best described by Langmuir isotherm and adsorption was a spontaneous and endothermic process. PVA/CS foam exhibited rapid adsorption rate, kinetic data was followed the pseudo-second order model, intraparticle diffusion was the rate limiting step and chemical and physical adsorption were involved in the adsorption process, which may be due to the network structure and many functional groups such as amine and hydroxyl groups. Finally, desorption efficiency and reusability of PVA/CS foam were assessed based on six consecutive adsorption-desorption cycles.2. Novel macroporous PVA/CS beads were prepared by using CaCO3as pore-forming agent and boric acid as cross-linking agent. Batch adsorption experiments were carried out to study the ability of PVA/CS beads for the removal of heavy metal ions from aqueous solution. The results showed that PVA/CS beads had the macroporous and three-dimensional network structure. PVA and CS exhibited a synergistic effect on removal of heavy metal ions. PVA/CS beads adsorbed heavy metals in the following order:Cu2+>Pb2+>Cd2+>Zn2+and showed faster kinetics for Pb2+and Cd2+than for Cu2+and Zn2+. PVA/CS beads could selectively remove Cu2+ions from the mixed-metal solution. In order to broaden the scope of application of PVA/CS beads, organic P doped PVA/CS/ATMPZ macroporous beads were prepared. PVA/CS/ATMPZ beads significantly enhanced the adsorption capacity and selectivity towards Pb2+ions, improved the adsorption rate and the efficiency in a wide range of pH. Various isotherm models (Langmuir, Freundlich, Tempkin and D-R), kinetic model (pseudo-first order, pseudo-second order and intraparticle diffusion) and thermodynamic models were used to study the mechanism and the rate-limiting step. The desorption efficiency and reusability of the adsorbents were assessed based on the consecutive adsorption-desorption cycles. Finally, dynamic experiments were conducted by using the fixed-bed continuous-flow column to further evaluate the potential of PVA/CS/ATMPZ for Pb2+removal.3. Amine functionalized ZrO2(ZrN) was prepared and was then embedded into PVA to form spherical macroporous adsorbent (PVA/ZrN). The adsorption performances of ZrN和PVA/ZrN for heavy metal ions in aqueous solution were studied in batch mode. It was found that the introduction of amine significantly improved the adsorption capacities for Hg2+, Ag+, Cu2+ions. The maximum adsorption capacities of PVA/ZrN beads for Hg2+, Ag+. Cu2+were higher than several adsorbents reported in the literature. The adsorption data of Hg2+, Ag+, Cu2+onto ZrN was best fitted the Langmuir isotherm while those onto PVA/ZrN followed the Freundlich isotherm. The kinetics was found to follow the pseudo-second order kinetic model. Surface adsorption, intraparticle diffusion and chemical reaction were involved in the adsorption process. From FTIR and XPS results, new complexes were formed between metal ions and nitrogen in amine groups and oxygen in hydroxyl groups through chelation and/or ion exchange.4. This work evaluated the macroporous PVA/CNTs-NC beads containing hydroxyl, carboxylate and amine groups for removing target pollutants Pb2+and Cu2+from aqueous solutions in batch and column modes. CNTs-NC exhibited higher adsorption capacities and efficiencies, rapid adsorption rate and wide application of pH for Pb2+and Cu2+ions. While adsorption capacities of PVA/CNTs-NC for Pb2+and Cu2+were lower than those of CNTs-NC. However, the spherical adsorbents were very easily separated from the solution and reused, which was especially important for continuous flow operations. The adsorption of Pb2+and Cu2+onto CNTs-NC and PVA/CNTs-NC was well described by Langmuir isotherm, indicating a monolayer adsorption. it was found that the adsorption rate of Pb2+was faster than that of Cu2+, surface adsorption and intraparticle diffusion were involved in Pb2+and Cu2+adsorption. FTIR and XPS indicated that nitrogen in amine groups and oxygen in carboxylate groups were the main active sites for metal ions binding. In column studies, PVA/CNTs-NC exhibited excellent performances in the removal of Pb2+, higher adsorption capacity and efficiency were obtained at low influent metal concentration and flow rate. Moreover, adsorption-desorption operations showed that PVA/CNTs-NC was a good reusable adsorption material.5. A novel magnetic sodium alginate-zirconium(IV) composite beads (Fe3O4@SA-Zr) were prepared by using Zr(IV) as the crosslinking ions and used as an adsorbent for the selective removal of Pb2+from aqueous solution by batch and fixed-bed column systems. The prepared Fe3O4@SA-Zr had the spherical and macroreticular structure, good stability and magnetic separation. Almost100%of Pb2+was removed by Fe3O4@SA-Zr when the initial metal concentration was lower than200mg/L. The competitive adsorption showed that Fe3O4@SA-Zr beads had good adsorption selectivity for Pb2+with the coexistence of Cu2+, Zn2+, Cd2+, Hg2+. Langmuir isotherm fitted the experimental data well and the maximum adsorption capacity was333.33mg/g. The kinetics was found to follow the pseudo-second-order model and the adsorption rate was controlled by a chemical sorption process. In the column study, flow rate and influent metal concentration significantly affected the shape of breakthrough curves, higher flow rate and influent metal concentration resulted in the earlier breakthrough time and exhaustion time. The dynamic adsorption of Pb2+by Fe3O4@SA-Zr followed the Thomas model. The adsorption capacity of Fe3O4@SA-Zr for Pb2+ions was maintained92%after10successive adsorption-desorption cycles.6. A novel polymer based on inorganic hybrid, Zr-(EDA/DETA/TETA), was prepared through the reaction Zr(Ⅳ) with three types of amine (EDA/DETA/TETA), which was then embedded into TA and SA-Ca organic polymer network and formed organic/inorganic ionically crosslinked polymer gel beads. The adsorption properties of Zr-(EDA/DETA/TETA)/TA/SA-Ca for Pb(Ⅱ), Hg(Ⅱ),Cr(Ⅵ) ions were studied by using the batch and column operations. Zr-DETA/TA/SA-Ca had the highest adsorption efficiencies for Pb(Ⅱ), Hg(Ⅱ) and Cr(VI) among all the beads prepared and the maximum adsorption capacities were reached to379.75,421.15和131.15mg/g, respectively. The equilibrium data of Pb(Ⅱ), Hg(Ⅱ) and Cr(Ⅵ) ions was fitted the Langmuir isotherm, indicating a monolayer adsorption. From kinetic studies, it was found that the adsorption rate of Pb(Ⅱ) and Hg(Ⅱ) was faster than that of Cr(VI) ions and reached the equilibrium around120,120and780min, respectively. For all the metal ions studied, chemical reaction may be the rate-controlling step and the pseudo-second-order kinetic model provided the best correlation of the experimental data. Importantly, Zr-DETA/TA/SA-Ca was able to remove97%of Cr(Ⅵ) in actual electroplating wastewater containing Cr(Ⅵ). Cr(Ⅵ) concentration in the effluent was0.5mg/L or less which was lower than the wastewater discharge standard, indicating that Zr-DETA/TA/SA-Ca had the very good potential in practical application.