Removal Of Heavy Metal Ions In Aqueous Solution And Municipal Solid Waste Incineration Fly Ash Via Adsorption By Nanoparticles Of Illite-Smectite Clay

Heavy metal ions pollution is one of the main problems, which can cause serious threat to the ecological safety and human health. Adsorption as an effective method has been widely used in waste water treatment. Due to the unique layered structure and fine particle size, clay minerals that are cheaper and chemical stable as well as have adsorption and ion exchange abilities, are often used in the adsorption of heavy metal ions in water. Illite/Smectite（I/S） clay as a transition type of minerals, which smectite under the diagenesis transforms to illite, is one of typical layered silicate minerals. However, little work on the use of I/S clay as an adsorbent for heavy metal ions treatment and disposal have been reported so far. The objective of this dissertation is to prepare nanoparticles of I/S clay for removal of heavy metal ions in water and municipal solid waste incineration（MSWI） fly ash. The adsorption behavior of nanoparticles of I/S clay for removal of heavy metal ions under different conditions was investigated.Firstly, nanoparticles of I/S clay were obtained via purification, superfine grinding, drying, surface modification and dispersion. The results show that the grinding time has a great effect on the grinding efficiency and the product fineness. Nanoparticles of I/S clay after refining process as a natural two-dimension nano-structured material appear a thin layer structure with the fineness of less than 100 nm of approximately 64%, surface area of 72.21 m2/g.Secondly, the nanoparticles of I/S clay were used for adsorption of each heavy metal ions like zinc（Zn）, cobalt（Co）, chromium（Cr）, cadmium（Cd）, manganese（Mn）, lead（Pb）, copper（Cu） and nickel（Ni） in water. Four affecting factors such as pH value of the solution, fineness of clay, adsorption time and amount of clay were selected in the orthogonal adsorption experiments. The adsorption for each heavy metal ions on nanoparticles of I/S clay in water was investigated. The results of orthogonal experiments show that besides Zn²⁺ ions, an order of four factors affecting the adsorption of each heavy metal ions onto nanoparticles I/S clay is the amount of I/S clay > clay fineness > pH value of the solution> adsorption time, and the effective adsorption can be achieved under the optimum conditions（i.e., solution pH value of 4.2, clay fineness of 55% less than 100 nm, adsorption time of 3.0 h, and clay addition amount of 10.0 wt.%）. In addition, the adsorption of each heavy metal ion onto dry and wet nanoparticles of I/S clay at different initial concentrations of each heavy metal ion in water was also investigated. Furthermore, the nanoparticles of I/S clay were used for adsorption of a mixture of eight heavy metal ions in water. The results show that the effective adsorption for all heavy metal ions in water onto nanoparticles of I/S clay mineral can be achieved, and the removal efficiencies of the heavy metal ions are over 80%. In addition, the use of high-shear mixing can enhance the adsorption for heavy metal ions onto the nanoparticles in water. Also, there exists a certain degree of competitive adsorption for heavy metal ions onto the nanoparticles in water, an order of competitive adsorption is Pb²⁺ > Cu²⁺ > Zn²⁺ > Cd²⁺. The ionic radius of heavy metal ions has an influence on the adsorption in water, heavy metal ions with high valence and small ionic radius are more easily adsorbed on the particle surface.Then, nanoparticles of I/S clay were used for the adsorption of Cu²⁺ and Cd²⁺ ions in water. The effects of parameters like solution pH value, amount of I/S clay, adsorption time, adsorption temperature and concentration of heavy metal ions on the adsorption performance of Cu²⁺ and Cd²⁺ ions onto the nanoparticles were investigated. In addition, the dynamics, thermodynamics and isotherm for the adsorption were analyzed. The results show that the adsorption amount of Cu²⁺ and Cd²⁺ ions increases with the increase of pH value, and the amount is stable when pH > 4. The maximum adsorption efficiency of Cu²⁺ and Cd²⁺ ions under the optimal condition is 95.15% and 91.53%, respectively. The adsorption kinetic was discussed based on the pseudo-first-order and pseudo-second-order kinetic models, indicating that the adsorption process for Cu²⁺ and Cd²⁺ ions follows the pseudo-second-order kinetic model. According to the thermodynamic analysis, the adsorption of Cu²⁺ and Cd²⁺ ions onto the nanoparticles in water is a physical process. The adsorption isotherm data were analyzed by the Langmuir and the Freundlich isotherm models, respectively. The results show that the adsorption process follows the Langmuir isotherm model. The Langmuir monolayer maximum adsorption capacities of nanoparticles of I/S clay for Cu²⁺ and Cd²⁺ ions are 7.99 mg/g and 12.68 mg/g, respectively.The adsorption process for heavy metal ions(i.e., Zn²⁺、Pb²⁺、Cu²⁺ and Cd²⁺ ions) in MSWI fly ash on I/S clay was also investigated. The results show that the removal efficiencies for Zn²⁺、Pb²⁺ and Cu²⁺ ions are above 90%, but that of Cd²⁺ ion is only 50% when 10 wt.% of I/S clay is used in MSWI fly ash leachate. The removal efficiencies for Zn²⁺、Pb²⁺、Cu²⁺ and Cd²⁺ ions in fly ash long-term landfill leachate are above 50% at 20 wt.% of nanoparticles of I/S clay. The adsorption at different amounts of chemical additives was also analyzed. It is indicated that when 1 wt.% of sodium sulfide is added, most of heavy metal ions in the leachate can be removed, the removal efficiency is more than 90%.Finally, the dissertation gives the major conclusions and some future work based on the experimental results obtained.