Preparation Of Composite Modified Bentonite And Its Application In The Adsorption To Cadmium

With the development of human society, water becomes more and more important. However, in the industrial and agricultural production and human life, large amounts of sewage containing heavy metals does not meet the emissions standards, but are directly discharged into the water, leading to heavy metals in excess of the standards in the river or lake, and the clean water significantly reduce. Therefore, the treatment of heavy metal pollution in the water body is imminent. Bentonite is a kind of natural clay mineral. It is rich in reserves and has a certain ability of adsorption to heavy metals. In this paper, the present situation of heavy metal pollution in water body, the properties, modification and application of bentonite(Bt) were reviewed. The modification of bentonite(M-Bt) was performed using the 3-aminopropyltriethoxysilane(y-APS) and sodium silicate(Na2SiO3), and the composite modified bentonite was applied to the adsorption of cadmium in wastewater. The main research works and results were as follows:1. The composite modified bentonite(M-Bt) was performed using the 3-aminopropyltriethoxysilane(y-APS) and sodium silicate(Na2SiO3) as main and auxiliary modifier, respectively. The preparation conditions were optimized by the adsorption test of Cd(?) in water. The optimum ratio of Bt to y-APS dosage was 1:1(g/mL); the dosage of Na2SiO3 was 10% of Bt quality; the ratio of liquid-solid was 40:1(mL/g); the pH was at 10; and the reaction lasted 3 hours at room temperature. The composite modified bentonite was characterized by Fourier transform infrared spectroscopy(FTIR), X-ray diffraction(XRD) and thermo gravimetric analysis(TGA). The y-APS successfully intercalated in the interlayer space of Bt and suggested a parallel-bilayer arrangement. The surface hydrophilicity of M-Bt decreased.2. The adsorption properties of the M-Bt to Cd(?) were discussed. When the amount of M-Bt was 5 g/L, the solution pH was 6.5, the ionic strength was 0.1 mol/L KNO3 medium, and in room temperature, the saturated adsorption amount of the M-Bt to Cd(?) reached to 32.5mg/g, which significantly improved compared with Bt(1.38 mg/g). The composite modified bentonite might be used as a treating agent for heavy metal polluted water body in the future.3. The adsorption mechanism of M-Bt to Cd(?) was discussed by thermodynamic and kinetic adsorption experiments. The adsorption of M-Bt to Cd(?) was in accordance with the Langmuir isotherm equation, and the correlation coefficients reached more than 0.99. The thermodynamic parameters (?G=-18.19 KJ/mol??H=17.24 KJ/mol, AS=118.88 J/mol·K) showed that the adsorption process was spontaneous and endothermic, and the increase of temperature was beneficial to the reaction, and the adsorption of M-Bt to Cd(?) was a chemical adsorption process. The adsorption kinetics of Cd(?) at different concentrations could be described by a quasi-second order kinetic equation, and the correlation coefficient was above 0.99. In the adsorption process of M-Bt to Cd, the chemical adsorption rate dominated the adsorptive steps, and the chemical adsorption was affected by the surface properties of the adsorbent.4. The dynamic adsorption of Cd(?) on Bt and M-Bt was carried out by using the down-flow-fixed-adsorption column (abbreviated as adsorption column). A mathematical model for the treatment of wastewater containing Cd(?) in the dynamic adsorption process was obtained. Through the relationship between adsorbent dosage(m), initial concentration of Cd(?) in the adsorption solution(co), cadmium discharge of national standards<GB 8978-1996 sewage comprehensive discharge standard) (0.lmg/L) and direct discharge volume after primary treatment(?). In this model, the amount of Cd(?) wastewater discharged was positively correlated with the amount of adsorbent, and negatively correlated with the initial concentration of Cd(?) in wastewater. The Cd(?) wastewater treatment model was established, which could provide theoretical guidance in amplification experiment for the M-Bt treatment of Cd(?) wastewater.