Studies On Modifying And Application Of Bentonite In Wastewater Treatment

With the rapid development of industry and agriculture, more and more severe environmental problem has been caused, especially heavy metals pollution. It has been received much attention by governments and researchers in worldwide. Because of the adsorption properties, the bentonite has been employed in the heavy metal waste-water treatment. However, its physical adsorption or ionic exchanges are all reversible, which cause low removing effect. In this thesis, the bentonite is modified by xanthated, which obtain a new kind of water treatment chemicals. They can both remove heavy metal ions and organic compounds.Firstly, on the basis of introducing the modification methods of bentonite and their application, we summarize the problem of modifying and foresee the prospect of the modified-bentonite.Secondly, a series of the xanthate-bentonites (XB) were prepared for the first time. They were characterized by FT-IR spectra, TGA/DTA and XRD. Their images and grain size were analyzed via photos, SEM and grain size distribution.Thirdly, we have investigated the adsorption ability of XB towards heavy metal ions (Pb²⁺, Cu²⁺ and Cr⁶⁺). (1) We have treated the Pb²⁺ containing simulated wastewater using XB as adsorbent. The optimal condition is as following: [Pb²⁺]: 500mg/L, XB: 2g/L, pH: 5.0, oscillating 60min in 25℃. Under the condition, the removal rate reached to 99.92%. The effluent meet the class I of National Intergated Wastewater Discharge Standard (GB8978-1996). (2) We also have treated the Cu²⁺ containing simulated wastewater using XB as adsorbent. The optimal condition is as following: The optimal condition is as following: [Cu²⁺]: 80mg/L, XB: 2g/L, pH:6.0, oscillating 60min in 25℃. Under the condition, the removal rate reached to 99.92%. The effluent meet the class I of National Intergated Wastewater Discharge Standard(GB8978-1996). At the same time, we have discovered that the separation of solid-liquid is very easy. (3) XB was also used to treat the electroplate wastewater. The result indicates that XB has high adsorption ability towards Cu²⁺and Cr⁶⁺.Fourthly, we have investigated the adsorption ability of XB towards dye, such as methylene blue, methyl orange and alizarin red. The result indicates that XB has much higher adsorption ability than natural bentonite. For instance, under the dosage of 2g/L and initial concentration of 100 mg/L, the decolor rate of methyl orange with natural bentonite and XB are 17.75% and 91.84%, respectively.In finally, we have modified bentonite with other seven methods, which gained a series of bentonite-inorganic-polymer flocculants. They were also applied to treat starch waste-water, and domestic sewage in partly. Thereinto, the effluents is clarifying and limpidity after the treatment of composite bentonite flocculant (NBF and PBF), the removal effect of suspension and COD is high. The effect of pH in treatment of starch waste-water were investigated in primary.