| Water is considered an important and scarce commodity in many countries round the world. However, the contamination of surface and ground water with heavy metals is a concern. Heavy metal pollution occurs in numerous industrial wastewater such as mining operations, battery manufacturing process, glass, paints and so on. Recently, some typical treatment methods have been developed for removing heavy metals from water, including precipitation, ion exchange, biosorption and adsorption and so forth.Diatomite is from the composition of amorphous SiO2 and containing a small amount of Fe2O3,CaO,MgO,Al2O3 and organic impurities. Diatomite is usually light-yellow or light-gray, soft, porous and light, commonly used in industry as insulation materials, filter materials, packing, grinding materials, silicate materials, decolorizing agents, such as catalyst carrier. At the same time, diatomite is a good adsorption of the environmentally friendly materials, especially the surface with negative electricity which is more conducive to the adsorption of heavy metals.Total reserves of diatomite in China is the second highest over the world, which has great potential for development, nevertheless most of them are generally low grade. As we all know, heavy metal is one of the main pollutant to harm human health. The traditional methods to remove heavy metal exist many shortcomings, such as high cost and secondary pollution. Research low-grade diatomite to remove heavy metals has far-reaching significance.To study lead, zinc, copper and cadmium using diatomite Adsorption in batch experiments, there were some impact of factors that were time, volume of soil, pH value and temperature. The adsorption of heavy metals in diatomite strongly was influenced by the pH value of solution. The acid (pH = 6) and the neutral conditions was benefit for adsorption. While it can soon reach the adsorption equilibrium, the adsorption capacity increased quickly in 10 minutes. With the increasing of using diatomite, the adsorption capacity rose. But the demand of diatomite to every heavy metal was different. The adsorption of Pb (Ⅱ) was the best, for example, the quality of diatomite with 10g / L can be able to reach the platform area. Temperature had little influence on the adsorption. Langmuir modelling exhibited a better fit to the data for zinc,copper and cadmium. And Freundlich model is better to lead. The pseudo-second-order equation fitted well with the experimental data.In a mixed system experiment, because the four ions interacted together, diatomite adsorption capacity of units declined. The most obvious decline appeared in zinc and cadmium.In the column adsorption test, while the speed of flow was 2.3±0.1mL/min, the breakthrough spot of adsorbate Pb,Cu,Zn,Cd was beneath 2 hours. Thomas model can describe the data very well.The experiment to identical batch of diatomite reused 5 times. It is not obvious that the removal of the first and the second time droped, but the latter several times, adsorptive capacity was extremely low, for example, the removal of the fifth time of reusing cadmium was only 9.03%. Therefore, considering about the efficient use and the economy, reusing diatomite twice is quite appropriate. At the same time, it is already a very effective method that the diatomite which adsorbs saturated was desorpted with the sour. In this experiment all of the desorption rate had achieved above 94%. |
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