Study On Comparison Of Adsorption Characteristics Of Cr⁶⁺ On Six Typical Clay Minerals

Chromium is widely used in industrial production process, including tanning, electroplating, metallurgy, metal processing, printing and dyeing, paint production process and so on. During these industrial production process, a large amount of chromium containing wastewater are produced and most of them are directly discharged in the environmental water without any treatment. Wantonly discharging of chromium containing wastewater cause the serious problems of environmental pollution, especially the water pollution, which has brought a huge threat to ecological safety and human health. Therefore, it has important significance to study the effective treatment technology and the related principle of chromium containing wastewater.There are many treatment method for chromium containing wastewater, in which adsorption method is the most widely used method because of its simple operation, stable effect and little secondary pollution. What’s more, clay mineral is the most widely used adsorption material because of its large specific surface area, rich of surface active groups and micropore, strong electronegativity, abundant reserves and low price. However, the adsorption properties and mechanisms of typical clay minerals (including bentonite, montmorillonite, hydrotalcite, vermiculite, zeolite, diatomite) on Cr6+are not systematic and in-depth. And it was lack of adequate theoretical support for practical applications. Therefore, the adsorption condition, property, behavior characteristics, adsorption mechanisms of typical clay minerals, including bentonite, montmorillonite, hydrotalcite, vermiculite. zeolite, diatomite. on treating chromium containing wastewater are investigated in this study by using static adsorption tests. Several important conclusions are obtained in this study, which could provide theoretical basis and technical support for the application of clay minerals in the treatment of chromium containing wastewater. The main results are as follows:(1) The influencing factors of the adsorption of clay minerals on Cr6+ and the results of the study indicate that hydrotalcite. zeolite, diatomite. montmorillonite. bentonite, vermiculite. the best additive quantity Wo (adsorbent) is respectively.1 g/L,1 g/L,1 g/L,1 g/L,1 g/L,1 g/L;the best concentration Co(adsorbate) of Cr6+is respectively,300 mg/L,300 mg/L,400 mg/L,300 mg/L,300 mg/L,300 mg/L; Optimum pH conditions respectively pH= 5, pH= 5, pH= 8, pH= 5, pH= 5, pH= 5; the best temperature is respectively,25 ℃,35℃,35℃,25 ℃,25℃,25℃;the optimum adsorption amount of Cr6+is respectively,24.28 mg,34.76 mg/g,36.25 mg/g.24.03 mg/g,27.65 mg/g,31.05 mg/g.(2) The results of adsorption condition optimization and adsorption capacity of clay minerals on Cr6+indicate that under the optimal adsorption conditions, the adsorption property of diotomite is best comparing with the other five clay minerals. The adsorption quantit for diotomite is also largest, followed by zeolite. The optimal adsorption conditions for hydrotalcite is consistent with the the montmorillonite. The adsorption effect is also very close for these two clay minerals.(3) The adsorption behavior and mechanism analysis of clay minerals on adsorpting Cr6+ indicate that, the most suitable model for describing the adsorption properties of hydrotalcite, zeolite, bentonite, montmorillonite and vermiculite on Cr6+ is Freundlich model. But Langmuir model is more suitable for the diatomite. At the same time, it is found that it is not clear or the parameter estimation error is large for the conventional models. The adsorption kinetics of hydrotalcite, zeolite, diatomite, bentonite, montmorillonite, vermiculite are more in line with the two order kinetic equation. The equation can describe the adsorption process of clay mineral on Cr6+ which include the Cr6+ in the solution spread to the adsorbent surface through the liquid membrane, and the adsorption sites on the adsorbent and the adsorption sites on the adsorbent react with the diffusion reaction in the inner of the adsorbent particles. The experimental error for pseudo first order kinetics is large, and there is little practical guiding significance.