The Adsorption Of Phenols On Cr(3+) Modified Bentonite

The wastewater containing chromium harms environment extremely, and what is even worse is that it is largely produced by economic activities, such as chromium mineral processing, electroplating, leather-making, printing and dyeing. The chemical precipitation, a common approach to treat such wastewater, can however cause problems of sludge, high cost, and secondary pollution. Using Cr³⁺ modified bentonite prepared by simulated wastewater containing chromium to treat the preferred controlled contaminants is expected not only to effectively treat phenol-wastewater, but also to solve the problem of sludge occurred in treating Cr-wastewater. In this experiment, the above mentioned bentonite was used to adsorb 1,4-dihydroxybenze, p-aminophenol, p-chlorophenol, and phenol-wastewater. Optimal experimental conditions, mass, stability, and requirements of regeneration in such sorption were studied. Based on the experimental results, a simple cost-technique comparison between the bentonite and the common adsorbents was made, and the mechanism, thermodynamics and kinetics of the sorption of phenol compounds by the bentonite were investigated. The results showed that, during the process of the sorption, the bentonite had a clearly-increased chromium content and its interlayer space was enlarged. In stronger acidity and stronger alkali as well as during the sorption of 1,4-dihydroxybenze with different concentrations, chromium ion was basically not dissolved out. A mass curve of the modified bentonite was obtained, where, at 25℃with pH 8, the equilibrium concentration of 1,4-dihydroxybenze reached the first national disposal criterion of the second class of contaminants of industrial wastewater. A mass equation was worked out, where y=0.126x-0.1971, R²=0.9473. And a sorption isotherm was also obtained, where the saturated sorption amount 88mg/g corresponded to that worked out theoretically. The bentonite could be regenerated by heating, acidity and alkali. The effect of alkali regeneration was better than that of acidity regeneration. The results of the orthorhombic experiment showed that the following factors had significant effects on the sorption of p-aminophenol and p-chlorophenol by the bentonite: initial concentration, time, acidity, and temperature. Thus, the optimal conditions for p-aminophenol was determined: 150min., pH=10, and 30°C; for p-chlorophenol: 60min, pH=10, 20°C. The bentonite had a good effect on the treating of phenol-wastewater practically. The removal of the COD of such water could be up to 80% . The laws with which such bentonite adsorbed 1,4-dihydroxybenze, p-aminophenol, and p-chlorophenol conform with H-bonging mechanism. The thermodynamic research on the sorption of 1,4-dihydroxybenze by the bentonite demonstrated that the sorption heat was ?H=-19.91KJ/mol, which is in the range of H-bonging formation. Its kinetic study indicated that the initial stage of sorption was controlled by diffusion, while the whole process conformed with the sorption law by single molecule layer. The simple cost-technique comparison showed that it only cost RMB seven yuan for the bentonite to treat 1kg of phenol each time, far lower than for active carbon and for organic bentonite. Therefore, using Cr-wastewater to prepare Cr3+ modified bentonite to treat phenol-wastewater is of a practical prospect.