| Various pollutants enter into environment accompanying with natural conditions, population explosion, economic development, and environmental emergency accidents. Sorption is a well-known equilibrium separation process and an effective method for wastewater treatment in terms of low cost, flexibility and simplicity of design, and ease of operation. It’s practical and significant for pollution controlling, removal, and environment improvement.This research focused on the issues of wastewater treatment to remove fluoride, bisphenol AF (BPAF), and 2-chlorophenol (2-CP). Firstly, the removal efficiency of representative pollutants onto various commercial sorbents were evaluated and their sorption mechanisms were also discussed, thus providing basic data for environmental emergency treatment. And then zeolite was suggested as a potential and low-cost sorbent for the removal of pollutants from water. To improve the sorption capacities for fluoride, BPAF, and phenolic compounds, different modified zeolites were prepared, the detailed parameters of the sorption process were determined, and the mechanisms were proposed. These studies were tried to provide essential principles and techniques of the functional modifications of zeolite and their applications on wastewater treatments. The specific work and results were shown below.1) According to theory researches of widely used sorption models of kinetics, isotherm, and thermodynamics, the linear and non-linear regression were used and compared to determine the best-fitting sorption model, and thermodynamic parameters were calculated by various methods. The results showed that nonlinear regression, a more complex mathematical method, and coefficients of determination combining with the error functions, provided more accurate determinations of best-fitting sorption model. Also, thermodynamic equilibrium constant need to be determined from the best sorption isotherm to ensure accuracy in the thermodynamic parameters calculation.2) The sorptive capacities and mechanisms of commercial sorbents for fluoride, BPAF, and phenolic compounds were compared. Results suggested that granule activated carbon, γ-aluminium oxide and artificial zeolite were selected as sorbents for defluoridation in acidic environment. And van der waals force, ion exchange, and hydrogen bonding interactions were considered to be responsible for defluorination. With regard to the removal of BPAF, there were no effective sorbents for its sorption due to the properties of 6F electron group. While granule and powder activated carbon were selected sorbents for removing phenolic compounds at acidic condition. As the sorption capacity increased with hydrophobicity of the phenols, hydrophobic interaction and electrostatic interaction were considered to be the main sorption mechanism.3) According to the synthesis and sorption study of biological nanometer materials in the removal of fluoride from aqueous solution, chitosan-modified zeolite (Ch-Z) had triple the defluoridation capacity as natural zeolite, even though chitosan did not fully coat the zeolite material. The sorption capacity of Ch-Z for fluoride depended mainly on the pH of the solution, the fluoride concentration and the types of coexisting ions. The most suitable range of pH was 5.0±0.5. The presence of anions had a negative effect on the sorption of fluoride, mainly due to the resultant pH changes. Ch-Z has a high potential to sorb fluoride by electrostatic force, and Ch-Z can be successfully used for the fluoride treatment in real water samples.4) It is worthwhile to investigate the performance of Ch-Z with sodium cholate (NaC) in removing bisphenol-AF (BPAF) from aqueous solution. The results indicated that the removal of BPAF onto Ch-Z was appreciably enhanced in the presence of NaC, and the maximum removal efficiency of BPAF approximately 78% was achieved in a system containing 1 g/L Ch-Z and 1.68 mmol/LNaC. It also confirmed that the co-effect of Ch-Z and NaC produced more rapid BPAF sorption and substantially higher sorption capacity than was achieved for Ch-Z without NaC over a wide range of BPAF concentrations and pH values. The sorption of NaC onto Ch-Z and the combination of BPAF with NaC were likely to be the main reasons for the enhanced BPAF removal, and this has great potential in environmental applications.5) To decrease the power, material, and time consumption in wastewater treatment, a zeolite/surfactant one-step process was proposed to replace the traditional two-step process to remove 2-CP. Compared with the two-step process, the one-step process achieved a higher 2-CP sorption capacity within a shorter time and maintained a high efficiency in a reuse test. For the one-step process,1 g/L Na-zeolite and 4CMC CTAB was chosen as the optimum sorbent dosage according to the pseudo-second-order kinetic parameters. Also, DA model was the best fit to the nonlinear sorption isotherm, and the performances of the sorbents in one-step process were stable over a wide range of 2-CP concentrations and temperatures. The uptake of 2-CP was heavily dependent on pH, increasing under weak acidic pH conditions. On one hand, the larger CTAB loading reflects existence of the partitioning process involved in the sorption process. On the other hand, the interaction of the phenolic group(s) with the positively charged "head" of CTAB bilayers significantly enhances the removal of phenolic compounds from aqueous solutions. Indeed, the surfactant binding to mineral material obtained by one-step process as a low-cost and environmentally friendly sorbent has good potential application in the in-situ treatment of organic wastewater. |
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