| Coking industry is highly polluting industries, which produces a large number of coking wastewater and the COD content(> 150 mg/L) of the tail wastewater is still high after pretreatment and biochemical treatment.The organic pollutants is transferred to the atmosphere and then deposited on the surface, so the advanced processing is imminent. High cost of activated carbon adsorption and oxidation limits its large-scale application. In this paper, the cheap coal powder was used as adsorbent based on its high adsorption capacity of organic matter. The static adsorption experiment was used to examine the adsorption performance of coal powder in different dosing quantity, p H, stirring intensity conditions.The influence of acid treatment and the feasibility of the adsorption process was investigated in the same time. Combining the analysis and characterization results, the structure-activity relationship between coal powder and organic pollutants was investigated, too. This study of adsorption technology by coal powder will be applied to a variety of organic wastewater treatment and provide the theoretical guidance.Shenmu long-flame coal was choosed as the adsorbent, the physical properties of coal were characterized through industry analysis, XRF and XRD analysis. The results show that the coal contains a lot of organic ingredients and less clay mineral impurities, it is conducive to the subsequent solid-liquid separation. The microstructure and pore structure of coal were characterized through SEM and BET, The results show that coal coal powder has rough surface and contains rich pore and functional group. Its pore-size distribution is suitable as natural high quality adsorbent.Pyrrole, indole and benzoic acid were selected as the organic pollutants. The impact of adsorbent dosage, adsorption time and p H on removal efficiency were investigated by single factor experiment. Under the optimal conditions, the removal efficiency of three kinds of pollutans are 91.14%, 63.43% and 43.69%, and low p H value is very important for the adsorption of benzoic acid. Through the research of adsorption thermodynamics and kinetics, which indicates that the adsorption of pyrrole and benzoic acid are mainly physical adsorption, adsorption of indole contains chemical adsorption.The adsorption of three kinds of pollutants conforms to pseudo-second order kinetics model, and the intra particle diffusion is not the sole step which control the adsorption rate.The order of adsorption strength by coal coal powder: indole > pyrrole > benzoic acid. Acid leaching of coal powder has a huge impact on its adsorption performance to promote the adsorption, it contains increasing the porosity and specific surface area of coal, reduce the surface electronegativity of coal, and change the existence state of adsorbate in aqueous solution.Coal powder has strong adsorption ability for organic pollutants of the biologically treated coking wastewater, the removal efficiency of COD is 75.66% when the initial p H value is 2 and the adsorbent additive amount is 40 g/L, and the COD value of 43.56 mg/L after adsorption which is far below the national standard. The adsorption isotherm of COD is not in conformity with the Langmuir model and Freundlich model, it shows that the process of adsorption is relatively complex, contains both physical adsorption and chemical adsorption. The thermodynamic parameters ΔH and ΔG are negative, which indicating that the adsorption is a enthalpy-driven spontaneous process;ΔS is negative, indicating that the adsorpdates transfer from three-dimensional space of the liquid phase to two-dimensional surface of the coal powder, with the reduce of degree of freedom. ΔH is-23.20 k J/mol, the reaction types include the vander Waals forces, hydrophobic bonding force, hydrogen bonding, chemical bonding and the like. Adsorption process by coal powder has great environmental, social and economic benefits, which greatly improves the utilization value of the coal. |
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