| The wastewater containing heavy metals has become a serious threat to the ecological environment and public health, especially Pb(Ⅱ) and Cr(Ⅵ). Adsorption is one of the most effective and promising technologies used to remove heavy metals. In recent years, various efforts have been focused on the research and development of low cost adsorption materials with excellent properties. Coal fly ash and gangue are the largest cumulants of industrial waste in our country. The synthesis of adsorption materials is a successful alternative to deal with fly ash and gangue waste, resulting in low-cost and environmentally friendly materials.In this study, several adsorption materials, such as modified coal fly ash, gangue-based activated carbon, activated carbon-zeolite composite materials and melamine formaldehyde resins, are synthesized in order to remove Pb(Ⅱ) and Cr(Ⅵ). The adsorption isotherm, kinetics, and thermodynamics have also been studied. The detailed novelties of this research can be categorized as following:1. Coal fly ash(CFA) was modified by NaOH to adsorb and remove Pb(Ⅱ) from wastewater. The effect of various parameters including pH, fly ash dosage, initial concentration and contact time on Pb(Ⅱ) removal were investigated. It was found that the modified coal fly ash(M-CFA) has higher removal efficiency for Pb(Ⅱ) when compared with that of raw coal fly ash. The removal efficiency could reach 99% within 30 min at pH of 4.5, modified coal fly ash dosage of 10 g/L, when Pb(Ⅱ) concentration was 50 mg/L-200 mg/L. The equilibrium data were found to fit well in the Langmuir isotherm and the kinetics of Pb(Ⅱ) adsorption is better described by the pseudo-second-order equation. It was also found that the adsorption process is endothermic and more favorable at higher temperatures.2. The adsorbent(GBAC) was prepared from gangue, coal-tar pitch and silica, and was used as an adsorbent for the removal of Cr(Ⅵ). The removal efficiency was 100% at pH 2, particle size 60 mesh, adsorbent dosage 10 g/L contact time 20 h, temperature 25℃ and initial concentration of Cr(Ⅵ) of 100 mg/L. The equilibrium data were found to fit well in the Freundlich isotherm and the kinetics of Cr(Ⅵ) adsorption is better described by the pseudo-second-order equation. Different thermodynamic parameters:Δ G0(free energy change), Δ H0(enthalpy change) and Δ S0(entropy change) were evaluated, which indicated that the sorption was favorable, spontaneous, and endothermic in nature.3. The composite materials containing activated carbon and zeolite(AC/X) was prepared from gangue, coal-tar pitch and silica, and the nitrogen-containing porous carbon materials(MF) was prepared through the carbonization of melamine formaldehyde resin with CaCl2 as a template, which were applied to Pb(Ⅱ) treatment. The results showed that both AC/X and MF had excellent adsorption performance for Pb(Ⅱ). The adsorption capacity reached to 248.12 mg/g and 230.30 mg/g, respectively. The adsorption followed Langmuir isotherm model and pseudo-second-order kinetics. In thermodynamics, the adsorption of Cr(Ⅵ) was exothermic and spontaneous process. The structure, morphology of MF and AC/X were characterized using zeta electric potential and N2-adsorption. Results showed that the adsorption of Cr(Ⅵ) was influenced by quanlity of electric charge. |
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