| China is the world’s largest producer and consumer of coal,coal gangue as a bulk solid waste in the process of coal production,its resource utilization has always been a major strategic need of the country in the comprehensive utilization and treatment of coal chemical solid waste.Coal gangue is mainly composed of SiO2 and Al2O3(60%-90%),so it can be used as raw material for zeolite synthesis,and the synthesized gangue-based zeolite can be applied to water pollution treatment as adsorbent to achieve high value utilization of coal gangue.However,the pore size of zeolite is small(the pore size of NaA zeolite is only 0.4 nm),and its adsorption capacity and types of pollutants(heavy metals,organic pollutants)are limited.Compounding synthetic zeolites with carbon materials can improve the adsorption capacity and types of pollutants by improving the pore size distribution of the material.It is worth noting that coal gangue contains 20%-30%carbon in addition to SiO2 andAl2O3,and the carbon in coal gangue is retained in the synthetic zeolite process and prepared into zeolite-activated carbon composites will be an effective way to achieve simultaneous removal of heavy metals and organic pollutants.However,there is a lack of systematic research on the removal of heavy metals and organic pollutants by gangue-based zeolite/zeolite activated carbon.Therefore,in this study,zeolite and zeolite activated carbon materials were synthesized by hydrothermal alkali activation method with coal gangue of a coal washing plant in Shanxi,and the properties of the prepared zeolite and zeolite activated carbon were characterized and analyzed,and their removal effects and adsorption mechanisms on heavy metal Cu2+ and organic dye MB were systematically investigated by batch adsorption experiments.The main research findings are as follows:(1)The gangue-based zeolites were synthesized by hydrothermal alkali activation method under different conditions,and the optimal conditions in the synthesis process were explored.The results showed that the best crystallinity of zeolite could be obtained when the molar ratio of SiO2/Al2O3 was 2,the molar ratio of Na2O/SiO2 was 2,the molar ratio of H2O/Na2O was 70,the crystallization temperature was 85℃,and the crystallization time was 12 h.(2)The adsorption of Cu2+ and MB by gangue-based zeolites was in accordance with the pseudosecond-order kinetic model and the Langmuir isothermal adsorption model,indicating that the adsorption systems were monolayer chemical adsorption.The equilibrium adsorption capacity of Cu2+was 46.08 mg·g-1 at pH=6,adsorbent dosage of 2 g·L-1 and temperature of 25℃,and the equilibrium adsorption capacity of MB was 11.16 mg·g-1 at pH=7,the adsorbent dosage was 3 g·L-1 and the temperature was 25℃.The removal of Cu2+and MB was probably achieved through electrostatic interaction,surface complexation and hydrogen bonding of oxygen-containing functional groups on the adsorbent surface.(3)The adsorption of Cu2+and MB by gangue-based zeolite activated carbon was in accordance with the pseudo-second-order kinetic model and the Langmuir isothermal adsorption model,indicating that the adsorption systems belonged to monolayer chemical adsorption.The equilibrium adsorption capacity of Cu2+ was 45.33 mg·g-1 at pH=6,adsorbent dosage of 2 g·L-1 and temperature of 25℃,and the equilibrium adsorption capacity of MB was 14.09 mg·g-1 at pH=7,the adsorbent dosage was 3 g·L-1 and the temperature was 25℃.The removal of Cu2+and MB may involve electrostatic interaction,surface complexation,π-π*complexation and hydrogen bonding of oxygen-containing functional groups on the adsorbent surface.The removal effect of gangue-based zeolite activated carbon for Cu2+was comparable to that of gangue-based zeolite,but the presence of activated carbon made the removal of MB by zeoliteactivated carbon better than that of zeolite,and the adsorption capacity was increased by 26.3%.(4)In the solution where Cu2+and MB coexisted,gangue-based zeolite/zeolite activated carbon would preferentially adsorb Cu2+before MB,and the removal rate of MB was gradually decreased with the increase of Cu2+concentration.The removal effect of zeolite activated carbon on MB was better than that of zeolite.When MB concentration was 50 mg·L-1,Cu2+concentration increased to 100 mg·L-1,the removal rate of zeolite activated carbon for MB was about three times of that of zeolite.When the concentration of Cu2+was 5 mg·L-1,the initial concentration of MB was 25 mg·L-1,the adsorbent dosage was 5 g·L-1,the temperature was 35℃,and the pH was 5,the zeolite activated carbon had the best removal effect on the solution with the coexistence of Cu2+and MB. |
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