Abstract:

There is a large amount of coal colloids around coal mines, which have a large specific surface area and stronger adsorption capacity for pollutants. Coal colloids may promote the migration of heavy metals after they enter the soil, but at present, there are few relevant studies. Therefore, studying the adsorption characteristics of coal colloids for the removal of heavy metal pollutants may provide a theoretical basis for predicting the trend of heavy metals in the surrounding soil of coal mining areas. Coal sample was collected from Changyan coal mine of Fuxin, Liaoning Province; their colloid with different sizes (0-2, 2-5, 5-10 μm) was isolated; and the adsorption kinetics and thermodynamic behavior of heavy metal pollutants, copper and cadmium, were examined. The results showed that as the particle size of coal colloid increases, its specific surface area gradually decreases and the organic matter content gradually decreases. The adsorption kinetics of copper and cadmium on the colloid could be well described by the pseudo-second-order kinetic equation (r²>0.99), which indicated that it mainly relies on chemical adsorption. When the particle sizes of coal colloid were 0-2, 2-5, 5-10 μm, the equilibrium adsorption rate constants of copper were 0.0818, 0.0796 and 0.0536, and the adsorption rate constants of cadmium were 0.0717, 0.0631 and 0.0336. The results indicated that with the increase of coal colloid particle size, the adsorption rate constants of copper and cadmium decrease, the adsorption rate constant of copper, on each particle size of coal colloid, is greater than that of cadmium, and the equilibrium adsorption time of copper on coal colloid is shorter than that of cadmium. When the particle sizes of coal colloid were 0-2, 2-5, 5-10 μm, the equilibrium adsorption capacities of copper were 19.292, 18.379 and 14.294 mg·g^-1, and the equilibrium adsorption capacities of cadmium were 25.537, 20.610 and 17.490 mg·g^-1. This finding indicated that as the particle size increases, the equilibrium adsorption capacity of copper and cadmium decreases, and the equilibrium adsorption capacity of cadmium on coal colloids at each particle size is greater than that on copper. The adsorption isotherm of copper and cadmium on the coal colloid with different particle sizes could be well described by the Freundlich equation. Temperature had a significant effect in the process. The adsorption capacity could be increased gradually with the increasing temperature. In addition, The thermodynamic changed on ΔG₀<0, ΔH>0, ΔS>0 suggested that the adsorption of copper and cadmium on coal colloid is a spontaneous, entropy increasing and endothermic process, which is chemical adsorption, and the reduction of coal colloid particle size also improves the adsorption capacity of copper and cadmium.

Key words: coal colloid, copper, cadmium, isothermal adsorption, kinetics, thermodynamics

摘要：

煤矿周围含有大量的煤胶体，其比表面积大，对污染物质的吸附能力更强。煤胶体进入土壤后，可能对环境中的重金属迁移有促进作用，目前，相关文献较少。因此，研究煤胶体对重金属污染物的吸附特征，可以为预测重金属在煤矿区周围土壤中的归趋提供理论依据。采集辽宁省阜新市长焰煤，提取不同粒级的煤胶体（0-2、2-5、5-10 μm），并研究其对重金属污染物铜与镉的吸附动力学和热力学行为。结果表明：煤胶体粒径越大，其比表面积越小，有机质含量越少。准二级动力学方程能更好的描述各粒级煤胶体对铜与镉的吸附动力学过程（r²>0.99），表明煤胶体对铜与镉的吸附以化学吸附为主。铜镉在0-2、2-5、5-10 μm粒级煤胶体上的吸附速率常数分别为：0.0818、0.0796、0.0536，镉的分别为0.0717、0.0631、0.0336，表明煤胶体粒径越大，对铜与镉的吸附速率越小，且煤胶体对铜的吸附速率大于镉，铜达到吸附平衡的时间更短。铜在0-2、2-5、5-10 μm粒级煤胶体上的平衡吸附量分别为：19.3、18.4、14.3 mg·g^-1，镉的分别为25.5、20.6、17.5 mg·g^-1，表明煤胶体粒径越大，对铜与镉的平衡吸附量越小，且煤胶体对镉的平衡吸附量大于对铜的平衡吸附量。Freundlich吸附等温模型能更好的描述各粒级煤胶体对铜与镉的等温吸附过程，温度对吸附过程有显著影响，温度越高，煤胶体对铜与镉的吸附能力越强。此外，各粒级煤胶体对铜和镉的吸附热力学参数ΔG₀<0、ΔH>0、ΔS>0，表明煤胶体对铜和镉的吸附是可自发的、熵增的吸热反应，为化学吸附，煤胶体粒径的减小也提高对铜与镉的吸附能力。

关键词: 煤胶体, 铜, 镉, 等温吸附, 动力学, 热力学