褐煤腐植酸吸附铜的热力学机理

为了实现腐植酸在治理重金属污染方面的资源化应用,以褐煤中提取的腐植酸为吸附剂,研究了pH值对腐植酸吸附Cu~(2+)的影响,探讨了吸附的热力学特征和作用机理。结果表明:腐植酸对Cu~(2+)的吸附明显受pH值影响,吸附量随pH值的升高而增大,pH值约5时吸附率约为95%;吸附等温线符合R-P方程、Langmuir方程、Freundlich方程及D-R方程,与R-P方程和Langmuir方程的相关程度更高;吸附过程放热,随pH值升高吸附焓增大,吸附熵由正到负逐渐减小,吸附自由能小于零且呈减小趋势;不同pH值时吸附机理有明显的差别,pH值较低时吸附作用力主要为范德华力和氢键,pH=5时配位交换反应成为主要作用。

Thermodynamics Mechanism on Adsorption of Copper Ion onto Humic Acid Extracted from Lignite

The effects of pH value on adsprption of Cu2+ onto humic acid extracted from lignite were investigated and the adsorption thermodynamic characteristics and mechanism were discussed in this paper.Results showed that the effect of pH value on adsorption was evident and the adsorption amount increased with the rise of pH value.When the pH value was about 5,the removal rate reached 95％.The adsorption isotherms followed R-P equation,Langmuir equation,Freundlich equation and D-R equation,of which R-P equation and Langmuir equation were more applicable.The adsorption was endothermic processes,and with the rise of pH value the adsorption enthalpy increased while the adsorption entropy decreased from positive to negative.Meanwhile,the adsorption Gibbs free energy changes were all negative with a decreasing tend.Besides,the adsorption mechanism varied substantially with the change of pH value.Furthermore,van der Waals forces and hydrogen bonds were the main adsorption forces at low pH values and the ligand exchange was dominant at pH =5.