酯化改性铁杉木屑制备重金属吸附剂及其吸附性能

Modification of hemlock sawdust by esterification as adsorbents for heavy metal ions removal

木屑是一种常见的农林废弃物,来源广泛、价格低廉。木屑作为一种天然的生物质材料对水中的重金属离子有一定的吸附能力,但吸附效率较低。为提高木屑的吸附效率,实现农林废弃物的资源化利用,以铁杉木屑、2-氨基对苯二甲酸(2-ATP)、2-巯基丙酸(2-MPA)为原料,制备2-氨基对苯二甲酸改性铁杉木屑(AmS)和2-巯基丙酸改性铁杉木屑(MmS)两种酯化改性的新型吸附剂,并研究它们对溶液中Hg^2+的吸附性能。考察Hg^2+初始浓度、溶液pH、干扰离子以及吸附时间等对吸附性能的影响,结果表明:两种吸附剂在pH 4~8时具有较高的吸附性能,在pH 5时,AmS和MmS吸附剂的最佳吸附效率分别为93.3%和95.5%;当溶液中存在0.2mol/L的干扰离子Ca^2+时,AmS和MmS吸附剂的吸附效率仍能维持在70.4%和73.4%;吸附剂的动态吸附行为均符合伪二级动力学模型,速率控制步骤为化学吸附过程,能够在60min内快速到达吸附平衡;吸附剂的等温吸附曲线均符合Langmuir模型,为单分子层吸附。吸附试验表明,298K时AmS和MmS吸附剂对Hg^2+的最大吸附容量分别为121.8和149.1mg/g,远高于改性前的铁杉木屑(5.6mg/g),具有良好的应用前景。

The rapid development of modern industry has led to serious environmental pollution problems.The sewage discharged from industries contains various heavy metal ions with high concentrations,such as Pb^2+,Hg^2+,Cd^2+,Cu^2+ and Ni^2+,which poses a great threat to human s health.Sawdust is a kind of common agricultural and forestry waste,which has a wide range of sources and low cost.As a natural biomass material,the adsorption capacity of sawdust itself towards heavy metal ions in water is limited.To improve the adsorption efficiency of sawdust and value-added utilization of agricultural and forestry wastes,two new adsorbents,2-amino terephthalic acid(2-ATP)modified sawdust(AmS)and 2-mercapto propionic acid(2-MPA)modified sawdust(MmS),were prepared from the hemlock sawdust by esterification in this work;followed by the characterization of Hg^2+ adsorption in aqueous solution.The resulting cellulose-based adsorbents demonstrated the excellent binding ability and selectivity to Hg^2+,which grafted with thiol groups in particular.The effects of initial concentration of Hg^2+,pH,interference ions and adsorption time on the adsorption performance were investigated.The results showed that the maximum adsorption capacity of AmS and MmS adsorbents for Hg^2+ reached 121.8 mg/g and 149.1 mg/g,respectively,which were significantly higher than that of the unmodified hemlock sawdust(5.6 mg/g).AmS and MmS adsorbents had high removal efficiency of Hg^2+ at pH 4-8,and the optimum removal efficiencies were 93.3% and 95.5%,respectively,at pH 5.In addition,the results showed that the adsorption efficiency of AmS and MMS adsorbents could be maintained at 82.2% and 73.4% with 0.2 mol/L of Na^+ and Ca^2+ interfering ions in the solution.The isothermal adsorption follows Langmuir model,and the adsorption type is monolayer.The adsorption kinetics analysis indicated that the pseudo-second-order kinetic model better described the dynamic adsorption behavior of adsorbents,and the adsorption reached equilibrium in a short time(60min).The two ester-modified sawdust adsorbents prepared in this work via a facile preparation process,were green-based,cost-effective promising for various applications related to wastewater treatments.