碳纳米管-羟磷灰石对铅的吸附特性研究

Adsorption Behaviors of Lead on Multi-Walled Carbon NanotubeHydroxyapatite Composites

采用多壁碳纳米管-羟磷灰石(MWCNT-HAP)复合材料,通过间歇试验研究了MWCNT-HAP对Pb(Ⅱ)的吸附特性.主要探讨了固液比、p H、离子强度、反应时间、Pb(Ⅱ)的初始质量浓度及温度等因素对吸附的影响.结果表明,固液比、p H与温度对于去除Pb(Ⅱ)的影响较大,离子强度影响较小.当温度为20℃,固液比为0.08 g·L-1,p H0为5.5,Pb(Ⅱ)的初始质量浓度为100 mg·L-1时,吸附量为716.13 mg·g-1.动力学试验结果表明,MWCNT-HAP吸附Pb(Ⅱ)为快速反应过程,在30 min时,吸附量可达最大吸附量的90%,60 min即可达平衡.伪二级动力学模型可较好地拟合动力学试验数据,可采用该模型描述MWCNT-HAP对Pb(Ⅱ)吸附的动力学过程.热力学试验结果表明,在不同温度下的自由能变均为负值,表明MWCNT-HAP对Pb(Ⅱ)的吸附为自发反应,升温有利于反应进行.Langmuir模型拟合不同温度下的等温试验结果得到可决定系数(R2为0.999 8~1.000 0),可采用该模型模拟MWCNT-HAP对Pb(Ⅱ)的等温吸附过程.MWCNT-HAP去除Pb(Ⅱ)的主要机制为MWCNT-HAP表面含氧官能团与Pb2+间的络合反应、HAP的分解-沉淀、Pb2+与Ca2+离子交换等.

Multi-walled carbon nanotube-hydroxyapatite composites( MWCNT-HAP) were employed as the sorbent to study the sorption characteristic of Pb( Ⅱ) using batch experiments.Effects of dosage of adsorbent,p H,ionic strength,contact time,initial concentration of lead and temperature were investigated.The results indicated that the removal of lead to MWCNT-HAP composites was strongly dependent on dosage of adsorbent,p H,temperature,and independent of ionic strength.The maximum adsorption capacity of lead was about 716.13 mg·g- 1at 20℃,with a solid / liquid ratio of 0.08 g·L- 1,p H0= 5.5 and an initial concentration of 100mg·L- 1.The adsorption of Pb( Ⅱ) on MWCNT-HAP composites was a fast process and could reach the equilibrium within 60 minutes.Ninety percent of the maximum adsorption capacity could be reached in 30 minutes.The kinetic data were fitted to pseudosecond-order kinetic model reasonably well.The kinetic sorption of Pb( Ⅱ) on MWCNT-HAP was well described by pseudo-secondorder kinetic model.The negative free energy calculated from the temperature dependent sorption isotherms suggested that the sorption of Pb( Ⅱ) on MWCNT-HAP composites was a spontaneous process,and high temperature favored the adsorption process.The higher correlation coefficient values( R2= 0.999 8-1.000 0) of Langmuir isotherm model at different temperatures suggested that Langmuir model could be used to simulate the sorption of Pb( Ⅱ) on MWCNT-HAP.The adsorption mechanism mainly involves surface complexation between the lead ions and the surface oxygen-containing functional groups of the MWCNT-HAP,dissolution of HAP and precipitation of pyromorphite [Pb10( PO4)6( OH)2],ion exchange reaction between Pb2 +and Ca2 +of hydroxyapatite.