pH及共存金属离子对生物质炭吸附铅稳定性的影响

摘要

The stability of adsorbed heavy metals onto biochars is one of the most important factors to evaluate the biochar's remediation performance. In this study, the effects of pH and coexisting ions Cd/Al on Pb desorption were investigated. It was found that Pb desorption increased with the decrease of pH which was mainly due to the competing effect of H+ and the protonation of functional groups which promoted the activation of Pb. However, with the presence of Cd/Al, the desorption efficiencies of Pb were further promoted. At pH 3.5, apromotion effect was observed from the presence of Cd, with Pb desorption efficiencies increasing by 13.9%, 1.0%, 3.4% for CM100, CM400 and ZKZ700, respectively; the increases were even stronger for Al at 26.8%, 13.0% and 11.3%. The more metal hydrolyzed, the more release of H+, which helped to activate more Pb from the surface of biochars. The desorption efficiencies of Pb increased with the increasing contact time. During the first 4 h, Pb was quickly desorbed from biochars to account for 70% of their maximum Pb desorption. However, the rate of Pb desorption gradually decreased during the next 20 hours. Desorption of Pb from biochars followed the pseudo-first order kinetic model and the intraparticle diffusion model during the first 4 h. The presence of Cd/Al and preferential desorption of these coexisting ions reduced Pb desorption rate and extended the time to reach equilibrium.%生物质炭对重金属吸附性能的稳定性是评价生物质炭修复效果的重要指标.本文研究了不同pH、金属离子Cd和Al存在下,Pb在不同炭化温度(100℃、400℃、700℃)生物质炭上的脱附性能及脱附过程.结果表明,pH越低,Pb的脱附率越大.其主要是由于H+的竞争效应,以及生物质炭表面官能团的质子化,促进了Pb的重新活化.在Cd和Al共存时,Pb的脱附率进一步增加.当pH=3.5时,Cd和Al的存在分别使Pb从CM100、CM400和ZKZ700上的脱附率提高了13.9%、1.0%、3.4%和26.8%、13.0%、11.3%.这主要归因于多金属的水解使得更多的H+得以释放,进而促进了Pb的脱附.Pb在生物质炭上的脱附率随脱附时间的延长而不断增加,反应前4 h,脱附率迅速增加并均已达最大脱附率的70%,4 h后脱附速率减慢.Pb的脱附动力学符合伪一级动力学模型及颗粒内扩散模型(前4 h).当Cd和Al存在时,解吸液对Cd、Al易解吸态的优先脱附降低了Pb的脱附速率并延长了其脱附所达平衡的时间.