Enrichment and removal of heavy metals contained in PCB boards by multiwalled carbon nanotubes for WEEE directive

L. Hua, H. Hou
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引用次数: 4

Abstract

PCB board is an important part of electronic and electrical equipment. In place of piling e-wastes, much of heavy metals in PCB boards percolate into soil, air, river etc. which is a great threaten to environment. In order to removal the hazardous materials for WEEE directive, in this paper, a study on enrichment of lead, cadmium ions by multiwalled carbon nanotubes (MWCNTs) as a solid-phase extraction adsorbent was employed. ICP-OES was used to determine the adsorbed concentrations. Some valuable guidelines can be drawn from the following discussions. MWCNTs has proven to be a promising materials for the removal of contaminants owing to its amazing effects of enrichment, the objective content was concentrated about 50-100 fold, and limit of detection (LOD) was 0.5 mugmiddotkg-1 for Pb, 0.2 mugmiddotkg-1 for Cd. The ion exchange or hydrogen binding mechanism can very well explain the heavy metals such as Pb, Cd adsorption onto CNTs. Sorption can be modeled by Freundlich isotherms from which thermodynamic parameters such as free energy change (DeltaG), enthalpy change (DeltaH), and entropy change (DeltaS) can be calculated. DeltaG<0, DeltaS>0 indicated the process to be feasible and spontaneous nature. DeltaH>0 suggested that the process to be an endothermic nature. Enrichment can be influenced by factors as contact time, temperature, pH and initial concentration of adsorbate, etc. Sorption increased with increasing contact time, and temperature, initial concentration of adsorbate. For each of analyte, there is a neutral pH beyond which MWCNTs will be either positively or negatively charged. Desorption studies have shown the applicability to regenerate the CNTs used. The process is economically feasible and easy to carry out. All those add more credits to MWCNTs for removing pollutants from e-wastes, which is meaningful for complying with WEEE directive.
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多壁碳纳米管富集去除PCB板中重金属的研究
PCB板是电子电气设备的重要组成部分。由于电子垃圾的堆积,PCB板中的重金属大量渗入土壤、空气、河流等,对环境造成了极大的威胁。为了去除WEEE指令中的有害物质,本文采用多壁碳纳米管(MWCNTs)作为固相萃取吸附剂富集铅、镉离子的研究。ICP-OES法测定吸附浓度。从下面的讨论中可以得出一些有价值的指导方针。MWCNTs以其惊人的富集效果被证明是一种很有前途的去除污染物的材料,其目标含量浓缩约为50-100倍,检出限(LOD)为Pb的0.5 mugmiddotkg-1, Cd的0.2 mugmiddotkg-1。离子交换或氢键结合机制可以很好地解释铅、Cd等重金属在CNTs上的吸附。吸附可以用Freundlich等温线来模拟,从中可以计算出热力学参数,如自由能变化(DeltaG)、焓变化(DeltaH)和熵变化(DeltaS)。DeltaG0表示该过程是可行的、自发的。δ δ >表明该过程为吸热性质。影响富集的因素有接触时间、温度、pH、吸附质初始浓度等。吸附量随接触时间、温度、吸附质初始浓度的增加而增加。对于每一种分析物,都有一个中性pH值,超过该pH值,MWCNTs将带正电荷或负电荷。解吸研究表明,该方法可再生所使用的碳纳米管。该工艺经济可行,易于实施。所有这些都为MWCNTs清除电子废物中的污染物增加了更多的积分,这对遵守WEEE指令具有重要意义。
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