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电镀、化学镀等表面处理过程产生的废水中通常含有铬、锌、铜、镍等重金属及氰化物等污染物,必须对其进行严格处理[1]。铜是主要镀种之一,含铜废水主要来自镀件漂洗,其中含有大量铜和有机污染物[2]。电镀过程中广泛使用的络合剂(乙二胺四乙酸(EDTA)、柠檬酸、酒石酸)会与铜形成稳定性高且形态复杂的络合铜[3],如EDTA-Cu稳定常数比Cu(OH)2高5个数量级[4]。络合态重金属多数具有很高的水溶性,且在广泛的pH范围内能够稳定存在,使得铜难以从废水中有效去除[5]。以碱沉淀法和硫化物沉淀法为代表的化学沉淀法是目前广泛使用且经济性较好的方法[6-9],但在铜浓度较低时效果不佳,且沉淀物在酸性条件下不稳定。吸附法[10-12]、电解法[13]、离子交换法[14-15]、高级氧化还原法[16-18]等其他方法也存在成本较高、再生困难等问题。因此,废水中络合铜的有效、经济去除是一个亟待解决的问题。
重金属捕集剂能与废水中的重金属或络合态重金属迅速发生螯合作用,产生难溶的螯合沉淀,具有反应速率快、沉淀物稳定、选择性好的优点,已成为重金属污染处理领域关注的热点,具有广泛的应用前景[19-22]。在重金属捕集剂中,二硫代氨基甲酸盐(DTC)类捕集剂使用广泛。谭聪等[23]用二硫化碳、碳酰肼为原料,合成了重金属捕集剂DT-SC,对Cu2+、Cd2+、Mn2+去除率均在90%以上。张翔等[24]采用二并哌嗪、二硫化碳等在碱性条件下合成重金属捕集剂TDDP,在最佳反应条件下对Cu2+和Pb2+去除率均超过96%,对Zn2+去除率也超过91%。二乙基二硫代氨基甲酸钠(DDTC)、SDDC[25]等小分子螯合剂及二硫代羧基化羟甲基聚丙烯酰胺(DTMPAM)[26]、聚-二硫代氨基甲酸铵(PADTC)[27]等高分子螯合剂,对Cu具有良好的去除性能。其中高分子螯合剂沉降性能较好,但其较大的空间位阻使得DTC基团利用率较低,且存在成本较高的问题[28]。同时,小分子螯合剂DTC基团利用率相对较高,但含有单个螯合基团的小分子螯合剂去除能力有限。分子质量大小适当并拥有多个DTC基团的螯合剂可提升捕集效率和去除性能。因此,采用三乙烯四胺等为原料合成多硫代氨基羧基基团的重金属捕集剂,一方面可提升二硫代羧基的数量,去除能力显著增强;另一方面具有适当分子链长,可降低空间位阻,使得基团利用效率进一步提升。综上所述,本文以三乙烯四胺等为原料,在操作简单、条件温和的条件下合成重金属捕集剂N,N-双(二硫代羧基)三乙烯四胺(TDTC),对EDTA-Cu等具有优异的去除效果,以期为含铜废水的高效处理提供参考。
高效重金属捕集剂TDTC对络合铜的去除性能
The performance of highly-efficient dithiocarbamate-based heavy metal chelating agent on complex copper removal
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摘要: 传统化学沉淀法存在对酸性及低浓度的络合态重金属去除率低的问题,为解决此问题,以三乙烯四胺、二硫化碳为原料合成了重金属捕集剂N, N-双(二硫代羧基)三乙烯四胺(TDTC),并采用红外光谱等分析方法对其结构和主要官能团进行了表征。以酒石酸铜、柠檬酸铜和EDTA铜3种络合铜为去除对象,研究了TDTC对络合铜的去除性能及去除机理。结果表明,在pH为3.0~9.0、TDTC投加量为1 mmol·L−1、Cu质量浓度为 50 mg·L−1、PAM投加量为1 mg·L−1条件下,Cu去除率可达到99.6%以上。进一步的沉淀表征分析结果表明,TDTC对络合Cu的去除过程存在螯合配位反应,具有与相应络合剂的竞争优势,能够把Cu从相应的络合剂中脱除并形成难溶的螯合沉淀,从而实现废水中Cu的有效去除。以上研究结果可为利用特异重金属捕集剂去除重金属的工程实践提供参考。Abstract: Wastewater containing complex heavy metal in acid and low-concentration is difficult to be treated effectively by traditional chemical precipitation. Triethylenetetramine and carbon disulfide were taken as raw materials to prepare a heavy metal chelating agent of N, N-bis(2-mercaptoethyl) triethylene-tetramine (TDTC) in a mixing solvent of ethylene glycol and deionized water. Fourier transform infrared spectra, scanning electron microscopy and elemental analysis were used to characterize the structure of TDTC. The removal performance and mechanism of TA-Cu(tartaric acid, TA), CA-Cu(citric acid, TA-Cu) and EDTA-Cu by TDTC were discussed. The experimental results show that at pH of 3.0 to 9.0, TDTC dosage of 1 mmol·L−1, reaction time of 3 min and PAM dosage of 1.0 mg·L−1, over 99.6% Cu could be removed from a simulated wastewater containing complex Cu with initial concentrations of 50 mg·L−1. IR, XPS and SEM analysis on the chelate precipitate showed that the chelating reaction occurred between TDTC and Cu. The competitive edge on Cu cheating by TDTC could withdrew Cu from other complexing agents and led to the occurrence of insoluble chelated precipitate. Thus, Cu could be efficiently removed from wastewater. This research can provide theoretical guidance for removing heavy metal by heavy metal chelation in engineering practice.
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Key words:
- heavy metal chelating agent /
- complex copper /
- chelate /
- removal mechanism
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表 1 TDTC的元素分析
Table 1. Elementary analysis of TDTC
元素 比例/% 物质的量相对值 C 33.97 1.91 H 3.28 3.96 N 18.64 0.9 S 40.75 1.1 表 2 TDTC与其他重金属捕集剂去除效果对比
Table 2. Comparison of heavy metal removal effect between TDTC and other sulfur-containing heavy metal chelation agents
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