巯基重金属捕集剂脱除电镀废水中低浓度Ni的效能及机理研究

Research on the efficiency and mechanism of low-concentration Ni removal from electroplating wastewater by the heavy metal capturing agent with thiol

以某电镀厂经Na2S预处理后的废水作为研究对象,选用Na OH、Na2S和有机巯基类化合物(EDTC)作为重金属捕集剂,对废水中低浓度Ni进行深度脱除.通过处理效果对比,最终选用EDTC作为Ni理想的捕集剂,重点考察了加药方式、p H、EDTC投加量、反应时间、PAC投加量及不同含Ni电镀废水对Ni去除效果的影响并探讨了EDTC去除Ni的机理.结果表明,Ni初始浓度为6.41 mg·L-1时,最佳工艺条件依次为:p H为7.0,EDTC投加量为摩尔比nEDTC/nNi=4,反应时间为15 min,PAC投加量为100 mg·L-1,PAM投加量为2.5 mg·L-1,此时出水Ni2+浓度为1.08 mg·L-1,去除率达83.15%.在此基础上,针对3种不同含Ni电镀废水,经EDTC处理后Ni去除率均在80%以上,部分废水出水Ni2+浓度低于0.1 mg·L-1,达到了《电镀污染物排放标准(GB21900-2008)》中关于Ni污染物特别排放限值的要求(<0.1 mg·L-1).红外光谱图和有机元素分析结果表明,EDTC与Ni会发生螯合反应,即EDTC巯基中硫捕捉Ni2+并趋向成键,生成难溶的螯合产物,从而有效地去除废水中Ni.

NaOH、Na2S and an organic sulfhydryl compound（ EDTC） were selected as a heavy metal capturing agent and used to remove low-concentration nickel deeply from the electroplating plant wastewater pretreated by Na2 S. Due to its better treatment effect,EDTC was finally chosen as the most ideal option. The influence of way of reagent addition,p H value,dosage of EDTC,reaction time,dosage of PAC and different kinds of nickel containing electroplating wastewater on Ni removal was studied. Besides,the reaction mechanism of EDTC and Ni2 ＋was also discussed. The results showed that EDTC had a high efficiency under the following conditions in order： 6. 41 mg·L- 1of initial nickel concentration,p H 7. 0,molar ration of nEDTC/ nNiis 4,15 min of reaction time,100 mg·L- 1of the coagulant（ PAC） dosage and 2. 5 mg·L- 1of the coagulant aid（ PAM） dosage,leading to 1. 08 mg·L- 1of residual Ni2 ＋concentration with the removal rate of 83. 15%. Furthermore,EDTC was tested for three kinds of nickel containing electroplating wastewater. The removal rates were above 80% and the residual Ni2 ＋concentrations of one effluent was lower than 0. 1 mg·L- 1,meeting the nickel special emission limit of the emission standard of pollutants for electroplating（ GB21900- 2008）（ 〈0. 1 mg·L- 1）. The results of infrared spectrum and organic elemental analysis showed that： EDTC and Ni2 ＋can have chelate reaction. The sulfur of thiol of EDTC captures Ni2 ＋and tends to bond to product insoluble chelate. Therefore the removal of Ni from wastewater was efficient.