臭氧预破络-重金属捕集耦合体系高效去除废水中络合态镍的机理研究

Mechanism of high efficiency removal of complex nickel in wastewater by ozone pre-decomposition- coupling heavy metal capture system

电镀废水处理厂化学镀镍废水经常规物化处理后,仍存在低浓度、高稳态的重金属污染物,导致后续出现难处理、难生化、难达标排放的普遍技术问题.本文提出一种新型高效的臭氧预氧化破络-重金属捕集螯合深度处理技术体系,即臭氧-重金属捕集剂(O3-SN-9)耦合体系.通过单因素静态实验,重点考察了臭氧(O3)氧化初始pH值、氧化时间、臭氧载气流量、重金属捕集剂(SN-9)投加量等对出水总镍(Ni)去除率的影响,并探讨了臭氧氧化破络络合态Ni的途径及SN-9捕集重金属Ni的机理.结果表明,在化学镀镍废水初始总Ni浓度为2.76 mg·L^-1,臭氧预氧化初始pH值范围为7.0~11.0,反应时间为40 min,载气流量为3 L·min^-1,SN-9投加量为40 mg·L^-1的条件下,处理后出水总Ni浓度稳定低于0.1 mg·L^-1,可达到《电镀水污染物排放标准》(DB44/1597-2015)水污染物特别排放限值中总Ni的排放限值要求.液相色谱-质谱(LC-MS)、叔丁醇(Tert-Butyl Alcohol,TBA)捕获羟基自由基(·OH)实验和傅里叶变换红外光谱(FTIR)分析表明,在臭氧预氧化破络与螯合捕集Ni前后协同耦合的高效体系中,前端臭氧氧化以间接氧化为主,直接氧化为辅;氧化进程可控制为部分氧化破络,将高稳态镍络合物氧化成易失稳的小分子Ni络合物及部分离子态Ni;后续SN-9高效螯合捕集Ni的主要官能团为巯基官能团(-SH),可从低分子易失稳的Ni络合物上竞争夺取Ni离子,或直接与游离态Ni(Ⅱ)反应,形成稳定的四边形配位螯合沉淀物,从而达到去除Ni的目的.

After the conventional physicochemical treatment, there were still low-concentration and high-stable heavy metal pollutants in electroless nickel- plating wastewater. These pollutants leaded to the general technical problems of wastewater treatment. In this paper, a new and efficient ozone pre-oxidation decomposition coupling with heavy metal chelation trapping treatment system, namely ozone-heavy metal chelating agent (O3-SN-9) coupling system, was proposed. Through the single factor static test, the effects of initial pH, oxidation time, ozone gas flow rate and SN-9 dosage on the total Ni removal rate of the effluent were investigated. Pathway of ozone oxidation for de-complexation of Ni and mechanism of SN-9 capturing heavy metal Ni were studied. The results show that the O3-SN-9 coupling system had a high efficiency for wastewater with 2.76 mg·L^-1 of initial nickel concentration. The total Ni concentration of the treated effluent was stable below 0.1 mg·L^-1 under the condition as follows: neutral alkali pH (7.0~11.0), 40 min of reaction time, 3 L·min^-1 of ozone flow rate and 40 mg·L^-1 dosage of SN-9. The treated effluent meets the total Ni emission standard (<0.1 mg·L^-1) of the special discharge limit of water pollutants in the discharge standard of electroplating water pollutants (DB44/1597-2015). Results of liquid chromatographymass spectrometry (LC-MS), tert-butyl alcohol (TBA) capture hydroxyl radicals (·OH) test and Fourier transform infrared spectroscopy (FTIR) analysis show that the ozone indirect oxidation was main reaction during the high-efficiency synergy system of ozone pre-oxidation and co-coupling chelation. While ozone direct oxidation was subordinate in the system. The oxidation process can be controlled as partial oxidation and complex breaking. Firstly, the highly stable nickel complex was oxidized into labile small molecule of Ni complex and part of the ionic state Ni. Subsequently, SN-9, the high-efficiency Ni chelation captures with the main functional group of -SH, captured the Ni ion from the low molecular and instable Ni complex or directly reacted with Ni (Ⅱ) to form a stable tetragonal coordination precipitate to remove Ni from wastewater.