层状双金属氢氧化物去除废水中重金属的研究

Study on removal of heavy metals from wastewater by layered double hydroxides

针对燃煤电厂脱硫废水中存在多种重金属离子的水质特点,采用模拟废水研究了层状双金属氢氧化物(LDHs)对重金属的去除效果和去除机理。采用共沉淀法制备了弗里德尔盐(Fs)和钙矾石(Ett)2种LDHs重金属吸附剂,探究了其投加量、废水初始pH和废水中共存离子对重金属去除效果的影响,结合动力学研究,阐释了LDHs对重金属的吸附机理。结果表明:当Ett和Fs投加质量浓度分别为0.15、0.07 g/L时,模拟废水中Zn(Ⅱ)、Cd(Ⅱ)、Pb(Ⅱ)、Cr(Ⅵ)的去除率均可达90%以上;当废水初始pH>5.0时,重金属去除率较为理想,均在80%以上,最佳pH为9.0;模拟废水中的共存离子对LDHs去除重金属存在干扰,但增加吸附剂投加量,废水中重金属残余量均能满足DL/T 997—2020排放标准;机理研究表明,LDHs可通过表面沉淀和同构取代实现对重金属阳离子的快速吸附,通过表面吸附和层间离子交换实现对重金属阴离子的高效去除。

In view of the water quality characteristics of the existence of various metal ions in desulfurization waste water from coal-fired power plant,the removal effect and mechanism of layered double hydroxides(LDHs)on heavy metals were studied by using simulated wastewater.In this paper,two kinds of LDHs heavy metal adsorbents,Friedel salt(Fs)and Ettringite(Ett),were prepared by coprecipitation method.The effects of their dosage,initial pH of wastewater and coexisting ions in wastewater on the removal of heavy metals were investigated.The adsorption mechanism of LDHs on heavy metals was explained in combination with kinetic study.The experimental results suggested that,when the mass concentration of Ett and Fs was 0.15 g/L and 0.07 g/L respectively,the removal rates of Zn(Ⅱ),Cd(Ⅱ),Pb(Ⅱ)and Cr(Ⅵ)in simulated wastewater could reach more than 90%.When the initial pH of wastewater was more than 5.0,the removal rate of heavy metals was ideal,which was more than 80%,and the optimal pH was 9.0.The coexisting ions in the simulated wastewater interfered with the removal of heavy metals by LDHs,but the residual amount of heavy metals in the wastewater could meet the DL/T 997-2020 by increasing the dosage of adsorbent.LDHs could quickly adsorb heavy metal cations through surface precipitation and isomorphic substitution,and heavy metal anions could be effectively removed through surface adsorption and interlayer ion exchange.