垃圾渗滤液污泥基生物炭吸附Pb(Ⅱ)、Cd(Ⅱ)的效果及机理研究

Effect and Mechanism of Pb(Ⅱ)and Cd(Ⅱ)Adsorption by Sludge-Based Biochar from Landfill Leachate

以垃圾焚烧发电厂垃圾渗滤液处理后产生的污泥为原料,热解制备垃圾渗滤液污泥基生物炭(Landfill leachate sludge-derived biochar,LLSDB)。单因素实验发现,在LLSDB热解温度为500、600℃,投加量为0.3、0.3 g,吸附温度为40、20℃,Pb(Ⅱ)、Cd(Ⅱ)的溶液初始浓度分别为1000、200 mg/L时,Pb(Ⅱ)、Cd(Ⅱ)的去除率分别达到96.4%和94.9%。竞争吸附实验说明Cd(Ⅱ)对Pb(Ⅱ)的吸附起一定促进作用,而Pb(Ⅱ)对Cd(Ⅱ)的吸附起强烈抑制作用。通过吸附等温线、电镜扫描以及X射线衍射分析,推测其吸附机理:LLSDB中碳酸盐和氢氧化物热解生成氧化物,氧化物在水溶液中生成氢氧化物,与Pb(Ⅱ)、Cd(Ⅱ)发生置换反应及竞争反应,最终生成PbCO3、Cd(OH)2,沉淀在LLSDB的表面,即LLSDB对Pb(Ⅱ)和Cd(Ⅱ)的吸附,浓度低时遵循线性分配,以物理吸附为主;浓度高时发生一系列化学反应,以化学吸附为主。

Preparation of leachate desiccate-drived biochar(LLSDB)by pyrolysis of sludge generated from landfill leachate treatment in waste incineration power plants as raw material.The single-factor experiment found that the removal rates of Pb(Ⅱ)and Cd(Ⅱ)reached 96.4%and 94.9%at the LLSDB pyrolysis temperature,dosage,adsorption temperature,and the initial concentrations of Pb(Ⅱ)and Cd(Ⅱ)solutions of 500℃and 600℃,0.3 g and 0.3 g,40℃and 20℃,1000 mg/L,and 200 mg/L,respectively.The competitive adsorption experiments indicated that Cd(Ⅱ)improved the adsorption of Pb(Ⅱ),while Pb(Ⅱ)strongly inhibited the adsorption of Cd(Ⅱ).The adsorption mechanism was proposed by adsorption isotherms,scanning electron microscopy(SEM),and X-ray diffraction(XRD)analysis.The adsorption mechanism of LLSDB is speculated that the carbonate and hydroxide in LLSDB were pyrolyzed to generate oxides,and the oxides generate hydroxides in aqueous solution.The hydroxides reacted with Pb(Ⅱ)and Cd(Ⅱ)to form PbCO3and Ca(OH)2by displacement and competition,and final precipitation on the surface of LLSDB.Thus the adsorption of Pb(Ⅱ)and Cd(Ⅱ)by LLSDB follows a linear distribution at low concentrations by dominated physical adsorption,and a series of chemical reactions occurred by dominated chemical adsorption at high concentrations.