铅、镉在给水厂残泥免烧陶粒上的竞争吸附特性

Competitive adsorption characteristics of lead and cadmium on UCWTR

为探究给水厂残泥免烧陶粒(UCWTR)作吸附剂应用于多元重金属复杂废水治理的可行性,本研究采用静态吸附实验,分析重金属Pb、Cd在UCWTR上的竞争吸附特性,以及影响重金属吸附的主要因素.结果显示:UCWTR表面颗粒呈规则的柱状体结构,裂隙多、比表面积大,有效提高了其吸附能力.陶粒在内部-OH、Al-OH和Fe-O活性基团及C-S-H凝胶作用与重金属Pb、Cd发生反应.Pb、Cd竞争吸附过程中,UCWTR对Pb、Cd的最大吸附量分别为0.36 mmol·g^(-1)和0.25 mmol·g^(-1),其吸附过程与准二级动力学模型拟合较优(R^(2)_(Cd)=0.963、R^(2)_(Pb)=0.987).Cd可有效促进UCWTR对Pb的吸附,且在一定浓度范围内溶液中Cd浓度越高,这种促进作用越强;较高浓度的Pb对UCWTR吸附Cd产生明显的抑制作用.Langmuir模型和Freundlich模型能分别更好的描述Pb、Cd在UCWTR上的竞争吸附过程.升高pH有利于促进UCWTR吸附Pb、Cd;增加初始投加量会抑制UCWTR对Pb、Cd的单位吸附量.Pb、Cd在UCWTR上的赋存形态以酸提取态占比最高.与单一吸附相比,竞争吸附Pb、Cd赋存形态中酸提取态占比下降、还原态和残渣态占比增加,重金属稳定性增加.

In order to explore the practicability of the Unburned ceramsites derived from water treatment residuals(UCWTR)for remediating multiple heavy metals-contaminated wastewater,a series of static adsorption experiments were carried out here to analyze the competitive adsorption performance of Pb and Cd on the surface of UCWTR and the main factor affecting its adsorption behavior for heavy metals.Results showed that the regular columnar structured UCWTR particles of abundant cracks possessed large specific surface area and rich adsorption sites,which were conducive to improve the adsorption capacity for heavy metals.Meanwhile,the functional groups within UCWTR,such as-OH,Al-OH,Fe-O and C-S-H,also were beneficial to adsorbing Pb and Cd.During the competitive adsorption process of Pb and Cd,the maximum adsorption capacities of UCWTR for Pb and Cd were 0.36 mmol·g^(-1) and 0.25 mmol·g^(-1),respectively,and the adsorption kinetics were fitted better with the pseudo-second-order model(R^(2)_(Cd)=0.963,R^(2)_(Pb)=0.987).The presence of Cd significantly promoted the adsorption of Pb on UCWTR,and more Cd boosted the promotive effect increasingly in a certain range of concentration of Cd.On the contrary,the high concentration Pb obviously inhibited the adsorption of Cd.Competitive adsorption isotherms of Pb and Cd were fitted better by Langmuir and Freundlich models,respectively.The higher pH value led to higher adsorption capacity of UCWTR for Pb and Cd,while the increased adsorbent dosage decreased that.The dominative existence speciation of adsorbed Pb and Cd was acid-extracted state.Compared with single adsorption by UCWTR,the competitive adsorption declined the proportion of the acid-extracted state,increased reduced and residue states,and enhanced the stability of Pb and Cd.