硅酸盐学报

水泥窑协同处置含重金属固废作为一种无害化资源化处理方式具有巨大的优势，但是由于水泥水化产物对于重金属存在固溶极限，导致固废处置量受到限制。本工作提出制备具有高效吸附重金属离子性能的乙二胺四乙酸联合氨基硫脲改性壳聚糖(TS-EDTA-C)，加入到水泥基材料中提升吸附重金属的性能。通过胶砂强度、离子浸出浓度分析、Tessier五步连续提取法、SEM-EDS分析、XRD分析和水化热分析测试改性壳聚糖对含重金属水泥性能的影响。结果表明：掺入TS-EDTA-C材料后，含有重金属的水泥胶砂试样强度在各个龄期均有所提高和重金属离子的浸出浓度明显降低。Tessier五步连续提取法和SEM-EDS试验证明了TS-EDTA-C在水泥中成功吸附了重金属并以更加稳定的形态存在。XRD和水化热分析结果也证明了TS-EDTA-C添加后含重金属水泥的早期水化产物更多，弱化了重金属离子对早期水化带来的不利影响。

Introduction Co-disposal in cement kilns is a disposal method to achieve harmless and resourceful reuse of solid waste.However,cement kiln co-disposal technology is constrained by some specific components in solid waste.For solid wastes with a high content of heavy metals,such as waste battery slag,fly ash and electroplating sludge,heavy metals are involved in the clinker firing process through solid-phase and liquid-phase reactions during co-disposal in cement kilns,which may ultimately increase the content of heavy metals in the cement clinker,which can be re-released in the course of use,posing a threat to the environment and human safety.Also the presence of heavy metal ions can have a hindering effect on cement hydration.In recent years,fiber adsorbent materials have been widely used to treat heavy metal ions in wastewater,and researchers have prepared related materials with excellent performance.Chitosan is one of them,which is a natural biopolymer similar in structure to cellulose fibers commonly used in construction projects.Chitosan has its unique advantages:renewable resource,wide range resource,relatively low cost,having functional groups such as hydroxyl and amino,which,makes it an excellent adsorbent for metal ions.This work prepared modified chitosan material and its application on heavy metal-containing cement was investigated.Mthods Chitosan,disodium EDTA,1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride,N-hydroxysuccinimide,formaldehyde,aminothiourea,copper nitrate,lead nitrate,zinc nitrate,anhydrous ethanol and other compounds at analytically pure grade were supplied by Beijing Jiashiteng Trade Limited Liability Company.The cement P·I 42.5 and standard sand used in this study were produced from Fushun Ausair Technology Limited Liability Company.In this study,an aminothiourea combined with ethylenediaminetetraacetic acid modified chitosan material (TS-EDTA-C) was prepared to increase its adsorption and stability of heavy metal ions by modification.TS-EDTA-C was added to the cement containing heavy metal ions to test the leaching concentration of heavy metal ions in the cement specimens at 7,14 d and 28 d as well as the compressive and flexural strengths of the cement specimens at 3,7,14 d and 28 d.In addition,the heat of hydration of the cement specimens at 7 d was tested.Cement specimens at various ages were tested by XRD.The presence of heavy metals in the cementitious materials was tested by Tessier's five-step sequential extraction method.Results and discussion The adsorption of modified chitosan (TS-EDTA-C) for Zn²⁺,Cu²⁺and Pb²⁺in solution was greatly improved and far exceeded that of unmodified chitosan (CS).The higher adsorption is mainly due to the introduction of a large number of groups such as—OH,—COOH,—NH₂ and S on chitosan that can react with metal ions,while the modified chitosan surface is rougher,providing a larger adsorption surface.By comparing the cement specimens,it was found that the strength of the cement specimens containing heavy metals with the addition of TS-EDTA-C was higher than that of the specimens containing heavy metals without the addition of TS-EDTA-C at all ages,and the strength of the cement specimens without the addition of heavy metal ions was the highest.Because the hydration of cement occurs in an alkaline environment,heavy metal ions preferentially calcium ions react with OH~–to generate some insoluble products,and the precipitation adsorbed on the surface of the cement particles impedes the further dissolution of cement mineral ions,leading to a decrease in the hydration products contributing to the cementitious properties and causing a significant decrease in the early strength of the cement mortar.The additional TS-EDTA-C will react with the heavy metal ions in the cement and adsorb them on the modified chitosan material,reducing the presence of free heavy metal ions and insoluble hydroxyl compounds,weakening their influence on the hydration reaction of the cement as well as lowering the leaching concentration of heavy metal ions.From the heat of hydration and XRD plots of the cement specimens at 7 d,it can be seen that Zn²⁺,Cu²⁺and Pb²⁺played an obvious inhibitory effect on the early hydration of cement and prolonged the hydration induction period of cement.The addition of TS-EDTA-C attenuated the effect of heavy metal ions on the early hydration of cement.Because when TS-EDTA-C was added to the heavy metal-containing cement,TS-EDTA-C adsorbed the heavy metal ions in the cement,which led to an increase in the heavy metal ions in the Q4 form and a decrease in the heavy metal ions in the Q1+Q2+Q3 form,reduced the presence of free unstable heavy metal ions,and lowered the unfavorable effects of the heavy metal ions.To a certain extent,it enabled Ca²⁺to react with OH~-,which promoted the hydration reaction.Meanwhile,the adsorbed heavy metal ions existed in a more stable form,reducing the leaching toxicity of heavy metal ions in cement.Conclusions In this paper,modified chitosan TS-EDTA-C (aminothiourea combined with ethylenediaminetetraacetic acid modified chitosan),which can effectively adsorb heavy metal ions,was prepared,and TS-EDTA-C had a good adsorption effect on Zn²⁺,Cu²⁺and Pb²⁺,with the maximal adsorption amounts of 21.92,68.08 mg/g,and 36.27 mg/g,respectively.TS-EDTA-C can effectively mitigate the adverse effects of heavy metals on cement properties.The 3,7,14 d,and 28 d compressive strengths of cement specimens with TS-EDTA-C were increased by 41.6%,7.87%,14.46%,and 2.51%,respectively,compared with those of heavy metal-containing cement specimens without modified chitosan.The heat of hydration and XRD tests proved that the addition of TS-EDTA-C attenuated the adverse effects of heavy metals on cement hydration.Modified chitosan is beneficial for cement stabilization and curing of heavy metals.The leaching concentrations of heavy metal ions were lower than those of the heavy metal-containing cement specimens without the addition of TS-EDTA-C.This is understood like that the addition of TS-EDTA-C stables the organic bound state (Q4) of heavy metals in cement,leading to a more stable form of heavy metal inos in cement.