基于2种典型固废制备托贝莫来石及其对Cd^(2+)的吸附性能

Study on tobermorite preparation from fly ash aluminum extraction slag and papermaking white mud and its adsorption capacity on Cd^(2+)

以2种典型固体废弃物粉煤灰提铝酸渣和造纸白泥为原料,采用一步水热法制备托贝莫来石,并用于吸附Cd^(2+)实验。通过X射线衍射仪、扫描电子显微镜、傅里叶变换红外光谱仪、全自动比表面及孔隙分析仪和差示扫描量热同步热分析仪等表征手段,阐明了托贝莫来石形成机理以及对Cd^(2+)的吸附机制。结果表明:当Ca/Si摩尔比为0.8、水热时间6 h、温度180℃、NaOH加入量为2.5%~5.0%时可制备出比表面积80.956 m^(2)/g、总孔容为0.218 cm^(3)/g、孔径为1.21 nm、相对结晶度为97%、以短纤维为主,且在650℃以下具有较好热稳定性的托贝莫来石,其形成过程可分为4个步骤:造纸白泥中氧化钙转变成氢氧化钙和粉煤灰提铝酸渣非晶态二氧化硅转变成硅酸钠,氢氧化钙与硅酸钠溶液形成的凝胶块体材料,托贝莫来石晶须形成,晶须逐渐剥落并不断劈裂并长大形成托贝莫来石纤维状材料。将制备的托贝莫来石吸附Cd^(2+),结果表明:当托贝莫来石添加量为2.5 g/L、含Cd^(2+)废水pH=3、Cd^(2+)质量浓度为100 mg/L时,托贝莫来石对Cd^(2+)去除率达99.99%;托贝莫来石吸附Cd^(2+)符合准二级动力学方程和Langmuir模型,由膜扩散和颗粒内扩散联合控制,以化学吸附为主,是单层吸附。研究结果表明利用粉煤灰提铝酸渣和造纸白泥制备的托贝莫来石对Cd^(2+)具有良好的吸附效果,实现了2种不同行业典型固废资源的协同综合利用,为处理含Cd^(2+)等重金属离子废水提供一种潜在方法。

In this study,tobermorite was prepared by hydrothermal method using two kinds of typical solid waste as raw materials,i.e.,fly ash aluminum extraction slag(by-product in the process of fly ash hydrochloric acid aluminum extrac-tion)and papermaking white mud.The XRD,SEM,FTIR,TG-DSC and Specific surface area and porosity were used to investigate the influence of Ca/Si ratio,alkalinity,hydrothermal conditions and other factors on the synthesis products,and the formation mechanism of tobermorite.The adsorption capacity of tobermorite was investigated by adsorption experi-ments.The effects of different dosage,initial concentration of Cd^(2+)and adsorption time on the adsorption behavior were investigated to understand the adsorption mechanism of tobermorite on Cd^(2+).The results show that the well crystal tober-morite can be synthesized at 180°C for 6 h with the Ca∶Si molar ratio of 0.8 and the NaOH addition amount of 2.5%-5.0%.The specific surface area of tobermorite is 80.956 m^(2)/g,the total pore volume is 0.218 cm^(3)/g,the pore size is 1.21 nm,and the crystallization of tobermorite is 97%.The microstructure of tobermorite is dominated by short fibers and has a good thermal stability below 650°C.The formation process of tobermorite can be described that the CaO in paper-making white clay is converted into Ca(OH)2 and the amorphous silicon dioxide is transformed into sodium silicate.The gel blocks material is formed by calcium hydroxide and sodium silicate solution.Tobermorite whiskers are formed,and the whiskers gradually exfoliate,split and grow to form tobermorite fibrous materials.The Cd^(2+)removal rate of tobermor-ite can reach 99.99%at pH value of 3,the dosage of tobermorite is 2.5 g/L,and the concentration of Cd^(2+)is 100 mg/L.The adsorption of Cd^(2+)by modified tobermorite fits the quasi-second-order kinetic equation and the Langmuir model,and is controlled by membrane diffusion and intra-particle diffusion,and the chemisorption is the main control step.The study indicates that tobermorite can be prepared from aluminum extraction slag with fly ash and white paper mud.The tober-morite prepared had a good adsorption effect on heavy metals and can be used as a high efficient adsorbent for heavy met-al ions.Also,the study realizes the collaborative utilization of two typical solid waste resources in different industries,and provides a potential method for the treatment of wastewater containing Cd^(2+)and other heavy metal ions.