Attenuation of Zn(II) and Cu(II) by low-alkali activated clay-fly ash liners

• Published in: Applied clay science Vol. 250; p. 107298
• Main Authors: Fashtali, Ali Rezapour, Payan, Meghdad, Zanganeh Ranjbar, Payam, Khaksar Najafi, Elmira, Jamshidi Chenari, Reza
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.03.2024
• Subjects: Attenuation; Column leaching test; Fly ash; Heavy metals; Hydroxide precipitation; Low-alkali activated cement; Physical adsorption; Column leaching test; Fly ash; Low-alkali activated cement; Attenuation; Hydroxide precipitation; Physical adsorption; Heavy metals
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2024.107298

This study is aimed at evaluating the performance of low-alkali activated clay-fly ash liners as an environmentally friendly approach to attrap heavy metals cations and prevent the leachate containing such hazardous materials from spreading through the soil medium. For this purpose, a series of unsaturated experimental column leaching tests is carried out on clay-fly ash samples containing 20% fly ash activated by 1, 2 and 4 M NaOH solutions, leading to different Na/fly ash ratios. The leachate, synthesized by various equal concentrations of copper sulfate CuSO4 and zinc nitrate Zn(NO3)2, i.e. 50 mg/L, 100 mg/L and 150 mg/L, is monitored while passing through various treated clayey soils to assess their time-dependent attenuation capacity and permeability at three different leaching times so as to select the sample with the best overall performance. The leaching test is then continued for the corresponding sample until 57 days in order to determine the unsaturated breakthrough curve and effective diffusion coefficient of the pollutants. The results of experiments show the mutual contribution of hydroxide precipitation and physical adsorption to the attenuation process, where the lower alkali concentration favors the former; thus the clay-fly ash liner activated by 1 M NaOH solution exhibits the best attenuation performance, achieving appreciably high removal rates of >99.71% for Zn(II) and 94.47% for Cu(II), after 192 h of leaching. Furthermore, having a lower breakthrough time and effective diffusion coefficient, 1 M alkali-activated clay-fly ash is observed to considerably work better than the untreated clay in the long-run attenuation. Microstructural analyses also reveal the presence of new crystalline phases and rise in amorphous content, referring to new chemical bonds produced due to the immobilization of heavy metals. [Display omitted] •Performance of low-alkali activated clay-fly ash liners to attrap heavy metals is evaluated.•Unsaturated experimental column leaching tests is performed on clay-fly ash liners.•Attenuation capacity, permeability, breakthrough curve and diffusion coefficient are evaluated.•Mutual contributions of hydroxide precipitation and physical adsorption are assessed.