Leaching and microstructural properties of lead contaminated kaolin stabilized by GGBS-MgO in semi-dynamic leaching tests

• Published in: Construction & building materials 2018-05, Vol.172, p.626-634
• Main Authors: Wu, Hao-Liang, Jin, Fei, Bo, Yu-Lin, Du, Yan-Jun, Zheng, Jun-Xing
• Format: Article
• Language: English
• Subjects: Acid deposition; Air pollution; Analysis; Clay; Contaminated soil; Environmental aspects; Leaching; Leaching test; Reactive MgO; Slag; Solidification/stabilization
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2018.03.164

•Leaching is diffusion-controlled at pH 7 and 4 while dissolution-controlled at pH 2.•Observed diffusion coefficient is affected by the SAR pH and binder dosage.•Pb is primarily precipitated as hydrocerussite (Pb2(CO3)2(OH)2) in soil matrix.•ANC and pore structure of the treated soil affect diffusive properties of Pb. Ground granulated blast furnace slag (GGBS) is widely used to stabilize soils due to its environmental and economic merits. The strength and durability of reactive MgO activated GGBS (GGBS-MgO) stabilized lead (Pb)-contaminated soils have been explored by previous studies. However, the effects of simulated acid rain (SAR) on the leachability and micro-properties of GGBS-MgO stabilized Pb-contaminated soils are hardly investigated. This research studies the leachability and microstructural properties of GGBS-MgO stabilized Pb-contaminated kaolin clay exposed to SAR with initial pH values of 2.0, 4.0 and 7.0. A series of tests are performed including the semi-dynamic leaching tests using SAR as the extraction liquid, acid neutralization capacity (ANC), mercury intrusion porosimetry (MIP), and X-ray diffraction (XRD) tests. The results demonstrate that as the SAR pH decreases from 7.0 to 4.0, the Pb cumulative fraction leached (CFL) and observed diffusion coefficient (Dobs) increases significantly whereas the leachate pH decreases. Meanwhile, increasing the GGBS-MgO content from 12% to 18% results in the decrease of CFL and Dobs. Further decreasing the SAR pH to 2.0 results in the dissolution-controlled leaching mechanism regardless of the binder dosage. The differences in the leaching properties under different pH conditions are interpreted based on the cemented soil acid buffering capacity, hydration products and pore size distributions obtained from the ANC, MIP, and XRD tests, respectively.