Strongly acidic lead contaminated soil solidification/stabilization using metakaolin-modified fly ash phosphoric-based geopolymer

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Vol. 496; p. 154336
• Main Authors: Pu, Shaoyun, Xu, Bomin, Cai, Guojun, Duan, Wei, Liu, Yang, Lang, Lei, Shen, Zewei, Yao, Huiran
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.09.2024
• Subjects: Acidic contaminated soil; Leaching properties; MAPG binder; Mechanical properties; Microscopic mechanism; Solidification/stabilization; Leaching properties; Mechanical properties; Acidic contaminated soil; Solidification/stabilization; MAPG binder; Microscopic mechanism
• ISSN: 1385-8947
• DOI: 10.1016/j.cej.2024.154336

•A MAPG binder was developed for strongly acidic Pb2+ contaminated soil solidification/stabilization.•MAPG binder is an acidic cementitious material prepared using fly ash, metakaolin, and aluminum dihydrogen phosphate.•Optimal mix ratio of MAPG binder is the L/S of 0.45, MK content of 3%, and ADP concentration of 35%.•MAPG binder had a good S/S effect on strongly acidic lead contaminated soil under different leaching environments. The existing binders are difficult to be compatible with the acidic environment of acidic heavy metal contaminated soil, it is hard to repair acidic heavy metal contaminated soil. In this study, a modified acid phosphorus-based geopolymer (MAPG) binder suitable for the solidification/stabilization (S/S) treatment of acidic heavy metal Pb2+ contaminated soil was fabricated using aluminum dihydrogen phosphate (ADP) as activator, fly ash and metakaolin (MK) as raw materials. The influences of liquid–solid ratio (L/S), MK content, ADP concentration, curing age and leaching environment on the compressive strength, toxic leaching, resistivity, pH and EC of MAPG stabilized acidic Pb2+ contaminated soil were studied. Meantime, the X-ray diffraction, scanning electron microscopy, fourier transform infrared spectroscopy, and mercury intrusion (MIP) experiments were used to study the chemical properties and microscopic performance of MAPG treated acidic Pb2+ contaminated soil. The results showed that the MAPG binder prepared from MK had an excellent S/S effect on the acidic Pb2+ contaminated soil, and the MAPG binders had good compatibility with the acidic environment. The compressive strength of each group of MAPG stabilized soil could meet the strength standard (>350 kPa) for solid waste landfill and Pb2+ leaching concentration is < 5 mg/L for toxicity identification criteria after 7 days of curing. With an increase in curing age, the strength of stabilized acidic contaminated soil decreased slightly, but the strength still met the requirements of landfill strength standard after 28 days of curing. In three different leaching environments, the Pb2+ leaching decreased with an increase in curing age. Microscopic analysis showed that the main crystalline compounds in stabilized contaminated soil were potassium feldspar, Berlinite and lead phosphate compounds, and their contents were related to L/S, MK content, ADP concentration, and curing time. Potassium feldspar, berlinite, and lead phosphate compounds could not only fill pores, but also had physisorption, encapsulation and chemical precipitation effects on Pb2+. The study could provide an economical, environmental friendly and efficient binder for the remediation of acidic Pb2+ contaminated soil, but the further investigation into the long-term effectiveness of the MAPG binder or its applicability to other types of contaminated soil is also needed.