Remediation of Cadmium and Lead in contaminated soils by a newly modified fly ash material: The possibility and safety

Abstract

Heavy metal (HM) contamination in soils harms the organisms through the food chain. A large number of methods have been used to alleviate soil pollution. However, there is a lack of information about soil security after amendments. A new material, modified fly ash (MFA), was developed by a low-temperature and alkali calcination technology, and explored the possibility and safety for remediation of lead (Pb) and Cadmium (Cd) contaminated soils. The remediation efficiency was studied through pots experiments. To ensure accuracy, soils were collected in three different areas; a similar material, zeolite (ZO), known for its good remediation of HMs, was introduced for comparison. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and Brunauer–Emmett–Teller (BET) were introduced to better understand the repair mechanism; the soil pH, the concentration of Cd and Pb in soil and plant, soil enzyme activity were detected to explore the possible and safety of MFA. The main remediation mechanisms may be ion exchange, surface affinity and complexation. The MFA reduces the concentrations of bio-available Cd (53.44%–92.01%) and Pb (28.96%–35.56%) in soils. Then their concentration in Solanum nigrum L. (S. nigurm) also be decreased (in the root and above-ground (stems and leaves): 44.58%–66.44% and 53.87%–73.28% for Cd, 21.01%–53.63% and 15.91%–33.27% for Pb.). Besides, the activities of urease (URE), alkaline phosphatase (ALP), and protease (PRE) were 3.12–5.28, 1.09–1.69, and 7.08–47.80 times of those in the initial phase of the experiment, respectively. Consequently, MFA has excellent remediation ability for contaminated soils in different areas and soil quality has been improved.