Remediation of heavy metal-contaminated mine soils using smoldering combustion technology
Jie Li, Qun Zhao, Yihuang Zhao, Hecheng Fu, Xiaoqing Li, Jianhong Huang, Yingjie Li, Xuewei Hu, Senlin Tian
Abstract
Self-sustaining smoldering is an advanced technology for remediating Cd- or Cr(VI)-contaminated soils, but the effectiveness of this emerging thermal treatment for multiple metal-polluted mine soils remains unclear. In this study, self-sustaining smoldering technology for remediating multiple heavy metal-contaminated mine soils was investigated. The results showed that smoldering treatment reduced the mobility and bioavailability of heavy metals and improved soil nutrient status, thus facilitating the growth of plants. Better (>70%) Cu, Pb, and Cd fixation rates were obtained after smoldering treatment of the contaminated soils, thus mitigating the toxicity of heavy metals, as evidenced by the 38.60%–82.55%, 28.13%–85.79%, and 45.55%–98.09% reductions in DTPA-Cu, Pb and Cd, respectively, compared with the untreated soils. Moreover, pH, organic matter, total N, P, K, and the available P and K in remediated soils were significantly improved. The ryegrass seeds did not germinate in the multiple metal-contaminated mine soils. Conversely, the germination rates of ryegrass seeds in the treated soils after 21 days of cultivation were 73.33%–95.00%. The mechanism analysis revealed that the solid products formed during smoldering improved the soil nutrient status rather than the mineralogy. Due to the carbon-neutral nature of biomass energy and the self-sustainability of smoldering, this study provides a low-cost, energy-efficient, and low-carbon footprint method for remediating metal-contaminated mine soils in reclamation practices.