Dechelation of Cd-EDTA complex and recovery of EDTA from simulated soil-washing solution with sodium sulfide

Qingwei Wang; Jiajun Chen; Aihua Zheng; Lanxiang Shi

doi:10.1016/j.chemosphere.2018.12.212

Dechelation of Cd-EDTA complex and recovery of EDTA from simulated soil-washing solution with sodium sulfide

Chemosphere. 2019 Apr:220:1200-1207. doi: 10.1016/j.chemosphere.2018.12.212. Epub 2019 Jan 2.

Authors

Qingwei Wang¹, Jiajun Chen², Aihua Zheng³, Lanxiang Shi¹

Affiliations

¹ Key Laboratory for Water and Sediment Sciences of Ministry of Education, School of Environment, Beijing Normal University, Beijing 100875, PR China.
² Key Laboratory for Water and Sediment Sciences of Ministry of Education, School of Environment, Beijing Normal University, Beijing 100875, PR China. Electronic address: jeffchen@bnu.edu.cn.
³ Analysis and Testing Center, Beijing Normal University, Beijing 100875, PR China.

PMID: 33395805
DOI: 10.1016/j.chemosphere.2018.12.212

Abstract

Washing water containing poorly degradable heavy metal-EDTA complexes is produced by ethylenediaminetetraacetic acid (EDTA) washing of heavy metal-contaminated soil. A series of batch experiments were performed to explore the dechelation of heavy metal-EDTA complexes and the recovery of EDTA from simulated soil-washing solution using sulfide precipitation with Na₂S. The results showed that the effect of Na₂S dosage on the dechelation of Cd-EDTA solution was greater than that of other factors (reaction temperature, time, and pH) and excess EDTA suppressed cadmium removal. Additionally, the Cd removal efficiency reached 99.99 ± 0.001%, and the residual amount of Cd-EDTA was below the detection limit of ion chromatography (IC) measurements under the following optimal conditions: an initial Cd-EDTA solution pH of 6, a sodium sulfide-to-Cd-EDTA ratio of 2:1, a reaction temperature of 25 °C, and a contact time of 20 min. Furthermore, the results of analysis using inductively coupled plasma optical emission spectroscopy (ICP-OES), Fourier transform infrared (FT-IR) spectroscopy, and ion chromatography (IC) confirmed that the dechelation process could be completed in less than 20 min and that EDTA was completely recovered as trisodium EDTA (HNa₃EDTA). The mechanism for the dechelation of Cd-EDTA and recovery of EDTA using sulfide precipitation with Na₂S was also proposed. The recovered EDTA with acidification had the same ability to extract heavy metals from soil with fresh EDTA. This study may facilitate the recycling of soil-washing wastewater and reduce the cost of extracting heavy metals from soil using EDTA.

Keywords: Cd removal efficiency; Dechelation; Orthogonal experiments; Recovery; Trisodium EDTA (HNa(3)EDTA).