The dissolution characteristics of cadmium containing birnessite produced from paddy crusts

• Published in: The Science of the total environment Vol. 914; p. 169811
• Main Authors: Peng, Liang, Li, Dan, Song, Huijuan, Kuang, Xiaolin, Zeng, Qingru, Ao, Hejun
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.03.2024
• Subjects: Birnessite; Dissolution; Paddy crusts; Birnessite; Cd; Mn; Paddy crusts; Dissolution
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2023.169811

The cadmium (Cd) accumulates in birnessite as it forms on the surface of paddy crusts (PC). The stability of Cd-containing birnessite is influenced by environmental factors, and destabilized birnessite releases dissolved Cd. We report the effects of pH, oxalic acid, and light on the dissolution of Cd-containing birnessite. We found that at pH 4.0, with light and 0.20 mol/L oxalic acid, the ratio of dissolved Cd and manganese (Mn) peaked after 24 h at 2978.0 μg/g and 326.8 mg/g, respectively. The three environmental factors affected the dissolution of Cd-containing birnessite in the following order: pH > oxalic acid > light. During dissolution process, Cd and Mn did not dissolve simultaneously, and the dissolved Cd/Mn ratio in the solution was significantly lower than that of the pristine mineral (33.5 × 10−3). Compared with Mn, Cd dissolution was inhibited by strong acidity (pH 4.0–5.0), and the dissolved Cd/Mn ratio was 5–10 × 10−3. Mild acidity (pH 6.0) was weakly inhibitory, with a Cd/Mn ratio of 6–15 × 10−3. In an alkaline (pH 8.0) oxalate environment, light illumination inhibited Cd dissolution, and the Cd/Mn ratio decreased over time due to the stability of the products formed by oxalate and carbonate, with Cd being more stable than those formed by Mn. Our findings would provide insights into the migration and transformation of PC-associated Cd in paddy fields. [Display omitted] •The CO32- ion is adsorbed on its surface simultaneously throughout the dissolution process of Cd-containing birnessite.•The factors influencing the dissolution of Cd-containing birnessite can be ranked as follows: pH > Oxalic acid > Light.•The dissolved Cd/Mn ratio was significantly lower than the Cd/Mn value of the pristine mineral itself.