Adsorption of bensulfuron-methyl on kaolinite as influenced by Pb contamination

• Published in: Journal of soils and sediments Vol. 9; no. 5; pp. 476 - 481
• Main Authors: Wu, Wei-Hong, Xu, Jian-Ming, Feng, Zi-Song, Xie, Zheng-Miao
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Berlin/Heidelberg : Springer-Verlag 01.10.2009; Springer-Verlag; Springer Nature B.V
• Subjects: Adsorption; Agriculture; Cations; Contamination; Earth and Environmental Science; Environment; Environmental Physics; Filtrate; Heavy metals; Kaolinite; Liquid chromatography; Metal ions; Metals; Minerals; Pollution; Sec 3 • Remediation & Manage of Contaminated Lands • Research Article; Soil Science & Conservation; Soils; Sorption; Studies; China; China, People's Rep., Zhejiang Prov; Bensulfuron-methyl; Pb; Kaolinite; Isotherm models; Agro-ecological environment; Adorption
• DOI: 10.1007/s11368-009-0088-7
• ISSN: 1439-0108

Background, aim and scope The combined pollution of bensulfuron-methyl (BSM) and heavy metal Pb has been a common problem in agro-ecological environment in southern China. As an important natural clay mineral, the kaolinite structure possesses great advantages in many processes due to its high chemical stability and low expansion coefficient. The adsorption of BSM on kaolinite was therefore investigated at varying Pb²⁺ concentrations (0, 100, 500 and 1,000 mg kg⁻¹) and different pH levels (3, 4 and 5) using the batch equilibration experiment. Materials and methods BSM was purchased from Aldrich Chemical Co. (purity, 98%), used as the model compound in this study. The experimental kaolinite was sampled from Yuhang in Zhejiang Province. The metal salts used in the study are Pb(NO₃)₂. The kaolinite samples were spiked with Pb at a rate of 100, 500 and 1,000 mg kg⁻¹ air-dried soil, respectively. The adsorption of BSM on kaolinite was investigated using the batch equilibration experiment. The BSM concentration of the filtrate was determined by high-pressure liquid chromatography. Results and discussion The adsorption of BSM on kaolinite could be described by the Freundlich isotherm equation, with the R ² values greater than 0.959 in all experimental treatment. The presence of Pb²⁺ in kaolinite promoted the adsorption of BSM, and the higher Pb would generally lead to the stronger sorption of BSM by kaolinite based on the observed K f values. The adsorption of BSM on kaolinite declined with the increase of pH, and the spiked Pb²⁺ aggravated the reduction of adsorption of BSM. The exclusion between BSM and kaolinite was strengthened with the increase of pH, which partially elucidated the adsorption of BSM decreasing with increasing pH of the solution. Some adsorption of Pb²⁺ took place along the outer hydroxyl plane, therefore releasing H⁺ ions located there. The spiked Pb²⁺ would promote the adsorption of BSM onto kaolinite by increasing the hydrogen (H⁺) ions concentration in solution. The interactions of the heavy metal cations with the kaolinite could affect the structure and other properties such as swelling capacity, compaction capability and the double-layer behaviour of kaolinite. In addition, the substitution of H⁺ ions for metal ions could change the Van der Wals force within the kaolinite structure. All these might lead to the increased sorption of BSM onto kaolinite at the presence of Pb²⁺. Conclusions The addition of Pb²⁺ and the reduction of pH in solution would enhance the retention of BSM and thus effectively retard BSM from entering the aqueous phase. The mechanisms involved in the promotion effects of the spiked Pb²⁺ on adsorption might be primarily attributed to the increased hydrogen (H⁺) ions as a consequence of the addition of Pb²⁺. Recommendations and perspectives Further investigation would be required to give insight into the specific mechanism controlling the adsorption of BSM on kaolinite.