Adsorption comparison of Cu(II) on riverbank soil from north of Sichuan and Chongqing, China

Abstract

Riverbank soil is the final barrier to prevent pollutants from migrating into the river. Surface and subsurface soil samples of Cangxi, Nanbu, Jialing, Hechuan, Santai, Chuanshan, Quxian, and Guangan were collected from the three rivers in the north of Sichuan and Chongqing, China to explore the effects of riverbank soils on Cu(II) adsorption. Basic physicochemical characteristics of the riverbank soils were analyzed. The isothermal and thermodynamic characteristics of each soil sample on Cu(II) adsorption were studied by batch method, and the adsorption differences under various pH, temperature, and ionic strength were compared. Meanwhile, the adsorption form of Cu(II) on different riverbank soils was analyzed. Results show the following: (1) the adsorption isotherms of Cu(II) on different soil samples were all L-shaped and consistent with Langmuir model. The maximum adsorption capacity (qm) of Cu(II) on the test samples was between 83.63 and 247.24 mmol/kg, and the adsorption capacity of Cu(II) in Jialing soil was the highest under the same equilibrium concentration. (2) The adsorption amount of Cu(II) on different soil samples increased with the increase in temperature, showing a positive temperature effect. The adsorption amount of Cu(II) increased with the increase in pH; it initially increased and then decreased with the increase in ionic strength. Cu(II) adsorption on soil samples was a spontaneous, endothermic, and entropy-increasing process. (3) The adsorbed Cu(II) on banksoils was mainly in the form of carbonate bound and iron manganese oxidation, accounting for more than 60% of the total adsorbed Cu(II). Cu(II) in exchangeable form was the second, and the organic matter form was the lowest. (4) CEC and SBET of soil samples are the key factors affecting the adsorption capacity of Cu(II), and pH and CEC are the key factors determining the adsorption form of Cu(II) on riverbank soil.