Effect of modified bentonite on copper migration via bank soils in the Jialing River, Southwest China

Abstract

Bentonite and amphoteric, amphoteric–cationic, and amphoteric–anionic bentonite were uniformly added to the bank soils of Cangxi, Nanbu, Jialing, and Hechuan from Jialing River (Sichuan and Chongqing sections) with a mass ratio of 1% to explore the effect of modified clay on copper migration in riverbank soil. The morphological features and migration rules of copper in different amended bank soils were simulated through a column experiment. As Cu2+ passes through a soil column, the balance time of copper (when the Cu2+ concentrations at inlet and outlet are identical) was the highest in the bank soil amended by amphoteric–anionic bentonite. The balance time of copper in different bank soils amended by the same ameliorant was ranked in the order of Jialing > Nanbu > Cangxi > Hechuan, Compared with balance time, the mean flow rate of copper in different soil columns was changed from 7.6 mL d−1 to 39.3 mL d−1. The total cumulative copper in different amended soils (21.17–42.50 g kg−1) showed the same trend with balance time. The proportion of copper in carbonate form was the largest (54.33%), followed by that in exchangeable forms (19.88%). The proportions of copper in iron–manganese oxide (13.77%) and organic matter forms (12.01%) were low in each amended bank soil. Copper in exchangeable and carbonate forms decreased with the increase in the vertical depth of the column, whereas the distributions of iron–manganese oxide and organic matter forms were uniform. The cation exchange capacity and specific surface area of bank soil were crucial in determining the exchangeable and carbonate form content of copper in different amended soils. This study can be applied in the prevention of pollutant migration to rivers via bank soils.