Effects of soil components, solution chemical properties, and temperature on Cu(II) adsorption by alluvial acid soil: A case study in Southwest China

The specific soil components such as soil organic matter, Fe and Mn oxides exert a significant influence on Cu(II) adsorption in soil. In the present study, clay fraction was separated from an alluvial acid soil, Then the selective chemical extraction method was used to remove the specific components in the bulk soil and clay fraction. Adsorption experiments showed that the adsorption capacity of the clay fraction of Cu(II) is greater than that of the bulk soil, regardless of whether it is treated by selective chemical extraction or not. Compared with untreated soil samples, after the removal of organic matter by H 2 O 2 , K d decreased by a maximum of 82.8% for the bulk soil and 73.5% for the clay fraction. After the removal of manganese oxides by NH 2 OH·HCl, K d decreased by a maximum of 68.1% for the bulk soil and 73.2% for the clay fraction. However, after the removal of free iron oxides by dithionite-citrate-bicarbonate, K d increased by a maximum of 422% for the bulk soil and 195.5% for the clay fraction. K d increased by 4263.3% when the initial pH increased from 2 to 3.5 and, then, increased to 6. The amount of Cu(II) adsorbed did not change significantly. Within a range greater than 6, the increased Cu(II) adsorption may be due to the precipitation of Cu(II). When the concentration of NaNO 3 changes from 0.01 to 0.1 M, the adsorption capacity decreased by a maximum of 36%, K d decreased by a maximum of 84.3%. The presence of foreign ions decreased Cu(II) adsorption; their order of effect on Cu(II) adsorption is Na + < K + < Mg 2+ < Ca 2+ for cations and NO 3 − < SO 4 2− ≈ Cl − for anions. The adsorption of Cu(II) was an endothermic and spontaneous process under the experimental conditions.