The Effect of Various Plant Covers on the Adsorption and Desorption of Copper Ions in Calcareous Soil

Abstract

Abstract Four soils calcareous with different plant covers (tree cover, vegetable cover, field crop cover, and natural grass cover) were selected from Erbil city of northern Iraq. Six samples (2g form each sample) were prepared in the laboratory for four soils. The samples placed in plastic containers and treated with a solution containing copper sulfate. The concentration of copper ions was (0,5,10,25,50,100, and 200) mg L-1, shaken 24 hours, then left to settle down, then was filtered and the soil used was preserved. It was treated with the solution of Calcium chloride (0.01 M) to remove copper from the soil samples. Left for 4 hours with shaking then left to settle down and then filtered. Copper was measured in adsorption and filters by using AAS at 293 K where the amount of adsorption and liberation for copper was calculated. The Langmuir and Freundlich equations were chosen to detect the ability of soil to hold and release copper. A comparison between the two equations was done to choose the best one for describing adsorption using the coefficient of determination, which proved the superiority of the Langmuir equation at a rate of (91%), the four soils showed a high ability to hold copper, with a remarkable superiority for the soil of trees and vegetables, if the adsorption values ranged between (909-5000) mg kg-1. It was highest in the soil of trees and lowest in the soil of field crops. As for the binding energy, it was ranged between 1.16-7.0 mg L-1. The highest values were in the soil of vegetables and the lowest in the soil of grasses. In addition, Maximum buffering capacity was calculated, and its values ranged (1932-29950) L. Kg-1 had the highest values in the soil of trees and the lowest in the soil of grasses. As for the release process, the four soils showed a high ability to hold copper, and the percentages of release ranged (2.12-4.4%), the highest in the soil of grasses and the lowest percentages in the soil of trees.