Fate and Transport of Lead and Copper in Calcareous Soil

Heavy metals transport to groundwater relies on the characteristics of soil, such as carbonate and clay minerals, organic matter content, soil pH, and some other factors. Most of the heavy metals in calcareous soils are precipitated as metal carbonate minerals; consequently, their transport to the groundwater is not anticipated. Therefore, the current study focused on the impacts of calcium carbonate presence on the adsorption and transport of lead (Pb) and copper (Cu) in calcareous soil using batch and column experiments. To elucidate the contaminants removal mechanisms in calcareous soils, extensive laboratory batch investigations were conducted to study the equilibrium kinetic and adsorption isotherm characteristics of the two studied heavy metals. The quick adsorption of Pb2+ and Cu2+ by soil was seen in kinetics trials. In addition, Pb2+ and Cu2+ sorption onto the soil was best described by the pseudo-second order kinetic model (R-2 = 0.9979 and 0.9995 for Cu2+ and Pb2+, respectively). To explain the equilibrium sorption data, the Freundlich isotherm showed the best fitness to Pb2+ (R-2 = 0.96) and Cu2+ (R-2 = 0.98), collectively. The Freundlich parameters revealed that the Pb2+ has favorable adsorption; however, Cu2+ has unfavorable adsorption onto the soil. The results of column experiments showed the higher binding of Pb2+ than Cu2+ to the top surface of the soil column, making the movement of these two metals very slow. In columns, most of the Pb2+ and Cu2+ ions were sorbed at an initial 5 and 10 cm, respectively. The findings of this study will help in understanding the fate of heavy metals in calcareous soils.