Retardation and hydrodynamic dispersion of potassium, copper and chloride in Itarare subgroup residual soils in the State of Sao Paulo

Abstract

Hydrodynamic dispersion coefficient (D_h) and the retardation factor (R_d) to chemical species of K⁺, Cu²⁺ and Cl^- were evaluated in sandy and clay-rich residual soils of Itarare Subgroup, collected from Mogi Mirim and Capivari counties respectably, located in the eastern region Sao Paulo State. Laboratory tests were carried out percolating of potassium chloride and copper chloride solutions of variable concentrations (250 mg/L, 500 mg/L and 1000 mg/L of K⁺ and Cu²⁺), through saturated soil columns and steady-state flux. Breakthrough curves (BTC) were constructed and transport parameters were calculated by fitting theoretical curve to the experimental data using the STANMOD software. Mineralogical alterations and precipitates were examined in soil samples using scanning electronic microscope. The calculated R_d for cations ranged from 9 to 3.9 in sandy soil and from 5.7 to 3.5 in clay-rich soil. For chloride it varied from 4.6 to 2.4. Hydrodynamic dispersion coefficients showed values ranging from 0.02 to 0.31 cm²/min for cations and from 0.01 e 0.11 cm²/min for chloride. The column tests showed that ionic retention was highly influenced by pore volume on soil, by flux velocity. Mineralogical analyses of the percolated soil samples did not indicate dissolution and precipitation of minerals.