Effects of ionic strength, electrolyte type, pH, and flow rate on transport and retention of atmospheric deposition particles in saturated porous media

Abstract

The aims of this study are to investigate whether fine atmospheric deposition particulate (diameter less than 2.5 μm, PM2.5 particles) carried some heavy metals and its transport behaviors in saturated porous media when the environmental conditions changed. The heavy metal concentrations (Cr, Ni, Cu, Zn, As, Cd, Hg, and Pb) of the PM2.5 particles were measured. Column experiments were conducted to investigate the effect of several important environmental factors (ionic strength, electrolyte type, pH, and flow rate) on transport of PM2.5 particles. The concentrations of Ni and Zn were higher than the corresponding environmental quality standard for agricultural soils in China. The mobility of PM2.5 particles at ionic strength of 0.1 mM was higher than that at ionic strength of 1 mM in CaCl2 solution, but in NaCl solution, the effect of ionic strength on the PM2.5 particle transport was opposite. Increasing pH and flow rate in CaCl2 solution could decrease the PM2.5 particle deposition in saturated sands. The modeling results from the two-site transport model suggested that straining and attachment might be the mechanisms responsible for PM2.5 particle retention in CaCl2 solution or NaCl solution with ionic strength of 0.1 mM. The results of this study showed that PM2.5 particle might be a potential source of heavy metals in the environment. The transport and deposition behaviors of PM2.5 particles were closely related to ionic strength, electrolyte type, pH, and flow rate in porous media.