Binding capacity and co-migration potential of Pb(II), Cu(II), and Cd(II) on colloids in road runoff

To evaluate the co-migration potential between heavy metal ions and road runoff colloids, the influence of contact time, temperature, initial concentration of metal ions, pH, humic acid (HA), and polymetallic coexistence on the binding capacity of heavy metals onto runoff colloids were investigated. The adsorption of heavy metals by runoff colloids was extremely rapid, approximately 80% of the equilibrium adsorption capacity was achieved in the first 30 min. The binding capacity exhibited an increasing trend with the initial concentration of metal ions increasing, and the maximum adsorption capacities of Pb(II), Cu(II), and Cd(II) achieved 159.13, 56.06, and 78.35 mg/g at 298 K, respectively. The adsorption capacity of Cu(II) and Cd(II) by runoff colloids increased with temperature increasing, while it displayed a converse trend for Pb(II). Neutral pH facilitated the combination of metal ions and runoff colloids. The presence of humic acid increased the binding capacity of Pb(II), Cu(II), and Cd(II) onto runoff colloids by 72.19, 63.31, and 13.83mg/g, respectively. Compared to the monometallic systems, the binding capacity of Pb(II), Cu(II), and Cd(II) by runoff colloids decreased by 18.44%, 22.35%, and 56.06% in polymetallic systems, respectively. Pb(II) bounded with colloids in the road runoff should be controlled preferentially to avoid their migrations to aquatic environments.