The effects of humic substances on the transport of copper(II) in ground water

Abstract

To improve the understanding of the movement of copper plumes in natural ground water systems, the partitioning and transport of Cu(II) in the presence of natural humic substances were investigated in the lab. The humic substances were isolated from high organic content ground water in Orange County, CA (5mgCL⁻¹). Batch and titration experiments produced one-site Langmuir isotherms for the sorption of Cu(II) (0.1-5.0 mgL⁻¹) to am-SiO₂ (K(L) = 1.46Lmg-1, Q = 5.92μgg⁻¹), α-Al₂O₃ (K(L) = 100L mg⁻¹,Q = 130μgg⁻¹), and aqueous humics (pK₁ = -5.5, pL₁ = 5.1). Results of the column experiments suggest that mobile humics facilitate the transport of Cu(II) by lowering the free Cu(II) concentration. Mineral-bound humics retarded the transport of Cu(II) by increasing the concentration of immobile binding sites and by binding considerably more Cu(II) per mass carbon than aqueous humics. The measured Langmuir isotherms accurately predicted retention times and explained much of the tailing of the desorption breakthrough curves.