Copper and zinc distribution coefficients for sandy aquifer materials

Distribution coefficients (Kd) were measured for copper (Cu) and zinc (Zn) in laboratory batch experiments for 17 sandy aquifer materials at environmentally relevant solute concentrations (Cu: 5–300 μg/l, Zn: 20–3100 μg/l). The Kd values ranged two to three orders of magnitude (Cu: 70–10,800 l/kg; Zn: 6–22,800 l/kg) and correlating them to the characteristics of the aquifer material (particle size distribution, organic C content, surface area, pH) revealed good correlation with pH in the range 5.3–8.9 (Cu: r2=0.72; Zn: r2=0.94). Including any other of the measured aquifer characteristics improved the correlation only a few percent. The results indicate that the mobility of Cu and Zn in sandy aquifers, as reflected in the measured Kd values, is very restricted at pH values above 6, since the relative migration velocity is less than 1%. However, at lower pH values, Zn seems to become mobile in sandy aquifers.