Cd Fractions in Unvegetated Vertical Subsurface Flow Constructed Wetland Using Different Supporting Media

A metal fractionation study of cadmium was carried out to examine the proportion and changes of five metal species in five mixed substrates named SSFGF, FSSGF, FSSFF, FSSFG and FSFGF, consisting of fly ash, sludge, soil, fine cinder, gravels and fine sand at 5mg/L, 10mg/L, 20mg/L, 30 mg/L and 50mg/L initial concentration. The fractions in the sediments dominated on account of the exchangeable, bound to carbonates and bound to Fe-Mn oxides fractions. The contents of Cd in SSFGF, FSFGF and FSSFG were greater than those in the other two substrates at different sample time.