The effect of humic substances on the geochemical forms of cadmium in Urmia landfill soil

The mobility of heavy metals plays an important role in soil and groundwater contamination. The aim of this study was to investigate the influence of leonardite on distribution of chemical forms of cadmium (Cd) in the compacted soil of Urmia landfill. For this purpose, soil samples were collected from the landfill and physico-chemical properties and clay mineralogy was determined. The rate of leonardite (0, 2.5, 5, 7.5 and 10 %) were added to soils and then treatment soils compacted in the columns. Cadmium solution (100 mg/l) poured to the soils and then soil samples collected from three depths of column (surface, middle and subsurface) after 72 days for determine chemical forms of Cd in soils. The studied soil contain 43.9% clay and illite (49%), montmorillonite (21%) kaolinite (20.5%) and chlorite 9.5% were dominate clay in soil. Compaction reduced the infiltration rete and concentration of Cd in the middle and subsurface layers but application of leonardite increased the Cd concentration in supernatant more than 10 times compared to control. Also, geochemical forms of Cd (Fe-Mn oxides, exchangeable and carbonate forms) decreased in the surface layer (P