Significant of soil properties on cadmium mobility evaluated by soil thin-layer chromatography by SAUD AL-OUD

INTRODUCTION Cadmium: Cd is a toxic heavy metal. The pure Cd is a soft silver- white metal. Usually it combined with other elements such: oxygen, chlorine, or sulfur. Cd 2+ activities in soils is about M. levels of Cd in most waters is one µg/L or less. Typical topsoil levels of Cd about 260 µg/kg. Intake of Cd from the diet is about mg/kg/day

Sources of Cadmium : Igneous rocks ( mg/Kg) Metamorphic ~.3 & Sedimentary rocks ( g/kg) ZnS minerals (Sphalerite & Wurtzite), ZnCO3 Up to 5% Fertilizers in cultivated soils Most Cd is obtained as a by-product from the smelting of Zn, lead, or copper. Cd used in metal plating, pigments, batteries, and plastics.

Several processes tend to keep Cd concentrations low in groundwater Sorption by organic matter and clay minerals. Complexes by oxides. Precipitation of Cd as CdS in the presence of sulfide. Precipitation of Cd as carbonate at relatively high pH.

Cadmium Mobility Minimizing the threat of soil and ground water pollution by accurately predicting the movement and cycling of hazardous contaminants is an ultimate goal

Cadmium Mobility Overview: Above pH 7 Cd co-precipitate with CaCO3 can occurred. Mobility of Cd in soil with low CEC, pH & O.M can be high. Cd should be fairly mobile in soils of pH 4.6 to 6.6 and moderately mobile in those of between pH units.

OBJECTIVES To Study Cd mobility in soils by thin layer chromatography (Soil TLC). To use a simple, fast and an inexpensive method to estimate heavy metals movement in soils To Study the effect of soil properties on Cd mobility.

Cadmium Mobility Study: Soil TLC procedures The Soil samples were ground and sieved through a 160- µm nylon mesh sieve. TLC plates were coated with soil water slurry. The plates then dried at in a desiccating chamber. A 5 µL of Cd(NO 3 ) M was applied as spot on the base line & The plates developed by ascending chromatographic tank using distilled water.

The plates sprayed (0.05% dithizone in (CCl 4 ) and Cd was detected as orange spots of Cd dithizone. Mobility of Cd ( Rf ): The frontal Rf =. Fm Fd Where Fm is frontal distance moved by the Cd & Fd is the one moved by the developer solution.

RESULTS AND DISCUSSION General Description of Soils The soil pH Y 4.9 to 8.8 The CEC Y 4. to 99.0 cmol/kg The O.C Y 0.6 to g/kg. Iron Oxides: The Feo Y 1.7 to 31.0 g/kg The Fep Y 0.1 to 8.0 g/kg The Fed Y 2.7 to 51.0 g/kg.

Cadmium Mobility in Soils (Rf) The Cd mobility Rf Y 0.25 to 0.95 Cd mobility were: Slightly mobile in 64 %, moderately mobile in 29% and very mobile in 7 % of the soils. The variability in the Cd mobility (Rf) in the soils is mostly accounted for by: Sand% (r = 0.63), Silt % (r = -0.59) the exchangeable Ca (r = -0.55); Clay % (r = -0.55)

Distance(cm)moved by Cd over a 10 cm soil TLC.

Cadmium Mobility in Soils Cd retardation factor The Cd retardation factor, Rcd at 12.8 ppm Cd load & unadjusted pH varied from 2.9 to Rcd values at four levels of pH (5-8) varied from 1.14 to The Rcd values were increased with increasing amounts of(Feo, Fep, and Fed).

Log Rcd versus pH for two different amounts of HFO in a soil/water system.

CONCLUSIONS 1) Cd mobility in these soils is highly variable. 2) Soil texture seemed to play the most important roll in Cd mobility

3) Rf factors showed Cd mobility to be higher in those soils with a high percentage of sand. 4) The influence of soil properties in Cd mobility can help in choosing the right landfill for dumping industry waste of contaminates.

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