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Adsorption of Cadmium in Soils and in Their Clay Fraction

J. C. Joardar
Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000, Bangladesh.

M. H. Rashid
Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000, Bangladesh.

S. M. Imamul Huq
Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000, Bangladesh.

Abstract/ Executive Summary:

Cadmium adsorption by three selected soils and clay fraction extracted from the corresponding soils were studied individually. The soil series were Ghior (high clay content). Ghatail (medium clay content) and Rajoir (organic soil). The adsorption pattern followed the order: Rajoir>Ghiorc>Ghatuil soil. Adsorption variations among the soils were attributed to the presence of organic matte, types or the clay fraction, phosphorous content and magnitude or CEC. A significant positive relationship was noticed between the adsorption of cadmium and CEC (r = 0.943**) and organic matter (r = 0.885**) of the soils. A fairly noticeable inverse relationship (r = 0.790) was observed between the adsorption of cadmium and the presence of phosphorous in the soils. Cadmium adsorption by clays showed a different order to that or cadmium adsorption by the whole soil. The order was Ghior>Ghatail>Rajoir clay. The illitic and montmorillonitic minerals present in the clays might have a key rule in adsorption or cadmium.

Keywords: Adsorption, Cadmium, Clay mineralogy

Location: Gopalgonj, Mymensingh and Madaripur, Bangladesh

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Commodity: Contamination of soil

Objectives:

To investigate the adsorption of Cd in a few soils of Bangladesh and in their clay fraction as potential binding agents for the remediation of the polluted soils and to clean up contaminated sites.

Methodology:

One organic soil and two mineral soils were selected in the research work. The soils viz., Rajoir, Ghatail, and Ghior were collected from three districts- Gopalgonj, Mymensingh, and Madaripur of Bangladesh, respectively. After collection, the soils were air-dried and ground to pass through a 2-mm sieve. The bulk sample was thoroughly mixed and stored. Particle size analysis was performed by hydrometer method (Day 1%5). The textural class was determined following Marshall's triangular co-ordinates. Cation exchange capacity (CEC) was determined by using neutral 1N NH₄OAc saturation technique. The soil organic matter was estimated by Walkley and Black's wet oxidation method. Moreover, soil pH, the total content of Fe, N, P, K. Ca and Mg in the soils were determined by using prescribed laboratory methods. For total Cd, the samples were digested with aqua-regia for approximately 4-5 hours, using a sand bath as a heating source and the water soluble Cd was extracted by shaking 10g samples of soil with 50 ml distilled water at a 1:5 soil-water ratio for 24 hours. After dissolution, samples were diluted to volume, mixed and filtered prior to analysis. Then cadmium content in the extracts was estimated by Atomic Absorption Spectrometer. With every set of digestion a certified reference material (CRMs) was included to ensure the QA/QC. Soil clay fractions were separated by the method. Solutions for batch tests with concentrations ranging between () to 10 mg/I Cd were prepared with deionized water from Cd(NO₃)₂. 4H₂O. The pH of the soil suspensions was adjusted to 6.0 using 0.1M HCI or 01M NaOH. Adsorption tests were carried out by the process as described. Cadmium concentrations in the supernatant were determined with a Varian Spectra-220 Atomic Absorption Spectrometer. All assays were carried out in triplicate and only mean values are presented (the variation coefficients were less than 5%). Adsorption of Cd by soil/clay was calculated. A comparative study of cadmium adsorption capacity on the different soils and their respective clays were carried out separately with the following conditions: Adsorbent dose: 1 g soil or 0.1 g clays in every 25 ml solution, shaking time 2 hours, pH 6.0, the applied rates of cadmium concentration were 0, 0.05, 0.25, 0.5, 2.5, 5 and 10 mg/l (made from Cd(NO₃)₂. 4H₂O).

Source of Information: Bangladesh J. Agric. and Environ. 1 (1): 19-27, June 2005, ISSN; 1816-0808

Article Link (Online Journal):

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Cadmium adsorption by clays showed a different order to that or cadmium adsorption by the whole soil. The order was Ghior>Ghatail>Rajoir clay. The illitic and montmorillonitic minerals present in the clays might have a key rule in adsorption or cadmium.

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