I have two different soil and I want to determine the kind of cations (Al3+, Ca2+, Mg2+, K+ , Na+ , ...) reside on the exchangeable site of the soil particles.
Dear Ebrahim,
You can also experiment sequential chemical extractions using ultra-pure water during 2 to 4 weeks. Samples should be powdered and sieved at 50 micrometers, and the ratio solid/water is 100 mg/100mL Two centrifugations (10000 t/mm) per day should be processed. after ultra-pure water extractions you can also use 0.5 M magnesium chloride (MgCl2) as explained in the attached paper. Then the total residuum collected is filtered at 0.2 micrometers and analyzed using ICP-AES that will allow you to characterize and quantify the easily extractable chemical elements (in microg/L) among which the potentially exchangeable cations. Best wishes, Anicet
Ebrahim, you can also use a method as simple as the MgCl2 technique I propose you above, alternatively to ultra-pure water, which is a technique rather dedicated to characterize element speciation . This second method is
Barium Chloride Method for Determining Cation Exchange Capacity and Exchangeable Cations, William H. Hendershot and Martin Duquette, Soil Science Society of America Journal, Vol. 50 No. 3, p. 605-608, 1985. doi:10.2136/sssaj1986.03615995005000030013x
Best regards,
Anicet
Barium chloride extraction is the pretty old method to estimate CEC; the principle is simple - when a fixed amount soil is washed with barium chloride solution, the whole exchangeable seats will be occupied by Barium; proper washing afterwards in distilled water can ensure that no free barium is in the soil and then, the whole attached barium (occupied in the exchange capacity) can be washed out using HCl. The barium came out can be estimated using sulphuric acid precipitation and the amount can be assessed gravimetrically
Dear Ebrahim,
Here is a more complete overview of methods and techniques (different reagents) used to quantify CEC in soil fractions. Regards, Anicet
Dear Ebrahim
There are 7-8 extractants used for extraction exchangeable cations from soils, but 1N NH4Cl is considered and proved suitable for calcareous alkaline soils.
I appreciate good contributions from several colleagues for estimating exchangeable cations in soils. Exchangeable Al3+ may be present soils having pH
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