University Colleges of Science & Technology, Calcutta
Quantitative measurements of exchange for and by trace element cations reveal that a part of the cations is adsorbed strongly so that they are incapable of participating in normally rapid exchange reactions. However, repeated treatments with N/30 H2SO4 (100 ml for each 0.5 g or less of clay) slowly release the ‘fixed’ cation but not completely. Cu++ and Mn++ are released to the extent of 80 to 90 per cent, so that the remaining quantities are ‘fixed’ for all intents and purposes. Except the Cu - and Mn-clays, the amounts so ‘fixed’ vary with the degree of saturation of clay with the trace element cation. Cr+++ is adsorbed so strongly that not more than 50 to 65 per cent could be released even by resorting to more vigorous acid treatments. Acetic, oxalic, citric and phosphoric acids in N/10 solutions do not extract more of the ‘fixed’ trace elements than N/30 or N/10 sulphuric acid. Even electrodialysis was unable to liberate the ‘fixed’ cations.
