University Colleges of Science & Technology, Calcutta
Exchange study was done with ‘crude humic acid’ portion, (designated as ‘humic acid’), obtained from a black cotton soil by sodium carbonate extraction, acidification and electrodialysis. Its b.e.c. was 613 me/100 g. Cu-, Mn- and Ni-humates were prepared by leaching with the respective salt solutions and the amounts of Cu++, Mn++ and Ni++ adsorbed were determined.
The adsorption isotherms of humic acid against Cu++, Zn++, Ni++ and Mn++ were obtained. The amounts of the metal ions released by N/30 H4SO4 from the metal hydrogen humates, were determined. The corresponding adsorption isotherms were in general somewhat higher than the release isotherms, showing the extent of the metal ion ‘fixed’. The amounts ‘fixed’ by humic acid, compared to clays, are much smaller. The adsorption of the metal ions for H+ follows the order: Zn≥ Mn < Ni < Cu. The order of release from the respective humates for H+ and Mg++ is: Mn > Ni > Cu. The actual amounts released by H+ are much greater than those by Mg++. Adsorption by humic acid is high but the major portion of the adsorbed cations can be released in the usual way.
