Abstract
The regenerated hurnic acids (powder) prepared by oxidation of 6 Japanese bituminous coals (C: 75.7-89.5%) have studied on their ion exchange properties in heavy metal ion solutions. The adsorption ability of humic acids on Cd ion in its dilute chloride solution (1/5000M) increased in following order: natural humic acids extracted from lignites <those prepared by the oxidation with air <those by the oxidation with nitric acid (nitrohurnic acids), though the content of carboxyl group in humic acid increased in following order: those by the oxidation with nitric acid<natural hurnic acids <those by the oxidation with air. Nitrohumic acid was characteristic of its high ion exchange velocity comparable with that of Amberlite CG-120 and its high ion exchange velocity comparable with that of Amberlite CG-120 and its high adsorption ability on Zn, Cd and Cu ions from their dilute solutions at pH≥3.5. The adsorption of Cd ion was more effective on the nitrohumic acid of partial sodium salts type, on which saturation adsorption in Cd-, Zn-, Ca- and Mg-chloride solutions at initial pH 5 was ca. 1.0, 0.9, 0.6 and 0.5meq./g, respectively. The regeneration of nitrohumic acid having adsorbed Cd ion could be effectively done with 1M NaCl solution or 1M NaCl solution in two steps, and the adsorption ability after repeating regeneration of 6 times did not decrease. When the regeneration has been done with varying amounts of hydrochloric acid (0.5 N initial concentration), Cd ion concentration in equilibrated solutions at 99-100% and 90-92% regeneration ratio of humic acid was ca. 10-2M and 1M, respectively.
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