RETENTION OF METALLIC CATIONS BY LIGNITES AND HUMIC ACIDS

Adsorption of strontium, lead, uranium and thorium ions from their solutions by several Spanish lignites have been studied. Adsorption isotherms are adequately described by means of the Langmuir equation and can be characterized by two numerical constants: the sorption capacity of lignite, and the geochemical enrichment factor (GEF). Very high values of this GEF have been found for heavy metals. Humic acids were extracted from the lignites and their metal binding ability was determined as a function of pH. Higher pH favours metal retention, also higher atomic weight and valency. A role of humic substances in the retention and accumulation of metals in coals is suggested. © 1979.