THE ENERGY OF THE ADSORPTION OF O-PHOSPHATE ONTO FERRIC HYDROXIDE

The enthalpy of the adsorption of orthophosphate onto iron hydroxide w as measured with isothermal calorimetry and found to decrease with dec reasing ratios of Fe/P. The Langmuir adsorption isotherm seems, theref ore, not to be appropriate to describe this phenomenon. For the moment the Freundlich adsorption isotherm seems to be a superior descriptor of this adsorption process and should, therefore, be applied in phosph ate flux models taking sediments into account. The Ca2+ concentration of the water and pH enforce the adsorption process, but do not change the enthalpy.