ASPECTS OF THE ESTUARINE BEHAVIOR OF HUMIC ACID, IRON, PHOSPHATE AND URANIUM (ADSORPTION, DESORPTION)

The estuarine behaviours of iron, humic acid, phosphate and uranium have been investigated using a laboratory estuarine mixing system. Seawater was added continually to artificial freshwater, the mixture pumped out at the same rate, and analysed. A method for the simultaneous spectrophotometric determination of humic acid and iron in fresh and estuarine waters which required sample volumes of less than 15 ml has been developed. Two absorbance measurements were required, one on an untreated sample aliquot, and the other on an aliquot treated to form the iron(II) ferrozine complex. Limits of detection for each component varied with concentration of the other, but 0.01 mg 1('-1) for humic acid and 0.04 uM for iron were achieved.; Humic acid behaviour was dependent on freshwater pH and the presence of iron. It was conservative when no iron was present in the freshwater at pH 8.2. The humic acid stabilized iron as colloidal iron oxyhydroxide in the freshwaters, but both were removed when seawater was added. They were coaggregated in the same ratio that they were present in the freshwater. The salinity range over which removal occurred decreased, and the degree of removal increased as the freshwater ratio of iron to humic acid increased, but were not significantly affected by temperature, mixing rate, freshwater pH or phosphate concentration in the ranges studied. Iron aggregation did not consistently follow first or second order kinetics, but the latter provided a reasonable representation in most experiments.; Phosphate was adsorbed onto the colloidal iron oxyhydroxide particles in competition with humic acid, and was removed when these particles aggregated. As more seawater was added desorption of phosphated occurred. Desorption was primarily controlled by increased pH and to a lesser degree by competition from seawater anions. These factors outweighed any increased adsorption that might have resulted from increased ionic strength. A preliminary study showed that uranium from seawater was also removed by adsorption onto aggregating iron-humate particles, and subsequently desorbed as further seawater was added.