CONCENTRATION OF HUMIC AND FULVIC-ACIDS IN LARGE AQUEOUS SAMPLES BY CONTINUOUS-FLOW COPRECIPITATION-FLOTATION

Humic and fulvic acids are quantitatively coprecipitated in a stream (0.5 l/min) of sample solution with indium hydroxide at pH 8 and continuously floated with the aid of sodium dodecyl sulphate and numerous tiny nitrogen bubbles. The precipitate and foam on the surface of the solution are collected by suction and the latter is ruptured with ethanol. By these procedures the original sample volume is reduced to less than 1/100. After dissolving the precipitate in 2 mol/l hydrochloric acid, the solution (pH 0.5) is introduced onto the pulverized XAD-2 resin to collect humic and fulvic acids, leaving indium ions in the solution. The humic substances are desorbed with 0.1 mol/l sodium hydroxide solution. The recoveries of humic and fulvic acids are ca. 95% for coprecipitation-flotation, > 90% for sorption and 80-90% for desorption.