Preconcentration of humic acid in water by coprecipitation/flotation with iron(III) hydroxide followed by ultrafiltration

Abstract

To 1 liter of water containing humic acid was added 1 ml of iron(III) solution (10 mg Fe/ml) and the pH was adjusted to 7 to collect the humic acid on iron(III) hydroxide precipitates. Three ml of 70% ethanol solution of sodium oleate (0.2 mg/ml) and sodium dodecyl sulfate (0.6 mg/ml) was added to render the precipitate surfaces hydrophobic. The precipitates were rapidly floated with numerous nitrogen bubbles (0.10.5 mmin diam.), collected and then dissolved in 10 ml of 2 M hydrochloric acid. Humic acid was filtered off on an ultrafilter (molecular weight cut-off, 10000) and ultrasonically dissolved in 10 ml of 0.1 M potassium hydroxide solution for the spectrophotometric determination. Within 1 h of the entire procedure, 0.015 mg/l of humic acid was recovered at more than 92%.