Cause and control of losses of chromium during nitric-perchloric acid oxidation of aquatic sediments

Abstract

The extraction of chromium from aquatic sediments by using boiling nitric-perchloric acid was studied. The amount of chromium extracted was found to depend upon the time that heating was continued after the nitric acid had boiled off and to decrease significantly with prolonged heating. The decrease was shown to be due to adsorption on to the silica residue, as the lost chromium could be recovered by digestion of the residue with hydrofluoric acid. An extraction procedure in which the time of heating in perchloric acid was carefully controlled gave satisfactory precision for the determination of chromium, zinc, copper, lead and cadmium, as well as adequate recoveries of added amounts of these metals.