Trace Metals in Humic Substances from Marine Sediments

Abstract

Elements involved in humic acids extracted from marine sediments were determined by ICP emission spectrometry. Humic acids were extracted from sediments with 0.2M NaOH and precipitated with HCl below pH 2. The precipitate was redissolved into NaOH, filtered and reprecipitated with HCl. These procedures were repeated three times. After passed through an ion-exchange resin column, humic acid was obtained as acid type. Humic acid samples were digested with HNO₃ and HClO₄ and aqueous solutions were served to metal determination. Fe, Al, P and Cu were found in large amounts in marine humic acids. Commercially available Aldrich humic acid contains metals of one or two order of magnitude smaller concentration compared to marine humic acids. Metals in sediments were also determined and the ratio of metal association to humic acid was calculated. The large portion of Cu was found to bind with humic acid. Zn, Mo and Ni were also rich in the humic acid. The effect of HF wash on metal contents of humic acid was shown by the fact that the ash content and the amount of Al, Fe and Mg were remarkably decreased.