Study of water and sediment interactions in the Das Velhas River, Brazil : Major and trace elements

Surface adsorption of metallic elements in aqueous solution by colloidal hydroxides affects the transport of elements in surfac e water systems. The study of the adsorption ability and the chemistry of hydroxides is important to the knowledge of the geological ar ea, effluent and sewage treatments, and environmental management. In areas of ore exploitation, surface waters are subject to modifications of physicochemical properties: pH, dissolved oxygen, conductivity and alkalinity. A comparative study of the concentration of major and trace elements in water and sediment samples of the Das Velhas River, Brazil, was conducted using instrumental neutron activation analysis – INAA, and Inductively coupled plasma with mass spectrometry - ICP-MS. Water samples were collected and acidified in situ inducing a change in the natural pH, and consequently in the dispersion of metallic elements associated with Fe hydroxides (colloids) and with the particles in suspension. Results show the differentiated behaviour of the metal elements because of their chemical forms (cations or anions), solubility degree, Fe and rare earth elements (REEs) concentratio ns and pH variations.