Mass balance of heavy metals contained in mid-gut gland of scallops for incineration process

Abstract

The mass balance of heavy metals (iron, copper, zinc and cadmium) contained in the mid-gut gland (MGG) of scallops in the incineration process was studied. The metal contents in bottom ash, deposited on the tube wall, fly ash, and absorption solutions were measured by atomic absorption spectroscopy (AAS). Although wet MGG contained about an average of 20 ppm cadmium, about 57% was vaporized when heated at 900°C in air. Most of the vaporized cadmium was deposited on the tube wall, and a certain amount of it was detected from fly ash. When MGG was heated in nitrogen, the remaining cadmium ratio was around 10%, and cadmium of about 83% was detected from the tube wall, 6% from the fly ash, and 1.8% from the absorption solutions. In the case of heating cadmium metal, only oxidation proceeded in the air atmosphere, while cadmium vaporized nearly 100% in the nitrogen. It was thus considered that the vaporization of cadmium found during the incineration of MGG was caused by a partial insufficiency of oxygen was generated when the organic mass was burned.