Abstract
Harmful heavy metal ions concentrations in scallop viscera wastes were found as: 26.58 ppm Cd (II), 23.27 ppm Cu (II), 371.55 ppm Zn (II) and 7.69 ppm Pb (II) (ppm=mg/kg dry wastes), respectively. The existence of these metals in such wastes have incurred big problem due to the large amount of wastes. Traditionally those wastes are burning in incinerator, but this treating retains harmful metal ions in out-streams residues, such as bottom and fly ashes. This study proposes a new method using sub-critical water treatment to produce useful material and simultaneous recovery of the metal ions. Reaction conditions involved temperature between 443-653 K, and reaction time 1-30 minutes. The results showed that metal ions are concentrated in solid-phase by increasing temperature to 653 K (6 times). The oil and fat extracted during this method, acted as a chelating agent to catch almost all metal ions from original wastes with order of recovery as Zn2+ > Cd2+ > Cu2+. The triglyceride and fatty compounds are responsible to make complex with metals in fat and oil phases. These two phases illustrated maximum concentration of metal ions in fat-phase at 513 K (max. 8000 ppm) and in oil-phase at 513-553 K (max. 340 ppm). Finally, aqueous phase illustrated lowest concentration of metal ions especially at temperature above 550 K. The distribution coefficient of metal ions defined as concentration in fat, solid and oil phases to concentration in aqueous phase were found highest in the fat (max. 44,000), following by solid (max. 27,000) and oil (max. 1,300).
