Extraction of Metals from Scrap Marble Cutting Segments in Nitric Acid Solutions

Extraction of cobalt, copper, and silver from scrap saw-blade segments using nitric acid solutions (0.1–0.4 M, 20–60°C) were investigated using response surface methodology. Extraction of cobalt and iron was more extensive than copper and silver, i.e., 35.7–96.2% Co and 72.6–100% Fe versus 8.50–35.4% Cu and 8.11–22.5% Ag. Statistical analysis of the experimental data has shown that increasing the acid concentration or temperature enhances the rate and extent of leaching of metals. Under suitable conditions, almost complete leaching of cobalt (99.9%), as well as high extractions of copper (95.9%) and silver (94.9%), were achieved. The activation energy, calculated to be 40.3 kJ/mol, indicates that nitric acid leaching of these metals occurs as a chemically controlled reaction. These findings have demonstrated that nitric acid as an effective oxidant/leaching agent could be suitably used for the extraction of cobalt, copper, and silver from scrap segments.