Recovery of critical and strategic metals from scrap marble-cutting tools by oxidative leaching and precipitation

Scrap marble-cutting tool segments (SMCTSs) generated within marble-cutting applications can be regarded as an important secondary resource owing to their high content of base/precious/critical metals (i.e. Co, Cu and Ag) as well as synthetic diamonds. In this study, sulphuric acid-hydrogen peroxide leaching of copper cobalt and silver from SMCTSs was studied using the central composite design for experiments. Extractions of cobalt (>= 73.8 %) and iron (>= 86.6 %) were more extensive than copper (<= 78.3 %) and silver (<= 35.1 %), linked with their relative nobilities. Data analysis has confirmed that increasing the acid concentration or temperature enhances the leaching of metals. Copper and silver leaching improves with H2O2 concentration, while high cobalt and iron leaching can be readily achieved without H2O2. Silver was selectively precipitated (98.9 %) as AgCl with 8.8 % Cu and 0.7 % Co losses from the leach solution. Copper and cobalt were also recovered selectively by increasing the pH to 5.5 and 8.5 respectively after the removal of iron at pH 3.5. These findings have revealed that cobalt, copper, and silver could be selectively recovered by the proposed leaching and precipitation approaches from SMCTSs.