Recovery of metals from scrap saw-blade segments

In this thesis, recovery of critical/valuable metals (Co, Cu, Ag) from scrap saw-blade segments used in marble/natural stone industry using hydrometallurgical methods was investigated. Leaching of scrap saw-blade segments was carried out in different acidic leaching systems. In sulphuric acid (H2SO4) leaching tests carried out in the presence of different oxidants (H2O2 or Fe3+), it was observed that the increase in the concentration of the oxidant and temperature improved the extraction of metals. In acidic copper(II) sulphate assisted chloride (H2SO4-CuSO4-NaCl) and acidic copper(II) chloride (HCl-CuCl2-NaCl) leaching tests, increasing the concentration of cupric copper (Cu2+) positively contributed to the metal extractions while the increased levels of chloride (Cl-) adversely affected the recovery of metals. In acidic solutions (H2SO4 or HCl-NaCl) metals (Co, Cu, Ag) can be completely leached under aggressive conditions (i.e., at high concentrations of H2O2) over a prolonged period of 24 hours. In the oxidative leaching tests, the introduction of air or O2 improved the leaching efficiency through the regeneration of ferric iron (Fe3+) or cupric copper (Cu2+). In solution purification and metal recovery tests, silver was completely precipitated in AgCl form from the acidic sulphate leach solution. Iron was removed as Fe(OH)3 by precipitation at ⁓pH 3.5. By gradually increasing the pH level of iron-free solution, copper (⁓ pH 5.5) and cobalt (⁓ pH 8.5) were precipitated as Cu(OH)2 and Co(OH)2, respectively. In addition, cobalt was precipitated with persulphate as CoO(OH) and, copper with acetone (C3H6O) as copper sulphate at 99.3% recovery. All of the iron (⁓ pH 2.7), copper (⁓ pH 5.5) and cobalt (⁓ pH 8.5) were selectively precipitated from acidic chloride leaching solution through gradually increasing the pH of the leach solution. In addition, synthetic diamonds were also recovered after leaching of scrap segments as-received i.e., without being subjected to size reduction. Key Words: Hydrometallurgy, Leaching, Solution Purification, Metal, Cobalt, Copper, Silver, Iron, Marble, Natural Stone, Scrap, Saw-Blade, Segment, Synthetic Diamond