Enhancement of copper mobilization using acidic AlCl3 − rich lixiviant

• Al 3+ (aq) leads to the formation of AlSO 4 + (aq) species and alunite at pH 1–3. • Al-sulphate phases lower the sulphate activity for jarosite and sideronatrite. • Al-rich phases formed in AlCl 3 -rich lixiviants are amorphous and porous. • The Fe-diffusion rate to Cu mineral surfaces is highest in AlCl 3 lixiviants. • The initial rate of Fe 3+ (aq) -promoted copper release is fastest in AlCl 3 lixiviants. Copper (Cu) extraction from low-grade ores is limited by the formation of secondary minerals that can passivate the surfaces of Cu-sulphide minerals in these ores. Hence, a novel approach utilizing AlCl 3 as a lixiviant was developed to modify coupled dissolution-reprecipitation processes at the mineral interface. The formation of Al-rich phases instead of Fe-hydroxysulphates enhanced Cu extraction through combined ferric-iron and proton-promoted dissolution. AlCl 3 accelerated chalcopyrite and bornite dissolution by forming soluble intermediate Cu-phases (e.g., covellite) at consistently high Eh (550–650 mV) and acidity due to the Lewis acid property of AlCl 3 . X-ray diffraction analysis revealed that Na-bearing jarosite [(K 0.61 Na 0.41 ) Fe 3 (SO 4 ) 2 (OH)] and sideronatrite [Na 2 Fe(SO 4 ) 2 (OH)(H 2 O)] formation in lixiviants without AlCl 3 decreased Fe 3+ (aq) availability for Cu-sulphide minerals dissolution. In contrast, significant amounts of AlSO 4 + (aq) formed in the AlCl 3 -rich lixiviant at pH 1–3, which reduced the sulphate activity and decreased the saturation state of the Fe-hydroxysulphates. Further, AlCl 3 promoted the formation of amorphous, porous Al-rich phases, facilitating quick Fe diffusion through the passivating layer and improving Cu recovery compared to lixiviants containing CaCl 2 , NaCl, or acid-only.