Enhanced leaching of manganese from low-grade pyrolusite using ball milling and electric field

In this study, electric field and ball milling were used to leach Mn²⁺ from low-grade pyrolusite (LGP). The effects of current density, reaction time, reaction temperature, ball-to-powder weight ratio, and ball milling time on the leaching efficiency of Mn²⁺ from LGP as well as the leaching mechanism were systematically studied. The results showed that the combined use of electric field and ball milling enhanced the leaching of Mn²⁺ from LGP. The leaching efficiency of Mn²⁺ reached 97.79% under the optimum conditions of LGP-to-pyrite mass ratio of 1:0.18, current density of 30 mA/cm², LGP-to-H₂SO₄ mass ratio of 1:0.4, liquid-to-solid ratio of 5:1, ball-to-powder weight ratio of 1:1, ball milling time of 2 h, temperature of 80 °C, and leaching duration of 120 min. This value was 25.95% higher than that attained without ball milling and 41.45% higher than that attained when neither ball milling nor electric field was employed. Pyrite was fully oxidized to generate additional SO₄^2- and Fe³⁺, and was further hydrolyzed to form jarosite (KFe₃(SO₄)₂(OH)₆) and hydronium jarosite (Fe₃(SO₄)₂(OH)₅·2H₂O) via ball milling and electric field application. Moreover, the electric field changed the surface charge distribution of the mineral particles and promoted collisions between them as well as the collapse of the crystal lattice, further improving the leaching efficiency of Mn²⁺ from LGP. This study provided a new method for leaching Mn from LGP.