High-efficiency selective leaching of valuable metals from spent lithium-ion batteries: Effects of Na2S2O8 on the leaching of metals

A new method was presented for the high-efficiency selective leaching of Li and the efficient recovery of transition metals (TMs) from the cathode materials of spent lithium-ion batteries (spent LIBs). Selective leaching of Li was achieved by carbothermic reduction roasting and leaching with Na2S2O8. After reduction roasting, high-valence TMs were reduced to low-valence metals or metal oxides, and Li was converted to Li2CO3. Then Na2S2O8 solution selectively extracted 94.15% of Li from roasted product with leaching selectivity of more than 99%. At last, TMs were leached with H2SO4 without adding reductant with the leaching efficiency of metals all exceeding 99%. Na2S2O8 added during the leaching process destroyed the agglomerated structure of the roasted product to open the way Li entered the solution. Under the oxidative environment of Na2S2O8 solution, TMs would not be extracted. At the same time, it helped to regulate the phase of TMs and improved the extraction of TMs. Furthermore, the phase transformation mechanism of roasting and leaching was discussed through thermodynamic analysis, XRD, XPS, and SEM-EDS. This process not only realized the selectively comprehensive recycling of valuable metals in spent LIBs cathode materials; but also followed the principle of green chemistry.