Li-ion batteries (LIB) should be recycled because of the environmental reasons and this type of waste represents an important secondary source of metals. This work aimed to evaluate the recovery of Co and Li from LIBs by hydrometallurgy. The efficiency of three types of leachants was tested: H₂SO₄ (2 M), fermentation effluent with supplementation of organic acids (lactic, acetic, butyric and propionic acids) (3.4 M) and a combination of fermentation effluent (0.75 M) and H₂SO₄ (1.25 M). In addition, the effect of H₂O₂, glucose P.A., lactose P.A. and from milk whey permeate (MWP) as reducing agent was tested. The leaching solution composed of H₂SO₄ and fermentation effluent showed high potential of metals recovery in addition to being an alternative of reducing the volume of inorganic acid and the cost by using a fermentation effluent since its use may be integrated with a waste treatment process. Based on Central Composite Designs, optimum conditions of leaching were established, as temperature of 86 °C, solid-liquid ratio of 18.5 g/L, leaching time 2.5 h, agitation of 300 rpm and concentration of 0.09 M of lactose from MWP and recovery level achieved was 93.35% of Co and 90.50% of Li. In order to evaluate the influence of each organic acid present on the fermentation effluent, testes were carried out using pure organic acid with H₂SO₄ (0.75 M:1.25 M) or isolated (3.4 M) and inferior recoveries were detected proving that mixture of organic acids and further compounds as phenolic groups characteristic of fermentation effluent improves the leaching process.