Abstract
The role of aluminum concentration and pH in the purification of waste Li-ion battery leach solution was investigated using NaOH and LiOH as neutralization agents ([H2SO4] = 0.313 M, t = 6 h). Solution was prepared from synthetic chemicals to mimic real battery leach solution. Results demonstrate that pH (3.5–5.5) has a significant effect on the precipitation of metals (Fe, Al, Ni, Cu, Co, Mn, and Li), whereas higher temperature (T = 30 and 60 °C) decreases the precipitation pH of metals. Iron and aluminum were both found to precipitate at ca. pH 4 and the presence of aluminum in PLS clearly decreased the separation efficiency of Fe vs. active material metals (Ni, Co, Li). In the absence of dissolved aluminum, Fe precipitated already at pH 3.5 and did not result in the co-precipitation of other metals. Additionally, the Al-free slurry had a superior filtration performance. However, aluminum concentrations of 2 and 4 g/L were found to cause loss of Ni (2–10%), Co (1–2%) and Li (2–10%) to the Fe-Al hydroxide cake at pH 4. The use of LiOH (vs. NaOH) resulted in 50% lower co-precipitation of Ni, Co and Li. Overall, these results demonstrate that hydroxide precipitation can be an effective method to remove iron from battery waste leach solutions at aluminum concentrations of < 2 g/L only. Although the highest level of lithium loss in the cake was found at pH 4, the loss was shown to decrease with increasing pH.
Highlights
The role of aluminum concentration and pH in the purification of waste Li-ion battery leach solution was investigated using NaOH and LiOH as neutralization agents ([H2SO4] = 0.313 M, t = 6 h)
Results from the NaOH precipitation at 30 and 60 °C in a solution containing 4 g/L of Al are displayed in Fig. 1 an indicate that at 30 °C iron was completely precipitated at pH 4.5, whereas at 60 °C this precipitation occurred already at pH 4, as suggested previously by Wang et al.[29]
When a 100 mol% ratio of Al3+ to F e3+ was used, the resultant equilibrium was achieved at a pH proximal to 4 and such a wide shift in the precipitation pH correlates with the findings outlined in this study
Summary
The presence of Al, Cu and Fe fragments can benefit leaching processes as they serve as efficient reducing agents for the active material, and the use of externally introduced reducing agents, like hydrogen peroxide, can be o mitted[19,20] Of these elements, Al is the most challenging to remove from the solution, the purity of the recovered elements, especially lithium and graphite, must be of pristine quality which can be a challenge to achieve in the presence of such metal fragment impurities[8,16,21,22,23,24,25]. Such technologies could allow for sustainable recycling or reuse of battery components[15]
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