Recovery of Lithium as Li3PO4 from Waste Water in a LIB Recycling Process

Abstract

This study was conducted to obtain engineering design data for a process to recover lithium in the form of Li3PO4 from the waste water of a lithium ion battery (LIB) recycling process. The influence of temperature, pH, and concentration on the solubility of Li3PO4 and the reaction rate in the Na3PO4-Li2SO4-H2O system was investigated. As a result, the solubility of Li3PO4, 372 mg/L, increased to 417 mg/L as the reaction temperature increased from 20 to 90 ℃. At the same time, the reaction rate increased from 0.0174 × 10-4 to 2.32 × 10-4 mol/L·s. The yield of lithium phosphate rises in proportion to increases in the concentration of salt, temperature and pH, in the reaction of 3Li2SO4 + 2Na3PO4 → 2Li3PO4 + 3Na2SO4. That is, the higher the concentration, temperature and pH solution are, the more Li3PO4 precipitates. The temperature must be 70 ℃ or higher to obtain 90% or more Li3PO4 as a precipitate. The lithium phosphate particle formed at 20 ℃ are composed of secondary particles or their agglomerate, which is composed of primary particles of 0.01 µm or less size. The size of the primary particle becomes bigger when the reaction temperature is raised and at 90 ℃ it becomes a large columnar particle, with a 10~20 µm length and 5~10 µm breadth. Key words: lithium, recovery, lithium phosphate, lithium ion battery, waste water