<p>The treatment and utilization of rare earth alkaline wastewater generated during the treatment of Bayan Obo mixed rare earth concentrate using the liquid alkali decomposition method have consistently presented a technical challenge. This article proposes a segmented water washing strategy for rare earth alkaline cake, beginning with the source of rare earth alkaline wastewater. Firstly, the first slurry water washing is carried out using the same ion effect, salt effect, and supergravity filtration technology, which achieves the pre-separation of NaOH from NaF, Na₃PO₄, and Na₂CO₃. The water washing solution obtained in this step can be directly returned to the liquid alkali decomposition process for further use, while NaF, Na₃PO₄, and Na₂CO₃ remain in the alkaline cake. Subsequently, the introduction of mineral phase transformation and ultrasonic-enhanced cleaning technology for the second ultrasonic water washing significantly improved the separation effect of rare earth minerals in the alkali cake from NaF, Na₃PO₄, and Na₂CO₃. The water washing solution obtained in this step can be directly evaporated and crystallized into a mixed sodium salt, which can be used as a raw material for preparing glass. Under the optimal conditions, the washing rate of NaOH can reach over 85%, while the water washing rates of NaF and Na₃PO₄ can reach 99.64 and 99.45%, respectively. This technology not only reduces the generation of rare earth alkaline wastewater from the source, but also achieves high-value utilization of rare earth alkaline wastewater. This has certain reference value for the decomposition of rare earth minerals in liquid alkali.</p> Graphical Abstract <p></p>