“…An additional cycle of biosorption may be applied to purify the mixed REEs precipitate in the secondary impurity removal process. Alternatively, various techniques such as solvent extraction using Cyanex 272 and Cyanex 572 [44,45], D2EHPA and TBP [46], or HEHEHP and HDEHP [44,47]; ion exchange using different cationic or anionic resins such as Dowex 50X8 [44,48,49]; or precipitation using CaCO 3 and Ca(OH) 2 [50,51] or MgO and NaOH [51] can be explored for further purification of the mixed REE precipitate obtained in this study (Figure 9). These techniques have been utilized for impurity removal from REE-containing solutions, and their applicability in refining the mixed REE precipitate can be investigated.…”