## 3 Rare Earth Flotation from Primary Resources
### Flotation Reagents
#### 3.1.1 Collectors
Another notable feature of monazite flotation using hydroxamate was described by [PERSON] and [PERSON] [72; 73]. These authors observed the high affinity of monazite to float at pH 9, likely due to hydrolyzed species (e.g., Ce(OH)\({}^{2+}\), Ce(OH)\({}^{2+}\), La(OH)\({}^{2+}\), and La(OH)\({}^{2+}\), which increased the active sites on monazite. However, the flotation response of monazite was very similar to its associated gangue minerals like apatite, ilmenite, quartz, rutile, and zircon when octanohydroxamic acid was used [74]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Collectors** & **Samples** & **pH** & **Depressants** & **Recovery [\%]** & **Grade [\%]** & **References** \\ \hline  & Batstneneetic & 8-9 & – & 67 & – & [71] \\  & Batstneetic and calcite & 9 & – & 90 & 36-4 & [75] \\  & Batstneetic and dendritic & 9 & EDTA & 80-88 & 68 & [76] \\  & Batstneetic and dendritic & 10 & Sodium silicate & 65 & – & [77] \\  & Batstneetic, calcite, and bartie & 9-10 & Lignin sulfonate & 28-85 & 23-33 & [59] \\  & Monazite & 9 & – & 95 & – & [72] \\  & Monazite & 7 & – & 80 & – & [78] \\  & Monazite and calcite & 9 & Sodium silicate & 80 & – & [79] \\  & Monazite, apatite, ilmenite, quartz, rutile, and zircon & 8-10 & – & 5-90 & – & [74] \\  & Monazite, zircon, school, staurolite, and limentie & 9 & Sodium silicate & 86-63 & 35.14-9.8 & [52] \\  & Anylite, strontium, and calcite & 8 & Ammonium liposomalonate & 79-88 & 348-501 & [52] \\ \hline  & Batstneetic & 9 & – & 67-97 & 10.71-0.9 & [52] \\  & Batstneetic and calcite & 9 & – & 68-75 & – & [32,70] \\  & Batstneetic and quartz & 9 & Sodium silicate & 68 & – & [84] \\  & Monazite & 9 & – & 61 & – & [70] \\ Benzohydrodynamic acid & Monazite and dolomite & 8 & – & 68 & – & [52] \\  & Alanine and quartz & 4 & – & 37 & – & [34] \\  & Batstneetic, synthesize, alanine, monazite, & 9 & – & 25-30 & – & [85] \\  & gegeomite, geologic quartz, and others & 9 & Sodium silicate & 61-80 & 25-34 & [86] \\  & Nibce REe cons & 9 & – & 72 & – & [69] \\ \hline  & Batstneetic and calcite & 8 & – & 72 & – & [69] \\  & Batstneetic, herbicide, and calcite & 7-9 & – & 67 & 334 & [83] \\  & Batstneetic, feldspar, calcite, quartz, flourite, andotite & – & – & 80 & – & [87] \\  & Tailings from Bayan Cho mine & 8 & Sodium silicate & – & – & [89] \\ \hline  & Batstneetic, calcite, and fluorite & 9 & Sodium silicate & 70-82 & 42.74-31 & [90] \\  & Batstneetic, dichroite, apatite, hematite, and quartz & 7-10 & – & 70-80 & – & [92] \\  & Batstneetic and (sulfide, silicate, and carbamid) mineral & – & Sodium silicate & 55-63 & 13.0–14.5 & [93] \\ \hline  & Batstneetic and monazite & 7-9 & – & 60-90 & – & [94] \\  & Batstneetic, monazite, calcite, dolomite, and quartz & 9 & – & 62-66 & 60.7 & [55] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: A summary of recent studies on REM flotation using hydroxamate collectors. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Callectors** & **Samples** & **pH** & **Depressants** & **Recovery [\%]** & **Grade [\%]** & **References** \\ \hline  & Monazine & 7 & & 91-95 & -0 & [59-96] \\  & Monazine, quartz, and hematite & 7 & Sodium silicate and starch & 93 & -0 & [59-96] \\  & Monazine, bloodlike, scientific, benzene, & 7  
Table 3 summarizes the studies applying organo-phosphoric acids as collectors. The adsorption mechanism of this collector type is similar to carboxylates and hydroxamates, and their optimum pH is around 4-9. The (ROPO\({}_{3}\)H\({}^{\ast}\)) and (ROPO\({}_{3}\)\({}^{2-}\)) are the dominant species of phosphate collectors [32; 106], which interact with REEs (e.g., Ce, La) on REMs via monolayer chemisorption. Surface precipitation of REE phosphate complexes was also reported at high collector concentrations, along with the presence of Ce\({}^{3+}\), CeF\({}^{2+}\), CeF\({}^{2+}\), and CeCO\({}^{3+}\)[106; 107; 108; 109]. Lauryl phosphate and Flotino 1682 are the two most frequently studied organo-phosphoric acid collectors.