Montana Tech has been engaged in fundamental research on the processing of critical materials for more than a decade. Efforts include examining novel reagents for the flotation of Rare Earth Minerals (REMs). For this paper, results for a collector, salicyl hydroxamic acid (SHA), are presented. Various REMs were examined and include oxides (RECs), carbonates (RECs) and phosphates (REPs). A suite of Rare Earth Elements (REEs) were studied particularly involving several that were light (LREE), middle (MREE) and heavy (HREE). Differences are attributed to lattice spacing, solution chemistry, coordination number and REE ionic diameter. SHA adsorption follows an ion-exchange process that leads to chemisorbed or surface-precipitated states, depending mostly on atomic spacing and pH. Many effects are directly attributed to lanthanide contraction; however, results should be applicable to other REM/collector systems.