Dialkyl(5-ethyl-2-hydroxyphenyl)phosphonates as extractants for the selective recovery of lithium from alkaline media

O,O′-dialkyl(5-ethyl-2-hydroxyphenyl)phosphonates (HL) in combination with the synergistic additive, trioctylphosphine oxide (TOPO), were considered as lithium-selective extractants for the first time. The possibility of these compounds to exhibit lithium-selective properties in the extraction of alkali metals (Li, Na, K) was predicted by quantum chemical calculations, the results of which were confirmed by extraction experiments. It is shown that the composition of the extracted species can vary depending on the extraction conditions. At the same time, O,O′-dialkyl(5-ethyl-2-hydroxyphenyl)phosphonates can participate in extraction both as cation-exchange extractants and as neutral extractants, competing with TOPO.