Magnesium ions, along with other unavoidable impurities, are usually contained in solutions obtained during the hydro-metallurgical conversion of ore raw materials and in the aqueous part of the flotation pulp. It is of interest to clarify the composition and properties of compounds formed by magnesium ions with naphthenic acid, the possibility of using it for extraction of non-ferrous metals from solutions and flotation of some non-sulfide minerals has been established by many studies...