Abstract The flotation chemistry of soluble salts has been studied for many decades. In this work, the flotation behavior of arcanite (K2SO4) and epsomite (MgSO4·7H2O) with both the cationic collector, dodecylamine hydrochloride (DAH), and the anionic collector, sodium dodecyl-sufate (SDS), has been studied. The results show that K2SO4 can be floated with both the cationic and anionic collectors at natural pH. In contrast, MgSO4·7H2O cannot be floated by either collector. The results indicate that the flotation response of these salts cannot be explained based on surface charge considerations. It is now known that interfacial water structure has been found to be a significant factor in the explanation of soluble salt flotation. In this regard, the water structure of K2SO4 and MgSO4 solutions was investigated by FTIR-transmission and FTIR-ATR methods which are useful to detect changes in water structure as influenced by dissolved salts. FTIR transmission spectra suggest that MgSO4 is a water structure making salt, while it is expected that K2SO4 is a structure breaker, although such an expectation is not confirmed from FTIR transmission spectra due to the low solubility of K2SO4. In this regard, FTIR-ATR measurements can also be used to determine the influence of dissolved salts on water structure. After subtraction of the O–H band spectrum of salt solutions from that of pure water, the change in the “ice-like” water structure as influenced by the dissolved salt (K2SO4 and MgSO4) can be observed even in solutions of K2SO4 at low concentrations. In summary, the results from FTIR spectroscopy of solutions show that K2SO4 is a water structure breaker, while MgSO4 is a water structure maker. This conclusion is further confirmed from a macroscopic view point by viscosity measurements. Again for these sulfate salts flotation is achieved with DAH and SDS as collectors if the salt is a water structure breaker.