Ionic Size in Flotation Collection of Alkali Halides

Long-Chained aliphatic amine salts have been used for the separation of sylvite (KC1) from halite (NaC1) by flotation. It is puzzling how these two minerals, which are so similar chemically and crystallographically, can be separated by this method. Gaudin as postulated that the difference in floatability of halite and sylvite with salts of primary amines depends on ionic size: In the case of amine flotation, the cation would attach itself to the chloride. I have a speculation there, which I cannot prove, that the ammonium group, that is the –NH3 group in the amine, floats potassium chloride because the dimensions of this group as it has been measured in other compounds is almost identically the dimensions of the potassium ion, quite different from the sodium ion, and so it fits where potassium had been, in place of it and not attached to it.