Abstract: A process is disclosed for removing heavy metal contaminants from impure alkali metal nitrates containing them. The process comprises mixing the impure nitrates with sufficient water to form a concentrated aqueous solution of the impure nitrates, adjusting the pH of the resulting solution to preferably within the range of between about 2 and about 4, adjusting the nitrite ion concentration to between about 0.07 molar and about 1.0 molar, to effect reduction of the heavy metal contaminants, adjusting the pH of the reduced solution to effect precipitation of heavy metal impurities, and separating the solid impurities from the resulting purified aqueous solution of alkali metal nitrates. The resulting purified solution of alkali metal nitrates may be heated to evaporate water therefrom to produce purified molten alkali metal nitrate suitable for use as a heat transfer medium. If desired, the purified molten form may be granulated and cooled to form discrete solid particles of alkali metal nitrates.