The components of aqueous ammonium fluoride solutions are recovered as ammonia and potassium fluoride by adding potassium hydroxide, di stilling to remove and secure the ammonia, concentrating the remaining solution and combining it with a water soluble, dipolar, aprotic solvent, such as N-methylpyrrolidone, and distilling to remove the remaining water to obtain the potassium fluoride as a slurry in the solvent. Slurries of potassium fluoride are useful in the replacement of chloride in heterocyclyl and aryl chlorides by fluoride.