Production of maddrell salt

Abstract From the Canadian patent

Pure Maddrell salt is produced by heating sodium phosphate to temperatures of 250 to 420°C. The sodium phosphate used as starting material is sodium trimetaphosphate or a mixture of sodium trimetaphosphate with Maddrell salt, monosodium orthophosphate or disodium pyrophosphate, the mixture containing Na and P in a molar ratio of 1 : 1. Prior to heating the starting material, it is admixed with 0.5 to 5 weight% of orthophosphoric acid, polyphosphoric acid phosphorus, pentoxide or at least one salt of a volatile base forming polyphosphoric acid at the temperatures specified, The resulting mixture is calcined over the period necessary to transform the starting material to Maddrell salt.