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24AB-307, AB-308, AB-314, AB-316Determination of sulfate and phosphate in variousfertilizersThis series of Application Bulletins deals with the determinationof sulfate and phosphate in liquid fertilizers and granular fertilizerssuch as MAP (monoammonium phosphate), DAP (diammoniumphosphate) and TSP (triple superphosphate). Sulfate can be rapidlyand easily titrated thermometrically using a standard solution of Ba 2+as titrant. This procedure is already used for the determination ofsulfate in wet-process phosphoric acid. Results are reported as percentageof elemental sulfur (%S).Phosphate can be rapidly and easily titrated thermometrically usinga standard solution of Mg 2+ as titrant. This titrimetric phosphatedetermination method is based on a classical gravimetric procedure.The phosphate-containing solution is buffered with NH 3/NH 4Clsolution immediately before the titration. The formation of insolubleMgNH 4PO 4 is exothermic. Results are reported as percentage of Pand P 2O 5. The phosphoric acid content in liquid fertilizers can beeasily titrated thermometrically with a standardized NaOH solutionc(NaOH) = 2 mol/L. The interfering calcium content in phosphoricfertilizer can be eliminated by adding a saturated oxalate solution.AB-313Determination of total caustic, total soda and alumina inBayer process liquorsTotal caustic 1 , total soda 2 and the aluminum content (as alumina)of aluminate liquors from the Bayer process have to be determined.This can be accomplished with high precision and speed by using athermometric acid-base titration. A complete titration to determineall three parameters takes approximately five minutes. The procedureis an automated adaptation of the traditional Watts-Utley method 3 ,and is similar to the Van Dalen-Ward thermometric titration method 4 ,but with the added advantage of being able to analyze the carbonatecontent of the liquor as well.An aliquot of Bayer liquor is dispensed into a titration vessel. Potassiumsodium tartrate solution is added to complex the aluminateion. One mole of hydroxide ions is released per each mole aluminateion present. These hydroxide ions, together with hydroxide ions alreadypresent in the liquor are titrated with standardized hydrochloricacid. The titration is permitted to continue so that carbonate ionspresent in the liquor are also titrated. The first titration is then automaticallystopped, and potassium fluoride solution added to breakthe alumino-tartrate complex and release 3 moles hydroxide ions pereach mole aluminum present. These liberated hydroxide ions are thentitrated with the standardized hydrochloric acid, and determined asthe alumina content of the liquor.