A novel flow injection procedure for determination of phosphate in industrial raw phosphoric acid

Abstract

A new method for the rapid determination of the phosphate content of highly concentrated industrial raw phosphoric acid, as obtained in the Tunisian mining industry, is reported. The method is based on the injection of the phosphate-containing sample in to a stream of FeCl₃ and subsequent measurement of the decrease in absorption at 334 nm due to the formation of an iron(III) phosphate complex. With the developed method, a linear calibration curve from 0.1 to 20 g l⁻¹ H₃PO₄ was obtained. For the analysis of samples drawn from a phosphoric acid production site, dilution by a factor of 100 was necessary in order to fit the linear range of the calibration curve. With the developed procedure a sampling frequency of 30 samples per hour and a standard deviation of 1.4% was achieved. The developed method was applied to the analysis of natural samples and the results obtained were in excellent agreement with those obtained by gravimetry.