ASTM E278-01 Test Method for Determination of Phosphorus in Iron Ores by Phosphomolybdate Coprecipitation and Nitric Acid Titrimetry

Scope:

ASTM E278-01 Test Method covers the determination of phosphorus in iron ores, concentrates, and agglomerates. The phosphorus is measured from the range ( 0.01 % to 1.00 %).

Test Procedure:

In ASTM E278-01 test method, the sample is dissolved in HCl and HNO₃. After the addition of HClO₄, the solution is evaporated to strong fumes to dehydrate the silica. The insoluble residue is filtered off, ignited, and treated for the recovery of any contained phosphorus. Ammonium molybdate is added to precipitate phosphomolybdate. The precipitate is filtered off and washed free from acid. It is then dissolved in excess of standard sodium hydroxide solution. The excess sodium hydroxide is titrated with a standard solution of HNO₃ using phenolphthalein as an indicator.

Figure 1: Titration Setup (Source: chem.libretexts.org)

Specimen size:

A pulverized Iron ore sample weight ±25 mg

Data:

Calculate the percent of phosphorus as follows:

Where:

A = standard NaOH solution used, mL,

B = standard HNO₃ required for titration of the excess of NaOH in the test sample, mL, 

C = standard NaOH solution equivalent to 1 mL of the standard HNO₃, mL, 

D = standard NaOH solution required for blank determination, mL,

E = standard HNO₃ required for titration of the excess NaOH in blank determination, mL, 

F = phosphorus equivalent of the standard NaOH solution, g/mL, and

G = weight of test sample used