Determination of free acid in rare earth solution by a fixed pH method

Abstract

A fixed pH method was developed for free acid determination in solutions containing large amounts of rare earths, especially Ce(IV). With Ca–EDTA as the masking regent at a fixed pH of 4.5, free acid was determined in a solution containing about 100 g/L of rare earths including about 50 g/L Ce(IV) with a relative standard deviation (RSD) of less than 1%. The deviation error for 50 measurements in 5 groups for a known amount of H₂SO₄ solution was −1.44%. Compared with other reported methods, the newly developed method has the advantages of higher precision, higher accuracy, simpler procedure and no need for an indicator.