Coprecipitation with lanthanum phosphate as a technique for separation and preconcentration of iron(III) and lead

The usefulness of coprecipitation with lanthanum phosphate for separation and preconcentration of some heavy metals has been investigated. Although lanthanum phosphate coprecipitates iron(III) and lead quantitatively at pH 2.3, iron(H) can barely be collected at this pH. This coprecipitation technique was applicable to the separation and preconcentration of iron(III) before inductively coupled plasma atomic-emission spectrometric (ICP-AES) determination; the recoveries of iron(III) and iron(II) from spiked water samples were 103-105% and 0.2-0.7%, respectively. The coprecipitation was also useful for separation of 20 mug lead from 100 mL of an aqueous solution that also contained 1-100 mg iron. Coprecipitation of iron was substantially suppressed by addition of ascorbic acid, which enabled recovery of 97-103% of lead added to the solution, bringing the recovery to within 1.6-5.0% of the relative standard deviations. Lanthanum phosphate can also coprecipitate cadmium and indium quantitatively, although chromium(III), cobalt, and nickel and large amounts of sodium, potassium, magnesium, and calcium are barely coprecipitated at pH 3.