Titrimetric determination of free and total acidity and the subsequent deduction of zirconium content in process samples of zirconium nitrate

Abstract

A simple titrimetric method for the rapid determination of free nitric acid concentration and total acidity in process samples of zirconium nitrate is described. This paper also details a theoretical method of deducing the zirconium oxide content of these samples based on the free and total acidity values. Sodium fluoride is used to complex the hydrolysable ions and sodium hydroxide is used as the titrant for the free acid. A mixed indicator of Bromocresol Purple and Bromothymol Blue (sodium salt, 0.1% each in water) was used to detect the endpoint where there is a sharp change in colour from yellow to deep blue. A precision of ±0.02 mol l^–1 and ±0.5 g l^–1 is attainable for acidity values and zirconium oxide concentrations, respectively. The free acidity values are in good agreement with those calculated, based on the total acidity and total concentration of the hydrolysable ions present in the medium. The zirconium throughput values calculated from the total and free acidities compared favourably with the gravimetric values estimated by precipitating zirconium (hafnium) as mandelate followed by ignition to produce the oxide. Applicability of various ligands such as oxalate, tartrate, citrate and ethylenediaminetetraacetic acid as alternative complexants is also investigated and it is observed that the zirconium complexes formed with these complexants (except that with cupferron) hydrolyse significantly and cannot be used as complexants for the direct determination of free acidity. The use of cupferron was found to be limited because of poor precision.