LED based optical dip-probe spectrophotometer for in situ monitoring of uranyl and uranous ions in aqueous process stream

Abstract

A miniature setup for the “transmission absorption spectrophotometry” was developed for in situ monitoring of U(VI) and U(IV) concentrations in the aqueous process streams of extraction, conversion, reprocessing, refinement and electro-chemical production of U(IV). The miniature setup used in the present work consisted of a LED light source (λmax = 471.5 nm for U(VI) and 665 nm for U(IV)), miniature spectrophotometer, mirror fitted and PEEK sheath protected dip-probe assembly or flow cell, and optical fibers with connectors. The characteristics absorbance peaks of U(VI) were used for concentration monitoring in the samples taken from the aqueous feed of uranium extraction process. There was a reasonable good agreement in the sensitivity values obtained by using the flow cell, dip probe and cuvette at 415, 466, and 485 nm having upper measurement limits of 25, 100 and 400 g/L of U(VI), respectively, in 2 mol/L HNO3. The absorbance peak at 485 nm did not exhibit any significant dependency on the HNO3 concentrations ranging from 0.5 to 3 mol/L. However, other absorbance peaks varied with the HNO3 concentrations. The various parameters such as effect of variation in HNO3 concentration and analytical range of the uranium concentration in the feed were studied. The robustness and analytical performance of the present method were studied by statistically analyzing the results of the real off-line samples from different batches of the feed of uranium extraction plant. From the results of statistical analyses, it could be seen that the measured U(VI) concentrations were in the good agreement with the other off-line methods such as gamma spectrometry, EDXRF and ICP-AES, and all the measured U(VI) concentrations results obtained were within ± 3σ values. There was no observable bias in the results with respect to concentration, acidity, date of experiment etc. This setup was also studied for the continuous monitoring of the production of U(IV) from the electrolytic reduction of U(VI) by monitoring 665 nm absorbance peak using a LED light source.