Development of a simple and fast ultrasound-assisted extraction method for iodine determination in phosphate rock and phosphogypsum by-product using titrimetric method

Abstract

ABSTRACT Phosphate rocks, as well as their derivatives and by-products, are complex minerals that make elemental analysis very complicated. Iodine is commonly found in these matrices, and its concentration must be controlled. The present work describes the development of a novel rapid digestion protocol based on ultrasonic-assisted acid digestion for the determination of iodine in phosphate rock and phosphogybsum samples by Iodometric titration. The developed method occurs at low digestion temperature and uses a dilute nitric acid 5% (v/v) solution instead of concentrated acid. The investigated parameters influencing UAD, were completely optimised using experiments design methodology (DOE). Iodine recoveries from dilute nitric acid digestion without sonication were generally lower overall when compared to UAD results, illustrating the effect of ultrasound on iodine dissolution. This technique effectively addresses iodine volatilisation and sample losses problem encountered while using classical digestions. Method validation included: defining the detection and quantification limit of iodine using this method were about 2.2 and 8 mg.kg−1, respectively, and it's suitable for the proposed application. Moreover, the repeatability and reproducibility, expressed as RSD for phosphogybsum sample was 7%, 8.3% respectively, while for phosphate samples is tacked as the mean of relative standard deviation 3.4%, 3.8%. Additionally, accuracy of the method was assessed by analysing a certified reference material and the iodine concentration was found to be in good agreement with the indicative values for this CRM. Thus, the mean recoveries in fortified sample were between 96% and 107%.The developed method is fast, accurate, and it is applicable to the monitoring of iodine in the phosphate industries.