Extraction of natural radionuclides in TENORM waste phosphogypsum

Abstract

Phosphate ore is the raw material for the production of fertilizers. Phosphogypsum with a high content of natural radionuclides, specifically those present in the decay series of 238U and 232Th, is a byproduct (waste material) of a chemical reaction between sulfuric acid and phosphate rock in phosphoric acid production. Due to these characteristics, the phosphogypsum is considered a TENORM (Technologically Enhanced Naturally Occurring Radioactive Materials). For each ton of phosphoric acid produced, 4 to 5 tons of phosphogypsum are generated, representing a great environmental liability. Because of the similar chemical properties of phosphogypsum and conventional gypsum, both calcium sulfate, there is a great interest in the scientific community to find technological solutions for reuse of this material. This study aimed to develop methodologies and processes for separating calcium sulfate from the main radionuclides present in the phosphogypsum, based on the difference in solubility between these compounds, among them the radium sulfate. Chemical processes were developed for the recovery of the calcium sulphate in the solid form from the extraction of the radionuclides made by dissolution of the phosphogypsum. This study shows that it is possible to extract radionuclides from waste TENORM - phosphogypsum – obtaining more than 80% of the material in the form of hydrated gypsum. Using gamma-ray spectrometry technique, no signal was detected for the presence of radionuclides in the treated material. The results indicate the benefits that the process used in this work can provide when implemented on an industrial scale.