Posphogypsum waste valorization by acid attack with the presence of metallic iron

During the classical production of phosphoric acid using phosphate rock, a high quantity of phosphogypsum “PG” waste is produced. Storage and management of this quantity present a serious problem, because the elevated levels of impurities which originate primarily from the source phosphate rock. The consumption or the re-use of this waste generates several environmental risks due to its composition. Several valorization processes of the PG, economic and environmental, are in phase of development and study.
Among the valorization processes, we can find desulphurization, bacteriological or thermal methods, allowing to produce sulphur dioxide SO2 used in the synthesis of the sulphuric acid. The main objective of the present study is to develop an alternative technique to valorize the PG and produce sulphur dioxide “SO2”, using an alternative procedure based on a strong acid attack with the presence of a metal catalyst. The results indicate that the leaching of the PG with acid alone does not allow reduction of the sulfates ions dissolved in SO2. However, when the leaching occurs with the presence of the metal elements, the release of SO2 is observed. The values of the calculated ΔGr and ΔHr permit to discuss the possibility of the reactions involved and to argument the experimental results found.