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

In phosphoric acid factories using phosphate rock, the major problem known is the high
quantity of produced phosphogypsum “PG” waste. Storage and management of this
quantity present a serious problem. 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
tests of valorization, we can find methods of desulphurization, bacteriological or thermal,
allowing to produce sulphur dioxide SO2 used in the synthesis of the sulphuric acid. The
object of our work is to develop an alternative technique to valorize the PG and produce
sulphur dioxide “SO2” following an attack by a strong acid in the presence of a metal
catalyst. We have shown that the leaching of the PG with acid alone does not allow
reduction of the ions sulphates dissolved to the SO2. However, if the leaching is made in
the presence of the metal elements, the release of gaseous SO2 is observed. The values of
ΔGr and ΔHr calculated allowed us to discuss the possibility of the reactions involved and
to argument the experimental results found.