Abstract :
[en] The production of phosphoric acid from phosphate rock generates a large amount of waste in the form of phosphogypsum "PG". The storage strategy and management of this amount of phosphogypsum is a serious problem. The reuse or recycling of this waste remains limited despite the efforts made in this regard, because of the environmental risks that certain toxic elements (i.e. As, Ba, Cd, Cr, and Pb) could generate. The recovery of phosphogypsum has been studied using two approaches, namely desulphurization, which produces sulfur dioxide SO2, used in the synthesis of sulfuric acid, and the stabilization of bentonite intended for road construction.
Desulfurization has made it possible to develop an alternative technique for upgrading PG and producing sulfur dioxide “SO2”, following attack by a strong acid in the presence of a metal catalyst “iron”. The results obtained showed that the leaching of PG with acid alone does not make it possible to reduce the sulphates of ions dissolved in SO2. However, if the leaching is carried out in the presence of iron, the release of SO2 gas is observed. The calculated values of ΔGr and ΔHr made it possible to prove the possibility of the reactions involved and to discuss the experimental results obtained.
The stabilization of bentonite by adding phosphogypsum and lime as aggregates for road construction has been investigated, as well as the effect of these aggregates on cementitious properties has been discussed. Properties examined include chemistry (XRF), mineralogy (XRD, IR), calorimetry (ATD / TG), mechanical strength, and microstructure (SEM) of the mortar based on different mixtures of bentonite, phosphogypsum and lime. The results showed that the addition of lime and PG involves the formation of new nanocrystalline phases (CSH, stratlingite) and the disappearance of certain minerals such as portlandite. The CSH gel appeared in the mixture with 8% lime, while stratlingite was neoformed in the mixture with 8% L + 8% PG. These nanocrystalline phases are responsible for improving the mechanical strength due to the pozzolanic reaction.
