Removal of impurities released from phosphogypsum waste in aquatic environment using bentonite

Phosphogypsum (PG), CaSO4,2H2O, is an acidic residue derived from the phosphate industry produced in very large quantities. Phosphogypsum is mainly calcium sulfate dihydrate, it contains elevated amount of impurities that originated primarily from the phosphate rock used for the production of phosphorus fertilizers. Large quantities are produced world-wide and are being thrown out on the seas, thus causing adverse effects on marine environment. It is known that PG causes disturbances, mainly chemical pollution of the aquatic environment (e.g. phytoplankton efflorescence and continuous regressions of Posidonia herbarium).
In order to fully understand the environmental impact of phosphogypsum, it is necessary to understand the geochemical processes that control the composition of phosphogypsum leachates and the attenuation of environmentally sensitive chemical species when these leachates enter aquatic environments. The aim is also to use natural adsorbent as raw bentonite to reduce the impact of the acidity and heavy elements on the environment. For that purpose, XRD, XRF, LOI and ATD/TG analyses were performed on raw bentonite (B). Afterwards, in distillated water, we mixed 10g of different proportion of PG and bentonite (0% ≤PG/B≤ 100%) in order to follow the characteristics of the liquid phase (pH, conductivity, chemical composition ...).
The results indicate that the pH of the solutions containing only PG remain constant, however, for the PG and bentonite mixtures, the environment became more alkaline. A proliferation of algae starts to be observed in the mixture 5PG/5B, and after a long stay in natural conditions, a proliferation of algae is observed in all the mixtures. We note the absence of algae when only the phosphogypsum or bentonite is put in contact with water. Overall, the preliminary results show that the mixture "PG + bentonite" has two important effects: (1) fertilization of the aquatic environment, (2) depollution by trapping of the chemical impurities released by the PG into the solution.