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Phosphogypsum (PG) is an acidic by-product that is created during the production of phosphoric acid using the sulfuric acid route. The management of PG poses a significant environmental challenge worldwide due to its large quantity and chemical composition. While PG primarily consists of calcium sulfate dihydrate, it also contains various impurities such as phosphorus, fluoride, heavy metals, and radionuclides. These toxic impurities, when present in high concentrations, can have adverse effects on the environment and human health. In this review, we provide a detailed examination of the behavior of the most abundant impurities found in PG. Furthermore, we discuss the factors that influence the presence of different types of impurities in PG. Understanding the overall behavior of these impurities is crucial for selecting appropriate environmental methods for PG management and identifying suitable avenues for its valorization. [ABSTRACT FROM AUTHOR]

This study presents an efficient and sustainable procedure for converting phosphogypsum (PG) waste, along with hydrofluoric acid (HF) and ammonia (NH3), into valuable materials. The results obtained demonstrate the high efficiency of this proposed procedure, resulting in the synthesis of relatively pure calcium fluoride (CaF2) nanoparticles and ammonium sulfate ((NH4)2SO4). The latter is recommended for agricultural use as a fertilizer, while the obtained CaF2 can be utilized in the metallurgical industry. Furthermore, this procedure not only offers a solution for reducing fluorine gas emissions and managing PG waste but also contributes to the conservation of fluorite reserves. [ABSTRACT FROM AUTHOR]

CaAl-Layered double hydroxide (LDH) of hydrocalumite-type with nitrate anions in the inter-lamellar region was synthesized via the co-precipitation method at fixed pH and with a selected Ca/Al molar ratio of the starting salts equal to two. The obtained CaAl–NO3 compound was characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). In this context, this material has been employed as an adsorbent for the retention of the reactive azo dye, alizarin yellow R (AYR), from an aqueous solution. To further investigate the practical potential of CaAl–NO3 for AYR dye adsorption, the effects of various parameters such as temperature, the concentration of dye, pH, adsorbent dose, and contact time on adsorption capacity were separately exanimated. The findings results suggest that a pH of 9 is more suitable for the AYR dye adsorption process. The adsorption kinetics was better explained by the pseudo-first-order model, and equilibrium was achieved after 30 min of contact. The equilibrium adsorption data of AYR dye on the prepared CaAl–NO3 was well fitted to the Langmuir model, and it was characterized by an excellent adsorption capacity of 2107 mg/g at 293 K. Thus, due to the 2D structure and its positively charged layers, CaAl–NO3 material exhibits an exceptional ability to remove alizarin yellow R dye from aqueous solutions. [ABSTRACT FROM AUTHOR]

The production of phosphoric acid generates an enormous amount of phosphogypsum with emission of toxic fluorine acid gas. To remedy these environmental problems, a novel and a simple procedure permits converting phosphogypsum waste by recycled fluorine acid into valuable products. The obtained results confirm the efficiency of this procedure, which synthesises at room temperature the calcium fluoride in the form of nano-crystalline powder and the ammonium bisulphate salt from the exact stoichiometric proportions of phosphogypsum, hydrofluoric acid and ammonia. The total conversion of phosphogypsum is achieved after reaction time equal to one hour and a half. Generally, this novel procedure offers not only a solution for reducing phosphogypsum waste and fluorine gas emission, but also gives rise to valuable products, useful to industry and agriculture. [ABSTRACT FROM AUTHOR]

The phosphoric acid production in Morocco generates a large amount of phosphogypsum (PG) which is a significant source of environmental contamination. In this work, PG has been characterized by different analysis techniques that allow to study the effect of the impurities on its physical and chemical properties. Thus, a method to purify the PG from phosphates and fluorides was proposed in order to improve its quality and to make it usable in plaster and cement. The purification process consists to sieve PG under 200 μm and to treat it by sulfuric acid to dissolve the insoluble impurities. The obtained results show that the treatment of PG by sulfuric acid 20 and 50% at 60 °C for 2 h is sufficient to make it suitable for used in the plaster and the cement respectively. [ABSTRACT FROM AUTHOR]

CaAl-Layered double hydroxide (LDH) of hydrocalumite-type with nitrate anions in the inter-lamellar region was synthesized via the co-precipitation method at fixed pH and with a selected Ca/Al molar ratio of the starting salts equal to two. The obtained CaAl–NO3 compound was characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). In this context, this material has been employed as an adsorbent for the retention of the reactive azo dye, alizarin yellow R (AYR), from an aqueous solution. To further investigate the practical potential of CaAl–NO3 for AYR dye adsorption, the effects of various parameters such as temperature, the concentration of dye, pH, adsorbent dose, and contact time on adsorption capacity were separately exanimated. The findings results suggest that a pH of 9 is more suitable for the AYR dye adsorption process. The adsorption kinetics was better explained by the pseudo-first-order model, and equilibrium was achieved after 30 min of contact. The equilibrium adsorption data of AYR dye on the prepared CaAl–NO3 was well fitted to the Langmuir model, and it was characterized by an excellent adsorption capacity of 2107 mg/g at 293 K. Thus, due to the 2D structure and its positively charged layers, CaAl–NO3 material exhibits an exceptional ability to remove alizarin yellow R dye from aqueous solutions. [ABSTRACT FROM AUTHOR]