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Portlandite (Ca(OH)2) preparation from phosphogypsum waste (PGW) was evaluated in numerous works; however, the use of this compound is not applied yet in the brine water salinity reduction. In this work, the purity of Ca(OH)2 prepared from PGW and soda aqueous solution was tested for different NaOH/PG molar ratios (MR) close to the stochiometric value (1.5 < MR < 3). The obtained Ca(OH)2 at the optimal conditions was used for both the CO2 capture and brine water (BW) salinity reduction, resulting in high-quality calcium carbonate synthesizing. The XRD results show that a MR higher than the stochiometric value (MR > 2) is most efficient to obtain high-quality portlandite (P2.5 and P3). An estimation of the carbon capture efficiency of the prepared portlandite was made. Based on the results of this work, using 4 g of P2.5 allows to capture 2.4 L of CO2 and treat 0.4 L of BW. Overall, our work confirms the technical viability of the proposed route to synergize CO2 capture, BW and PGW recycling. From an economic and ecological standpoint, our investigated routes were eco-friendly and cost-effective. [ABSTRACT FROM AUTHOR]

We describe herein a detailed study on the effect of molar ratio MR = n(OH−)/n(Ca2+) on the Phosphogypsum (PG) waste ammonia-carbonation process. The use of an aqueous NH3 solution/gaseous CO2 mixture as an alternative and environmental medium compared with other mediums [(NH4)2CO3 for example] is proposed for CO2 capture and PG recycling. The main purity, reaction time, and production efficiency of the obtained products were systematically studied for the different molar ratios using several physicochemical techniques: XRD, XRF, FTIR, SEM/EDX, pH, and electrical conductivity meters. For economic reasons, the molar ratio was varied to obtain values close to those of the stoichiometry, MR (2 ≤ MR ≤ 4). The obtained results show that the MR presents an important effect on the conversion process. In parallel, a comparative study between the conversion process of the synthetic gypsum (SG) and PG shows that the two samples are similar. All these findings revealed that PG waste could be used as a substituent to the SG in the general application of this last useful product. [ABSTRACT FROM AUTHOR]