Experimental Investigation of the Effects of Synthesis Parameters on the Precipitation of Calcium Carbonate and Portlandite from Moroccan Phosphogypsum and Pure Gypsum Using Carbonation Route

Due to the yearly enormous amounts of produced phosphogypsum waste and the continuous increase of CO2 emissions in the atmosphere, it is necessary to find attractive approaches to solve these two environmental problems. The present work proposes an efficient method, which allows both the valorization of the Moroccan phosphogypsum waste (MPG) by synthesizing marketable products and the reduction of the emission of greenhouse gases especially the carbon dioxide (CO2). We have examined the effect of the following operational parameters: Molar Ratio KOH/MPG (2 ≤ MR ≤ 3), CO2 injection flow rate (5 ≤  $${\text{V}}_{{\text{CO}}_{2}}$$ ≤ 20) mL min−1, Portlandite concentration (10 ≤ CPort ≤ 25) g L−1 and the temperature (18 ≤ T ≤ 37)  °C on the precipitation of calcium carbonate (CC) from the Portlandite (P) prepared by dissolving Moroccan phosphogypsum (MPG) in a KOH solution. The simultaneous change in electrical conductivity and pH of saturated solutions has also been studied. This technique can be particularly useful when we are interested in controlling the chemical reaction process. In all cases, we have observed a general similarity between the corresponding X-ray diffraction patterns of calcium carbonate (CC) precipitated from pure Gypsum (G) and from Moroccan phosphogypsum (MPG). This study can pave the way towards using Moroccan phosphogypsum, originated from phosphate chemical plants producing phosphoric acid, as a substituent for natural gypsum. This leads to effective waste management and environmental sustainability. K2SO4 and CaCO3 produced were highly recommended in the field of the agriculture, chemical and construction industries.