New procedure for water-salinity reduction using Phosphogypsum waste and carbon dioxide resulting in useful compounds formation

Desalination plants produce huge amounts of reject brine water (RBW), which are usually sent back to the sea, where they could, in the long run, result in detrimental effects on the aquatic life. The Phosphogypsum waste (PG) is a raw material, mostly discharged into the sea or deposited in large stockpiles without any pretreatment, which represents serious disposal problems with the phosphoric acid production units. This work tries to manage two types of wastes: (1) Reject brine water (RBW) from the sea water desalination plants and (2) Phosphogypsum waste (PG) from the H3PO4 production units, for commercial products preparation (such as Ca(OH)2, Na2SO4, and CaCO3), reduction in salinity of RBW and CO2 capture. Different alkali bases (Ca(OH)2 and NaOH) were dissolved into RBW solution under continuous CO2 flow bubbling. The structure and the morphology of all the samples and prepared materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The precipitated phases were calcite and a mixture of calcite and aragonite when we use Ca(OH)2 prepared from PG and pure Ca(OH)2, respectively. In addition, the treatment of RBW with these bases could minimize the salinity of the RBW to produce useful water for possible application in the agriculture especially in the irrigation operations. Treating RBW with Ca(OH)2 prepared from PG may reduce the salinity up to 19%, whereas this value decreased to 12 and 9% for commercial Ca(OH)2 and NaOH, respectively. This work was able to calculate the amount of CO2 removed as well as the cost analysis, salinity reduction, final products purity and the profits related to the extracted products. The process gain ratio (output cost/ input cost) was calculated as 1.66.