Phosphogypsum is a by-product of the wet phosphoric acid production. In this study, chemical compositions of phosphogypsum waste (PG) in Hai Phong diammonium phosphate plant (DAP1) and Lao Cai diammonium phosphate plant (DAP2) in Vietnam were surveyed for the purpose of gypsum recovery by P2O5, F removal to meet TCVN11833 for use treated gypsum as cement retarder. Studies of impurities P2O5, F, TOC removal by sulfuric acid 10 % at 28 0C was presented. The results found that the combination of a low concentration of sulfuric acid treatment, washing, lime neutralizing, and thermal treatment was successful in Phoshogypsum treatment for use as cement retarder. The cement test proved that treated PG could partially replace natural gypsum as a retarder.Keywords: phosphogypsum treatment, phosphorus pentoxide removal, calcium sulfate transition phase, cement retarder.
This study reports creating CaCO3 nanoparticle (NPs) and microparticles (MPs) from treated phosphogypsum of Dinh Vu Diamon phosphate plant in Vietnam. In this research, CaCO3 NPs and MPs were received in the system of Ca(OH)2 ‐ CO2 gas ‐ H2O by aeration method. The research samples are characterized by ultraviolet visible spectrophotometry (UV‐vis), scanning electron microscopy (SEM), X‐ray diffraction (XRD) and dynamic light scattering (DLS). The study investigated the conditions for obtaining calcium carbonate NPs and MPs when changing the aeration speed of CO2 from 40 to 120 ml/min, the concentration of Ca(OH)2 from 0.04 M to 0.5 M, the temperature from 28 to 60 oC. This research showed that the clear influence of Ca(OH)2 concentration and reaction temperature on the CaCO3 particle size in the CO2‐Ca(OH)2 system. CaCO3 morphological structure has the form of calcite with rhombohedral block (rhomboid cylindrical box).
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