Enhancing wet phosphoric acid production efficiency with vanadium catalyst waste derived silica

Filtration of phosphogypsum (PG) is an important step in the production of wet phosphoric acid (WPA). In recent years, the phosphate rocks used for WPA production in Morocco started showing deficiencies in terms of their reactive silica content that affects PG crystallization and as such decreases PG filtration efficiency and subsequently the overall efficiency of the WPA production. In this work reactive silica waste from spent vanadium catalysts, used in the production of sulfuric acid for WPA production, was added to the digestion process in an attempt to increase WPA production efficiencies. The laboratory work presented here shows that the added silica improved the quality of the produced dihydrate WPA by 6 %. Besides, the chemical yield of the reaction was improved by 5 % as a result of the shape-change of the PG crystals that allowed for better filtration. The results of this work are promising and we strongly recommend testing this approach on larger pilot- and ultimately industrial scale.