MgO Removal from Phosphate Pebble by Flotation
Phosphate rock as it is mined in Florida contains an increasing quantity of magnesium. The magnesium is present as discrete particles of dolomite (calcium magnesium carbonate) and generally in particles of rock larger than 1 mm. The higher magnesium both adversely affects the production of phosphoric acid (lowers phosphate recovery or rate) and acts as a diluent in the final fertilizer products.
Numerous surfactants and surfactant systems were used to coat mixtures of dolomite and phosphate rock. The coated rock (sizes up to 10 mm) was then immersed in a weak (2-3%) sulfuric solution. The acid reacted with the dolomite, generating carbon dioxide that could be trapped by the surfactant and cause the dolomite to float to the surface. Of the surfactant/surfactant systems tried, polyvinyl alcohol (PVA) was found to be the best performer. This surfactant could float particles up to 8 mm in size.