Agrico Chemical Company

Kyle D Clevenger

Charles W Weston

Padraic S O'Neill

Kenneth L Parks

Daniel P McDonald

Jesse S Chang

An economical process for treating the acidic pond water to be used in the internal grinding circuit of a wet process phosphoric acid plant. Water is added to a quantity of a hydratable calcium compound, such as quicklime, to form a slaked lime slurry. A sufficient quantity of the slaked lime slurry is reacted with the acidic pond water to obtain a low fluoride solution having a fluoride content less than about 300 ppm and a pH in the range from about 2.0 to about 3.0, preferentially in the range 2.6-2.8, whereby calcium fluoride is precipitated. The precipitate bearing low fluoride solution is then clarified and the precipitate removed as underflow from the clarifier and transferred to the gypsum pond. In the preferred embodiment, the clarified low fluoride water is fed to the ball mill and is mixed with the phosphate rock being crushed. Removal of fluoride from the pond water solution reduced the 'blinding effect' of the fluoride and permits the calcium carbonate in the phosphate rock to neutralized the acidic pond water to minimize corrosion in the mill and elsewhere in the plant. The resulting slurry from the ball mill is about 55% to 65% solids and ranges in pH range from about 5.0 to about 5.5. The phosphate rock slurry is then passed through a hydroclone circuit where the larger (heavier) particles are removed for recycling to the ball mill and the remaining lightweight particles in the rock slurry are processed by phosphoric acid plant.

Neutralization of cooling pond water in phosphoric acid plants

Magnesium and aluminum impurities may be removed from wet process phosphoric acid by adding a fluoride ion donating compound, such as hydrofluoric acid, for example, to thereby provide about four fluoride ions for each aluminum ion. Also, preferably, an aluminum ion donating compound, such as alum is added to the wet process acid to bring the aluminum ion to magnesium ion ratio up to about two to one to facilitate formation of crystalline compounds having the general stoichiometry MgAl.sub.2 F.sub.8. The treated filter grade acid is then further treated in a crystallizer to form large crystals which will readily precipitate so the purified liquid phase, low in magnesium and aluminum containing impurities, may be separated from the crystalline phase.

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Baton Rouge, LA, United States of America

Kyle D Clevenger