Agrico Chemical Company

Goulding Chemicals Limited

Padraic S O'Neill

Charles W Weston

Ralph E Worthington

Kyle D Clevenger

Jesse S Chang

Paul F Hackett

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

A process for the manufacture of phosphoric acid from phosphate rock is provided. The phosphate rock is digested or acidulated with an acid solution containing oxalic acid to produce phosphoric acid and calcium oxalate. Useful by-products are also formed and include calcium carbonate and ammonium oxalate. More specifically, the process provides for the production of phosphoric acid, ammonium phosphate and useful by-products utilizing synthesis gas and air to produce oxalic acid and ammonia. The synthesized oxalic acid is utilized for phosphate rock digestion to produce phosphoric acid, which can be reacted with ammonia to produce ammonium phosphate. Calcium oxalate from phosphate rock digestion is utilized to produce calcium carbonate, ammonium oxalate and oxamide.

Process for manufacturing ammonium phosphate utilizing an oxalic acid

A process for obtaining calcium fluoride from the pond water of phosphoric acid plants and recycling the high phosphate defluorinated water to the pond is disclosed. Sufficient calcium carbonate is added to a solution having a pH of about 0.8, containing about 1% fluoride, 1% phosphate and less than 0.4% sulfate, to raise the pH thereof to 2-3, whereby calcium fluoride is precipitated as a major component, calcium phosphates and calcium sulfates are precipitated as minor components. The calcium fluoride precipitate obtained is washed with raw pond water to reduce the phosphate content and with ammonium carbonate solution to reduce the sulfate content. In this manner an industrially useful fluorspar is obtained. The low fluoride supernatant liquid is then mixed with sufficient raw pond water to bring the pH into the range 1.5-2.0 and the resulting suspension is then held in a lagoon for 5-21 days to permit separation of silica. After separation by sedimentation, the water containing unprecipitated phosphate is returned to the pond for further use. The silica-rich sediment may be further dewatered by centrifugation and used in the phosphoric acid plant to promote better recovery of fluoride. To minimize sulfate contamination of the calcium fluoride product, a separate pretreatment step may be provided to reduce the sulfate content of the pond water to approximately 0.4%. In this step, sufficient calcium carbonate is added to raise the pH of the pond water to about 2.0, and after adequate aging to cause precipitation of calcium sulfate with minimal precipitation of calcium fluoride which precipitates at a higher pH. After pretreatment, the suspension is treated by the first step of the process to remove calcium fluoride.

Recovery of fluorine from pond water of wet process phosphoric acid

Hydrogen Fluoride is manufactured from fluorosilicic acid. The fluorosilicic acid is reacted with ammonia to produce aqueous ammonium fluoride and solid silica. The ammonium fluoride is hydrolised in the presence of a mixture of ammonium fluoride and ammonium bifluoride, and the net production of ammonium bifluoride is converted to sodium bifluoride. The sodium bifluoride is decomposed by heating to hydrogen fluoride gas.

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Baton Rouge, LA, United States of America

Padraic S O'Neill