Chemical Characteristics of Aerosol Mists in Phosphate Fertilizer Manufacturing Facilities

Abstract

Of the carcinogens listed by the National Toxicology Program (NTP), strong inorganic mists containing sulfuric acid were identified as a known human carcinogen. In this study, aerosol sampling was conducted at 24 locations in eight Florida phosphoric acid and concentrated fertilizer manufacturing plants and two locations as background in Winter Haven and Gainesville, Florida, using dichotomous samplers. The locations were selected where sulfuric acid mist may potentially exist, including sulfuric acid pump tank areas, belt or rotating table phosphoric acid filter floors, sulfuric acid truck loading/unloading stations, phosphoric acid production reactors (attack tanks), and a concentrated fertilizer granulator during scrubbing with a weak sulfuric acid mixture. An ion chromatography system was used to analyze sulfate and other water soluble ion species. In general, sulfate, fluoride, ammonium, and phosphate were the major species in the fertilizer facilities. For the rotating table/belt phosphoric acid filter floor, phosphate and fluoride were the dominant species for PM₁₀, and the maximum concentrations were 170 and 106 μ g/m³, respectively. For the attack tank, fluoride was the dominant species for PM₁₀, and the maximum concentration was 462 μ g/m³. At the sulfuric acid pump tank, sulfate was the dominant species, and the maximum PM₁₀ sulfate concentration was 181 μ g/m³. The concentration of PM₁₀ sulfate including ammonium sulfate, calcium sulfate, and sulfuric acid were lower than 0.2 mg/m³ at all locations. The aerosols at the filter floor and the attack tank were acidic. The coarse mode aerosol at the sulfuric acid pump tank (an outdoor location) was acidic, whereas the fine mode aerosol was neutral to basic.

Keywords:

• fertilizer facilities
• fluoride
• phosphate
• PM₁₀
• sulfuric acid

ACKNOWLEDGMENTS

The authors greatly appreciate the efforts of Robert Ammons, Tom McNally, Cheng-Chuan Wang, and environmental/safety staffs at fertilizer plants who helped carry out the sampling. The authors are especially grateful to Alan Pratt who provided insightful knowledge.

This project was funded by Florida Institute of Phosphate Research.