Effective and affordable methods of cleaning a variety of water sources from the fluorine-containing inorganic impurities

Abstract

The paper presents effective and affordable methods of purification of water with different mineral composition and origin from fluoride. The complex approach was applied to the choice of reagents-precipitators and conditions (weight of reagent, pH of process, time of process, deposition rate) of water purification from fluorine-containing inorganic components. The approach allowed us to achieve the required standards for fluorine, both for drinking water bodies and for fishery purposes, excluding unacceptable secondary pollution by the components of the used reagents. The hydrolytic stability has been carefully studied for various complex inorganic fluorides; values of the stability play an important role in the organization of water purification from fluorine-containing inorganic impurities by reagent methods. Waters containing fluorine in the form of fluoride ions (F) were shown to be effectively purified with the help of sulfate compounds of titanium or aluminum chloride. Titanium sulfate compounds are also suitable for purification of water containing fluorine in the form of a complex anion SiF6-2, molar ratio Ti4+:F-=9.7 is sufficient to achieve the degree of purification to the standards of fishery water bodies applied in Russia (0.75 mg/l). For purification of water containing fluorine in the form of complex anions FeF63-, TiF62-, AlF63- we proposed to use cerium (III or IV) sulfate compounds, which, at the molar ratio of Cen+ F=3.76-5.65, provide a high degree of fluorine extraction. At this degree the residual fluorine content in water is 1.3-1.7 mg/l, which does not exceed the norms for drinking water bodies applied in Russia. Cleaning up to standards for reservoirs of fishery appointment is also possible at an increase in the reagent consumption; however, the degree of secondary pollution by cerium increases. Cerium sulfates, if necessary, can be used in the purification of water from fluorine in the form of F and SiF62- All the developed methods were tested in the treatment of the effluents of the Lovozero Mining and Processing Plant (Karnasurt mine) and Apatit Ltd. (ANOF-II) with an average annual fluorine content of 8-12 mg/l. The use of titanium sulfate compounds, with a molar ratio of Ti4+: F-=7.76, makes it possible to achieve a residual fluorine content in the purified water 0.5 mg/l. The use of aluminum chloride, with a molar ratio of Al3+:F-=5.34, allows us to achieve a residual fluorine content in water 0.7 mg/l. The use of cerium compounds as precipitating agents also leads to a significant decrease in the fluorine content in water, the degree of purification up to 0.7-1.45 mg/l is achieved at a molar ratio of Ce:F-=1-1.25, respectively.