Fluoride emissions

Fluorides Two EPA reference methods, Method 13A and Method 13B, can be used to determine total fluoride emissions from a stationary source. The difference in the two methods is the analyti-... 

Why are total fluoride emissions from an aluminum smelter of more concern than gaseous or solid fluoride emissions ... 

The waste materials produced during the primary production of aluminum are fluoride compounds. Fluoride compounds are principally produced during the reduction process. One reason that prebaked anodes are favored is that the closure of the pots during smelting facilitates the capture of fluoride emissions, although many modern smelters use other methods to capture and recycle fluorides and other emissions. 

The contrast in the organism observations before and after fluoride emission abatement was dramatic. During July 1973, pH-meter readings that were remarkably low for estuarine samples were observed within... 

Hyland etal. [37] have recently reviewed sulfur and fluoride emissions (including particulate emissions) from Hall-Heroult cells and concluded that operational changes over the past few years, such as a tendency toward lower ratio (more volatile) electrolyte may have made emission control more difficult. 

This article has described the Hall-Heroult cell that is the mainstay of the aluminum industry throughout the world. Emphasis has been on the electrochemistry and electrochemical engineering that govern cell performance. The cell operation, electrolyte chemistry, thermodynamics, and electrode kinetics have been reviewed. Some complexities, notably the anode effect and the environmentally important fluoride emissions and anode gas bubbles and their effect on cell voltage, flow, and CE, have been examined. The incorporation of these phenomena, along with current distribution, magnetic fields, electromagnetically driven flow, heat and mass transport, and cell instability into mathematical models was summarized. 

Fluoride emissions into the atmosphere are derived mainly from modern-day anthropogenic sources, particularly industrial sources. They include steel industry, phosphate fertilizer industry, aluminum industry, ceramics... 

Explain why fluoride emissions are often of concern in aluminum manufacturing process. 

FIGURE 10.6 Emission control devices used with the vapor from a phosphoric acid evaporator to decrease fluoride emissions. The water used to condense steam by direct contact with cold water also serves to control fluoride vapor losses quite efficiently. (From Slack [55], page 747, by permission, Marcel Dekker, Inc.)... 

TABLE 12.7 Preabatement and Postabatement Atmospheric Fluoride Emission Rates in Primary Aluminum Smelters Operating in the U.S.A. and Canada"... 

Fluorides represent the discharge component of greatest hazard to plant life, and to nearby grazing and predator animals [34]. The injury threshold to plants from sulfur dioxide is about 0.1 ppm (100 ppb) whereas the equivalent value for fluoride to fluoride-sensitive plants is <1 ppb [26]. Thus, since fluoride emission has represented the largest mass loss to the atmosphere, this has a significant potential for biotic impact [35]. 

Clay materials used in the brick industries are currently monitored to control air and groundwater pollution. Some areas suffer from severe pollution by emission of fluorine to the atmosphere and its subsequent transport into the groundwater since clay may contain 200 to 1200 mg kg of F. As an example, the brick and ceramic industry is responsible for 50 /o of the total fluoride emission in The Netherlands. The emissions are calculated from the difference in the F content of the clay and the final product (brick). In some cases, raw materials are rejected if the fluoride contents are too high which cause an economic concern. As a consequence, many European countries have implemented regulations for the maximum authorised amount in gaseous emission of F from brick industries, which strongly stresses the need for the control of the quality of measurements using representative CRMs. 

Determination of total fluoride emissions from stationary sources—SPADNS zirconium lake method Determination of total fluoride emissions from stationary sources—specific ion electrode method Determination of fluoride emissions from potroom roof monitors for primary aluminum plants Determination of total fluoride emissions from selected sources at primary aluminum production facflities Determination of hydrogen sulfide, carbonyl sulfide, and carbon disulfide emissions from stationary sources Determination of total reduced sulfur emissions from sulfur recovery plants in petroleum refineries Semicontinuous determination of sulfur emissions from stationary sources Determination of total reduced sulfur emissions from stationary sources (impinger technique)... 

Fluoride Emission Rate Reinforced and Chemically Stabilized Membrane.589... 

Reduction in fluoride emissions by over a factor of 40 compared to MEAs made with nonreinforced, chemically stabilized membrane. 

In order to solve this chemical stability problem, a new proprietary PFSA ionomer synthesis procedure has been developed at DuPont that results in a reduction of the reactive end groups. This approach has been referred as chemical stabilization (CS) technology. Fluoride emission from chemically stabilized polymer in a Fenton s test was found to be eight times lower than a nonchemically stabilized polymer. 

Hydrogen fluoride is determined either by a gas probe (Table 2), or, more often, by a fluoride ISE (lanthanum fluoride based) after absorption in a suitable medium. Hydrogen fluoride emissions can be measured down to a content of 0.1 pgm . ... 

---