VCE Environmental ScienceUnit 4: Area of Study 1: Pollution
Fluoride compounds are all relatedby containing fluorine. Fluorine is anaturally occurring element in theearth. It is usually found in the formof the mineral fluorspar, CaF2.Fluorine is a yellow-green gas witha strong, sharp odour (like poolchlorine). It combines withhydrogen to make hydrogenfluoride, a colourless gas with astrong irritating odour.
Hydrogen fluoride dissolves in water to make hydrofluoric acid. Hydrogen fluoride will corrode most substances except lead, wax, polyethylene, and platinum. Hydrogen fluoride is used to manufacture other fluorine- based chemicals including Sodium fluoride, which is a white powder, although sometimes it is dyed blue for identification purposes.
Hydrogen fluoride is used:• In Aluminium production• In Chlorofluorocarbon (CFCs) production• In the production of aluminium fluoride, sodiumfluoride and other fluoride salts.• Petroleum, chemical, and plastics industries.• To separate uranium isotopes.• To clean metals, bricks, or remove sand frommetal castings.• To etch glass and enamel, polish glass andgalvanize iron.• Brewing and to cloud light bulbs.
The primary sources of fluoride emissions are the industries that manufacture it or use it in production: Aluminium industry, Oil drilling and refining, Chemical and plastics industries, Agricultural and pesticide chemical manufacturers, Dye manufacturers, Manufacturers of metal parts.These are emissions to the air unless there is a spill.
Other possible emitters of fluoride are metal cleaning operations, glass and enamel manufacturing and glazing, toothpaste, and fluoride enhanced water. These emissions may be to the soil, water, or air. Fluorine is a naturally occurring element in the earth, but elemental fluorine is too reactive to be found in nature. Fluorine is found in nature as part of the mineral fluorspar. Water in rivers or streams that flow over rocks rich in fluorine-containing minerals such as fluorspar may naturally contain dissolved fluoride.
Toothpaste, pesticides, ceramic and glass polishing etching and frosting materials, special dyes, drinking water in some areas may be naturally or artificially enriched in fluoride.Australian DrinkingWater Guidelines(NHMRC and ARMCANZ, 1996):Maximum of 1.5 mg/L (i.e. 0.0015 g/L).
Fluorine was produced for the first time by Henri Moissan in 1886, for which he received the Nobel Prize in chemistry in 1906. The unique properties of fluorine have led to the development of fluorine chemistry and numerous synthetic fluorinated compounds have been prepared and tested for different applications. The commercial use of organofluorine compounds has grown significantly during recent years, mainly because of increased uses in industrial, pharmaceutical and pest-control applications. It is estimated that the world market for fluorochemicals amounts to 11.6 billion dollars with an expected growth of 5 percent annually. The USA is the largest fluoroorganics market, followed by China (Baharatbook Market Research, 2004).
When fluoride is emitted to the air as a gas or particulate it may be carried by the wind and deposited on surrounding vegetation and soil. The gas dissolves in clouds, fog, rain, or snow. This impacts the environment as wet acid deposition (acid rain). In the environment it will react with other chemicals present (ammonia, magnesium, calcium) to form salts, neutralising the acid.
Industrial emissions of fluoride compounds can produce elevated concentrations in the atmosphere. Hydrogen fluoride will exist as a particle, which may dissolve in clouds, fog, rain, dew, or snow. In clouds and moist air it will travel along the air currents until it is deposited as wet acid deposition (acid rain, acid fog, etc). In waterways it readily mixes with the water.
“The substitution of HCFC’s and other chemicals for hydrofluorocarbons and the increased growth in fluorinated refrigerants and coatings will boost the demand for fluorochemicals in the coming years. Much of the usefulness of organofluorine compounds rests in their chemical stability and recalcitrance to biological degradation. Of all types of bonds in organic chemistry, the carbon-fluorine bond is the most inert and resistant to cleavage (Hiyama, 2000). Given the chemical inertness of fluorinated organics, their bioactivity persistence, it is important to understand their environmental fate and the mechanisms by which they can be degraded.”
Workers in the industries that use orproduce fluoride compounds are atgreatest risk of exposure.Consumers are most likely to beexposed to fluoride compounds whenusing consumer products containingfluoride compounds; especiallytoothpaste or fluoride enhanced water.Residents in close proximity toproduction and processing facilitiesusing fluoride compounds may alsoreceive very low levels of fluorideexposure.
Fluorides are everywhere throughout the environment, but at very low levels that are not believed to be harmful. Small amounts of sodium fluoride help prevent tooth decay, but high levels may harm your health. In children whose teeth are forming, excessive fluoride levels may cause dental fluorosis with visible changes in the teeth.
High levels of fluorine or hydrogen fluoride gas can cause muscle spasms, harm the lungs and heart and cause death. At low levels they can irritate the eyes, skin and lungs. Contact with hydrofluoric acid (even diluted) can burn the eyes (causing blindness) and skin, causing severe burns deep beneath the skin damaging internal tissues. This can occur hours after contact, even if no pain is initially felt. Contact with hydrofluoric acid happens mainly in the workplace. Long-term exposures may damage the kidneys and liver.
In adults, high fluorideover a long time maylead to skeletal fluorosiswith denser bones, jointpain, and limited jointmovement. This is rarein developed countries,but many people in Indiaand Africa may beaffected.
Hydrogen fluoride will exist as a particle in the air if releasedto the atmosphere. It dissolves when mixed with water.Insufficient data are available to predict the short-term orlong term effects of hydrogen fluoride to aquatic life, plants,birds or land animals. Concentrated hydrogen fluoride isvery corrosive and would badly burn any plants, birds orland animals exposed to it. The concentrations of hydrogenfluoride found in close proximity to sources may adverselyaffect some species of plants. Small quantities of hydrogenfluoride will be neutralised by the natural alkalinity in aquaticsystems. Larger quantities may lower the pH for extendedperiods of time. Fluorides are not expected to bio-accumulate.
“Both Point Henry and Portland Aluminium smelters continue to focus on minimising and sustaining fluoride emissions within internal (Alcoa) targets, which is reflected in the long-term historical trends (see graph). Alcoa’s internal targets are more stringent than those set by the Victorian Environmental Protection Authority.”http://www.alcoa.com/australia/en/inf o_page/environ_air.asp
“Portland Aluminium continues to progress a long-term management program for fluoride emissions, to further understand and manage the effects of low level fluoride emissions on local fauna inhabiting the land surrounding the smelter. Fluoride emissions were sustained at around 0.3kg/tonne of aluminium produced in 2009, making Portland Aluminium one of the lowest fluoride-emitting smelters in the world.”
The Portland Aluminium smelter is situated on 600 hectares of land, 500 of which form “Smelter in the Park”, a once-barren area that has been revegetated with a large variety of indigenous plants. This area forms a buffer zone, that protects surrounding residents from the full impact of gaseous emissions from the smelter. There are five monitoring stations at different locations around the smelter that provide data on fluoride and sulfur emissions on a regular basis. Portland Aluminium also routinely test their workers, using urine and blood tests, as well as exposure badges, which monitor the levels of fluoride that staff have been subjected to.
Environmental scientists also dowater testing and take tail-bonesamples of the local kangaroos andteeth, bone and horn samples of thebeef cattle , to test for long-termfluoride exposure. An internationalbotany expert visits annually tocheck for signs that toxic emissionsmay be affecting local vegetation.Signs of fluoride exposure includeyellowing and curling of leaves andtissue death.
Inthe potrooms, the major point source of fluoride emissions, Portland Aluminium have laser air monitoring of gaseous fluoride, with a traffic light system – green, amber and red. Between 045ppb and 600ppb, the lights are green; between 600ppb and 800ppb the lights are amber and above 800ppb the lights are red, which indicates an error in the process – too many hoods open at the same time.
Portland Aluminium use several methods to preventexcessive fluoride emissions, including the A398 fluoriderecovery system, in which fluoride emissions are capturedfrom the hooded aluminium pots and forced through aconveyor of alumina, to form reacted or fluoride-enrichedalumina. This is then added to the pots, which reduces thetemperature (and therefor the energy required) to obtain thepure aluminium. The particulate and gaseous emissions arefiltered through huge canvas bags, also coated withalumina, which traps 98% of fluoride.When the laser monitoring systems indicate excess fluoridelevels, staff will be evacuated to prevent critical exposure.
Research-Cottrell is the exclusive worldwide licensee for Alcoas A-398 and A-446 fluidized bed dry scrubbing technologies. The technologies provide emission control and fluoride recovery from both primary aluminum potline and bake oven applications. A-398 systems are currently installed on more than 20 smelters (56 potlines) worldwide, treating over 20 million cfm of potroom gases from both prebake and reduction cells. The A-398 and A-446 technologies routinely achieve greater than 99.9% fluoride removal efficiencies. In addition to controlling fluorides and particulate, the A-446 scrubbing process significantly reduces hydrocarbons (Tars, POM, B(a)P) and SO2 emissions from bakeoven furnaces, without a separate spray cooling chamber. The systems combine fluid bed scrubbers with air pollution controls such as fabric filters, electrostatic precipitators, wet and dry scrubber’s and VOC-removal technologies, to reduce emissions. http://www.tms.org/Meetings/Annual-98/Exhibitors/ResearchCott.html