“ENVIRONMENTAL EFFECT OF SPENT POT LINING FROM ALUMINIUM SMELTER and ITS DISPOSAL”
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Posted By: Ravindra Dubey Member Level: Silver Points/Cash: 10
Aluminium is one of the most widely utilized material starting from the production of utensils, Coins, electrical goods, food packing material etc. to the alloys formation of aircraft etc.It never occur in nature in free state, however, in combination it is terrestrially the most plentiful of all the metals, being nearly twice abundant as iron. It is produced by Hall-Heroult by the electrolytic reduction of alumina in cryolite bath.
Spent Pot Lining is a waste product from the smelting of aluminium. SPL is considered to be a hazardous waste in various countries because it contains significant quantities of absorbed fluorides along with traces of cyanide. An increasing number of countries are banning the traditional method of landfill disposal of SPL. Approximately 20 tonne of SPL is generated for every 1000 tonne of aluminium produced. Hundreds of thousands of tonne of SPL are stored around the world awaiting a suitable means for its disposal. Disposal of SPL is the largest environmental problem of the aluminium industry. SPL contains materials that are valuable if recovered and used for specific purposes. The main components having potential value are carbon and fluorides. The difficulties in developing a practice to recycle materials contained within SPL lie in the physical characteristics of SPL; the corrosive and toxic nature of the environment and products which occur within the treatment process; and the end products of that process.
Aluminum Production in India
Aluminium Industry in India is a highly concentrated industry with the top 5 companies constituting the majority of the country's production. With the growing demand of aluminium in India, the Indian aluminium industry is also growing at an enviable pace. In fact, the production of aluminium in India is currently outpacing the demand.
Though India's per capita consumption of aluminium stands too low (under 1 kg) comparing to the per capita consumptions of other countries like US & Europe (range from 25 to 30 kgs), Japan (15 kgs), Taiwan (10 kgs) and China (3 kgs), the demand is growing gradually. In India, the industries that require aluminium most include power (44%), consumer durables, transportation (10-12%), construction (17%) and packaging etc.
Though the existence of Aluminium was first established in the year 1808, it took almost 46 years to make its production commercially viable. The research work of several years resulted in extracting the aluminium from the ore. Aluminium is third most available element in the earth constituting almost 7.3% by mass. Currently it is also the second most used metal in the world after steel. Due to the consistent growth of Indian economy at a rate of 8%, the demand for metals, used for various sectors, is also on the higher side. As a result, the Indian aluminium industry is also growing consistently. In FY09, the aluminium industry in India saw a growth of about 9%.
The production of aluminium started in India in 1938 when the Aluminum Corporation of India's plant was commissioned. The plant which was set up with a financial and technical collaboration with Alcan, Canada had a capacity of producing 2,500 ton per annum. Hindustan Aluminum Corporation (Hindalco) was set up in UP in the year 1959; it had a capacity of producing 20,000 ton per annum. In 1965, a public sector enterprise Malco which had a capacity of 10,000 ton per annum was commissioned; by 1987, National Aluminium Company (NALCO) was commissioned to produce aluminium. It had a capacity of producing 0.218 million ton.
During the 1970s, the government started regulating and controlling the Indian aluminium industry. Restrictions in entry and price distribution controls were quite common in the Indian aluminium sector. Aluminium Control Order was implemented where the aluminium producers had to sell 50% of their products for electrical usages. However, in 1989, the order was removed as the government decontrolling was revoked. With de-licensing of industry in 1991, the liberal import of technologies and capital goods was started. The liberalization resulted in a growth rate of 12% of the industry, comparing to the growth rate of 6% during the 1980.
India lies at the eighth position in the list of leading primary aluminium producers in the world. India saw a significant growth in aluminium production in the past five years. In 2006-07, the production target of aluminium in India laid by the Ministry of Mines, Government of India was 1,153 KT, which was augmented to 1,237 KT in the next year (2007-08). Due to the growing demand from the construction, electrical, automobiles and packaging industry, the production of aluminium also hiked up. In FY 09, the total aluminium production in India was around 1.35 tonnes.
After a stagnant consumption of primary aluminium in India from the end of 1990s to 2002 (when the consumptions were between 500 – 600 KT), it started rising sharply since 2002. The consumption reached at 1,080 KT in 2006. The consumption of aluminium in India is dominated by the industries like power, infrastructure, and transportation etc.
The Indian aluminium industry is dominated by four or five companies that constitute the majority of India's aluminium production. Following are the major players in the Indian aluminium industry:
• Hindustan Aluminium Company (HINDALCO)
• National Aluminium Company (NALCO)
• Bharat Aluminium Company (BALCO)
HINDALCO: Hindalco is the biggest player in the aluminium in-dustry in India with around 39% of market share. An Aditya Birla Group flagship company, Hindalco has its aluminium plant at Renukoot in Uttar Pradesh. It has various aluminium products with a market share of 42% in primary aluminium, 20% in extrusions 63% in rolled products, 31% in wheels and 44% in foils.
Sterlite Industries: The aluminium business of Sterlite Industries Limited comprises of two Indian aluminium giants – BALCO and MALCO. While BALCO is a partially integrated, MALCO is a fully integrated producer of aluminium. Sterlite has got a market share of around 32%.
NALCO: It is also one of the leading aluminium producers in India. Government of India has a stake of 87.15% in this company. Its aluminium refinery is located at Damanjodi. It also has a smelter located at Angul, Orissa. Currently, NALCO is concentrating on a capex programme to increase its production from 345,000 tonnes to 460,000 tonnes.
Spent Pot Lining-Background
Safe disposal of spent pot lining (SPL) of the cryolite bath is the greatest solid waste problem from aluminium smelting process. Pot lining is a layer of carbon situated between the molten metal and refractory material in side the steel shell of an aluminium reduction cell. The Primary purpose of the pot lining is to provide high electrical conductivity through the cell and to protect steel from corrosive attack by the molten both. Pot lining made with carbon blocks and rammed car bon paste or of rammed paste alone. Generally the useful service life of a pot(cathode or reduction cell) is 3 to 7 year. Due to operating at high temperature (940 c) the lining get cracked which allow the electrolyte to come into contact with the steel shell. Once the crack appears, the whole pot lining are removed and the steel shell is relined. The removed lining is called SPL.
BESICS ‘S FOR SPENT POTLINING (SPL)
• Pot lining life 6-7 years
• Cathode carbon porosity 10-25%
• Approx 30% of SPL is penetrated salts.
• Contaminations include: NA3AlF6, NaF, CaF2, AIN, Al4C3, NaCN.
•Fluorides and Cyanides of specific environmental concern;
• Na(S) and Al4C3 react with water to form H2 and CH4;
• Typically SPL contains approximately 25% fluorides with AlN and Al4C3 approximately
1-2% and NaCN varying between 0.005 – 1%;
• Found in both SPL carbon (first cut) and SPL Refractory (second cut);
• SPL is one of the Aluminium Industry’s major environmental concerns.
• Major recovery potential – fluorides and energy content.
• Landfill disposal has created many problems.
During electrolysis at high temp. Molten bath, metal and other chemicals are absorbed by the carbon lining which become saturated in first 80-85 week of operation. The foremost constituents, which are absorbed, are sodium, fluoride and cyanides. General composition f SPL is given in Table bellow’s often contains 1% ammonium and phosphate which on interaction with water gives off an unpleasant odors.
USE OF SPL
1. Energy savings in the brick and cement industries;
2. Beneficial fluxing properties in the brick, cement and steel industries;
3. Enhances strength development from cement.
4. Recycle into cathodes, and anodes for use in the aluminium ramming paste industry;
5. Fluorides recovery (cryolite).
Environmental hazards due to SPL
At an average mass of 35-55 tones per pot every 3-7 years, the volume of SPL generated and its chemical composition created potentially serious environmental and logistic concerns for the industry. About 30% of fluoride content of SPL is water leachable. Cyanide concentration various from 60-1000 ppm. Some cyanide are free but after coming in contact with water they are mostly as co-ordination compound are very stable and are reported to be nontoxic. However spigel and pelis (1990) reported that the free and ion complex cyanides, both are toxic n nature. The stable co-ordination compound decomposed into free cyanide on exposure to UV radiation. During rainy season fluoride and cyanide are leached out from SPL stored at an unprotected disposal site and thus polluting the nearby environ-ment.
Cyanide is any chemical compound that contains the group C=N, with the carbon atom triple bonded to the nitrogen atom. Inorganic cyanides contain the highly toxic cyanide ion CN- and are the salts of the acid hydrogen cyanide (HCN). Organic cyanides contain the cyano group (CN) single-bonded to another carbon atom are also known as nitriles. Two cyanide ions can bond to each other via their carbon atoms, forming the gas cyanogen (NC-CN).
Effects on the human body
To deal with the cyanides contained in many foods, the body has an enzyme (rhodanide synthetase) which can convert small amounts of cyanides to the harmless sulfur-containing thiocyanate (SCN-). The cyanide ion is also a component of vitamin B12, where it is one of the ligands for the cobalt ion.
In larger amounts, cyanides are harmful. Symptoms of moderate poisoning include vomiting, convulsions, deep breathing, shortness of breath and anxiety; more serious cases result in convulsions, loss of consciousness, and death after apnea and cardiac arrest due to hypoxemia. The lethal dose for adults is 200–300 mg of potassium or sodium cyanide, or 50 mg of hydrogen cyanide.
Exposure to lower levels of cyanide over a long period (e.g. after use of cassava roots as a primary food source in tropical Africa) results in increased blood cyanide levels. These may result in weakness of the fingers and toes, difficulty walking, dimness of vision, deafness, and decreased thyroid gland function, but chemicals other than cyanide may contribute to these effects. Skin contact with cyanide can produce irritation and sores.
It is not known whether cyanides can directly cause birth defects in people. Birth defects were seen in rats that ate diets of cassava roots. Effects on the reproductive system were seen in rats and mice that drank
There are medical tests to measure blood and urine levels of cyanide; however, small amounts of cyanide are not always detectable in blood and urine. Tissue levels of cyanide can be measured if cyanide poisoning is suspected, but cyanide is rapidly cleared from the body, so the tests must be done soon after the exposure. An almond-like odor in the breath may alert a doctor that a person was exposed to cyanide.
FLUORIDE HEALTH EFFECTS
“Over the past ten years a large body of peer-reviewed science has raised concerns that fluoride may present unreasonable health risks, particularly among children, at levels routinely added to tap water in American cities.”
ENVIRONMENTAL WORKING GROUP, July 2005.
"In summary, we hold that fluoridation is an unreasonable risk."
US ENVIRONMENTAL PROTECTION AGENCY HEADQUARTERS' UNION, 2001.
“Carefully conducted studies of exposure to fluoride and emerging health parameters of interest (e.g., endocrine effects and brain function) should be performed in populations in the United States exposed to various concentrations of fluoride.”
US NATIONAL RESEARCH COUNCIL, 2006
"I am quite convinced that water fluoridation, in a not-too-distant future, will be consigned to medical history."
Dr. ARVID CARLSSON, Pharmacologist, Nobel Laureate in Physiology and Medicine, 2000.
FLUORIDE ACCIDENTS & POISONINGS
Fluoride, the active ingredient in many pesticides and rodenticides, is a powerful poison - more acutely poisonous than lead. Because of this, accidental over-ingestion of fluoride can cause serious toxic symptoms.
Each year there are thousands of reports to Poison Control centers in the United States related to excessive ingestion of fluoride toothpastes, mouthrinses, and supplements?
Water fluoridation accidents, resulting in excess levels of fluoride in water, have been one of the sources of acute fluoride poisoning.
FLUORIDE & DENTAL FLUOROSIS (Click for more detail)
Excessive ingestion of fluoride during the early childhood years can damage the tooth-forming cells, leading to a defect in the enamel known as dental fluorosis.
Teeth impacted by fluorosis have visible discoloration, ranging from white spots to brown and black stains.
According to the Centers for Disease Control, 32% of American children now have some form of dental fluorosis, with 2 to 4% of children having the moderate to severe stages (CDC 2005).
According to Dr. Hardy Limeback, Head of Preventive Dentistry at the University of Toronto, "it is illogical to assume that tooth enamel is the only tissue affected by low daily doses of fluoride ingestion.
FLUORIDE & ALLERGY/HYPERSENSITIVITY (Click for more detail)
As acknowledged by the Physicians' Desk Reference, some individuals are allergic/hypersensitive to fluoride. The largest, government-funded, clinical trial found that 1% of individuals exposed to 1 mg/day of fluoride exhibited allergic/hypersensitive reactions, including skin reactions, gastric distress, and headache.
FLUORIDE & the KIDNEYS (Click for more detail)
The kidneys play a vital role in preventing the build-up of excessive fluoride in the body. Among healthy individuals, the kidneys excrete approximately 50% of the daily fluoride intake. However, among individuals with kidney disease, the kidneys' ability to excrete becomes markedly impaired, resulting in a build-up of fluoride within the body.
It is well recognized that individuals with kidney disease have a heightened susceptibility to the cumulative toxic effects of fluoride.
Of particular concern is the potential for fluoride, when accumulated in the skeletal system, to cause, or exacerbate, renal osteodystrophy - a bone disease commonly found among people with advanced kidney disease.
In addition, fluoride has been definitively shown to poison kidney function at high doses over short-term exposures in both animals and humans. The impact of low doses of fluoride, given over long periods of time, has been inadequately studied. A recent animal study, conducted by scientists at the US Environmental Protection Agency (Varner 1998), reported that exposure to just 1 ppm fluoride caused kidney damage in rats if they drank the water for an extended period of time, while a new study from China found an increased rate of kidney disease among humans consuming more than 2 ppm (Liu 2005). Hence, the adverse effects to kidney function that fluoride causes at high doses over short periods of time, may also be replicated with small doses if consumed over long periods of time.
FLUORIDE & the BRAIN (Click for more detail)
Fluoride's ability to damage the brain represents one of the most active areas of research on fluoride toxicity today.
Concern about fluoride's impact on the brain has been fueled by 18 human studies (from China, Mexico, India, and Iran) reporting IQ deficits among children exposed to excess fluoride, by 4 human studies indicating that fluoride can enter, and damage, the fetal brain; and by a growing number of animal studies finding damage to brain tissue (at levels as low as 1 ppm) and impairment of learning and memory among fluoride-treated groups.
According to the US National Research Council, "it is apparent that fluorides have the ability to interfere with the functions of the brain."
FLUORIDE & the PINEAL GLAND (Click for more detail)
In the 1990s, it was discovered that the pineal gland is a major site of fluoride accumulation within the body - with higher concentrations of fluoride than either teeth or bone.
Subsequent animal studies indicate that the accumulation of fluoride in the pineal gland can reduce the gland's synthesis of melatonin, a hormone that helps regulate the onset of puberty. Fluoride-treated animals were found to have reduced levels of circulating melatonin and an earlier onset of puberty than untreated animals. The scientist who conducted the research concluded:
"The safety of the use of fluorides ultimately rests on the assumption that the developing enamel organ is most sensitive to the toxic effects of fluoride. The results from this study suggest that the pinealocytes may be as susceptible to fluoride as the developing enamel organ" (Luke 1997).
The fact that fluoride's impact on the pineal gland was never studied, or even considered, before the 1990s, highlights a major gap in knowledge underpinning current policies on fluoride and health.
According to the US National Research Council, "any agent that affects pineal function could affect human health in a variety of ways, including effects on sexual maturation, calcium metabolism, parathyroid function, postmenopausal osteoporosis, cancer, and psychiatric disease.”
FLUORIDE & the THYROID GLAND (Click for more detail)
According to the US National Research Council, "several lines of information indicate an effect of fluoride exposure on thyroid function" - particularly among individuals with an iodine deficiency.
Fluoride's potential to impair thyroid function is most clearly illustrated by the fact that -- up until the 1970s -- European doctors used fluoride as a thyroid-suppressing medication for patients with hyperthyroidism (over-active thyroid). Fluoride was utilized because it was found effective at reducing the activity of the thyroid gland - even at doses as low as 2 mg/day.
Today, many people living in fluoridated communities are ingesting doses of fluoride (1.6-6.6 mg/day) that fall within the range of doses (2 to 10 mg/day) once used by doctors to reduce thyroid activity in hyperthyroid patients. This is of particular concern considering the widespread problem of hypothyroidism (under-active thyroid) in the United States. Symptoms of hypothyroidism include obesity, lethargy, depression, and heart disease.
FLUORIDE & BONE DISEASE (Click for more detail)
Excessive exposure to fluoride is well known to cause a bone disease called skeletal fluorosis.
Skeletal fluorosis, especially in its early stages, is a difficult disease to diagnose, and can be readily confused with various forms of arthritis including osteoarthritis and rheumatoid arthritis.
In its advanced stages, fluorosis can resemble a multitude of bone/joint diseases.
In individuals with kidney disease, fluoride exposure can contribute to, and/or exacerbate, renal osteodystrophy.
FLUORIDE & BONE FRACTURE (Click for more detail)
The majority of animal studies investigating fluoride's effect on bone strength, have found fluoride to either have no effect or a negative effect on strength. According to the US National Research Council, "The weight of evidence indicates that, although fluoride might increase bone volume, there is less strength per unit volume."
Studies on human populations consuming fluoride in drinking water have found an association between dental fluorosis and increased bone fracture in children; and between long-term consumption of fluoridated water and increased hip fracture in the elderly.
Carefully conducted human clinical trials - including two "double-blind trials" - have found that fluoride (at doses of 18-34 mg/day for just 1-4 years) increases the rate of bone fracture, particularly hip fracture, among osteoporosis patients.
FLUORIDE & CANCER (Click for more detail)
According to the National Toxicology Program, "the preponderance of evidence" from laboratory 'in vitro' studies indicates that fluoride is a mutagenic compound. Many substances which cause mutagenic damage also cause cancer.
While the concentrations of fluoride causing mutagenic damage in laboratory studies are higher than the concentrations found in human blood, there are certain "microenvironments" in the body (e.g. the bones and the bladder) where the concentrations of fluoride can accumulate to levels comparable to, or in excess of, those causing mutagenic effects in the laboratory.
Fluoride has been found to cause bone cancer (osteosarcoma) in government animal studies and rates of osteosarcoma among young males living in fluoridated areas have been found to be higher than young males living in unfluoridated areas. Osteosarcoma, while rare, is a very serious cancer. Children who develop osteosarcoma face a high probability of death (usually within 3 years) or amputation.
Fluoride exposure has also been linked to bladder cancer - particularly among workers exposed to excess fluoride in the workplace. According to the US National Research Council, “further research on a possible effect of fluoride on bladder cancer risk should be conducted.”
FLUORIDE & the GASTROINTESTINAL TRACT (Click for more detail)
Among people hypersensitive to fluoride, gastrointestinal ailments have been produced following ingestion of 1 mg tablets of fluoride or consumption of 1 ppm fluoridated water.
A single ingestion of as little as 3 mg of fluoride, in carefully con-trolled clinical trials, has been found to produce damage to the gastric mucosa in healthy adult volunteers. No research on the gastric mucosa has ever been conducted to determine the effect of lower doses with repeated exposure.
FLUORIDE & TOOTH DECAY (Caries) (Click for more detail)
According to the current consensus view of the dental research community, fluoride's primary - if not sole - benefit to teeth comes from TOPICAL application to the exterior surface of teeth, not from ingestion.
Perhaps not surprisingly, therefore, tooth decay rates have declined at similar rates in all western countries in the latter half of the 20th century - irrespective of whether the country fluoridates its water or not. Today, tooth decay rates throughout continental western Europe are as low as the tooth decay rates in the United States - despite a profound disparity in water fluoridation prevalence in the two regions.
Within countries that fluoridate their water, recent large-scale surveys of dental health - utilizing modern scientific methods not employed in the early surveys from the 1930s-1950s - have found little difference in tooth decay, including "baby bottle tooth decay", between fluoridated and unfluoridated communities.
Regulation on Disposal of SPL
No specific regulation on disposal SPL available so far. However, central and state pollution control board keeps a check on such solid waste disposal fro Indian aluminium industries. It has, However been reported in EPA listing background documents for primary aluminium reduction that improper transportation ,treatment ,storage or disposal of SPL may pose a hazards to human health or the environmental due to-
1. Presence of free and iron complex cyanide in SPL at significance concentration levels which are toxic in nature.
2. Historical practice by aluminium industry for disposal of spl in unprotected piles or open dumps.
3. Leach ability of free and iron cyanide especially from unprotected disposal site and under condition of acidic precipitation.
4. Photo reactivity of iron cyanide which may result in the release of hydrogen cyanide.
5. Generation of SPL in large quantities.
In October 1986, EPA withdraw the then proposed rule to realist SPL as a hazardous waste and indicated that it will study these waste and determined how they should be regulated under recourses conservation of recovery act (RCRA).Prior to 1988 at U S A, SPL was commonly treated in rotary kiln or other furnace but now EPA regulation is that it should be landfills(Goldman,1991).This change is not only costly but to some observed even more hazards then combustion. According to Goldman (1991) aluminum association’s director for environmental affairs at USA, some change may be affected in the next edition of RCRA. That change would probably take the from of side by side delisting or certified for the producers, productive ways.
USUAL PRACTICE OF DISPOSAL
Over the years much of the SPL was placed in land filling or stored in large above ground piles (Blaydon and Epstein, 1984: Goldman, 1991).Now a days at some of the reduction plants (Smelter) some valuable products are recovered to reduce the volume of SPL which required ultimate disposal. However many reduction plants still store SPL onside or transport them offside for subsequent directs disposal. Final disposal of the material, however, is typically achieved by a variety of land filling or stock piling options. Land filling options presently used include transportation to a hazardous waste landfill it, land filling in an onside hazardous waste landfill and land filling on site in a sanitary landfills. Stockpiling options presently used included piling material inside a designated disposal building, piling material on a concrete pad outdoors and covering it with clay asphalt or trap and stockpiling outdoors within a diked area. (Spigel and Pelis, 1990).
Due to new stickers environmental regulations(EPA)at places where storage piles are unlined and uncovered and pre exposed to rainfalls, the leachate prior to discharge to natural water (Goldeman,1987).However ,preparation and maintenance of an environmentally sealed disposed site is very costly affairs. The major objection to the sealed type disposal is that it will have to monitored identifiably. There is, therefore a real need to find a safe, acceptable alternative ways to land fills disposal. Indian Aluminium co., India’s first smelter 1943 at always, Karla, since 198,is staring SPL under shad to avoid leaching. This material is dispatched to begume for cryolite recovery in polyethylene bags to avoid spilling during transportation (Bhatnagar 1990).At NALCO SPL’s are land filled after prop lining with concrete and polyethylene. More sophisticated disposal methods are being developed wit the intention of elimination or greatly reducing the volume of SP to be land filled or stockpiled.
Production of Aluminium Fluoride
The formation of aluminium fluoride from the processing of SPL and the reuse of this material in the aluminium smelting process was a very significant challenge for the SPL team. Development work was undertaken with CSIRO on a small scale experimental process to determine if it was possible to convert low concentration synthetically produced hydrogen fluoride gas and smelting grade alumina to aluminium fluoride. The results of the tests indicated aluminium fluoride had been formed and this was confirmed in limited trials using gases produced from processing SPL.
Reactor Design and Operation
Figure 3 shows the schematic of the reactor operation. Hydrogen fluoride laden gases from the pyrometallurgical furnace and gas cooling and filtering processes are reheated and passed through the bottom fluidized bed of partially reacted smelting grade alumina. The gases, partially stripped of hydrogen fluoride, continue to pass through two further fluidized beds and intersect with the alumina in a counter flow configuration. The reactor does not absorb all the hydrogen fluoride gas and some residual amount is passed to the smelter’s dry scrubbing reactors for final absorption before being released to the atmosphere.
OBJECTIVES OF FLUORIDE RECYCLING
The prime objective was to develop a treatment process for SPL that would destroy its Hazardous condition, recover and recycle its fluoride content and dispose of the generated slag in an EPA approved method.
The specific objectives were:
To destroy the cyanide component of the SPL
To effectively use the carbon component of the SPL
To recover the fluoride components as aluminium fluoride suitable for re-use in the aluminium smelting process
For the slag output product not to be harmful to the environment or human health
For the slag output product not to be disposed of by landfill
For the process to be economically viable
The prime objective, which was to develop a treatment process for SPL that would destroy its hazardous condition, recover and recycle its fluoride content and dispose of the generated slag in an EPA approved method, has been accomplished per the development of ‘The Alcoa Portland SPL Process.’
The projects specific objectives have also been accomplished and are elaborated as follows.
To Destroy the Cyanide Component Of The SPL
Cyanide and any other organic materials present in the SPL are destroyed when exposed to the temperatures of 1150oC -1250oC that are experienced in the pyrometallurgical phase of the process. Chemical analysis of the slag and the SPL aluminium fluoride from the process has never detected the presence of any residual traces of cyanide.
To Effectively Use the Carbon Component Of The SPL
The heat required for the pyrometallurgical phase of the process is achieved from the combustion of natural gas and carbon in the SPL. Once heat is available from the combustion of the carbon the use of natural gas is significantly reduced. Consequently the value of the carbon in the SPL is effectively utilised by supplying heat to the process and reducing the amount of natural gas consumed.
To Recycle The Sodium Fluoride Within The Process
Several problems were encountered and progressively solved in order to achieve the recycling of the sodium fluoride particulate. Sodium fluoride is now readily removed from the baghouse and recycled into the furnace where it reacts with available hydrogen to form hydrogen fluoride that in turn is used to produce aluminium fluoride in the aluminium fluoride reactor. Sodium is eventually removed from the process by containment in the slag as various sodium compounds.
To Recover The Fluoride Components As Aluminium Fluoride Suitable For Reuse In The
Aluminium Smelting Process
The successful generation of aluminium fluoride from the processing of SPL and the successful use of this material in the smelting of aluminium has been the significant difference between ‘The Alcoa Portland SPL Process’ and any other process that treats or has attempted to treat SPL. This outcome reduces the operating costs of the process by the savings through reduced purchases of imported aluminium fluoride and avoids using natural resources otherwise required for aluminium fluoride production.SPL aluminium fluoride has a purity of 65-70% aluminium fluoride compared to 88–92% for commercial grade aluminium fluoride. Impurities in the SPL aluminium fluoride are minimal and are compared to the smelting grade alumina used in the process as shown in
Table 1: Impurities in SPL Aluminium Fluoride and Smelting Grade Alumina (SGA)
(All values in ppm)
Fe2O3 Na2O SiO2 CaO TiO2 Ga2O3 K2O
SGA 80 4000 120 420 40 95 5
SPL AlF3 79 3000 30 290 29 68 8
Two major trials using SPL aluminium fluoride in aluminium smelting operations have been performed. In June 1999, approximately 40 tone of product was added to the pots in Alcoa’s Point Henry smelter in Gee long, Australian and a larger and longer trial (140 tonne and six weeks duration) was carried out in Portland Aluminum’s pot rooms in July/August 2001. Harpley (1999) and (2001) indicated no significant differences were experienced in pot operation efficiency and metal purity from the usage of SPL aluminium fluoride compared to pots using commercial aluminium fluoride.
For The Slag Output Product Not To Be Harmful To The Environ-ment Or Human Health
The modified slag composition in combination with the granulation rapid quenching process, has resulted in increased resistance of the slag to leaching, due to the physical structure of the slag being highly amorphous and of a vitrified nature. The leachability values now being achieved for the granulated vitrified slag meet the Victorian EPA criteria for the unrestricted use of the granulated slag product. Increased resistance of the slag to sodium leachability was evident by a reduction in leachate pH values for the granulated slag from 11 - 11.5 for standard slag chemistry to 9 – 9.5 with the modified slag chemistry. The increased resistance to fluoride leachability is demonstrated. granulated slag are expected to be in road and pathway construction, replacement for specific types of sand and in cement and concrete manufacture.
For The Process to be Economically Viable
The operating costs of the SPL treatment process are lowered significantly by the savings
achieved by using SPL aluminium fluoride instead of the expensive imported aluminium fluoride in the aluminium smelting process. ‘The Alcoa Portland SPL Process’ is very
competitive compared to other known independent SPL treatment processes which usually do not achieve end products that are acceptable to EPA requirements re elimination of hazardous characteristics.
1. The process is a practical and economic solution to the largest environmental problem in the aluminium industry - namely effectively disposing of hazardous SPL waste.
2. The process produces aluminium fluoride from SPL and subse-quently recycles fluorides within the aluminium smelting process. thereby conserving natural resources that would otherwise be consumed in the production of the equivalent amount of commercial grade aluminium fluoride.
3. The process produces a granulated slag having Victorian EPA approval for unrestricted use. The end uses of the slag are expected to be as in road construction and as a substitute for coarse sand in concrete manufacture.
4. The process avoids the need to landfill SPL or any of the process output products.
5. The process consumes a waste product from the electric steel manufacturing industry.
SOCIAL AND ENVIRONMENTAL RESPONSIBILI-TIES
From the outset of the establishment of the Portland Aluminium smelter the social and environmental concerns of its location and operation were of prime significance, and are entrenched as a part of the operating culture of the smelter in its day to day activities. The social and environmental responsibilities of Portland Aluminium have been illustrated by
many actions, some of which are:
Achieving levels of fluoride emissions that are approaching world bench mark and which are the lowest of any Balco smelter
Maintaining and protecting the rare species of plants that exist in the area.
Developing Portland Aluminium as a ‘Smelter in the Park’ with specific areas for the community to use for relaxation; for learning and research such as educational walks and bird hides; for wildlife habitat and for the smelting and manufacture of aluminium
Reducing general waste materials to landfill from in excess of 1000 cubic meters per month in 1989 to less than two cubic meters in 2001
Conducting regular community consultation meetings for the general community and for particular interest groups on specific topics
Conducting regular tours through the smelter in association with the local tourist bureau
Assisting in establishing and protecting the only mainland gannet colony in Australia
Assisting in the protection and control of the numerous forms of wild life that enjoy the tranquility of the Smelter in the Park areas
Promoting the involvement of employees to assist in community activities
Providing financial assistance to selected community organizations, projects and causes
Liaising with the media on smelter activities that may impact on the local community.To fully appreciate many of the items in the above list would require considerable detail and is well beyond the scope or intention of this paper. The items are included to provide an awareness of practices that illustrate Portland Aluminum’s commitment to its responsibilities for the environment and the community.
SPENT POT LINING DISPOSAL STANDARDS AND GUIDELINES
PREFACE The standards on the following pages have been developed based on the best available scientific data and practical experience of Alcoa. These standards apply to locations worldwide in which Alcoa has a controlling interest or managing responsibility and performance against standards will be included in Alcoa Environmental Audits. In partnerships where Alcoa does not have a controlling or managing interest, Alcoa will encourage the other shareholders to apply these standards. Business Units shall advise the Executive Vice President, Environment, Health and Safety in writing if partners can/will not meet these standards. In some cases, guidelines have been incorporated into the standard for clarity or continuity, and to encourage locations to develop location specific requirements. Where this occurs, standards are in bold face text, and guidelines are in normal text. These standards may not be identical to local, state, national, or international regulations. Each location where these standards apply must ensure the applicable Regulatory Standards are met or that specific waivers or variances are formally agreed upon in writing with the responsible regulating authority and that they are consistent with these Alcoa worldwide standards. These standards will be maintained by Alcoa’s Corporate Environment, Health and Safety organization. Any comments or questions regarding applicability should be referred to the Business Unit or Corporate Environmental Affairs for resolution. These standards were approved by Alcoa’s Executive Council in March 1995. Performance against these standards will be subject to the Alcoa Environmental Audit process and will be reflected in the audit score beginning March 1, 1996.
Spent pot lining [SPL] is a by-product of aluminum production using Hall Héroult smelting cell technology and is generated by aluminum producers world wide at 0.01 to 0.04 kg of SPL / kg of aluminum metal produced. Due to its hazardous nature and various environmental regulatory requirements, SPL is a significant issue for Alcoa and the aluminum industry requiring appropriate management, storage, treatment and/or disposal of previous and continuing generation.
SPL is generated when carbonaceous and insulating lining materials are removed from the Hall Héroult smelting cell due to lining failure or wear out. It is alkaline in nature and exposure can cause eye, skin and upper respiratory irritation subsequent to handling. Because SPL contains leachable cyanides and fluorides, it may, if not managed appropriately, cause contamination of soils, surface water and ground water during removal, storage, treatment and/or disposal. Historically, SPL has been land disposed. For many years, disposal sites were in or on the land with minimal if any appropriate lining or cover materials used and no provisions made for leachate collection. Today these land disposal sites may represent liability to the environment and significant financial liability for the land owners and SPL generators. World wide regulatory requirements relating to SPL disposal range from “none” to “strict control”. In some countries SPL is considered a “hazardous waste”. Within countries, regulatory requirements may vary by state. The focus of this standard is SPL. Appropriate management of used pot shells, collector bars, steel vapor barrier materials and other SPL contaminated materials also require due diligence. These materials may be recycled provided they are visibly clean of SPL materials. If land disposed, the land disposal unit should meet the requirements of this standard.
Documentation and record retention regarding SPL
The recommended design for a SPL landfill cell is a multi-layer system referred to as a double-liner, composite system. The components of the system, from the bottom up are as follows:
• Clay liner - natural clay, at least 90 cm [3 feet] thick, compacted in multiple lifts, hydraulic conductivity less than 1X10-7 cm/sec.
• Synthetic flexible membrane liner [FML] - referred to as the sec-ondary FML - usually PVC or HDPE, 1 to 2 mm [40 to 80 mil] thickness.
• Leak detection layer - also called secondary leachate collection & removal [LCR] layer - composed of granular material 30 cm [1 foot] thick with a hydraulic conductivity of 1X10-2 cm/sec or greater. The function of this layer is to collect any leachate that escapes the primary FML and minimize the hydraulic pressure on the secondary [bottom] liner. This layer may also be constructed of a synthetic drainage material [drainage mesh] which generally has higher hydraulic conductivity and much less thickness [6 mm] than granular material.
• Primary flexible membrane liner [FML] - the same material as the secondary FML, but may be thicker.
• Primary leachate collection & removal [LCR] layer - composed of granular material 30 cm [1 foot] thick with a hydraulic conductivity of 1X10-2 cm/sec or greater. The function of this layer is to collect any leachate from the SPL and minimize the hydraulic pressure on the primary FML. Synthetic drainage mesh is not usually used here because the granular material acts as additional protection for the primary FML.
• Filter layer - this may be either granular material [finer than the leachate collection layer] or a geotextile. The function of this layer is to prevent the leachate collection layer from being clogged by fine particles of soil or waste material.
• Surface or Protection layer - this is the layer of material onto which the SPL will be placed. This layer protects the primary leachate collection system from damage during placement of the waste.
The closure cap of the landfill is also a multi-layer system. The objective of the cover is to keep rainfall/snowfall out of the landfill. If no water enters the waste material, the potential for leachate production and the risk of ground water contamination is minimized. The cap is composed of the following layers [from bottom to surface]:
• Contour fill - this is either soil or waste placed to establish the desired slope of the closure. The cap should slope 5 to 8 percent toward the edges to shed rainfall/snowfall. The slope must be steep enough to accommodate some settlement without creating puddles, but must not be so steep that soil erosion would damage the cover.
• Clay barrier layer - natural clay, at least 60 cm [2 feet] thick, compacted in multiple lifts, hydraulic conductivity less than 1X10-7 cm/sec.
• Flexible membrane [FML] - usually PVC or HDPE, thickness should be no less than the thickness of the primary liner FML.
• Drainage layer - composed of granular material 30 cm [1 foot] thick with a hydraulic conductivity of 1X10-2 cm/sec or greater. The function of this layer is to collect any percolation and minimize the hydraulic pressure on the barrier layers. Synthetic drainage mesh can be used instead of granular material.
• Filter layer - this may be either granular material [finer than the drainage layer] or a geotextile. The function of this layer is to prevent the drainage layer from being clogged by fine particles of soil from the vegetation layer.
• Vegetation layer - composed of soil suitable for growing grass or other vegetative cover. This layer is usually about 60 cm [2 feet] thick, with the top 15 cm [6 inches] uncompacted top soil. The vegetation serves to minimize soil erosion and also plays an important role in the rainfall/snowfall water balance of the cover system through evapo-transpiration. The total thickness of the cover system above the clay barrier should be sufficient to protect the clay from freezing.
SPL POLLUTION PREVENTION — GENERAL
Balco Environmental policy and 8 step waste minimization guidelines establish that SPL be managed according to the following priorities:
1st Reduction at the source
2nd Treatment/process for reuse or recycling
3rd Treatment/process for disposal
4th Safe disposal to the environment (land in this case)
SPL source reduction will continue to be given high priority. Balco smelters have implemented changes aimed at closing the gap on pot life to achieve world class performance. Reuse and recycling options shall be vigorously pursued. Alcoa Brazil is pursuing technology which may permit SPL reuse into brick products. USMS is using the Reynolds Process for treatment, and work is in progress associated with residue reuse.
balco is pursuing treatment in fluoride recovery as major goals of the work in progress. Treatment processes for SPL to allow for safe disposal in normal land disposal units shall be vigorously pursued. Both the Reynolds and Ausmelt processes provide treatment of SPL which produces a residue acceptable for disposal in normal land disposal units. The Reynolds process is in commercial operation in the United States and being utilized by USMS. Development of the Ausmelt process is continuing under the direction of Alcoa of Australia. Land disposal of SPL shall meet the minimum requirements contained in this standard. Land disposal is the least preferred method of SPL disposal. Over time, all landfills present a probability of causing environmental concern and/or damage. Despite years of research there is no universally accepted and regionally available process to treat SPL for reuse, recycling or land disposal in a normally constructed land disposal unit. As a result, appropriately de-signed and operated land disposal units will continue to be required for SPL until other methods of treatment and resource recovery are commercially available within manageable proximity to smelting locations.
DISPOSAL — OFF-SITE If recycle and reuse options are not available, appropriately selected off-site land disposal sites provide Alcoa the best environmental and financial liability protection currently available by being designed and operated by professional waste management corporations in accordance with regulatory approval. REFERENCE: Transporter Storage & Disposal Facility (TSDF) Audit Criteria.
The preferred method of land disposal for SPL is off-site Feder-al/Local regulatory agency approved and monitored land disposal units, constructed for hazardous waste disposal using appropriate materials and methods, owned and operated to stringent regional regulatory standards and procedures by professional disposal corporations with adequate financial resources to manage the sites in perpetuity. In general, these landfills will conform to the design specified in Appendix 1 of this standard.
If option 5.1 above is not available, off-site landfills used for SPL must meet or exceed the following minimum acceptable criteria:
a) Multi layered design, natural clay and/or synthetic liner systems
b) Leachate collection and treatment system
c) Ground water monitoring systems
d) Appropriate written standard operating practices
e) Appropriate location, i.e.; not adjacent to public housing, public buildings or public water supplies.
f) Financial capability to protect Alcoa as much as possi-ble/warranted
g) Landfill approved by Alcoa personnel using landfill auditing criteria available from Alcoa Corporate Environmental Affairs Department
Landfill selection criteria and guidelines are available from Alcoa’s Corporate Environmental Affairs Department. REFERENCE: Transporter, storage & disposal facility (TSDF) Audit Criteria.
DISPOSAL — ON SITE The preferred method of land disposal for SPL specified in 5.1 and/or 5.2 above is not available in all countries or Balco locations, and in some instances, on-site land filling may be the only current option available.
No new on-site land disposal units for SPL are permitted unless prior written approval has been given by the Business Unit President and Balco’s Executive Vice President of Environment, Health & Safety.
Any new cells constructed for either new or existing on site SPL land disposal must conform to the minimum requirements contained in Appendix 1 of this standard or the equivalent as determined by Balco’s Corporate Environmental Affairs Department.
Appropriate written Standard Operating Procedures are required for on-site landfill operations. Operating procedure guidelines are available from Alcoa’s Corporate Environmental Affairs Department.
RECORD KEEPING AND RETENTION
Documentation and record retention regarding SPL genera-tion,transportation, recycle, reuse and/or disposal must conform to local country, state and regional regulatory requirements and to the following Alcoa Minimum Requirements. Where local requirements are less comprehensive, the following minimum requirements shall be used. Unless otherwise specified, records shall be maintained in perpetuity by the location.
Record keeping shall be regularly maintained, with records accumulated on a monthly basis and summarized by year. Records shall include the following data for each category [SPL, collector bars, vapor barrier steel and contaminated miscellaneous materials such as gloves, paper suits, rags, used dust collector bags, etc.]: weight generated, unit of measure, management method [disposal, recycle, reuse], transportation type, carrier name, manifest/paperwork number, transportation cost, disposal destination [site location], disposal cost, recycle/reuse destination [products, etc.], recycle/reuse ven-dor/supplier. Weighed values are preferable, estimated values shall be noted as such. See Appendix 2 for record keeping format guidance.
These standards will be reviewed prior to January 01, 1997. The review team will be convened by Alcoa Environmental Affairs and include appropriate members from all impacted business units.
• Alcoa land disposal unit design guidance - see Appendix 1
• Alcoa land disposal unit operating guidance (Preparation Required) - Corporate Environmental Affairs; includes leachate management, ground water management, long term maintenance plan
• Alcoa Industrial Hygiene Technical bulletin No. 86-S
• Alcoa MSDS No. 314 for Spent Pot Lining - Corporate Health Department
• Alcoa MSDS No. 353 for Leachate from Spent Pot Lining Areas - Corporate Health Department
• SPL properties - Environmental Technology Center at Alcoa Technical Center
• U.S.A. RCRA Delisting Criteria - Environmental Technology Center at Alcoa Technical Center
• Transporter Storage & Disposal Facility (TSDF) Audit Criteria - Corporate Environmental Affairs
• Alcoa SPL container requirements guidance - USMS - Knoxville Office
• Alcoa SPL storage building requirements guidance - Corporate Environmental Affairs
There have been several reported occurrences involving spillage of SPL and at least one explosive accident resulting in several fatalities.
SPL may be transported as bulk material in freight or sea containers or in appropriately designed trucks or rail cars. Transportation on water shall be in sea containers. Equipment shall be in good condition to minimize the potential for releases of SPL or SPL contaminated materials to the environment due to equipment failure.
Only “certified” transportation carriers with appropriate insurance for damages, injury and clean-up may be used for shipment of SPL. If regional regulatory procedures/requirements for “certification” of SPL transportation are lacking or do not exist, procedures for “internal Alcoa certification” of transporters is available from Alcoa’s Corporate Environmental Affairs Department. REFERENCE: Transporter Storage & Disposal Facility (TSDF) Audit Criteria.
When transported outdoors, containers and covers must be adequate to maintain the SPL in a dry state. “Closed” shipping containers must be vented, see 3.4 below.
Confined and/or closed spaces [e.g.; not generally accessible by people] containing SPL must be ventilated and the SPL must be maintained in a dry state to prevent accumulation of explosive concentrations of hydrogen and methane from forming. Concentrations of hydrogen and methane must be maintained at less than 1% [25% and 20% of the respective Lower Explosive Limit (LEL’s)]. Monitoring of gas concentrations is encouraged.
Regulations and requirements for domestic and international shipments of SPL are based on the United Nations (UN) Recommendations on the Transport of Dangerous Goods. Country specific requirements may be different than current U.N. recommendations due to timing, content selection and local variables in the implementation process. At the present time, efforts are under way in the domestic U.S. industry to reassess the classification of SPL involved in ground movement. While this assessment progresses, maintain the current dangerous goods classification for the product. Once new or additional information is verified, Alcoa may revise this Standard accor-dingly.
Containers, rail cars or trucks should be dedicated to SPL transportation if possible, and at a minimum, they must be thoroughly cleaned prior to use for other materials.
U.S. Requirements: Based upon current information, all Alcoa U.S. facilities offering SPL for transportation in containers, rail cars, trucks or vessels shall at a minimum handle such material as a regulated dangerous good and assign SPL the tentative hazard description: * Environmentally hazardous substance, solid, n.o.s., 9, UN 3077, III. Accordingly, each facility shall comply with the packaging, marking, labeling, and documentation requirements applicable when preparing SPL for transportation. * Per U.S. code, Hazardous waste, solid, n.o.s. may be used as an alternative proper shipping name.
India Requirements: Based upon current information, all Balco facilities offering SPL for transport in containers, rail cars, trucks or vessels shall at a minimum handle such material as a regulated dangerous good and assign SPL the shipping name : Water Reactive Solid, N.O.S., Class 4.3 , UN 2813, Packaging Group III; as per the current (fifth) edition of the Australian
Dangerous Goods (ADG) Code. Accordingly, each facility shall comply with the packaging, marking, labeling, and documentation requirements applicable when preparing SPL for transportation.
Adoption of the current UN Recommendations to include SPL under UN 3170 will occur when (as expected) these recommendations are adopted into the next (sixth) edition of the ADG Code due in early 1996.
Other Non U.S. Location Requirements: Based upon current information, all Non U.S. Alcoa facilities [except Alcoa of Australia] offering SPL for transportation in containers, rail cars, trucks or vessels shall at a minimum handle such material as a regulated dangerous good. If local country regulations & designations have been adopted based upon the United Nations (UN) Recommendations on the Transport of Dangerous Goods, containers and documentation should be so marked and managed. If no local country regulations & designations exist, the U.S. conventions detailed in paragraph 3.52 above shall be applied.
Shipping documentation must accompany all shipments of SPL, and must include a 24 hour contact telephone number for emergency response procedures in the event of a spill or release during transportation. In addition to information required above and by regulatory authorities, the documents should include information concerning the generator, transporter, and destination, as well as a description and quantity of material. See section 7.0 for record keeping requirements and Appendix 2 for record keeping format guidance.
ACCUMULATION AND TEMPORARY STORAGE
Accumulation storage is not considered “temporary storage”. Temporary storage is discouraged, but may be required regionally due to lack of environmentally appropriate recycling, treatment and/or safe disposal options.
Accumulation storage does not include land disposal.
Temporary storage does not include land disposal.
SPL storage areas, containers and/or confined spaces must be ventilated and the SPL must be maintained in a dry state to prevent accumulation of explosive concentrations of hydrogen & methane and toxic concentrations of phosphine & ammonia from forming. Concentrations of hydrogen & methane must be maintained at less than 1%, [25% and 20% of the respective LEL’s]. Concentrations of phosphine & ammonia must be maintained at less than 0.3 ppm and 25 ppm respectively [based on the respective 8 hour time weighted average TLV’s]. Monitoring of gas concentrations is encouraged.
Accumulation and temporary storage shall be in specially designed and designated containers or buildings which are designed and operated to:
a) Maintain stored SPL in a dry condition
b) Prevent build up of toxic gasses [ammonia & phosphine] above the levels specified in section 2.3 above
c) Prevent build up of explosive levels of gasses [hydrogen & me-thane] above the levels specified in section 2.3 above.
d) Prevent hazardous escape of SPL and SPL dust to the environ-ment
e) Prevent hazardous “tracking” of SPL dust out of the storage facility or storage area by personnel or vehicle traffic
f) Be secure and marked to prevent unauthorized, unrecognized and undetected entry
g) Prevent contact of SPL with acidic materials (NOTE: can generate lethal gas concentrations)
Assistance, details and recommendations for temporary storage buildings and/or containers is available from Alcoa’s Corporate Environmental Affairs Department.
Treatment Processes for SPL
Balco has established a priority of actions relating to the generation and disposal of SPL.
• Minimize generation of SPL per tones of aluminium produced
Increase pot life through improved construction and Pot operating practices.
Build new plotlines with large sized pots
• Reuse components of SPL
In the aluminium smelting processing other processes – industrial ecology
• Recover valuable resources
• Treatment processes
Eliminate hazardous conditions
Ensure safe operating conditions
Minimize waste output materials
Minimum long term liabilities
Effective end uses
Landfill as a last resort.
RECORD KEEPING GUIDANCE
Item Jan Feb Mar etc....
SPL - Wt. Generated [*= estimate]
Unit of measure
Collector Bars - Wt. Generated [*= estimate]
Unit of measure
Vapor Barrier - Wt. Generated [*= estimate]
Unit of measure
Miscellaneous materials - Wt. Generated [*= estimate]
Unit of measure
3. Balco land disposal unit operating guidance.
4. A book of Environmental management
6. Balco aluminium smelter process
7. balco Environmental hazards prevention guide.
8.www.world aluminium.com/recycling process
10. Guidelines for SPL containers, Guidelines for SPL storage buildings.
|Author: Col||Member Level: Bronze||Revenue Score: |
|The aluminium smelter in our town of Kurri Kurri Australia has closed and leaves an estimated pile of spent pot lining of 250,000 tonnes. I have been invited to join the supervisory committe of residents to oversee the site cleanup. I would appreciate any advice to this end. I am an electronics instrument technician and my partner is a science graduate. We have been approached by a company interested in treating the SPL to produce cement plant clinker but we are afraid there may be efforts by the smelter management to consign this waste pile to landfill in an old open cut coal mine nearby. Please advise, Col Maybury. email@example.com |
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