REPORT ON

NITRIC ACID AND ALUMINIUM-SODIUM

PRESENTED

BY- DISHA GARDI-205

STUTI SHAH-210

NITRIC ACIDNitric acid (H NO 3), also known as aqua fortis and spirit of nitre, is a highly corrosiveand toxic strong

acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides

of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming nitric acid.

Fuming nitric acid is characterized as white fuming nitric acid and red fuming nitric acid, depending on the

amount of nitrogen dioxide present. At concentrations above 95% at room temperature, it tends to rapidly

develop a yellow color due to slow decomposition.

HISTORYAqua regia (Latin for "royal water") is one of the chemicals the ancient scientists concocted. It is a highly corrosive, fuming yellow or red solution. The mixture is formed by mixing concentrated nitric and hydrochloric acid, usually in a volumetric ratio of one to three. It is one of the few reagents that can dissolve gold and platinum, the so-called royal, or noble metals—hence the name “royal water.” The effectiveness of aqua regia is partly because of the presence of both chlorine and nitrosyl chloride. Aqua regia is used in etching and certain analytical processes, and in laboratories to clean glassware of organic and metallic compounds.

Grades

The concentrated nitric acid of commerce consists of the maximum boiling azeotrope of nitric acid and water. Technical grades are normally 68% HNO3, (approx 15 molar), while reagent grades are specified at 70% HNO3.

White fuming nitric acid, also called 100% nitric acid or WFNA, is very close to anhydrous nitric acid.

A commercial grade of fuming nitric acid, referred to in the trade as "strong nitric acid" contains 90% HNO3 and has a density of 1.50 g/mL.

Red fuming nitric acid, or RFNA, contains substantial quantities of dissolved nitrogen dioxide (NO2) leaving the solution with a reddish-brown color.

An inhibited fuming nitric acid (either IWFNA, or IRFNA) can be made by the addition of 0.6 to 0.7% hydrogen fluoride (HF). This fluoride is added for corrosion resistance in metal tanks. The fluoride creates a metal fluoride layer that protects the metal.

PROPERTIES

Major Manufacturers 1. Deepak fertilizer and petrochemical

2. GNFC(Gujarat Narmada valley fertilizer corp)

3. Rashtriya chemicals and fertilizers

Deepak fertilizers and petrochemicals

• Deepak Fertilisers And Petrochemicals Corporation Limited is one of the largest producers of Dilute Nitric Acid (60%) in India with an installed capacity of 297,000 MT per year at Taloja near Mumbai.

• Assured Year-Round Supply Consistent supply of natural gas via DFPCL's own gas pipeline guarantees an uninterrupted feed stock for ammonia which is manufactured in-house assuring product purity and availability. Further, DFPCL's twin plants producing 300 TPD each of dilute nitric acid from on site ammonia ensure reliable year - round supply.

• International Technology World's finest know-how and technology from Weatherly Inc., USA guarantees consistent, high purity DNA.

GNFC(Gujarat Narmada Valley Fertilizers Company Ltd. )

Gujarat Narmada Valley Fertilizers Company Ltd. (GNFC), is a joint sector enterprise promoted by the Government of Gujarat and the Gujarat State Fertilizer Company Ltd.(GSFC). It was set up in Bharuch, Gujarat in 1976. Located at Bharuch in an extremely prosperous industrial belt, GNFC draws on the resources of the natural wealth of the land as well as the industrially rich reserves of the area.

Rashtriya chemical and fertilizer• Rashtriya Chemicals and Fertilizers Limited (RCF) is a Government of India

undertaking which produces fertilizers and basic chemicals for agriculture. 

Rashtriya Chemicals and Fertilizers Limited is quite well-known for producing basic chemicals like - 

Methanol Nitric acid Ammonium bicarbonate Methylamines Dimethyl Formamide Dimethyl acetamide 

PLANT CAPACITY

TYPES OF PROCESS USED

SINGLE PRESSURE

In the single pressure plants, the oxidation and absorption steps take place at essentially the same pressure. The oxidation and absorption steps can be classified as:

Low pressure (pressure below 0,1 MPa)                                                                      Medium pressure (pressure between 0,1 and 0,6 MPa)                                                      High pressure (pressure between 0,6 and 1,3 MPa)

DUAL PRESSURE

REACTION:Ammonia Oxidation Reaction:

1. 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g) ΔH = - 54 Kcal

Side Reactions:1. 4NH3(g) + 3O2(g) 2N2(g) + 6H2O(g) ΔH = - 75.7 Kcal

2. 2NH3(g) N2(g) + 3H2(g) ΔH = - 11 Kcal

3. 2NH3(g) + 2O2(g) N2O(g) + 3H2O(g)

4. 4NH3(g) + 6NO(g) 5N2 (g) + 6H2O(g) ΔH = - 107.9 Kcal

Nitrous Oxide Oxidation & Absorption:

1. 2NO(g) + O2(g) 2NO2 (g) ΔH = - 27.2 Kcal

2. 3NO2(g) + H2O(l) 2HNO3(aq) + NO (g) ΔH = - 32.2 Kcal

3. 2NO2(g) N2O4(g) ΔH = - 11.46 Kcal

4. 2NO2(g) + H2O HNO3(aq) + HNO2

5. 2HNO2 H2O + NO + NO2

Industrial productionNitric acid is produced by 2 methods:

The first method utilizes oxidation, condensation, and absorption to produce a weak nitric acid. Weak nitric acid can have concentrations ranging from 30 to 70 percent nitric acid.

The second method combines dehydrating, bleaching, condensing, and absorption to produce a high-strength nitric acid from a weak nitric acid. High-strength nitric acid generally contains more than 90 percent nitric acid

Weak Nitric Acid Production:

Nearly all the nitric acid produced in the U. S. is manufactured by the high-temperature catalytic oxidation of ammonia as shown schematically in Figure 8.8-1. This process typically consists of

3 steps: (1) ammonia oxidation, (2) nitric oxide oxidation, and (3) absorption. Each step corresponds to a distinct chemical reaction

Ammonia Oxidation -First, a 1:9 ammonia/air mixture is oxidized at a temperature of 1380 to 1470EF as it passes through a catalytic convertor, according to the following reaction:

4NH3 + 5O2 4NO + 6H2O

The most commonly used catalyst is made of 90 percent platinum and 10 percent rhodium gauze constructed from squares of fine wire. Under these conditions the oxidation of ammonia to nitric oxide (NO) proceeds in an exothermic reaction with a range of 93 to 98 percent yield. Oxidation temperatures can vary from 1380 to 1650EF. Higher catalyst temperatures increase reaction selectivity toward NO production. Lower catalyst temperatures tend to be more selective toward less useful products: nitrogen (N2) and nitrous oxide (N2O). Nitric oxide is considered to be a criteria pollutant and nitrous oxide is known to be a global warming gas. The nitrogen dioxide/dimer mixture then passes through a waste heat boiler and a platinum filter

Nitric Oxide Oxidation -The nitric oxide formed during the ammonia oxidation must be oxidized. The process stream is passed through a cooler/condenser and cooled to 100EF or less at pressures up to 116 pounds per square inch absolute (psia). The nitric oxide reacts noncatalytically with residual oxygen to form nitrogen dioxide (NO2) and its liquid dimer, nitrogen tetroxide:

2NO + O2 2NO2 N2O4

This slow, homogeneous reaction is highly temperature- and pressure-dependent. Operating at low temperatures and high pressures promotes maximum production of NO2 within a minimum reaction time.

Absorption -The final step introduces the nitrogen dioxide/dimer mixture into an absorption process after being cooled. The mixture is pumped into the bottom of the absorption tower, while liquid dinitrogen tetroxide is added at a higher point. Deionized process water enters the top of the column. Both liquids flow countercurrent to the nitrogen dioxide/dimer gas mixture. Oxidation takes place in the free space between the rays, while absorption occurs on the trays. The absorption trays are usually sieve or bubble cap trays. The exothermic reaction occurs as follows:

3NO2+ H2O 2HNO3+ NO

A secondary air stream is introduced into the column to re-oxidize the NO that is formed in Reaction3. This secondary air also removes NO2 from the product acid. An aqueous solution of 55 to 65 percent (typically) nitric acid is withdrawn from the bottom of the tower. The acid concentration can vary from 30 to 70 percent nitric acid. The acid concentration depends upon the temperature, pressure, number of absorption stages, and concentration of nitrogen oxides entering the absorber.

There are 2 basic types of systems used to produce weak nitric acid: (1) single-stage pressure process, and (2) dual-stage pressure process. In the past, nitric acid plants have been operated at a single pressure, ranging from atmospheric pressure to 14.7 to 203 psia. However, since Reaction 1 is favored by low pressures and Reactions 2 and 3 are favored by higher pressures, newer plants tend to operate a dualstage pressure system, incorporating a compressor between the ammonia oxidizer and the condenser. The oxidation reaction is carried out at pressures from slightly negative to about58 psia, and the absorption reactions are carried out at 116 to 203 psia.

DUAL PRESUURE PROCESSIn the dual-stage pressure system, the nitric acid formed in the absorber (bottoms) is usually sent to an external bleacher where air is used to remove (bleach) any dissolved oxides of nitrogen. The bleacher gases are then compressed and passed through the absorber. The absorber tail gas (distillate) is sent to an entrainment separator for acid mist removal. Next, the tail gas is reheated in the ammonia oxidation heat exchanger to approximately 392EF. The final step expands the

gas in the power-recovery turbine. The thermal energy produced in this turbine can be used to drive the compressor

High-Strength Nitric Acid Production:

A high-strength nitric acid (98 to 99 percent concentration) can be obtained by concentrating the weak nitric acid (30 to 70 percent concentration) using extractive distillation. The weak nitric acid cannot be concentrated by simple fractional distillation. The distillation must be carried out in the presence of a dehydrating agent. Concentrated sulfuric acid (typically 60 percent sulfuric acid) is most commonly used for this purpose. The nitric acid concentration process consists of feeding strong sulfuric acid and 55 to 65 percent nitric acid to the top of a packed dehydrating column at approximately atmospheric pressure. The acid mixture flows downward, countercurrent to ascending vapors. Concentrated nitric acid leaves the top of the column as 99 percent vapor, containing a small amount of NO2 and oxygen (O2) resulting from dissociation of nitric acid. The concentrated acid vapor leaves the column and goes to a bleacher and acountercurrent condenser system to effect the condensation of strong nitric acid and the separation of oxygen and oxides of nitrogen (NOx) byproducts. These byproducts then flow to an absorption column where the nitric oxide mixes with auxiliary air to form NO2, which is recovered as weak nitric acid. Inert and unreacted gases are vented to the atmosphere from the top of the absorption column. Emissions from this process are relatively minor. A small absorber can

be used to recover NO2. Figure 8.8-2 presents a flow diagram of high-strength nitric acid production from weak nitric acid.

Emissions And Controls:Emissions from nitric acid manufacture consist primarily of NO, NO2 (which account for visible emissions), trace amounts of HNO3 mist, and ammonia (NH3). By far, the major source of nitrogen oxides(NOx) is the tailgas from the acid absorption tower. In general, the quantity of NOx emissions is directly related to the kinetics of the nitric acid formation reaction and absorption tower design. NOx emissions can increase when there is (1) insufficient air supply to the oxidizer and absorber, (2) low pressure, especially in the absorber, (3) high temperatures in the cooler-condenser and absorber, (4) production of an excessively high-strength product acid, (5) operation at high throughput rates, and (6) faulty equipment such as compressors or pumps that lead to lower pressures and leaks, and decrease plant efficiency.

The 2 most common techniques used to control absorption tower tail gas emissions are extended absorption and catalytic reduction. Extended absorption reduces NOx emissions by increasing the efficiency of the existing process absorption tower or incorporating an additional absorption tower. An efficiency increase is achieved by increasing the number of absorber trays, operating the absorber at higher pressures, or cooling the weak acid liquid in the absorber. The existing tower can also be replaced with a single tower of a larger diameter and/or additional trays. See Reference 5 for the relevant equations.

In the catalytic reduction process (often termed catalytic oxidation or incineration), tail gases from The absorption tower are heated to ignition temperature, mixed with fuel (natural gas,

hydrogen, propane, butane, naphtha, carbon monoxide, or ammonia) and passed over a catalyst bed. In the presence of the catalyst, the fuels are oxidized and the NOx are reduced to N2. The extent of reduction of NO2 and NO to N2 is a function of plant design, fuel type, operating temperature and pressure, space velocity through theThe Ostwald process is a chemical process for producing nitric acid, which was developed by Wilhelm Ostwald (patented 1902). It is a mainstay of the modern chemical industry. Historically and practically it is closely associated with the Haber process, which provides the requisite raw material, ammonia.

Ammonia is converted to nitric acid in two stages. It is oxidized (in a sense "burnt") by heating with oxygen in the presence of a catalyst such as platinum with 10% rhodium, to form nitric oxide and water. This step is strongly exothermic, making it a useful heat source once initiated:[1]

4 NH3 (g) + 5 O2 (g) → 4 NO (g) + 6 H2O (g) (ΔH = −950 kJ/mol)

Stage two (combining two reaction steps) is carried out in the presence of water in an absorption apparatus. Initially nitric oxide is oxidized again to yield nitrogen dioxide:[1]

2 NO (g) + O2 (g) → 2 NO2 (g) (ΔH = −114 kJ/mol)

This gas is then readily absorbed by the water, yielding the desired product (nitric acid, albeit in a dilute form), while reducing a portion of it back to nitric oxide:[1]

3 NO2 (g) + H2O (l) → 2 HNO3 (aq) + NO (g) (ΔH = −117 kJ/mol)

The NO is recycled, and the acid is concentrated to the required strength by distillation.

Alternatively, if the last step is carried out in air:

4 NO2 (g) + O2 (g) + 2 H2O (l) → 4 HNO3 (aq)

Typical conditions for the first stage, which contribute to an overall yield of about 96%, are:

pressure  between 4 and 10 atmospheres (approx. 400-1010 kPa or 60-145 psig) and

temperature  is about 1173 K (approx. 900 °C or 1652 °F.).

A complication that needs to be taken into consideration involves a side-reaction in the first step that reverts the nitrogen back to N2:

4 NH3 + 6 NO → 5 N2 + 6 H2O

How Brink Pt filter works ?

In the nitric acid plant, the Brink Pt Filter is housed in a separate vessel and installed in a horizontal orientation following the waste heat boiler. As air and ammonia are burned at the platinum catalyst gauze, within the converter vessel, a gradual catalyst breakdown occurs and the resulting platinum dust is carried downstream to the Brink Pt Filter and is captured. This Pt Filter has an estimated platinum collection efficiency of nearly 100% of contactable and collectable Pt dust.

When the Pt Filter has been in service for one or two production campaigns, it is taken from service and the outer screens are removed so that the special ceramic fiber embedded with the platinum dust may be accessed. The platinum embedded ceramic fiber media is removed and returned to a precious metal processor for reclamation. A spare Brink Pt Filter is placed in the filter vessel and the empty Pt Filter cage is then returned to MECS to be repacked.

Based on reports from existing MECS customers, the Brink Pt Filter collects up to 60% of the platinum catalyst burn off losses. This overall recovery is based on credits secured from the precious metal processor compared with the platinum lost from the gauzes.

Uses

Use of nitric acid in rocket engines 

Nitric acid was commonly used as an oxidizer in liquid-propellant rocket engines between 1940 and 1965. It most often took the form of RFNA (red fuming nitric acid), containing 5–20% dissolved nitrogen dioxide. Compared to concentrated nitric acid (also known as white fuming nitric acid), RFNA is more energetic and more stable to store but produces poisonous red-brown

fumes. Because nitric acid is normally highly corrosive it can only be stored and piped by a few materials such as stainless steel. However, the addition of a small concentration of fluoride ions inhibits the corrosive action and gives a form known as IRFNA (inhibited red fuming nitric acid). Like nitrogen tetroxide, it is hypergolic (reacts upon contact with) hydrazine, MMH(monomethyl hydrazine), and UDMH (unsymmetrical dimethyl hydrazine). 

NITRIC ACID IN LABORATORY

The main use of nitric acid is for the production of fertilizers; other important uses include the production

of explosives, etching and dissolution of metals, especially as a component of aqua regia for the

purification and extraction of gold, and in chemical synthesis.

WoodworkingIn a low concentration (approximately 10%), nitric acid is often used to artificially age pine and maple. The

color produced is a grey-gold very much like very old wax or oil finished wood (wood finishing).[9]

Other usesIWFNA (inhibited white fuming nitric acid) may be used as the oxidizer in liquid fuel rockets.[10] IRFNA (inhibited red fuming nitric acid) was one of 3 liquid fuel components for the BOMARC missile.[11]

A solution of nitric acid and alcohol, Nital, is used for etching of metals to reveal the microstructure.

Commercially available aqueous blends of 5-30% nitric acid and 15-40% phosphoric acid are commonly used for cleaning food and dairy equipment primarily to remove precipitated calcium

and magnesium compounds (either deposited from the process stream or resulting from the use of hard water during production and cleaning).

Alone, it is useful in metallurgy and refining as it reacts with most metals, and in organic syntheses.

A mixture of concentrated nitric and sulfuric acids causes the nitration of aromatic compounds, such as benzene. Examination of the infrared spectrum of the acid mixture using a corrosive resistant diamond cell shows infrared peaks close to that expected for carbon dioxide. The species responsible for the peaks is the nitronium ion, NO+2, which like CO2, is a linear molecule. The nitronium ion is the species responsible for nitration: being positive, it is attacked by electron-rich benzene rings. This is described more fully in organic chemistry books.

SafetyNitric acid is a powerful oxidizing agent, and the reactions of nitric acid with compounds such as cyanides, carbides, and metallic powders can be explosive. Reactions of nitric acid with many organic compounds, such as turpentine, are violent and hypergolic (i.e., self-igniting). Due to its properties it is stored away from bases and organics.

Concentrated nitric acid dyes human skin yellow due to a reaction with the keratin. These yellow stains turn orange when neutralized.

Medical effects of nitric acid 

Concentrated nitric acid is capable of producing severe burns of the skin. Swallowing the acid leads to intense burning pain and ulceration of the mouth and throat. Treatment is by immediate administration of alkaline solutions, followed by milk or olive oil. 

Aluminium

Aluminium is a soft, durable, lightweight, malleable metal with appearance ranging from silvery to dull grey, depending on the surface roughness. Aluminium is nonmagnetic and nonsparking. It is also insoluble in alcohol, though it can be soluble in water in certain forms. Corrosion resistance can be excellent due to a thin surface layer of aluminium oxide that forms when the metal is exposed to air, effectively preventing further oxidation. The strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper. This corrosion resistance is also often greatly reduced when many aqueous salts are present, particularly in the presence of dissimilar metals.

Natural occurrenceIn the Earth's crust, aluminium is the most abundant (8.3% by weight) metallic element and the third most abundant of all elements (after oxygen and silicon). Because of its strong affinity to oxygen, however, it is almost never found in the elemental state; instead it is found in oxides or silicates.

Properties

Major manufacturers in India

1. Hindalco An industry leader in aluminium and copperAn industry leader in aluminium and copper, Hindalco Industries Limited, the metals flagship company of the Aditya Birla Group is one of the world's largest aluminium rolling companies and one of the biggest producers of primary aluminium in Asia.

Established in 1958, they commissioned our aluminium facility at Renukoot in eastern Uttar Pradesh, India in 1962. Later acquisitions and mergers, with Indal, Birla Copper and the Nifty and Mt. Gordon copper mines in Australia, strengthened theirr position in value-added alumina, aluminium and copper products.

The acquisition of Novelis Inc. in 2007 positioned us among the top five aluminium majors worldwide and the largest vertically integrated aluminium company in India. Today they are a metals powerhouse with high-end rolling capabilities and a global footprint in 12 countries. Their consolidated turnover of USD 15 billion (Rs. 600,128 million) places us in the Fortune 500 league.

2. NalcoNational Aluminium Company Ltd. (Nalco) is considered to be a turning point in the history of Indian Aluminium Industry. In a major leap forward, Nalco has not only addressed the need for self-sufficiency in aluminium, but also given the country a technological edge in producing this strategic metal to the best of world standards. Nalco was incorporated in 1981 in the Public Sector, to exploit a part of the large deposits of bauxite discovered in the East Coast.

3. Indal INDAL is a market leader in the upstream range of standard and speciality alumina products in India. Aluminium units across India encompass the entire operations, from bauxite mining, alumina refining, aluminium smelting to downstream rolling, extrusions and recycling.

Plant capacity of each company can be given as:

COMPANY NAME

INSTALLED CAPACITY

PRODUCTION QUANTITY

SALES QUANTITY

HINDALCO 488,000 523,453.00 NA

NALCO 345,000 360,457.00 343,911.00

INDAL 4,000 2,942.00 2,936.00

Manufacturing processes of aluminiumWöhler processThe Wöhler process was the former way in which aluminium was extracted from its ore. However with the advent of more efficient means of electrolysis, this process all but become extinct. It involved the reduction of anhydrous aluminium chloride with potassium, and produced powdered aluminium.

In 1827, Friedrich Wöhler refined a process discovered by Hans Christian Oersted, a Danish chemist, who first produced impure aluminium in 1825. This allowed him to establish the specific gravity of aluminium in 1845.

Hall–Héroult process

The Hall–Héroult process is the major industrial process for the production of aluminium. It involves dissolving alumina in molten cryolite, and electrolysing the solution to obtain pure aluminium metal.

Aluminium cannot be produced by the electrolysis of an aluminium salt dissolved in water because of the high reactivity of aluminium. An alternative is the electrolysis of a molten aluminium compound.

In the Hall–Héroult process alumina, Al2O3 is dissolved in an industrial carbon-lined vat of molten cryolite, Na3AlF6, called a "cell". Aluminium oxide has a melting point of over 2,000 °C (3,630 °F) while pure cryolite has a melting point of 1,012 °C (1,854 °F). With a small percentage of alumina dissolved in it, cryolite has a melting point of about 1,000 °C (1,830 °F). Some Aluminium fluoride, AlF3 is also added into the process to reduce the melting point of the cryolite-alumina mixture.

Hall-Heroult Industrial Cell/Pot

• Deville process• The Deville process was the first industrial process used to produce alumina from

bauxite.

• The Frenchman Henri Sainte-Claire Deville invented the process in 1859. It is sometimes called the Deville-Pechiney process. It is based on the extraction of alumina with sodium carbonate.

• The first stage is the calcination of the bauxite at 1200°C with sodium carbonate and coke. The alumina is converted in sodium aluminate. Iron oxide remains unchanged and silica forms a polysilicate.

• In the second stage sodium hydroxide solution is added, which dissolves the sodium aluminate, leaving the impurities as a solid residue. The amount of sodium hydroxide

solution needed depends upon the amount of silica present in the raw material. The solution is filtered off; carbon dioxide is bubbled through the solution, causing aluminium hydroxide to precipitate, leaving a solution of sodium carbonate. The latter can be recovered and reused in the first stage.

• The aluminium hydroxide is calcined to produce alumina.

Bayer process• Raw Materials used are:

Alumina

Coke

Cryolite flux

Tar and Pitch

Stage 1: converting bauxite to alumina

STEP 1- Crushing and Grinding: Alumina recovery begins by passing the bauxite through screens to sort it by size. It is then crushed to produce relatively uniformly sized material. The ore is then fed into large grinding mills and mixed with a caustic soda solution (sodium hydroxide) at high temperature and pressure. The grinding mill rotates like a huge drum while steel rods - rolling around loose inside the mill - grind the ore to an even finer consistency. The process is a lot like a kitchen blender only much slower and much larger. The material finally discharged from the mill is called slurry.

The resulting liquor contains a solution of sodium aluminate and undissolved bauxite residues containing iron, silicon, and titanium. These residues - commonly referred to as "red mud" - gradually sink to the bottom of the tank and are removed.

STEP 2-Digesting: The slurry is pumped to a digester where the chemical reaction to dissolve the alumina takes place. In the digester the slurry - under 50 pounds per square inch pressure - is heated to 300 °Fahrenheit (145 °Celsius). It remains in the digester under those conditions from 30 minutes to several hours.

More caustic soda is added to dissolve aluminum containing compounds in the slurry. Undesirable compounds either don't dissolve in the caustic soda, or

combine with other compounds to create a scale on equipment which must be periodically cleaned. The digestion process produces a sodium aluminate solution. Because all of this takes place in a pressure cooker, the slurry is pumped into a series of "flash tanks" to reduce the pressure and heat before it is transferred into "settling tanks."

STEP 3-Settling: Settling is achieved primarily by using gravity, although some chemicals are added to aid the process. Just as a glass of sugar water with fine sand suspended in it will separate out over time, the impurities in the slurry - things like sand and iron and other trace elements that do not dissolve - will eventually settle to the bottom.

The liquor at the top of the tank (which looks like coffee) is now directed through a series of filters. After washing to recover alumina and caustic soda, the remaining red mud is pumped into large storage ponds where it is dried by evaporation.

The alumina in the still warm liquor consists of tiny, suspended crystals. However there are still some very fine, solid impurities that must be removed. Just as coffee filters keep the grounds out of your cup, the filters here work the same way.

The giant-sized filters consist of a series of "leaves" - big cloth filters over steel frames - and remove much of the remaining solids in the liquor. The material caught by the filters is known as a "filter cake" and is washed to remove alumina and caustic soda. The filtered liquor - a sodium

aluminate solution - is then cooled and pumped to the "precipitators."

STEP 4-Precipitation: Imagine a tank as tall as a six-story building. Now imagine row after row of those tanks called precipitators. The clear sodium aluminate from the settling and filtering operation is pumped into these precipitators. Fine particles of alumina - called "seed crystals" (alumina hydrate) - are added to start the precipitation of pure alumina particles as the liquor cools. Alumina crystals begin to grow around the seeds, then settle to the bottom of the tank where they are removed and transferred to "thickening tanks." Finally, it is filtered again then transferred by conveyor to the "calcination kilns."

STEP 5-Calcination: Calcination is a heating process to remove the chemically combined water from the alumina hydrate. That's why, once the hydrated alumina is calcined, it is referred to as anhydrous alumina. "Anhydrous" means "without water."

From precipitation, the hydrate is filtered and washed to rinse away impurities and remove moisture. A continuous conveyor system delivers the hydrate into the calcining kiln. The calcining kiln is brick-lined inside and gas-fired to a temperature of 2,000 °F or 1,100 °C. It slowly rotates (to make sure the alumina dries evenly) and is mounted on a tilted foundation which allows the alumina to move through it to cooling eqipment. (Newer plants use a method called fluid bed calcining where alumina particles are suspended above a screen by hot air and calcined.)

The result is a white powder: pure alumina. The caustic soda is returned to the beginning of the process and used again.

Stage 2 : converting alumina to aluminiumSmelting: In 1886, two 22-year-old scientists on opposite sides of the Atlantic, Charles Hall of the USA and Paul L.T. Heroult of France, made the same discovery - molten cryolite (a sodium aluminum fluoride mineral) could be used to dissolve alumina and the resulting chemical reaction would produce metallic aluminum. The Hall-Heroult process remains in use today.

The Hall-Heroult process takes place in a large carbon or graphite lined steel container called a " reduction pot". In most plants, the pots are lined up in long rows, called potlines.

The reactions taking place inside are :

Bauxite purification:• Reactions

6NaOH + Al2O3 2Na3AlO3 + H2O

Na3AlO3 + 3H2O 3NaOH + Al(OH)3

2Al(OH)3 Al2O3 + 3H2O

Aluminium Extraction :2Al2O3 + 3C Al + CO2

C + O2 CO2

Thus the process can be summarized as :

Economic scenario :he Indian aluminium market is growing at a rapid pace and it is one metallic industry where India can emerge as a powerhouse within the next decade, said a spokesperson of Vedanta Aluminum Ltd, a leading producer of metallurgical grade alumina and other aluminium products in the country. 

According to industry sources, India with total bauxite reserves of about 3 billion accounts for almost 7.5% of the world’s 65 billion bauxite reserves and is ranked sixth among the countries with highest bauxite reserves. Indian bauxite reserves are expected to last over 350 year with proven and probable reserves are estimated at ~1200 Mt. Currently all the major Indian producers are trying to make good the opportunity by expanding furiously. Though India's per capita consumption of aluminium stands too low (under 1 kg) comparing to the per capita consumptions of other countries the industries that require aluminium mostly include power (44%), consumer durables, transportation (10-12%), construction (17%) and packaging. India is the eighth leading producer of primary aluminium in the world, with total production amounting to over 1,200 KT. The country has witnessed significant growth in aluminium production during the past five years. India is already amongst the lowest cost producers in the world with Hindalco and Nalco already known as some of the lowest cost producers in the world. India's low costs can be largely attributed to the easy availability of bauxite. 

At present, cost of aluminium production in India is about $1500 per tonne compared to the world average of $1,600 per tone

Uses of aluminium :• Transportation (automobiles, aircraft, trucks, railway cars, marine vessels, bicycles etc.)

as sheet, tube, castings etc. • Packaging (cans, foil, etc.) • Construction (windows, doors, siding, building wire, etc.) • A wide range of household items, from cooking utensils to baseball bats, watches.• Street lighting poles, walking poles etc. • Outer shells of consumer electronics, also cases for equipment e.g. photographic

equipment.

•

Introduction to Sodium :

• Elemental sodium does not occur naturally on Earth, but quickly oxidizes in air and is violently reactive with water, so it must be stored in an inert medium, such as a liquid hydrocarbon. The free metal is used for some chemical synthesis, analysis, and heat transfer applications.

• Stability: Unstable. Reacts violently with water. Hazardous Decomposition Products: Does not decompose but can form flammable hydrogen in contact with air. Hazardous Polymerization: Will not occur. Incompatibilities: Water, oxygen, carbon dioxide, carbon tetrachloride, halogens, acetylene, metal halides, ammonium salts, oxides, oxidizing agents, acids, alcohols, chlorinated organic compounds, many other substances. Conditions to Avoid: Air, heat, flames, ignition sources and incompatibles.

• Keep in a tightly closed container, stored in a cool, dry, ventilated area. Protect against physical damage. Keep away from water or locations where water may be needed for fire. Avoid high temperatures. Store under nitrogen or kerosene. Never store under halogenated hydrocarbons. A detached fire-resistive building is recommended for quantity storage. Isolate from air, acids, and oxidizing materials. Isolate from incompatible substances. Containers of this material may be hazardous when empty since they retain product residues (dust, solids); observe all warnings and precautions listed for the product.

Properties

Major Manufacturers in India• Sodium Metals Pvt LtdSodium metal lists nature and environment high on its priority list. The plant is located in the Chemical Complex at Nandesari, Gujarat.

The chemical complex has a Centralized Secondary Effluent Treatment Plant (CETP) for treating wastes from different chemical units and also a Solid Waste Disposal site.

• Alkali Metals Ltd

• Jai Radhe Sales

Jai Radhe Sales is one of the India's leading manufacturers of herbal extracts, active pharmaceutical ingriedients,agro chemical and other specialty phytochemicals.

Different manufacturing process

• Castner’s process

• Deville process

• Downs’ process

CASTNERS PROCESSThe Castner process is a process for manufacturing sodium metal by electrolysis of molten sodium hydroxide at approximately 330°C. Below that temperature the melt would solidify, above that temperature, the metal would start to dissolve in the melt.

DEVILLE ProcessAt the end of the 19th century, sodium was chemically prepared by heating Sodium Carbonate with Carbon to 1100 °C.

Na2CO3 (liquid) + 2 C (coke) → 2 Na (vapor) + 3CO (gas).

Downs’ processIn the commercial preparation of sodium, molten NaCl is electrolyzed in a specially ed cell called the Downs cell :

Schematic of a Downs cell used in the industrial production of sodium

The electrolyte medium through which current flows is molten NaCl. Calcium chloride, CaCl2, is added to lower the melting point of the cell medium from the normal melting point of NaCl, 804oC, to around 600oC. The Na(l) and Cl2(g) produced in the electrolysis are kept from coming in contact and reforming NaCl. In addition, the Na must be prevented from contact with oxygen because the metal would quickly oxidize under the high-temperature conditions of the cell reaction. The electrolysis reaction is:

2NaCl --> 2Na(l) + Cl2(g).

The cell is designed to collect sodium at the cathode and chlorine at the anode without allowing these two products to react with each other. The melting point of sodium chloride is about 800oC, so a mixture whose mole ratio is about one mole of NaCl to three moles of CaCl2 is employed to reduce the melting point to about 600oC. The cell does not produce calcium metal because the electrowinning of sodium occurs at a less negative cathode potential than does the electrowinning of calcium.

Uses • Sodium in its metallic form can be used to refine some reactive metals, such as zirconium

and potassium, from their compounds.

• In certain alloys to improve their structure.

• To descale metal (make its surface smooth).

• To purify molten metals.

• As a heat transfer fluid in some types of nuclear reactors and inside the hollow valves of high-performance internal combustion engines.

• In sodium vapour lamps, an efficient means of producing light from electricity.

Cost effectiveness by companies• They economize the use of resources and minimizing wastage in order that the

environment is protected and pollution is limited.

• Lab wastes are collected, neutralised and used as make up water for caustic lye preparation.  Solid wastes are treated with water and the liquid is used for caustic lye preparation. After recovery of active ingredients by solvent treatment, they are burnt in an incinerator.