Soda ash, or in chemical name known as sodium carbonate (Na2CO3), is an alkali chemical extracted from the mineral trona or naturally coming about sodium carbonate-bearing brines (both called as natural soda ash), the mineral nahcolite (called as natural sodium bicarbonate, from which soda ash can be generated), or produced from one of several chemical processes (referred to as synthetic soda ash).
The general classification of soda ash production processes currently in commercial use is as below.
1. Refining of natural soda ash
2. Carbonation of caustic soda
3. By-product from alumina production
4. Synthetic production using salt, carbon dioxide and ammonia as raw material
The first method is applied in the United States and Kenya for soda ash discovered in underground deposits or in lakes. The second process generates soda ash through the reaction of caustic soda (a by-product of chlorine production) with carbon dioxide but because of uncertainty regarding the supply of caustic soda this process is not used for wide scale production. As of the Soviet Union which employed the third process, alumina is gained from bauxite and it obtained soda ash as a byproduct. It is estimated that the Soviets are producing 500,000 tonnes per year of soda ash using this method. And the fourth method is generally known as the soda ash synthesis process mostly used, which have four methods namely:
1. Solvay Process
2. Hou Process
3. Full Ammonium Chloride (AC) Co-production Process
4. Partial Ammonium Chloride (AC) Co-production Process
The general classification of soda ash production processes currently in commercial use is as below.
A. Refining of Natural Soda Ash
The word “trona” along with its use comes from ancient Egypt, when the Egyptians nearly 5,000 years ago used the mineral to make glass containers and ornaments. Trona is widely mined and processed into soda ash and has become an important commodity worldwide. The soda ash application is mostly in manufacturing glass, explaining more than half of global demand. The major contributor of trona in the world is Sweetwater County, Wyoming, which is the state’s top international export. Wyoming also fulfills about 90 percent of the nation’s soda ash.
The largest foremost trona deposits in the world are in south-western Wyoming in the Wilkins Peak Member of the Green River Formation. The plied trona deposits range in depth from 800 to 2,200 feet below the surface. Known as “bedded trona,” this resource was deposited 40 to 50 million years ago in a fresh-water lake called Lake Gosiute, which covered most of what is now the Green River Basin.
Trona is mined and processed into soda ash and bicarbonate of soda which is a basic chemical building block used by industries throughout the world to make glass, food and pharmaceutical products. It is also effectively used to reduce air emissions. Mined trona is refined into soda ash using the mono process as shown below.
B. Synthetic Production Using Salt, Carbon Dioxide and Ammonia as Raw Material
1. SOLVAY PROCESS
This process is also known as the Ammonia Soda Process, the oldest of the three. The major raw materials are salt and limestone, which has the reaction as follows.
CaCO3 + C → CaO + CO2 (1)
CaO + H2O → Ca(OH)2 (2)
NaCl + NH3 + CO2 + H2O → NaHCO3 + NH4Cl (3)
2NH4Cl + Ca(OH)2 → CaCl2 + 2NH3 + 2H2O (4)
2NaHCO3 → Na2CO3 + CO2 + H2O (5)
and may be simplified to
2NaCl + CaCO3 → Na2CO3 + CaCl2 (6)
The major reaction in the production process is (3) when salt, ammonia and carbon dioxide react to form dense ash and intermediate ammonium chloride. The dense ash is segregated by settling. In the reaction (4), ammonium chloride is decomposed from the mother liquor using slaked lime. Recovered ammonia is recycled to (3) and stock is needed only to make up for loss. Dense ash is heated in a calciner and, as shown in (5), soda ash is formed with carbon dioxide which is recycled.
The Solvay Process has insufficiency in that energy is required to produce heat for (4), wherein the yield of salt is less than 73%, and there is no appropriate use for byproduct calcium chloride.
The decomposed mother liquor contains calcium chloride, unreacted salt, slaked lime and calcium carbonate. Once there is demand for calcium chloride, the above procedure will be applied for the production of purified calcium chloride. The mother liquor and carbon dioxide react to release the slaked lime as calcium carbonate, which is settled in the thickener and removed from the system. Top liquor of the thickener is assigned into the evaporator, where the crystal ammonia is separated as a product; in time of this evaporation operation salt is also recovered.
Generally, there is no sizable amount of requirement for calcium chloride, and hence the above-mentioned procedure will not be taken into consideration. Alternatively, the mother liquor is disposed of in a waste pond, where the insoluble materials are settled and top liquor is left behind.
2. HOU PROCESS
The Chinese chemist Hou Debang developed this process in the 1930s. It is similar to the Solvay process and mostly used in smaller coal-fired plants in China, which plants have a typical annual production capacity of 210,000 tonnes and it shows 25% of global production capacity. The Hou process does not yield calcium chloride as a byproduct, however rather ammonium chloride (a fertilizer).
The preceding steam reforming byproduct carbon dioxide was inflated through a saturated solution of sodium chloride and ammonia to produce sodium bicarbonate by the reaction as follows.
NH3 + CO2 + H2O → NH4HCO3 (1)
NH4HCO3 + NaCl → NH4Cl + NaHCO3 (2)
Due to the low solubility, the sodium bicarbonate was gathered as a precipitate and then heated to generate pure sodium carbonate similar to the last step of the Solvay Process.
2NaHCO3 → Na2CO3 + CO2 + H2O (3)
The Hou Process is more energy-intensive than the Solvay Process, and utilizes roughly 14.25 GJ of energy per tonne of soda ash.
3. FULL AMMONIUM CHLORIDE (AC) CO-PRODUCTION PROCESS
This process has been evolved in Japan where the salt resources are essentially limited, and has been commercially used in that country. The advantage is requiring low energy because heat for recovery of ammonia is not necessary, and the production cost of soda ash is reduced when there is demand for ammonium chloride. The reactions are as follows.
NaCl + CO2 + NH3 → NaHCO3 + NH4Cl (1)
2NaHCO3 → Na2CO3 + CO2 + H2O (2)
which can be simplified to
2NaCl + CO2 + 2NH3 + H2O → Na2CO3 + 2NH4Cl (3)
The reaction (1) is operated in two stages: carbonation and crystallization of ammonium chloride.
The mother liquor from the sodium bicarbonate separator reacts with ammonia, and it is mixed with crushed salt to gain ammonium chloride. The formed ammonium chloride is segregated by cooling crystallization followed by the thickener. Top liquor of the thickener is reprocessed back into the ammonia absorption section, then the crystal ammonium chloride is prilled and dried to be as the final product.
To decompose sodium bicarbonate to carbon dioxide and sodium carbonate (soda ash), it is heated in the calciner as shown in reaction (2). Later, carbon dioxide is recycled to the carbonation section.
In this process, the recycling solution is increased due to the appearance of moisture and impurities in the crude salt, and the impurities are accumulated; consequently it is required to blow down a certain amount of recycling solution so as to dispose of the impurities in the system.
4. PARTIAL AMMONIUM CHLORIDE (AC) CO-PRODUCTION PROCESS
This process is almost same with the Full Ammonium Chloride Co-production Process besides when the demand for ammonium chloride is limited, the part of ammonia recovery is added to Full Ammonium Chloride Process in order to regain ammonia by putting quicklime to waste chlorine as calcium chloride and recycle ammonia back to the process, as these are conducted in the Solvay Process. Compared to the Solvay Process, this process has advantages of higher salt yield and lower energy consumption.
SOAP AND DETERGENTS
Soda ash light is applied in soap and detergent industries wherein it acts as feeder and provides a smooth finish to the end product.
The high alkalinity of soda ash provides it to act as a solvent in destroying a range of stains. It is often used in commercial detergent mixtures to treat hard water. The soda ash binds to the minerals which make water hard and allows the detergent to be absorbed into fibers properly to clean clothes.
Adding soda prevents H2O from bonding with detergent, letting an extra even distribution of the cleansing agent throughout the laundry cycle. Usually detergents apply soda ash. The product operates as a builder within the formulations of soaps, detergents and alternative cleansing compounds, getting ready wash water it achieves the best level of soil removal. soda additionally adds advantages per se by aiding agglomeration, being a carrier for surfactants associated as an alkali supply for pH scale adjustment.
A large number of formulated domestic products, soaps, scouring powders, soaking and washing powders etc. have a varying content of soda ash. More and more, quality soda ash is being used in high performance compact powders production for both laundry and dish washing. These higher performing and environmentally friendly products offer greater value to the consumer.
In textile dyeing, pH plays a very important role. When soda ash light is added it changes the pH of cellulose fibre and fibre reactive dye, fibre molecules are activated which chemically attack the dye, so that the dye reacts with the fibre and permanently holds the dye onto the fibre.
Soda ash light can be added at three different stages i.e before, during or after dying. Generally it is added before the dye in tie-dye. Garments are tied or left loose. Half or one cup of soda ash is added per 3.875 litre of water as a makeup solution, and then the material is soaked for five minutes to an hour. Then the dye is applied to soda ash light pre-soaked garments. Soda ash light is added with the dye, generally used with dye painting. However during immersion dyeing and low water immersion dyeing, soda ash is added after dye.
Basically in textile dyeing the simple need is to increase the pH (alkalinity) of the reaction (pH around 10.5-11). However the ideal or exact pH depends on individual dye colour & fibre used.
Apart from soda ash various other chemicals caustic soda (NaOH), trisodium phosphate (TSP), sodium silicate, acetic acid, sodium bicarbonate etc, can be used to reach ideal pH. But handling pure caustic soda requires trained chemists as it is quite dangerous. Also if you use a bit too much or too little of soda ash it will increase the pH close to correct pH, but not the same with caustic soda. Low pH will not work and too high pH is dangerous to both fibre as well as people handling it.
RAW MATERIAL FOR SODIUM-BASE CHEMICALS
Soda ash light is an associate degree acknowledged supply of metal ions. It conjointly aids the solubility and reactivity of the many inorganic compounds in water. As such, it’s used as a significant staple for the economical production of metal phosphates, metal silicates, chrome chemicals and photographic chemicals. It is also used in sodium bicarbonate (baking soda) production, which is an essential ingredient in the beverage, coatings, detergents, food, dialysis, and personal care markets.
For many applications, soda ash is interchangeable with caustic soda, while offering a cost advantage. Thus, it can be used as a functional substitute for caustic soda in many applications, such as:
pH adjustment/acid neutralization
Manufacturing of sodium chemicals including sodium phosphates, sodium sulphate, sodium sulphite, sodium acetate, sodium nitrite and sodium citrate
Flue gas desulfurization
Soda ash or sodium carbonate may be an additive (E500) used as AN acidity regulator, anticaking agent, raising agent, and stabilizer. It's one among the parts of kansui, an answer of alkaline salts accustomed to give ramen noodles their characteristic flavor and texture. It’s additionally employed in the assembly of snus (Swedish-style snuff) to stabilize the pH of the final product.
Sodium carbonate is also used in the production of sherbet powder. The cooling and fizzing sensation results from the endothermic reaction between sodium carbonate and a weak acid, commonly citric acid, releasing carbon dioxide gas, which occurs when the sherbet is moistened by saliva.
It is used as a fluxing agent during the manufacture of glass. It also regulates the temperature in the furnace. It is responsible for equal distribution of energy. It supports the shaping of glass. Silica is the glass forming oxide, lime provides chemical stability and soda ash acts as the fluxing agent. Soda ash plays a vital role by reducing the furnace temperature necessary to melt the silica used, thus reducing the energy required to produce glass.
Glass manufacture described about 48% of domestic soda ash consumption as follows: container, 51%; ﬂat, 39%; and fiber and other, 5% each. Glass containers are made for beverages, chemical and household products, food, liquor, medical products, and toiletries and cosmetics.
Formerly soda ash is used in water treatment through a paper plant and in coating formulations, and can be a primary part in some pulp digestion and bleaching processes. In the Kraft paper process, soda ash plays a major role both as a vital component for minor pulping and as an intermediate chemical formed in the regeneration process.
Soda ash has been replaced for caustic soda when caustic prices rise in consequence of its direct relationship to chlorine production.