Raw materials for Glass Manufacturing:

Solvay’s Process: This process produces light soda ash. Soda Ash thus produced has a specific weight of 500 kg/m³. This specific weight is sufficient for using in detergent and chemical application. But for glass manufacturing higher specific weight of atleast 1000 kg/m3 is required.

The light soda ash produced in the solvay’s process can be converted to dense soda ash by the process of re-crystallisation. The light soda ash is transformed by re-crystallisation into sodium carbonate monohydrate and then into dense soda ash after dehydration. Dense soda ash can also be produced by compaction. The approximate production capacity of soda ash across the globe is about 43 million tons per year and Solvay’s process is the most widely used production method. About 25 million tons of the soda ash is produced by the solvay’s process. Theoretically Soda Ash in Solvay’s process is produced by the chemical reaction between Sodium Chloride and Calcium Carbonate

2NaCl + CaCO₃ —– > Na₂CO₃ + CaCl₂

But this equation cannot be practically converted into process. Practically the method for soda ash production is different.

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Ceramic – Glass

Raw materials for Glass Manufacturing:

Preparation of Soda Ash:

Soda Ash is present naturally in evaporated lake beds. Also it can be prepared from ashes of any plant or from sea weeds. But the world demand cannot be met by these natural resources. There are different synthetic methods for producing Soda Ash. It is only possible by these methods that the high demand of soda ash in glass and chemical industry can be met. Of these processes, the Solvay’s process is the most widely used process for manufacturing soda ash. This Solvay’s process is also called as the Ammonia Soda Process.

This process has a number of advantages to its credit. First being that the raw materials used for production are readily available anywhere in the world. The main raw materials used are Brine and Lime Stone. Lime Stone is naturally available. It can be mined and processed for beneficiation and grounded for size distribution and used in this process. Brine is naturally available in form of sea water. If the proposed location is not near sea, then salt can be dissolved and used in the process as Brine. Another advantage is that the ammonia used in the process can be fully regenerated in the process and recycled for use again. Also, to the original Solvay process there are so many modifications followed by different manufacturers. One is that the process can be modified to produce ammonium chloride as a by-product. This is an additional value add, as ammonium chloride has a very good use as fertilizer for rice cultivation. Other well known processes for soda ash manufacturing are Trona Process, Nacholite and Carbonation of Caustic Soda. We shall see the other processes later and we shall discuss in detail the Solvay’s process in the coming blogs…

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Ceramic – Glass

Raw materials for Glass Manufacturing:

We shall seen in detail the applicational value of Soda Ash. Soda Ash has a number of industrial application and as mentioned the main one being in glass industry.Soda ash is used in the production of flat glass for the housing, commercial building and automotive industries; for containers, fiberglass insulation, and for a host of other glass products such as light bulbs, tableware and decorative glass blocks. Though this is the costliest material used for glass manufacturing, this material does its part of cost saving too.. It is this material that helps melt the silica at a much lower temperature. This means savings in the form of energy used and also increase in the life time of the furnace. Dense type of the soda ash is used for glass manufacturing, other uses of soda ash includes

• Use in Detergent Manufacturing
• As Electrolytes
• As bonding agent in dyes (bleaching fabric)
• As a water Softener
• As an Food Additive (as acidity regulator and anti caking agent)
• As an wetting agent In Brick manufacturing
• As a foaming agent in tooth pastes
• Used in Paper Industry

The medium dense version of soda ash is used for making detergent products and light dense soda ash is used in chemical processes. The above mentioned application list shows that soda ash is a very versatile product and has an ample of applications that keeps this product in demand. Setting up a Soda Ash Manufacturing plant will be an ideal investment for people who want to set up an industry and also see high returns.

Ceramic – Glass

Raw materials for Glass Manufacturing:

Having seen the specification of Silica Sand for Glass manufacturing and techniques for silica sand beneficiation, we shall now see the required specifications and manufacturing process types for the next most important raw material used in Glass manufacturing - Soda Ash. As mentioned in the earlier blogs, 16% of the batch weight is Soda Ash and this is the most costly raw material used in the batch. Soda Ash is nothing but sodium carbonate. Soda Ash is mainly classified into two types; Light Soda Ash and Dense Soda Ash. Of this the dense soda ash variety is the preferred type for using in the glass manufacturing process.

About 50 percent of the globally produced soda ash is used in glass manufacturing process. This is used mainly for producing flat colourless glass variety. The flat glass targets end use as windows in building construction and in automobiles. Soda Ash is also used for making container glasses. Soda ash acts as the fluxing agent. It is an essential ingredient because it reduces the furnace temperature necessary to melt the silica, thus reducing the energy required to produce glass. Soda ash is generally used to supply the bulk of the alkali element needed in glass making because it is a cost-effective source of Na₂0.

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Ceramic – Glass

Raw materials for Glass Manufacturing:

Having seen the processing methods of silica sand, we shall now see the desired specification of silica sand for different varieties of glass.

Specification of Silica Sand for Optical Glass

Silica (SiO2) —————————– 99.5% (Min)
Iron Oxide (Fe2O3) ——————– 0.008% (Max)
Titanium (TiO2) ———————— 0.030% (Max)
Cr2O3 ———————————— 0.0002% (Max)

Specification of Silica Sand for Higher Grade Decorative Glass

Silica (SiO2) —————————– 99.5% (Min)
Iron Oxide (Fe2O3) ——————– 0.013% (Max)
Cr2O3 ———————————— 0.0002% (Max)

Specification of Silica Sand for Colourless Container Glass

Silica (SiO2) —————————– 98.5% (Min)
Iron Oxide (Fe2O3) ——————– 0.030% (Max)
Cr2O3 ———————————— 0.0006% (Max)

To be Contd…..

Ceramic – Glass

Raw materials for Glass Manufacturing:

For Silica Sand Processing, it is best to use gravity separation method than froth floatation process. The gravity separation method in combination with magnetic separation process will be the best cost effective silica beneficiation technique. The initial investment required for gravity separation and froth floatation does not vary much from each other. However there is a very significant difference in the operating costs of one another. The operational cost is higher in froth floatation process when compared to gravity separation. This difference in operation cost is mainly due to power consumption. Though the power required for gravity separation and froth floatation is same for the main circuit, the froth floatation process will consume additional power in the conditioning and floatation process. Another reason for this cost difference is the higher maintenance requirement of the floatation cells. Also the gravity separation process does not demand any additional costs on requirements of chemicals. The capacity utilized in gravity separation process is higher when compared to froth floatation process. So this will be an added advantage in gravity separation process. All the above said points make gravity separation better than froth floatation process for silica sand beneficiation.

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Ceramic – Glass

Raw materials for Glass Manufacturing:

• Contaminant Removal Process: Froth Floatation process can be followed for removing mineral contaminants in acidic conditions. In froth floatation process a cationic collector is used for removing mineral contaminants like feldspar and anionic collectors for removing mineral contaminants like iron or iron coated grains.
• Classification: After removal of contaminants, the sand has to classified to separate the grains into finely and coarse particles. Hydro Cyclones, screw classifiers or screens can be used for this separation process.
• De-watering: After the classification, the sand has to go through a de-watering process to remove the water content. Generally Hydro Cyclones or Dewatering screens are used in this step.

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Ceramic – Glass

Raw materials for Glass Manufacturing:

• Contaminant Removal Process: There are a few variety of methods followed for removing contaminants from the sand. The selection of the method mostly depends upon the type of contaminant present. The methods are gravity separation, magnetic separation and froth floatation. High specific gravity mineral particles can be removed by gravity separation method. Reichert cone concentrators or spiral separators are the general equipments used in gravity separation method. Magnetic Separation methods are used for removing magnetic mineral contaminants. Magnetic Drum separator is used for removing highly susceptible magnetic materials. As the magnetic drum separators are of low intensity they can remove only the highly susceptible magnetic contaminants and not effective for low magnetic materials. For removing low susceptible magnetic contaminants, a high intensity magnetic separator (HIMS) has to be used.

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Ceramic – Glass

Raw materials for Glass Manufacturing:

Following are the steps followed in processing silica sand for making it usable for glass industrial application.

• Preliminary Screening: The raw mined sand is first taken through an initial screening for removing
  trash materials. Vibrating Screen is the most commonly used equipment for this operation.

• Washing Process: After preliminary screening, the sand is washed well to remove material coatings
  and to liberate the sand particles. Washing equipments like rotary scrubber in combination with trammel screen or a classifying washing bin with hydro cyclone equipment can be used for this process. A screw classifier with hydro cyclone can also be used. Attrition of the sand in Attritor mills will also make an effective washing process.

To be Contd..

Ceramic – Glass

Raw materials for Glass Manufacturing:

As mentioned in the previous blog, Silica Sand of lower grade has to be processed before making it usable for higher grade applications. Equipments which are used for traditional mineral sand separation can be used for silica sand also. In terms of economics, it is better to follow gravity separation method than froth floatation process. In addition the size distribution is also an important aspect that plays a major role in both material handling and melting process. We shall discuss in detail the silica processing techniques which can be followed. Silica Sand is generally processed by following wet methods. We shall discuss in detail the steps involved in processing the silica sand in the coming blogs. Generally it is not necessary to follow all of the above steps. The process techniques followed varies from mine to mine depending upon the nature of the silica sand.

To be Contd…