Coagulants are used for treatment of all kinds of water
Coagulation is the oldest known water treatment method
In industry, coagulants are frequently used for water treatment
In drinking water production, coagulants remove particles, humic substances and colour
Coagulants produce healthy and enjoyable drinking water
Coagulants are used for treatment of all kinds of water

Sustainable usage of water is vital in a world where many people do not have adequate access to this scarce resource. For industry, coagulants provide a method of reusing water in a cost-effective way that does not comprise the industrial process. Onsite treatment of waste water increases the number of times the same water can be used and contributes favourably to environmental measurements such as fresh water usage.

Water for industrial use must be free from contamination and corrosive matter. Achieving this level of quality requires proper chemical treatment with coagulants. Use of untreated water can cause problems in heat-transfer and overall process quality.

In addition to the paper industry, inorganic coagulants (particularly those containing ferrous sulfate) have important applications in the agricultural and cement sectors.

Agricultural Crop Protection

Plants need nutrients from the soil in order to make chlorophyll. Chlorophyll gives leaves their green colour and is necessary for the plant to produce the energy it needs to grow, and resist disease or insects.

Deficiencies in trace elements can cause the plant to suffer. Iron deficiency – known as chlorosis, causes leaves to yellow, reducing their ability to produce chlorophyll.

Treatment of chlorosis requires the application of an iron-rich fertiliser which can be easily absorbed by the plant. A simple approach is to apply a mixture of iron sulfate to the soil.

Copperas (ferrous sulfate heptahydrate) can be applied to crops. A moist green salt, commonly known as iron vitriol or green vitriol, copperas has the consistency of wet snow. It dissolves easily in water which can be applied to iron-deficient crops and absorbed quickly by the plants.

Copperas is commonly available as a by-product created during the finishing of steel and the production of titanium dioxide using the sulfate process.

Chromate Reduction in the Cement Industry

Raw materials used in the production of cement contain water soluble chromate (Cr6+) which penetrates human skin to cause allergic reactions and diseases. To protect people and the environment, chromate must be rendered harmless through reduction. Since 17 January 2005 all European Union member states have had to limit the amount of Cr6+ in cement to 2 parts per million (ppm) dry weight (Directive 2003/53/EC).

To ensure that the chromate limit is met an economical reducing agent such as dried copperas (also known as ferrous sulfate) can be used.

Applications

Paper Industry
Inorganic coagulants are used in two critical parts of the paper production process: sizing and retention.
Waste Water
To ensure the water does no harm to people or the environment when it is released, waste water must be treated to reduce the level of contaminants to acceptable levels.
Other Applications
In addition to their role as inorganic coagulants, aluminium and iron salts are used in many other applications.
Industrial Uses
For industry, coagulants provide a method of reusing water in a cost-effective way that does not comprise the industrial process.
Drinking Water
In order to protect our health, all drinking water must be cleared of pathogens and impurities before it is used.

FAQs

How long have inorganic coagulants been used in water treatment?

Alum has been used at least since Roman times for purification of drinking water (cf. Chemistry of Water Treatment – Samuel D. Faust, Osman M. Aly (1999)). It is also reported that Egyptians used alum coagulant as early as 1500 BC to reduce the visible cloudiness in the water.

In the modern times, London became the first city to mandate that drinking water should be purified using coagulants, after an outbreak of cholera in 1854. By the start of the 20th Century, scientists better understood the role of inorganic coagulants in water purification and their use spread worldwide. The treatment of waste water with inorganic coagulants started on a large scale in the 1950s.

 

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