Aluminium sulfate, also known as cake alum or aluminum salt, is a chemical matter with the formula Al2(SO4)3. It is applied in various industries, such as waste water treatment industry, water purification and paper industry.
Aluminum sulfate is an odorless white or off-white crystalline solid or powder. It has the ability to absorb and hold water from surrounding, and this property is called hygroscopic. It’s also water soluble, non-volatile and non-flammable. Aluminum sulfate is made by reacting aluminum hydroxide and sulfuric acid. It is extremely acidic. When combined in solution with water, pH can be less than two; it can burn human skin and also corrodes metal.
Aluminum sulfate is dangerous if inhaled or swallowed. The inhalation will cause coughing and potentially shortness of breath. Eating or swallowing aluminum sulfate can make severe irritation of the intestines and stomach. An affected person may get vomiting, nausea, and diarrhea. If it contacts with skin or eyes, will cause irritation, redness, itching, and pain. Besides that, adding water to aluminum sulfate can cause sulfuric acid to form.
Generally, aluminum sulfate can be synthesized by mixing aluminum hydroxide. Al(OH)3 reacts with sulfuric acid H2SO4 and produce aluminium sulphate as shown:
2 Al(OH)3 + 3 H2SO4 ---> Al2(SO4)3.6H2O
In industrial scale, the production of aluminum sulfate is carried out in several stages:
1. Mixing aluminum hydroxide with sulfuric acid
Sulfuric acid is fed into the reaction vessel which is heat resistant and acid resistant. Then aluminum hydroxide is added to the vessel and heated. However, the aluminum sulfate manufacturing methods above requires high temperature (about 100oC to 130oC) and takes more time to produce (about 10 minutes to 2 hours) which makes it less efficient. Further, to increase the efficiency, high concentration of sulfuric acid as the reactant is necessary in this process.
2. Adding Nitric Acid into the vessel
Recently, a more advanced method has been developed to increase the efficiency of aluminum sulfate production, which can be held at a lower temperature, shorter time, and lower concentration of sulfuric acid without using a heating source. In this process, another compound is added to the reaction, which is nitric acid or hydrogen peroxide solution.
3. Separate aluminum sulfate from water
The product is obtained from the reaction vessel is concentrated aluminum sulfate diluted in water. To separate aluminum sulfate from water, the solution is cooled and is followed by evaporating process.
Aluminum sulfate is well known for waste water treatment. Because of its non-toxicity, Alum (Aluminum Sulfate) is used in a water treatment reactor to purify drinking water. It is also used to maintain the stability of the lake or reservoir. Excess Phosphorus in the lake water induces â€˜booming algaeâ€™, Alum can reduce the phosphorus concentrations and maintain the phosphorus normal concentration.
Aluminum sulfate is used as a buffer solution for balancing of soil PH. The flower changes its color when the PH of soil is different from standard. Gardeners even use aluminum sulfate to increase the acidity of soil.
Aluminum sulfate is also used for waterproofing and helps to accelerate the setting concrete. Aluminum sulfate is also used to produce antiperspirants and firefighting foaming, lubricating compositions, sizing paper, baking powder, molluscicide, material for fire retardant, catalyst, and decolourisation agent. Moreover, it is also applied as a coagulant to absorb the impurities that can be removed as particulate easily by filtration. Moreover, Aluminium sulfate is widely applied in the textile industry as well.