Water treatment process. Ceramic production forms two major streams of wastewater.
The first stream is formed at the stage of preparing the slip casting of ceramic products, their mandrel, filling and bonding of parts and includes, mainly, a large amount of suspended clay particles and glycerol. The second stream is formed in the preparation of ceramic colors and contains pigments, which are made from different metal oxides. Since the streams are different and require different cleaning methods, it is not recommended to mix the streams and use separate treatment plants for each of them instead.
The wastewater with suspended particles of clay needs coagulation and sorption treatments to return the purified water and sedimented clay into the production process. The stream containing pigments must pass through coagulation treatment. Since this mixture is not used in the ceramic industry, it can be added into molding mass in production of bricks.
Coagulation treatment is used for natural and industrial wastewater mainly to purify it from colloidal suspension contaminants. The essence of coagulation is adding special coagulants. In most cases they are aluminum and iron salts, as well as their mixtures, also used are the salts of other polyvalent cations such as magnesium and titanium. Since the coagulants are the salts of strong acids and weak alkalis, they are hydrolyzed to form hydroxide salts which have a developed surface and can absorb various impurities. These particles coagulate with colloidal substances. The most commonly used today are aluminum, steel, and mixed aluminium-iron coagulants, which are mixtures of aluminum and iron salts.
Aluminium compounds used as coagulants are aluminum sulfate, aluminum hydroxysulfate, aluminum chloride, aluminum sulphate, sodium aluminate.