| Chemical Industry-Zeolites |
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Caustic soda is used in the production of Zeolites.
Zeolites are crystalline, hydrated aluminosilicates with a framework structure. They have a three-dimensional polianionic network constructed of SiO4 and AlO4 tetrahedra linked through oxygen atoms. The pores contain water and cations to balance the negative charge of the framework. These cations are mainly alkali metal or alkaline earth, and can be exchanged, giving to zeolites its main use : binding cations.
A hydrothermal reaction of sodium aluminate, sodium silicate and caustic soda in an aqueous solution at elevated temperature and under high pressure is carried out for this production process. A strong basicity is necessary to build the cristallized form between silica and aluminium ions with oxides. Caustic soda is used for this synthesis. Zeolites containing a high amount of silica are synthesised at high temperatures and pressures, while low-silica zeolites are usually crystallized at 70 – 100 °C and with a pH in the range of 10 – 14, in a caustic soda solution. Different ratios between silica and aluminium contents give different types of zeolites.
Due to its high of cation binding capacity, zeolites are used as a component of detergents; as adsorbents, for separating and purifying substances; as catalysts, in a great number of important processes in the chemical and petrochemical industries. And they are used also in a great number of uses where the cations binding capacity is needed.
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