Document Type : Review article
Department of Chemical Engineering, Shiraz Branch, Islamic Azad University, Shiraz, Iran
Zeolites are a group of hydrated aluminosilicates crystallized with fine pores that contain equilibrium cations of alkaline and alkaline earth metals (Na+, K+, Mg2+ and Ca2+) and reversibly absorb and release water. One of their characteristics is that they are able to reabsorb and re-release water and exchange some of their own building cations without major changes in their building. The presence of metals in the water of rivers and seawater poses a serious threat to the health of the aquatic community, the most common of which is damage to the gills of fish. Metals such as lead, cadmium, copper, arsenic, nickel, chromium, zinc, mercury, iron are known as heavy metals. These metals tend to accumulate in environmental systems and seriously contaminate soil and water, which can be harmful to humans, animals and plants even in low concentrations. Unlike biodegradable organic matter, metal ions are not removed from aquatic ecosystems by natural processes, which encourages scientists to develop new methods for removing heavy metal ions from water. As a result, in many countries, laws have been introduced to control water pollution. Various regulatory bodies have set maximum limits for the discharge of toxic heavy metals into aquatic systems. However, metal ions with a much higher concentration than usual are discharged into the water by industrial activities, leading to health hazards and environmental degradation.