Ferrates are environmentally friendly treatment ions that effectively treat a wide range of contaminants in water and wastewater. A need for an adequate supply of clean water is an issue faced by communities all over the world, particularly in semi-arid and arid places, where the only source of potable water is treated wastewater. Treating water that would otherwise get wasted is an effective way to renew precious fresh water resources.
Iron VI – Background
For many years, water treatment has been accomplished by methods, such as filtration, use of disinfectants and ultraviolet radiation of water. However, each of these methods has its shortcomings. For example, filtration cannot reduce contamination levels by even 99% as it is ineffective against water-borne viruses. Disinfectants like chlorine leave behind a toxic byproduct, and drinking chlorinated water has been linked to colon and rectal cancer.
Hence, there arose an acute need for a new treatment method that did not form any toxic byproducts, while successfully treating a wide range of water-borne contaminants. The discovery of an oxidant called ferrate iron VI (or iron 6) soon answered this need.
Although iron is commonly found in +2 and +3 oxidation states, stronger oxidizing environments were found to produce higher states (+4,+5 and +6) of iron. Iron 6 (or iron VI), in particular, has been found to treat wastewater very effectively. Iron VI gets spontaneously oxidized when it comes into contact with water. The byproducts formed are molecular oxygen and ferric oxide [Fe (III)], both of which are non-toxic. The ferric oxide byproduct is a powerful coagulant which helps in the removal of pollutants that exist in the form of metals, non-metals, humic acids and radionuclides.
Iron VI’s effect on water-borne micro-organisms and pollutants
In a study on the effect of iron VI on various pollutants, such as hydrogen sulphide, thiourea, thioacetamide, cyanide and thiocyanate, it was found that iron VI reacted with each of them and destroyed them, leaving behind non-toxic byproducts. Sulphide turned into sulphate, and cyanide into cyanate and nitrate. With such promising results, it became necessary to look for ways to produce iron VI in laboratories. Researchers found that three different techniques – wet synthesis, dry synthesis and electrochemical synthesis – can produce the ferrate iron VI.
Iron VI disinfection has been examined for Escherichia Coli and coliforms, and was shown to achieve more than 99.9% removal rate of these bacteria. Iron VI also effectively destroys viruses, such as those belonging to the family Leviviridae (Enterobacteria phase f2 and Enterobacteria phage Qb), rapidly inactivating them even at low concentrations. Algae removal with alum was found to significantly increase when low doses of iron VI was added to the treatment water. Additionally, iron VI also destroys other toxins like microcystins that are produced by cyanobacteria. Iron VI has the ability of acting as both a coagulant and an oxidant in effectively remediating arsenic from source water by reducing arsenic levels.
In conclusion, research findings have substantiated the ability of iron VI to kill many chlorine-resistant organisms and toxic substances in aquatic environments that are difficult to get rid of by other techniques. Drinking contaminated water has led to several cases of illness and death in the world. With the Worth Health Organization estimating that a billion people do not have access to continuous supplies of drinking water, it is hoped that ferrates, such as iron VI, will help remedy the situation by becoming a safe water-treatment option.
Reference:
1. Sharma V.K, Kazama F, et al, (2005), Ferrates (iron(VI) and iron(V)): Environmentally friendly oxidants and disinfectants, Journal of Water and Health.
