Polluted(Waste) water can be treated and purified by using ferrate(VI) as the sole reagent. It is a very good reagent for waste water treatment because of its strong oxidising tendency and the non-toxic products after reaction with waste water and hence do not have any adverse effects towwards the environment or human health. Hence, the ferrates are termed as ‘green chemical’ and interestingly the single chemical possess several properties, which ultimately prompted to explore further the chemistry of ferrates and also their possible applications in various areas of interests.
The term ferrate is usually referred to the higher valence states of Fe(III), it may include +4, +5, +6 states. Among all these states, Fe(VI) seems to be the best konwn and well studied as due to its stability and occurence. Due to its high oxidizing capacity, it has an enhanced attention to be applied in water treatment process as it can easily oxidize even stable organic and mineral materials, bactericide agents etc.. The strong oxidizing capacity of the ferrate(VI) initiated various possible applications in (i) the development of a high capacity battery(so called super iron battery) (ii) waste and drinking water disinfections and purification along with coagulation/flocculation. The second point recieved potential interest as this compound can oxidize within few seconds the stable organic/inorganic compounds present in water without forming carcinogenic or mutagenic compounds as it may happen while chlorination. The reduction product Fe(OH)3 is an extremely good adsorbent and coagulant for treating the waste and also having no health hazard.
4FeO42- + 10H2O _______________ 4Fe(OH)3 + 8OH- + 3O2
The treatment of waste water comprises primarily two steps(i) to disinfect the harmful micro-organisms (eg. bacteris & viruses ) by using disinfectant along with the degradation/oxidation of organic matters followed by (ii) the coagulation/precipitation/sedimentation/filtration of the wastes.
Disinfection must be designed as to kill the harmful microorganism and to get the water free from any harmful pathogens/microorganisms. It was reported that ferrate(VI) is very effective to kill Escherica coli ( E. coli ) and total coliforms f2 coliphage at low concentrations and And a survival ratio of the virus decreased rapidly within 10 min after it was treated with ferrate(VI). Ferrate also inhibited the respiration of the bacterium sphaerotilus; suggesting potential role in treating sludge for disinfections. These proved excellent properties of ferrate to kill wide variety of bacteris and virus in water and waste water treatment processes.
On the other hand due to its strong oxidizing capability it can effectively and efficiently be used foe the degradation of even stable organic/inorganic matter in the waste water. Moreover, the degradation completed within a few seconds and giving out the harmless oxidizing by-products. It was reported that Fe(VI) oxidize various synthetic organic matters viz. benzene, chlorobenzene, allylbenzene and phenol etc. In line it is fairly effective to degrade the nitrogen-containing, sulphur-containing compounds and several organic matters as well. Potassium ferrate(VI) is found to be much effective over lime in oxidizing reduced sulphur and nitrogen compounds and also mitigating odors from conditioned sludge.
Several other reports also stated that hydrogen sulphide, mercaptans and amines can be degraded efficiently by ferrate(VI) giving out the non-toxic by-products(eg. sulphide degraded to sulphate).
8HFeO4- + 3H2S + 6H2O ____________ 8Fe(OH)3 + 3SO42- + 2OH-
The surfactants are not directly toxic but inhibit both setting of floating particles and dissolution of atmospheric oxygen into natural waters, causing several environmental concerns. The strong oxidizing capability of ferrate(VI) was prompted to investigate the possible oxidation of surfactants particularly the CPC(Cetylypyridinium chloride, C5H5N+ (CH2)14 CH3. H2O Cl- ). The study carried out at pH 9.2 reported that ferrate(VI) can remove CPC completely and the TOC(total organic carbon) also reduced to 95%. Ferrate(VI) has also been used to remove arsenic from river water. It was reported that the practical efficiency of the arsenic removal can be achieved by addition of small amounts of Fe(III) (a supplement coagulant).
2Fe(VI) + 3As(III) ______________ 2Fe(III) + 3As(V)
Ferrate(VI) is found to be potentially applicable in waste water treatment as due to its strong oxidizing tendency.It can effectively and efficiently oxidize stable organic/inorganic matters along with variety of pathogens viruses etc. and the by-product obtained followed by the oxidation are non-toxic hence it can be used as a ‘green chemical ‘ for such studies. Also the reduction of ferrate(VI) into ferrate(III) in the form of Fe(OH)3 at alkaline pH is found to be fairly good coagulant/precipitant and adsorbent. Hence the single chemical serves as an oxidant, disinfectant, coagulant, precipitant and adsorbent etc..