(micro)pollutants in the system; self-decompositions of all Fe(VI), Fe(V), and Fe
(IV) species; reactions between all iron species from iron(VI) to iron(II) and/or
oxygen species (i.e., H 2 O 2 ) formed from either self-decompositions or during
oxidation reaction of Fe(VI) with micropollutants (Sharma et al. 2015). Moreover,
radicals of oxidized compounds formed during the degradation reaction can further
react with mother compounds, with Fe(VI), Fe(V), Fe(IV), or with other radicals
from different substances etc.
Dyes, hardly biodegradable (in)organic substances, can be also present in wastewaters (Lubello and Gori 2004). They can have toxic, carcinogenic, teratogenic, and
mutagenic properties, some of them inhibiting the photosynthesis and biochemical
pathways of aquatic animals and plants (Rai et al. 2018). Ferrate(VI) has been found
to have great potential for their effective degradation. During the oxidation process,
less toxic products are formed (Barışçı et al. 2016).
8.8 Removal of Heavy Metals and Metalloids by Ferrates
Heavy metals associated with exposure of highly toxic compounds of lead, cadmium, chromium, mercury, arsenic and others represent a severe threat to human
health. Though toxicity and negative health effects of heavy metals have long been
recognized, metals are widely used in a range of products including household
appliances, paints, agriculture, motor vehicles, and electrical components. Contamination of all water types represents a growing danger in many countries all over the
world because of the severe impact of such compounds on the population’s health.
For example, Bangladesh, some parts of India, Nepal, and Vietnam are countries
where arsenic and heavy metals contamination of surface and drinking water is
particularly large, showing an upsurge of poisoning cases and, overall, an increased
life-risk for a large fraction of human and animal populations. Apart from contamination of toxic metals, phosphates often enter the environment. The presence of
high levels of phosphorus input into water causes eutrophication that adversely
affects aquatic ecosystems and water quality. The specific effects of excess phosphorus include blooms of harmful algae that can release toxins, create dead zones
(or hypoxia in water), cause fish death, and foul taste and odor of drinking water
(Faridmarandi and Naja 2014; Järup 2003).
For efficient removal of metal ions, the remediation process should combine the
properties of an oxidant, high adsorption capacity (with the low sorbent/metal ion
ratio), and it should also enable at least partial incorporation of metal ion into the
structure of the reaction products, thus preventing the metal(loid) leaching back to
water. The ferrates can meet all the mentioned criteria and can act as a highly
efficient constituent in various water treatment technologies.
Several studies have explored the use of ferrate(VI) for removal of inorganic
pollutants, in particular toxic heavy metals from various water samples (Table 8.2).
The removal efficiency can reach, in the case of some heavy metals (Zn, Cu, Mn),
almost 100% (Rai et al. 2018). Fe(VI) has the greatest potential to remove also other
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L. Machala et al.
(IV) species; reactions between all iron species from iron(VI) to iron(II) and/or
oxygen species (i.e., H 2 O 2 ) formed from either self-decompositions or during
oxidation reaction of Fe(VI) with micropollutants (Sharma et al. 2015). Moreover,
radicals of oxidized compounds formed during the degradation reaction can further
react with mother compounds, with Fe(VI), Fe(V), Fe(IV), or with other radicals
from different substances etc.
Dyes, hardly biodegradable (in)organic substances, can be also present in wastewaters (Lubello and Gori 2004). They can have toxic, carcinogenic, teratogenic, and
mutagenic properties, some of them inhibiting the photosynthesis and biochemical
pathways of aquatic animals and plants (Rai et al. 2018). Ferrate(VI) has been found
to have great potential for their effective degradation. During the oxidation process,
less toxic products are formed (Barışçı et al. 2016).
8.8 Removal of Heavy Metals and Metalloids by Ferrates
Heavy metals associated with exposure of highly toxic compounds of lead, cadmium, chromium, mercury, arsenic and others represent a severe threat to human
health. Though toxicity and negative health effects of heavy metals have long been
recognized, metals are widely used in a range of products including household
appliances, paints, agriculture, motor vehicles, and electrical components. Contamination of all water types represents a growing danger in many countries all over the
world because of the severe impact of such compounds on the population’s health.
For example, Bangladesh, some parts of India, Nepal, and Vietnam are countries
where arsenic and heavy metals contamination of surface and drinking water is
particularly large, showing an upsurge of poisoning cases and, overall, an increased
life-risk for a large fraction of human and animal populations. Apart from contamination of toxic metals, phosphates often enter the environment. The presence of
high levels of phosphorus input into water causes eutrophication that adversely
affects aquatic ecosystems and water quality. The specific effects of excess phosphorus include blooms of harmful algae that can release toxins, create dead zones
(or hypoxia in water), cause fish death, and foul taste and odor of drinking water
(Faridmarandi and Naja 2014; Järup 2003).
For efficient removal of metal ions, the remediation process should combine the
properties of an oxidant, high adsorption capacity (with the low sorbent/metal ion
ratio), and it should also enable at least partial incorporation of metal ion into the
structure of the reaction products, thus preventing the metal(loid) leaching back to
water. The ferrates can meet all the mentioned criteria and can act as a highly
efficient constituent in various water treatment technologies.
Several studies have explored the use of ferrate(VI) for removal of inorganic
pollutants, in particular toxic heavy metals from various water samples (Table 8.2).
The removal efficiency can reach, in the case of some heavy metals (Zn, Cu, Mn),
almost 100% (Rai et al. 2018). Fe(VI) has the greatest potential to remove also other
192
L. Machala et al.