Iron Removal by physical-chemical ways
| Iron is one of the most abundant metals of the Earth's crust. It occurs naturally in water in soluble form as the ferrous iron (bivalent iron in dissolved form Fe2+ or Fe(OH)+) or complexed form like the ferric iron (trivalent iron: Fe3+ or precipitated as Fe(OH)3). The occurrence of iron in water can also have an industrial origin ; mining, iron and steel industry, metals corrosion, etc. |
In general, iron does not present a danger to human health or the environment, but it brings unpleasantness of an aesthetic and organoleptic nature. Indeed, iron gives a rust color to the water, which can stain linen, sanitary facilities or even food industry products. Iron also gives a metallic taste to water, making it unpleasant for consumption. It can also be at the origin of corrosion in drains sewers, due to the development of microorganisms, the ferrobacteries.
In aerated water, the redox potential of the water is such as it allows an oxidation of the ferrous iron in ferric iron which precipitates then in iron hydroxide, Fe(OH)3, thus allowing a natural removal of dissolved iron.
4 Fe2+ 3 O2 --> 2 Fe2O3
Fe2O3 + 3 H2O --> 2Fe(OH)3
The form of iron in water depends on the water pH and redox potential, as shown in the Pourbaix diagram of Iron below. Usually groundwater has a low oxygen content, thus a low redox potential and low pH (5.5- 6.5)
Pourbaix diagram of Iron
However ground waters are naturally anaerobic: so iron remains in solution and therefore it is important to remove it for a water use.
Iron is often found in water in complexed forms. In order to be eliminated, iron complexed requests a coagulation stage, which comes in between oxidation and filtration.
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