Iron makes up about 5% of the total mass of minerals in the earth’s crust. Despite the fact that it is in a bound state in solid minerals, due to its rather high chemical activity, it is prone to interactions with the acidic components of water. Therefore, compounds of this element are often found in well water and less often in surface water.
- Metallic taste;
- Red plaque on plumbing, fittings;
- A gelatinous red precipitate appears in the initially clear water in the open air;
- The same happens in the process of cooking (when water is heated);
- The sediment does not settle to the bottom, but hangs in the water column (forms a colloid);
- Dark brown stubborn plaque;
- Colored items fade after washing;
- Drinks (for example, compote) darken.
How much iron is in the water?
For water, the “Total iron” indicator is normalized, which includes iron bound in all forms. The iron content in water is measured in milligrams per liter (mg/l).
The maximum allowable iron content for drinking water is 0.2 mg/l, for making drinks it is 0.1 – 0.2 mg/l. Concentrations above 0.2 mg/l or more result in a metallic taste and a yellowish tinge.
Water can contain several types of iron (several forms). Total iron is the sum of the concentrations of all types of iron found in water.
The effect of iron on the human body
Iron is an important trace element that is involved in the process of hematopoiesis. In the bone marrow, with the participation of iron, a special blood protein, hemoglobin, is synthesized, which is important for saturating the brain and other organs with oxygen. Also, iron plays a serious role in the functioning of the thyroid gland and takes part in the formation of many protein structures, in particular enzymes. Therefore, a lack of iron in the body is harmful, but water cannot be its source, since a very small amount of it is absorbed from it.
Increased iron content in the body has side effects. With the constant use of water with an abnormal amount of iron, its toxic effect is manifested. The first consequences of the regular use of such water are disturbances in the work of the gastrointestinal tract: flatulence, bloating, nausea.
Allergic reactions can also develop, less often hemochromatosis, as a result of which the liver, cardiovascular and endocrine systems are systemically damaged.
Chemical transformations of iron in water
In water, iron is most often found in the form of Fe2+ and Fe3+ ions, which form organic and inorganic compounds. So, in surface waters, iron is contained in natural organic complexes (humates), which form colloidal suspensions.
In groundwater, in the absence of dissolved oxygen, it is usually found in the form of soluble compounds with Fe2+ ions. Such features are due to the fact that Fe2+ is unstable and, when exposed to oxygen from the air, quickly transforms into Fe3+
This chemical process can be observed in well water with a high iron content: immediately after pumping, it is crystal clear (dissolved Fe2+) after standing in an open container in air or heating, depending on the content, the water may become cloudy and acquire a brown tint (Fe4+).
Types of glandular compounds
- Ferrous iron (Fe2+) is completely soluble in water. It can be found in well waters, as we wrote above. As it oxidizes (in the open air), the water acquires a yellowish tint.
- Trivalent iron – it forms a fine precipitate, sometimes flakes (“rust”), which are removed using mechanical filters. But more often, water contains a mixture of Fe2+ and Fe3+, so classical catalytic materials are used.
- Colloidal iron – This is iron, the particles of which are in suspension. This is due to the fact that they are very small (from 1 to 100 microns) and are not able to settle under the force of gravity. It is removed during the coagulation process, in which substances are introduced into the water that cause particles to stick together and settle. Then they are mechanically filtered.
- Organic Iron – Organic iron compounds are compounds of iron with anions of organic compounds such as tannins or humic acid. These impurities can be colorless, yellowish or red. Such iron is called organic, or complex, it is the most problematic due to its organic nature, it is removed by sorption, oxidation and microfiltration.
- Bacterial iron – There is a special kind of bacteria that use iron in metabolism, in other words for nutrition. Often it forms a film on the inner surface of pipelines. It is found in natural waters, as well as in some pipelines.
Removing iron from water
The classical technology for the removal of iron and manganese is based on aeration mainly with air oxygen and subsequent filtration on mechanical filters. This method is considered obsolete, since it is much inferior to modern catalytic technologies, both in terms of efficiency and energy consumption, as well as in terms of instrumentation and space occupied.
The simplest household method is mechanical filtration on main filters with polypropylene cartridges, they allow you to retain already oxidized iron (reddish turbidity) and somewhat contribute to its oxidation. The purpose of this stage is not to remove iron from the water, but only to mechanically clean it before subsequent filters. Backfill columns with inert chemical materials are often also useful.
The most modern method of removing all forms of iron from water are filters with catalytic materials. These are natural and artificial materials that contain an oxidation catalyst on the surface or in the porous structure of the granules.
Special attention should be paid to main filters for removing iron. Two BB20 flasks in series can be a convenient solution for iron removal in the home. Filters of the Ecosoft Aquapoint line are a solution designed to be as convenient as possible for domestic use.
Ecomix unique material developed by Ecosoft specialists. It contains a mixture of five components.
- FerroSorb is a catalytic sorbent that removes iron and manganese compounds.
- HumiSorb is a sorbent that removes organic and organo-iron compounds.
- Cation – an ion exchange resin that traps calcium and magnesium ions, exchanging them for safe sodium, thereby softening the water.
- Inert lightweight material to remove oxidized iron and facilitate loosening prior to backwashing.
- Quartz sand to evenly distribute the water flow in the loading layer.