Iron is present in water in the form of divalent and trivalent ions. How to clean drinking and technical fluid from these contaminants? Actual problem for an ordinary family and a large enterprise. Let us consider the reasons on which the solubility of iron in water depends, the forms of pollutants, and methods for removing ferro compounds.
Why is tap water yellow and brown?
Iron compounds give the water a yellowish color, often an unpleasant aftertaste appears, you can notice pollution in the form of brown flakes. The listed phenomena are a deterioration in the organoleptic properties of drinking water. Color change is what water consumers pay attention to first. In addition, there are consequences for human health. Negatively affects the condition of the liver, teeth, the entire gastrointestinal tract, skin and hair, the consumption of poor-quality tap water, in which iron is present.
Solubility in water is explained not only by the interaction of ferro compounds from rocks with other substances in nature. The concentration of Fe 2+ and Fe 3+ ions increases due to the corrosion process that constantly goes on in apparatus and water pipes made of iron alloys. Pipelines are gradually deteriorating, the properties of products in the production of which water with an admixture of iron was used are changing.
What is the solubility of iron in water?
The chemical element, which was given the Latin name Ferrum, is in second place after aluminum in prevalence in the earth's crust. In large quantities on the planet there are deposits of iron pyrite or pyrite (its formula is FeS 2) . Ferro compounds are found in rocks of volcanic and sedimentary origin in the form of hematite, magnesite, and brown iron.
The simple substance iron is a silver-gray ductile metal insoluble in water. Oxides and hydroxides, many salts of iron also do not interact with water. The solubility of FeO in water is discussed in connection with its ability to oxidize to ferric oxide. When talking about an aqueous solution of FeO, they mean the content of ferrous ions. In some water sources, this indicator reaches 50 or more milligrams per 1 liter. This is a high concentration, such drinking water should be purified.
How does iron get into natural waters?
Physical and chemical erosion leads to crushing, dissolution and destruction of rocks containing iron compounds. As a result of reactions occurring in nature, Fe 2+ and Fe 3+ ions are released. They are actively participate in redox processes. The divalent ion oxidizes, gives up the electron and becomes tricharged. The solubility of iron in water is the presence of a Fe 2+ cation. As a result of the reactions going on in the solution, different salts are obtained. Among them are soluble, for example sulfates, and insoluble (sulfides, carbonates). During iron removal of such water, the soluble form becomes insoluble, flakes are formed which precipitate. Ferrous iron is oxidized to ferric in the presence of oxygen or other oxidizing agents (ozone, chlorine).
As a result, ion transformations lead to the appearance of brown rust that is resistant to further oxidation; its conditional composition can be represented as follows: Fe 2 O 3 • nH 2 O. The Fe 3+ particle is a part of complex inorganic and organic substances that are found in surface waters .
Is the content of ferro compounds in natural waters the same?
The concentration of the chemical element and the types of iron in the water depend on the rock composition of the earth's crust and the state of different sources. Bivalent and trivalent iron compounds, organic forms such as iron bacteria and colloidal substances (soluble and insoluble) may be present at the same time.
If sulfate ore deposits are present, it is more likely that ferrous iron will be present in high concentrations. The solubility of ferro compounds in water increases with temperature near areas of volcanism. In rivers and lakes, the iron content is higher if there is a discharge of wastewater from metallurgical and chemical plants.
How to clean water from iron?
To remove ferro compounds reagent and non-reagent methods are used. The basis of most processes is the oxidation of a divalent ion to a trivalent cation. Do the same with other impurities in water - translate into insoluble compounds and remove using a filter. The operation of most industrial plants is based on this principle.
What solubility of iron in water is determined using instruments. Then iron removal is carried out with chemical reagents: oxygen, chlorine, ozone, potassium permanganate, hydrogen peroxide. Chemical oxidation reactions occur and an insoluble precipitate is obtained. It can be not only filtered, but also removed after settling by decantation (drain clean water from the sediment). With ozonation and chlorination, disinfection (disinfection) occurs simultaneously. It is believed that the use of ozone is a more promising method, because chlorine is dangerous to human health.
What are the ways of deferrizing small volumes of water?
At home, of the above reagents, you can use hydrogen peroxide and potassium permanganate. How to clean water from iron, if you want to get a small amount in a short time? When peroxide is added to the water, flakes precipitate. It is necessary to wait for it to settle on the bottom of the tank and drain the water, or pass it through a regular pitcher filter. Such purified water is suitable for drinking and cooking.
In relation to organic forms of iron, the listed methods are ineffective. Those reagents mentioned above do not precipitate colloidal particles fast enough .
Ion exchange and catalysis - water deferrization methods
There are autonomous installations operating on the principles of catalysis, ion exchange. Devices are used to purify water in small industrial enterprises and in cottages.
Iron in the catalytic method is removed using a special filling produced from natural and synthetic raw materials. The water deferrization filter is a metal container. Backfill is placed inside and water is passed. The substance is a catalyst for the oxidation of ferrous iron, translating it into an insoluble state from various forms.
When ion exchange deferrization cation exchangers are used, obtained from resin-ion exchangers, for example zeolite (mineral). In recent years, the production of synthetic products for water deferrization by the ion exchange method has been established.
Why is an alternative to reagents needed?
For a long time, chemicals are used if this harmful admixture exists - iron in water. There are different types of iron, therefore, it is necessary to search for the optimal solution, a method suitable for purifying water from a specific source for which the forms and concentrations of iron are established.
Chlorination is a thing of the past; this method negatively affects water quality and public health. Aeration or enrichment of water with air - a method almost devoid of flaws. Oxygen is passed through water, iron is oxidized, and insoluble sediment flakes can be removed by filtration or settling.
Iron removal is carried out without chemicals - using an electrochemical method. Two electrodes are immersed in a container of water that needs to be cleaned. The negative electrode - the cathode - attracts and holds positively charged iron ions, whatever form they may be. Another non-reagent method is the use of special membranes.
Each of the above methods has not only advantages, but disadvantages. The choice of method depends on the form in which iron is present in the water.