What is iron?
Iron is a white, white, malleable and ductile metallic chemical element, vital for animal and plant life, and the fourth most abundant element in the earth’s crust. Its chemical symbol is Fe, has an atomic weight of 55.85 gmol / g. This metal is found in minerals such as hematite, magnetite, limonite, pyrite, etc.
It is considered a transition metal and is the fourth most abundant element in the earth’s crust, representing 5%, and among metals only aluminum is more abundant. In terms of planetary mass, iron is the most abundant metal because the planet concentrates in its core the greatest mass of native iron, equivalent to 70%.
The earth’s core consists mainly of iron and nickel in metallic form, generating a magnetic field as it moves.
It is a malleable metal, has a gray to silver color and has magnetic properties. It is a very hard and dense metal.
It can be found in nature because it is part of numerous minerals and is rarely found free. To obtain iron in its elemental state, the oxides must be reduced with carbon and then undergo a refining process to remove the impurities present.
Iron is considered the most widely used hard metal, accounting for 95% by weight of the world’s metal production. Pure iron does not have many applications, with the exception of using its magnetic potential.
Its main application is to form steel products, using this metal as a matrix element to house other alloying elements, both metallic and non-metallic. An iron alloy is considered to be steel if it contains less than 2.1% carbon; if the percentage is considered higher, it is called cast iron.
Iron in Water.
Its presence in water is due to corrosion in pipes and storage tanks made of carbon steel containing a percentage of this element. In deep wells, when there is a high concentration of iron, it is due to an excess of iron minerals (such as hematite), which has contact with the water.
The reduction reaction of iron carbonate in well water is as follows:
FeCO3+ CO2 +H2O-> Fe+2 + 2HCO3-
This is an example of how this element dissolves in water in contact withCO2. This reaction is affected by pH, so high pH increases chlorine precipitation and low pH increases the concentration of dissolved iron.
The concentrations of this metal found in water generally do not present a health hazard. However, it can change the taste of the water, generate reddish-brown stains on clothes, as well as cause accumulation problems in pipes, pressurized tanks and even water softeners.
Some types of bacteria obtain their energy by reacting with soluble forms of iron and manganese. These organisms are generally found in waters that have high levels of soluble iron. The reaction exchanges this soluble metal into a less soluble form of the metal, resulting in precipitation and an accumulation of black gelatinous material (slime). Masses of slime from this element can clog plumbing and water treatment equipment, in addition to breaking off in clumps that become iron stains in laundries. Bacterial reactions with iron do not cause any additional precipitation compared to exposure to an oxidant. However, precipitation caused by bacteria occurs faster and therefore increases the dyeing of fabrics quickly.
How to treat water to remove iron and manganese?
The following processes can be used to retain dissolved manganese in water:
This method is recommended for water with high iron concentration in order to reduce reagent costs. The equipment normally used in this type of method is an aerator, a holding tank and filters. Oxygen from the atmosphere reacts with the iron in the raw water to produce relatively insoluble oxides of these elements. The reaction rate depends on the pH of the solution, being faster at higher pH values.
It consists of a chemical dosing system and filters. A holding tank and a system for adjusting the pH with sodium hydroxide, calcium hydroxide, hydrated lime or sodium carbonate may be required. Oxidizing agents such as chlorine gas or hypochlorite may be used.
Filtration in conditioned media:
Filter media conditioned to remove iron have a regeneration, adsorption and filtration capacity that depends on the particle size distribution of their shape and surface manganese oxide precipitates. Potassium permanganate is used as an oxidizing agent, which has a high cost and must be very well controlled in its application due to its toxicity.
Direct filtration with the application of chemicals:
The application of chemicals is required to agglomerate the oxidized particles and form flocs large enough to be filtered.
Softening is applied in order to remove existing hardness in the water where iron removal is a secondary effect. This method is not very efficient since precipitates are formed when coagulants are not added.
Stabilization due to sequestration:
Sequestering agents are chemicals that help prevent metals from precipitating. Normally, both sodium silicate and polyphosphates are used to sequester iron. The sequestering agents do not remove iron, they only prevent it from precipitating and their application is recommended in small systems and concentrations of less than 0.5 mg/L.
Biological treatments always require specific raw water qualities and conditions and not all groundwater or surface water is economically feasible to treat.