Ferric Hydroxide: A Versatile Material for Industrial Applications
Ferric hydroxide is an inorganic compound with the chemical formula Fe(OH)3. It is one of the most common iron oxide-hydroxides found in nature. Ferric hydroxide has a wide array of industrial uses due to its absorbent, catalytic, and corrosion inhibiting properties. This article discusses the various properties and applications of ferric hydroxide.
Chemical and Physical Properties
Ferric hydroxide is a yellow-brown solid that is practically insoluble in water. It exists in two main crystalline forms - alpha and beta. The alpha form is the more thermodynamically stable form. Both forms have an layered structures composed of sheets of octahedrally coordinated iron(III) ions that share edges to form infinite double hydroxyl spirals running parallel to the c-axis. These sheets are held together by hydrogen bonds between surface hydroxide groups and interlayer water molecules.
Ferric hydroxide has a bulk density ranging from 0.8 to 2.5 g/cm3 depending on particle size and pore structure. It is paramagnetic due to unpaired electrons in the Fe3+ ions. The point of zero charge, or pH at which the net surface charge is zero, is around 8. This means ferric hydroxide will be positively charged below pH 8 and negatively charged above pH 8.
Adsorbent Properties
One of the most important properties of Ferric hydroxide is its strong absorbent capability. It can adsorb anions such as phosphates, arsenates, sulfates, heavy metals such as lead, cadmium, zinc, and other toxins from aqueous solutions through surface complexation and ion exchange mechanisms. This properties allows it to be used as an effective adsorbent for water and wastewater treatment processes.
Ferric hydroxide is commonly used in secondary and tertiary wastewater treatment to remove phosphate, the main cause of eutrophication in water bodies. It finds application in removing arsenic from groundwater to make it safe for drinking. Ferric hydroxide is also used in soil remediation processes to remove pollutants like heavy metals that have leached into the soil from industrial waste.
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