Iron (III) hydroxide oxide

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Crystal structure
Crystal structure of ferric hydroxide oxide
__ Fe 2+      __ O 2−      __ H +
hydrogen bonds are drawn as dashed lines
General
Surname Iron (III) hydroxide oxide
other names
  • Iron (III) oxide hydrate
  • Iron hydroxide oxide
Ratio formula FeO (OH)
Brief description

yellow odorless powder

External identifiers / databases
CAS number
  • 20344-49-4
  • 51274-00-1 (iron hydroxide oxide yellow)
  • 1310-14-1 (goethite)
EC number 243-746-4
ECHA InfoCard 100,039,754
PubChem 91502
ChemSpider 82623
Wikidata Q412739
properties
Molar mass 88.86 g mol −1
Physical state

firmly

density

4.1 g cm −3

Melting point

> 180 ° C (decomposition)

solubility

practically insoluble in water

safety instructions
GHS labeling of hazardous substances
no GHS pictograms
H and P phrases H: no H-phrases
P: no P-phrases
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Precipitation of iron (III) hydroxide (iron (III) oxide hydroxide) from an iron (III) chloride solution
Iron (III) hydroxide (synthetic goethite) in powder form

Iron (III) hydroxide oxide is an inorganic chemical compound with the composition FeO (OH). This can also be written as Fe 2 O 3 · H 2 O with the same ratio of elements ; it belongs to the group of iron hydroxides or iron (III) oxide hydrates, which differ in the degree of their hydration .

Occurrence

α-Iron (III) hydroxide oxide occurs naturally as needle iron ore or goethite . The γ-form occurs naturally as ruby ​​mica or lepidocrocite .

Extraction and presentation

α-Iron (III) hydroxide oxide is a rust-colored, voluminous precipitate which is precipitated from iron (III) salt solutions (e.g. iron (III) nitrate ) when hydroxide ions are added .

γ-Iron (III) hydroxide oxide is obtained by reacting iron (II) chloride tetrahydrate with hexamethylenetetramine and reacting the intermediate iron (II) hydroxide with a sodium nitrite solution .

In industry, the Laux process is often used to produce yellow iron (III) hydroxide oxide , in which cast iron chips are oxidized with nitrobenzene in the presence of water and the latter is simultaneously reduced to aniline .

properties

The precipitate dissolves easily in acids , but is practically insoluble in a basic medium. This is used z. B. in the cations separation passage for the separation of iron.

Hydroxoferrate (III) can only be produced with hot, concentrated bases . When heated, iron (III) oxide hydroxide changes into α-Fe 2 O 3 .

α-Iron (III) hydroxide oxide has an orthorhombic crystal structure , isotypic to that of diaspore ( space group Pbnm (space group no. 62, position 3) ; a = 464 pm, b = 1000 pm, c = 303 pm). Template: room group / 62.3

γ-Iron (III) hydroxide oxide is a lightly dusting powder of deep orange-red color consisting of extremely fine needles. It can be prepared by heating in a vacuum or dry air stream in the range of about 250 to 400 ° C in pure y-Fe 2 O 3 are placed. With higher heating or even with very intensive grinding, the metastable preparations of the γ series turn into the stable α-modification via metastable β-FeO (OH). The γ-modification has an orthorhombic crystal structure (space group Bbmm (No. 63, position 5) , a = 1240 pm, b = 387 pm, c = 306 pm). Template: room group / 63.5

use

Iron (III) hydroxides have been used as pigments for yellow, red and brown shades under the name " ocher " since ancient times . They are lightfast, but can change their color (red color) when heated (splitting off of water). Iron (III) hydroxide oxide is used in granulated form as an adsorbent in water treatment. The most important application worldwide is the removal of arsenic from drinking water with the help of adsorption filters. Iron (III) hydroxide oxide is approved in Germany as a treatment substance for drinking water according to the §11 list of the Federal Environment Agency (UBA). The prerequisite is that the granulate meets the quality requirements of the European standard EN DIN 15029. Another area of ​​application is the removal of phosphate from surface water. Iron (III) hydroxide oxide is used in adsorption filters to eliminate nutrients and combats the risk of eutrophication in lakes. Iron (III) hydroxide oxide is also used for this purpose in the aquarium hobby and prevents excessive algae growth.

Individual evidence

  1. a b c d e Entry on iron (III) oxide hydrate in the GESTIS substance database of the IFA , accessed on December 19, 2019(JavaScript required) .
  2. a b c d e Georg Brauer (Ed.) U. a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume III, Ferdinand Enke, Stuttgart 1981, ISBN 3-432-87823-0 , p. 1648.
  3. http://bayferrox.de/uploads/tx_lxsmatrix/laux-brochure_deutsch_compressed_02.pdf Production of iron oxide pigments using the Laux process
  4. Entry on ocher. In: Römpp Online . Georg Thieme Verlag, accessed on July 14, 2017.
  5. Testing and optimization of a practicable treatment technology for arsenic removal in drinking water treatment. In: Cleaner Production Germany (CPG) - The portal for environmental technology transfer! Federal Environment Agency, accessed on August 7, 2019 .
  6. Stephan Haufe: Processing materials and disinfection methods (§ 11 list). Federal Environment Agency, September 13, 2013, accessed on August 7, 2019 .
  7. DIN EN 15029 - 2013-01: Products for the treatment of water for human consumption - Iron (III) hydroxide oxide; German version EN 15029: 2012. In: beuth.de. Beuth Verlag GmbH, 2013, accessed on August 7, 2019 .
  8. Hendrik Steinkuhl: Company produces poison binders: GEH Osnabrück: Would also get rid of dumber clean. In: New Osnabrück Newspaper . Verlag Neue Osnabrücker Zeitung GmbH & Co. KG, April 4, 2014, accessed on August 7, 2019 .