Stability of iron oxide suspensions

Low to medium amounts of sodium dodecyl sulphate and sulphonate make hematite hydrophobic and cause coagulation, but with higher levels of these surfactants, hematite again becomes hydrophilic and is redispersed (Fuerstenau and Colic, 

1) Each water molecule can form hydrogen bonds with four neighbours with the result that a three dimensional network of molecules, i. e. a structure, is estabUshed. This structure can be mcxiified by solute molecules 

The surfactants associate at the oxide surface to form hemi-micelles with their hydrophobic groups exposed to the aqueous phase at low concentrations, but at higher concentrations, with the hydrophilic groups turned outwards. Hematite coated with various proteins (ovalbumin, y-globulin, lysozyme) adopted either the iep of the proteins or a value between that of the oxide and the protein and displayed modified coagulation behaviour (Johnson and Matijevic, 1992). 

The colloidal behaviour of iron oxides is of great importance in the environment. 

A large range of unwanted chemicals, especially in soils and sediments may be transported with the moving water in porous substrates at the back of iron oxides. 

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The stability of iron oxide suspensions is relevant to fields as varied as the paint industry, extraction of iron from its ores, the structure of soils, hydrometallurgy and waste water treatment. The ease of homogensisation of paint, for example, is controlled by proper adjustment of the stability of the pigment suspensions. In ground waters, the settling behaviour of small iron oxide particles influences transportation of trace elements and radio-nuclides. The stability of a dispersion of magnetic particles can determine the quality of ferrofluids and magnetic tapes. 

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