Hexavalent chrome reduction in cements using iron sulfate
In 1950 Jaeger and Pelloni, two Swiss dermatologists, discovered the causes of a common occupational disease in the construction industry. The chrome contained in the cement was identified as the cause of allergic eczema on the skin of workers, which was known and feared for decades.
The substances that contain Hexavalent chrome are classified in the community legislation as carcinogenic, mutagenic and irritant. The Hexavalent chrome in cement enhances sensitization and causes serious allergic reactions that are frequently suffered by workers who handle it regularly, whether at the factory or in the construction sector.
The allergic or contact dermatitis it produces is very painful and can leave workers disabled. Directive 2003/53/EC of the European Parliament and of the Council required the governments of the member countries, as of January 17, 2005, to forbid the use and marketing of all those cements and preparations containing cement, whose content in soluble Chrome (VI), once hydrated, is greater than 2 ppm of the dry weight of the cement.
Depending on the raw material used, the chrome content in cements is between 10 ppm and 100 ppm. When mixed with water, the chrome contained in the cement can be dissolved as Chromium (VI), which causes the aforementioned skin irritation. The current European regulation requires chemically reducing Chromium (VI) (up to a maximum of 2 ppm) and converting it into Chrome (III), thus reducing the solubility dramatically, and therefore, its harmful effects on the skin.
Hexavalent Chrome can be reduced to Trivalent Chrome, a substance that is harmless to the skin, by using reducing elements. At present, the most widely used compound in the cement industry for this reduction is Ferrous Sulfate.
The reduction reaction that occurs when Ferrous Sulfate is used as a chemical reducer is as follows: CrO4 2 “+ 3 Fe2 + + 4 OH” + 4 H2O → Cr (OH) 3 I + 3Fe (OH) 3 i