CEGA CR Series is very effective in reducing Cr (VI) for all cement compositions and fineness’s. When the suggested dosage is used, Cr (VI) is reduced below the limits of detection(i.e. 0 ppm), and the level remains zero (or very close to zero) up to one year of age of the sample. Even when zero is not reached (i.e. LS cement), the initial value is kept without increases over time, contrary to the well-known situation normally happening with other reducers (e.g. ferrous sulfate or stannous sulfate).
|Reducing Agent||Physical Form||Average Shelf Life||Dosage(g/t per PPM of Cr (VI)|
|CEGA CR 200 Series||liquid||min 12 months||40-50 g/ t ppm|
|CEGA CR 300 Series||liquid||min 12 months||30g/ t ppm|
Chromium (VI) Reducing Agents
The raw materials for grey Portland cement manufacturing may contain chromium. Due to the highly oxidizing and alkaline conditions of the kiln, during clinker production chromium is partially converted to hexavalent chromium As a result, Portland clinkers and cements contain soluble chromates (usually in the range of 5 – 20 ppm or mg/kg, while the total chromium may reach 200 ppm) which are reported to cause skin irritation (allergic contact dermatitis).
For this reason, why European Community introduced the obligation (Directive 2003/53/EC) to maintain the level of soluble chromates below 2 ppm; this has a significant economic impact on the cement industry. The reduction of soluble chromate is usually obtained with the addition of ferrous or stannous salts (in powder or liquid form) during cement grinding. Both methods present advantages and disadvantages. Ferrous sulphate is very cheap, but presents serious problems related to the durability of the reducing properties: it is very sensitive to moisture and temperature and tends to lose efficiency after grinding and during cement storage. This requires the use of very high dosages of ferrous sulphate, causing costs to be higher than expected as well as triggering unfavorable side-effects formation of red spots on the concrete surfaces). This is particularly evident with liquid additives based on tin (II) compounds (stannous chloride/sulphate). The reason may lie in the fact that tin (II) has strong acid properties and during cement grinding it can react with free lime and water being partially converted to stannous hydroxide, similarly to the case of ferrous sulphate.
Cega Offers liquid additive for the reduction of hexavalent chromium in the cement. The reduction performance is unaffected by moisture and high grinding/storing temperatures. Several tests performed in our Central R&D facilities have demonstrated how the reducing properties Cega Chrome (VI) Reducers unchanged even after more than one year.
|Reducing Agent||Dosage (weight % over cement weight)||Dosage(g/t per PPM of Cr (VI)|
|Ferrous sulphate (FeSO4*7H2O)||0,2%||200 g/ t ppm|
|Stannous sulphate (SnSO4)||0,02%||20 g/ t ppm|
|CEGA CR Series||0,045%||30-50 g/ t ppm|