HEXAVALENT CHROMIUM IN PORTLAND-CEMENT

Due to increasing environmental and health-related concerns, the amount of hexavalent chromium found in portland cement is coming under increasing scrutiny. Hexavalent chromium has been classified as a carcinogen, and its release into the air or groundwater is regulated and controlled under many Federal and State regulations. In addition to carcinogenic risks, soluble chromium has long been linked to chromate-sensitive contact dermatitis of workers exposed to wet cement or concrete. As a consequence, Scandinavian countries have limited the amount of hexavalent chromium allowed in portland cement. This is generally accomplished by intergrinding clinker and gypsum with the chemical reducing agent, ferrous sulfate, which maintains hexavalent chromium below 2 ppm. Developments in this area are reviewed. Studies at a California cement plant showed that more than half of the hexavalent chromium in the cement was contributed by the grinding media in the finish mill. Attempts to reduce the chromium to its benign trivalent form with ferrous sulfate failed in full-scale trial grinds, due to oxidation of the ferrous iron. This indicates that further research is needed to find better methods for introducing ferrous sulfate into the cement or to develop more stable reducing agents.