Cement Plants in California were Taken by Surprise…
Let Us Help You be Prepared.

Recently, it has come to the attention of regulatory agencies and the general public alike that renegade dust from stockpiles of kiln feed may be inadvertently making its way into local communities. In particular, interest lies in the amount of hexavalent chromium that these dust particles may contain.

Our laboratories have been working closely with both the cement industry and the Air Quality Management District to develop the best approach to testing solid samples for hexavalent chromium concentration. A number of methodologies have thus far been identified as reasonable procedures for the characterization of chromium species and availability.

In summary, the total chromium (all species) in the sample is first determined. The sample is digested under microwave-induced radiation in the presence of nitric and hydrofluoric acids. The chromium is then measured by ICP/MS technology.

Total hexavalent chromium is extracted using a strong alkaline digest at 90 degrees Celsius. This procedure is susceptible to some interference if the digest is strong enough to release iron, sulfur or other ions or organic materials that may cause an oxidation-reduction reaction with the released chromium. Our experience has shown that hexavalent chromium can be reduced to trivalent chromium under these conditions, even if magnesium has been added to inhibit the reaction.

“Leachable” hexavalent chromium determinations are also available at our laboratories using more mild extraction procedures at the recommendation of the Air Quality Management District. The AQMD prefers to use a modified version of a procedure developed for measuring hexavalent chromium extracted from particles collected on filters during air sampling. One extraction uses only deionized water. A second extraction uses a weak sodium bicarbonate solution. For the samples we have analyzed, we have found that the bicarbonate solution extracts as much as 5 times the hexavalent chromium as does water alone. Interestingly, the weaker sodium bicarbonate solution extracts chromium with nearly the same efficiency as the stronger, hot alkaline solution. The hexavalent chromium extracted using any of the three above described procedures is measured using ion chromatography with an ultraviolet-light detector.

If you have any questions regarding this article, contact cmoore@babcocklabs.com.

Related links:

http://www.aqmd.gov/RiversideCement/RiversideCement.html

http://www.pe.com/localnews/inland/stories/PE_News_Local_D_cement16.3b90d46.html

http://www.pe.com/localnews/environment/stories/PE_News_Local_C_cement19.429ae55.html