Source and Control of Magnesium Chromium Bricks in Cement Production

The National Standardization Committee has approved the release of GB31893-2015 "Limits and Determination Methods for Water Soluble Chromium (VI) in Cement". As a mandatory national standard, it stipulates that the content of water soluble chromium (VI) in cement shall not exceed 10mg/kg. We know that the main sources of chromium in cement include: cement raw materials, crushing and grinding equipment, chrome containing refractory bricks, and industrial waste. To ensure that the chromium content of cement meets the national standard value, it is necessary to control the content of these chromium sources, in order to achieve the goal of reducing chromium and ultimately produce products that are qualified or even higher than the national standard.

Let's talk about one of the sources of chromium: chromium containing refractory bricks

We know that hexavalent chromium cannot be decomposed in nature and can contaminate soil and groundwater. It is easily absorbed by the human body and can accumulate in the body through digestion, respiratory tract, skin, and mucous membranes. It has been confirmed by the International Agency for Research on Cancer (IARC) as having strong carcinogenicity. Therefore, the pollution problem of hexavalent chromium has attracted worldwide attention, and countries have also issued policy directives targeting hexavalent chromium.

EU: On June 18, 2003, the EU passed Directive 2003/53/EC to prohibit the sale and use of cement and cement products containing more than 2ppm water-soluble hexavalent chromium during hydration. This directive was officially issued by the EU Health Substances Control Act on January 17, 2005, and the EU also issued two directives, WEEE and ROHS. Since July 1, 2006, the sale of hexavalent chromium products in the EU market has been officially prohibited.

United States: Eliminate hexavalent chromium process throughout the country.

Japan: The UE Committee has announced the adoption of two EU regulations to completely abolish the use of six prices.

China: Relevant regulations such as the Environmental Protection Law of the People's Republic of China, the Clean Production Promotion Law of the People's Republic of China, the Notice on Strengthening the Prevention and Control of Pollution from Hazardous Waste Containing Chromium, and the Water Pollution Prevention and Control Law of the People's Republic of China restrict the discharge of hexavalent chromium pollutants. The Ministry of Industry and Information Technology issued the "Catalogue of Toxic and Harmful Raw Materials (Products) Substitutes Encouraged by the State" in 2012, which clearly stated that chromium containing refractory materials should be replaced.

Before 2004, China had not conducted research on water-soluble chromium in cement and did not pay attention to its harm to human health. Therefore, before this, most refractory kilns in cement factories were made of magnesium chromium bricks. Magnesium chromium bricks have advantages such as high fire resistance, high high-temperature strength, strong resistance to alkaline slag corrosion, and excellent thermal stability. They also have certain adaptability to acidic slag and were the mainstream refractory material in the transition zone of the 1960s to 1980s. However, one of the drawbacks is that when the cement rotary kiln is in an oxidizing atmosphere, trivalent Cr3+oxidizes to hexavalent Cr6+. Subsequently, magnesium chromium bricks will be severely corroded by sulfates, transforming Cr6+compounds into water-soluble substances. These substances containing hexavalent chromium ions will be discharged into the outside along with refractory bricks and exhaust gas emissions after use.

Chromium containing refractory products have been included in the list of high pollution and high environmental risk products by the Ministry of Environmental Protection of the People's Republic of China. Moreover, the Ministry of Industry and Information Technology has issued a notice that all refractory materials containing chromium are prohibited from being used in cement rotary kilns unless special circumstances arise. That's why most cement factories now replace magnesium chromium refractory bricks.

Magnesium chromium bricks and other chromium containing refractory materials have made indelible contributions to the development of the cement industry, but as a serious pollution source that poses a threat to public and environmental health, their elimination trend is also inevitable. The implementation of the "Limits and Determination Methods for Water Soluble Chromium (VI) in Cement" will play an important role in promoting the green development of the cement industry. This process tests not only the execution power of the government, but also the sense of responsibility and mission of relevant enterprises.