Chromate cement

Direction of innovation (from the standpoint of market actors - 6al The cau-sahty between incidences of bricklayer s itch and the chromate content of cement has been suspected since the 1950s and was established conclusively in the early 1970s. However, it was contested by the cement industry. The labelling low-chromate as per TRGS 613 meant that both commercial users and DIY users were able to clearly select low-chromate cement. 

Direction of innovation (from the standpoint of the SubChem research group - 6b) The use of low-chromate cement may result in a significant reduction of sensitisations to chromate or new incidences of bricklayer s itch . The product security achieved, however, depends on whether chromates are reduced as an integrated part of the process or downstream (hmited storage stability of reducing agent in finished cement). 

Also the Quality Community on mineral wool and the industiy regulation on low-chromate cement are examples of a co-operation for hazardous substance substitution that does finally function. The example of UV-drying printing inks, on the other hand, does demonstrate under which combination of negative network effects in the innovation system the diffusion of a technology can also fail (at least provisionally). 

The Chilean nitrate deposits are located in the north of Chile, in a plateau between the coastal range and the Andes mountains, in the Atacama desert. These deposits are scattered across an area extending some 700 km in length, and ranging in width from a few kilometers to about 50 km. Most deposits are in areas of low rehef, about 1200 m above sea level. The nitrate ore, caUche, is a conglomerate of insoluble and barren material such as breccia, sands, and clays (qv), firmly cemented by soluble oxidized salts that are predominandy sulfates, nitrates, and chlorides of sodium, potassium, and magnesium. Cahche also contains significant quantities of borates, chromates, chlorates, perchlorates, and iodates. 

Zinc will initially react with cement-based materials with the evolution of hydrogen. This reaction can be controlled by the presence of soluble chromate either in the cement (over 70 ppm) or as a chromate passivation treatment to the zinc surface. Zinc can therefore be used to provide additional protection to steel in concrete. It is more effective in cmbonated concrete than in chloride-contaminated concrete. 

Sulfoalkylated naphthol compounds are effective as dispersants in aqueous cement slurries. The compounds can also be applied in an admixture with water-soluble inorganic compounds of chromium to provide additives of increased overall effectiveness. Particularly suitable are sodium chromate or ammonium dichromate. a-Naphthol is reacted in an alkaline aqueous medium with formaldehyde to create condensation products. The aldehyde can be reacted with bisulfite to produce sulfoalkylated products [1404,1410]. 

The high costs (approx. 30 m. per annum) of the construction employers liability insurance, caused by incidences of bricklayer s itch are important innovation drivers. Since the mid 1970s the construction employers habihty insurance, has endeavoured in consultations with the Association of German Cement Works to obtain a reduction of the chromate content in cement Further initiatives such as e.g. GISBAU" and also regulations have stepped up the pressure on cement manufacturers. 

The manufacturers of a mass product that is far from the end-user, such as cement or concrete, are under extreme price competition and slightest changes in, say, the cost stracture can be decisive. Elimination of water-soluble chrome-VI compounds that cause chromate-induced eczema would only increase the price of the product minimally. And even if the severe price competition did in fact permit this increased margin (which is highly probable in this example), there has been no significant iimovation push. Uirfortunately, this occupational disease is hardly perceived by the public and the costs incurred by this type of eczema evidently can be externalised by the cement industry (and covered by the employer s liability insurance). 

Catalysts, desiccants, and catalyst inerts. In 1988, the refinery began to recycle nonhazardous catalysts, desiccants, and catalyst fines. It recycles electrostatic precipitator fines, Claus catalyst, and catalyst support inerts for use in cement manufacture. Two other catalysts, zinc oxide and iron chromate from the hydrogen plant, are reprocessed at smelters to recover the metals. 

The most widely used anodic inhibitors are calcium and sodium nitrite, sodium benzoate and sodium chromate. With the exception of calcium nitrite, no other chemical is available in North America as a proprietary product. Nitrites have been used in the USA for more than 14 years and for nearly 40 years in Europe. Calcium nitrite is marketed as a non-chloride accelerator, as well as a corrosion inhibitor. For 25-30% solids in solution, dosage rates range from 2 to 4% by weight of cement depending on the application [50]. Calcium nitrite has been used in bridges, parking and roof decks, marine and other prestressed concrete structures that are exposed to chloride attack. 

Perkins, R. B. Palmer, C. D. 2001. Solubility of chromate hydrocalumite (3CaO A1203 Cr04 nH20 5-75 CC. Cement and Concrete Research, 31, 983-992. 

The biological effects of chromate are apparent in three main areas mutagenicity and carcinogenicity, an adverse immune response and the use of chromate in clinical chemistry to tag erythrocytes. The clinical use of chromate has recently been reviewed1441 and although reviews of the immune response to chromate are available1442 little is known of the chemistry involved this is surprising as chromate present in cement is a major cause of dermatitis. 

Due to the recent legislation in the European Union [2.32], from 2005 there will be a huge demand (ca. 1 million tons per year) for FeS04 as chromate reducing agent for cement This will have an enormous impact for the titanium dioxide industry. 

The recent development in the E U legislation concerning the necessity for reducing chromate in cement [2.32] might also have impact on the waste management from the chloride process. By turning the waste metal chlorides into FeS04 with sulfuric... 

Other aging effects Aging due to cementing of primary particles is difiScult to observe directly because of other simultaneous changes. Nevertheless, it may be inferred that such processes going on in the flocculated state render impossible the subsequent peptization, or dispersal, of an aged product. Kolthofif and others have discussed the cementing process for barium sulfate, lead chromate, and silver bromide. ... 

Metals Nickel, cobalt, mercury, silver, chromates (welding fumes and cement), beryllium... 

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