Magnesium vanadates

Several forms of magnesium vanadates have been characterized. Some physical properties ate summarized in Table 27 (28—30) (see also Vanadium AND VANADIUM ADLOYS). 

The recovery of vanadium from these slags is of commercial interest because of the depletion of easily accessible ores and the comparatively low concentrations (ranging from less than 100 ppm to 500 ppm) of vanadium in natural deposits (147,148). In the LILCO appHcations the total ash contained up to 36% 20 (147). Vanadium is of value in the manufacture of high strength steels and specialized titanium alloys used in the aerospace industry (148,149). Magnesium vanadates allow the recovery of vanadium as a significant by-product of fuel use by electric utiUties (see Recycling, nonferrous LffiTALS). 

Magnesium vanadates, as vanadium compounds in general, are known irritants of the respiratory tract and conjunctiva. The threshold limit value (TLV) for vanadium compounds in air recommended by the National Institute of Occupational Safety and Health is 0.05 mg/m based on a typical 8-h workday and 40-h workweek (7,147). Chronic inhalation can lead to lung diseases such as bronchitis, bronchopneumonia, and lobar pneumonia. These dust-related effects can be avoided by use of individual respirators in areas where exposure is likely. 

Magnesium vanadates, also known as VMgO catalysts, are known to be efficient catalysts for the ODH of light alkanes. Corma and coworkers [137] suggested that the incorporahon of small amounts of V on a MgO surface notably modified not only the redox properhes of the system but also the acid-base character of the oxygen species present on the catalyst surface. These acid-base properhes were related to the nucleophiUc character of the lathee oxygen anions. 

In the oxidative dehydrogenation of propane (Table U), the various magnesium vanadates have been the object of many studies, but other systems seem to have comparable performances (systems based on cerium, niobium, or vanadium, molybdates and noble metals on monoliths used with very short contact time). 

Sugiyama, S., Hashimoto, T., Shigemoto, N., and Hayashi, H. Redox behaviors of magnesium vanadate catalysts during the oxidative dehydrogenation of propane. Catal Lett. 2003, 89, 229. 

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