Coal is a major contributor to power and heat generation in the United States. According to economic forecasts coal mining and consumption as fuel will increase through 2010. Simultaneously, deposits of ash from coal combustion are expected to accumulate extensively. Today, about quarter of coal combustion solid waste is used for cement and concrete production. Many millions of tons of aluminum and silicon contained in the coal wastes are annually lost in landfills. Use of coal ash as a raw material for production of chemicals and construction materials can significantly fulfill the U.S. need for these commodities while at the same time decrease dusty pollution. A fairly large number of processes for recovering alumina and byproducts from coal ash have been proposed and developed. These processes are classified by methods of ash decomposition into sintering and hydrothermal technologies and by extractant type into alkaline and acidic groups. On the basis of the available calculations, preference should be given to a combined process including the alkaline pre-extraction of silicon followed by lime−soda sintering of desilicated solid remainder. This review covers 98 papers, patents, and reports issued over the last 30 years. U.S. chemical and metallurgical industries are expected to resume growing through the end of the decade, and coal ash should be recognized as a practicable domestic raw material which can be utilized in a number of ways.

No abstract

Deposits of bauxite ores near aluminum smelters often possess an excessively high percentage of silica. Development of such high-silica ores would be benefi cial to alumina producers. Therefore, unique industrial and operational experience in the fi eld of high-silica bauxite processing was gained at the R u s s i a n N a t i o n a l A l u m i n i u m -Magnesium Institute, St. Petersburg, pilot plant with the consecutive extraction of silica and alumina from low-grade ores. This article describes the chemistry, processing-unit operations, and results obtained from this process.