Process for obtaining treated coal and silica from coal containing fly ash

Abstract

A process for treating mixtures of solid coal and fly ash containing metallic oxides, silicon dioxide and sulfur compounds in order to produce treated coal and substantially pure silicon dioxide comprising (1) reacting a mixture of the coal and fly ash with hydrogen fluoride in water to produce a liquid stream comprising silicon fluoride and metal fluorides and a solids stream comprising unreacted coal and sulfur compounds; (2) reacting the sulfur compounds with metallic nitrates dissolved in water to form an aqueous solution of nitrate, metallic and sulfur ions; (3) separating the aqueous solution of nitrate, sulfur and metallic ions from the solid coal; (4) washing the previously treated solid coal with water; (5) reacting the silicon fluorides and metal fluorides with metallic nitrates in an aqueous mixture to form solid silicon dioxide; and separating the solid silicon dioxide from the aqueous mixture.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a process for removing mineral impurities present in coal containing particulate fly ash, including metal oxides such as Al2O3, SiO2, Fe2O3, as well as sulfur, calcium and other oxides normally found in coal ash. The process results in a treated and cleaner coal product, while at the same time allowing for the separation and recovery of relatively pure (commercial grade) silicon dioxide (SiO2) as a valuable byproduct.

[0002] The commercial use of untreated coal as fuel, particularly coal containing sulfur and fly ash, has long been known to result in potentially unacceptable levels of air pollution as well as high maintenance costs for industrial plants relying on coal as the primary hydrocarbon fuel source. The presence of contaminants such as nitrogen and sulfur-based compounds in coal fly ash has two significant drawbacks. First, the presence of fly ash tends to reduce the potential heat value of the coal, making it ...

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