I found this interesting. Written by a materials science team...

I found this interesting. Written by a materials science team exploring use of landfill materials as proppant feedstock . They've also looked at flyash elsewhere.

From the Jan/Feb 2014 edition of American Ceramic Society Bulletin

"Impact and opportunity

The development of unconventional energy resources, such as shale gas and oil, represents a sizable opportunity for participation by the ceramics community. New materials for drilling, stimulation, detection, and production are needed.

Proppants alone, for example, represent an impressive need and opportunity. Demand for proppants has exceeded our domestic raw materials supply and manufacturing capacity. None of the existing manufacturing capacity resides near the areas of intense exploration and production of shale oil and gas."

"Industrial waste streams and under utilized minerals from other industrial processes are a potential raw material source. Such materials are ubiquitous throughout the regions where new domestic energy reserves are being tapped, for example, in the Marcellus, Utica and Bakken plays. The potential cost benefits associated with their ready availability and minimized transportation are enormous."

an interesting read intellectually if interested:
http://ceramics.org/wp-content/uploads/2009/06/bulletin_janfeb_14.pdf