Geopolymers Used to Encapsulate Environmental Wastes
Geopolymers, an ancient technology rediscovered in the mid-20th century has been known to man for at least 25,000 years, but the technology was lost to the west when the Roman Empire fell. It was rediscovered by Dr. Joseph Davidovits of France over thirty years ago. Davidovits claimed it was used by the ancient Egyptians to build the pyramids by casting the stones in place rather then having hundreds of thousands of slaves dragging cut stones up a slippery slope.
Geopolymers can be used in the same places as conventional concrete, but is environmentally more friendly leaving a a carbon footprint less then 20% of that of Portland cement. It also makes a far better product because it is stronger and more chemical resistant then conventional concrete. It can be made from waste materials with one exception the activating fluid that is made from a mixture of sodium hydroxide and sodium silicate solutions at a ratio of 1:2.5. Enough of this is mixed with a pozzolan material composed of any number of materials including volcanic ash, ground glass, pulverized brick or ceramics. The pozzolan can also be fly or bottom ash from coal fired generators.
In the western Pacific countries and east Asia a wonder pozzolan material is burned rice husks that are extremely rich in silica. A great deal of research is ongoing in the countries found in this area involving the use of this in creating building materials.
Geopolymers can be used in lieu of conventional concrete and mixed using the same equipment. They are unaffected by exposure to salt or magnesium sulfate and are not affected as much as conventional concrete by strong mineral acids.
One of the many uses for geopolymers is encapsulating wastes including mine wastes. This quickly becomes a win-win situation because many of the encapsulated waste products can be changed into valuable castings used in the building trades or as decorative products.
Geopolymers are an alumino-silicate material that creates double bonding of silicon atoms with aluminum atoms creating a tetrahedra molecule that forms chains similar to organic polyesters. The structure is similar to naturally occurring minerals that it is virtually impossible to determine if they are natural or manmade. They resemble zeolites of feldspathoids with the only way of proving they are manmade is with a nuclear magnetic spectrometer where they create a spike in the readout that gives away their origin.
You can include up to 10 parts of any kind of inert matter with 3 parts of geopolymer matrix to encapsulate virtually anything including nuclear wastes. Shown in the photographs are samples of geopolymers encapsulating various mine wastes: l-r barite, dolomite, basalt, granite.
Geopolymers and Roman Concrete, John Carter, http://www.geopolymersandromanconcrete.blogspot.co.
Geopolymer Institute, http://www.geopolymer.org