Let’s take a step back and review why we’re doing this.
The traditional use for recycled glass, melting it back into new containers, requires that the glass be collected, sorted by color, and processed to the standards of the container manufacturers. Environmentally, it’s a plus because re-melting old containers to make new ones saves about ten percent of the energy it takes to make a new container.
In addition to the energy savings, using recycled glass reduces emissions. When virgin batch materials are melted, they lose about 15 percent of their initial weight up the stack. Most of the emissions are in the form of nitrous oxides and carbon dioxide. Not so long ago we thought carbon dioxide emissions were benign. Now we know better. At least most of us do.
Re-melting recycled glass emits almost zero emissions. The only measurable emissions come from burning off the organic contaminants (labels), which are less than one percent of the processed glass.
Over the last fifteen years, thanks to minimum content laws in California, the fiberglass industry has also become a major user of recycled glass. The advantage of using recycled glass in fiberglass is that it doesn’t need to be color sorted. One disadvantage is that it needs to be crushed finer. And it still needs to be quite clean, or it can ruin very expensive equipment in the melting and spinning of fiberglass.
A relatively recent development in the glass processing industry has been the installation of automated optical-pneumatic sorting equipment. The sorting machines eliminate the need for hand-sorting glass, and do an excellent job of getting rid of inorganic contaminants like ceramics. The automated equipment, however, creates a new large waste stream. To sort the glass, first the system breaks the bottles into pieces smaller than one inch. Then the optical equipment is able to pick out contaminants and colors down to as small as 3/8-inch. But when you break a bottle, some of the pieces are inevitably smaller than 3/8-inch. So now the large glass processors are generating thousands of tons per year of 3/8-inch and smaller glass mixed with labels and small pieces of aluminum. This project is partially about developing uses for that material. The ceramic processes described below can tolerate a high level of contaminants.
Using recycled glass in either container manufacturing or fiberglass manufacturing presupposes the existence of a container or fiberglass manufacturing plant within a reasonable distance. Years ago Argonne Labs conducted a research project that determined the breakeven point for shipping recycled containers by truck at about a one hundred mile radius, in terms of the energy used in transport vs. that saved in manufacturing. And transport fuel prices being what they are, that relationship may be worse today.