The future of mining might be rotting in your compost bin
The ceramics lab at Colorado School of Mines smells like apple pie and banana bread. Inside an oven, apple cores and banana peels retrieved from an elementary school trash can have been laid out to dry. These food scraps accompany a fridge and deep freezer packed with corn husks, egg shells and ground avocado seeds and skins, all of which will be burned into ash.
The researchers here are trying to answer a fundamental question: What’s in the waste?
Ivan Cornejo, who conducts research in the lab at the Colorado School of Mines in Golden, believes the future of mining resides not in caves or mountains, but in the city dump. The waste in our landfills, he said, is full of valuable materials that can be extracted and used in our everyday lives.
“My goal is go to the municipal waste site, look for the footprints of minerals we have thrown away, and treat it as a mine,” he said.
Consider glass, for example. The main ingredient in glass is silica, a mineral found in sand. Silica is abundant on Earth, Cornejo said. But the glass we use to manufacture windows, bottles and smartphone screens requires other chemicals too, such as boron, calcium oxide, magnesium oxide and potassium oxide. These chemicals make the glass more transparent, stronger, or more conductive to electricity, like the glass used in a touchscreen.
In the lab, ash from disposed eggshells, banana peels and rice husks contains all the elements needed to make glass, says Jason Fish, a postdoctoral researcher in the lab — silica, oxides, magnesia, phosphorus, potassium. It will be cooked in an oven between 2,600 – 3,000 degrees Fahrenheit, where it will melt into a liquid that will cool into glass.
Husks from grains like corn and rice contain silica. Eggshells are 98 percent calcium carbonate, another key ingredient in glass, which is typically extracted from limestone.
Cornejo’s goal: to build a comprehensive catalog of glass-making raw materials and track their source in food waste. In the last year, his team has analyzed and catalogued 38 products.
Cornejo had been studying glass for 20 years when he heard about a forest in South America that was torn down to mine a calcium carbonate deposit beneath it. That’s how he landed on his latest research project.
“I know that calcium is abundant in many shells and bones,” he said. “I said, ‘Well, why not use that?’ For the last year and a half, I haven’t bought any chemicals from commercial places. Everything we use in the lab is from waste.”
The apple cores and banana skins generate a more pleasant odor than onion and potato skins, which they’ve also tested, Fish said.
In the lab, food waste straight from the trash fill a refrigerator and freezer. Among them, walnut shells, ground avocado skins and seeds, banana skins, used tea leaves, mango skins, sunflower seed shells, egg shells, peanut shells, corn and rice husks. Cornejo and Fish also collect spent coffee grounds and banana peels from the Higher Grounds coffee shop down the street, and spent grain from Golden City Brewery, a few blocks north of campus. (The coffee shop has a small wastebasket for customers’ banana peels, which it donates to the scientists.) An elementary school in Denver also collects cafeteria trash for the lab to test.
But many of the materials come from his own kitchen trashcan — with his mom’s help.
“My mom is my best technician,” he jokes. “She’s 86 years old. She helped me start collecting the materials and classifying them.”
The waste materials have another advantage over mined minerals, Fish says. Plants and animal shells naturally filter out impurities that plague conventionally mined minerals, like arsenic, lead, mercury and cadmium.
But the trash is lacking in other chemicals needed to make specialty glasses. Boron is used in glass cookware, and sodium is used to make glass for LCD and touch screens, but both are hard to come by in food waste, Fish said. Still, the glasses they are making are completely new to science, and each experiment is full of surprises. Fish holds one sample up to the light. It’s a deep red, a result of a slight gold impurity in the crucible used to pour it.
The trash-to-glass research group is small — just Fish, Cornejo and his son Nico conduct the work — but they believe they are the only scientists currently experimenting making glass solely using food waste. Funding for the lab, provided by the National Science Foundation*, expires next year, and Cornejo is trying to generate interest from the glass industry.
“This is not a weird science. It’s a real science,” Cornejo said.
*For the record, the National Science Foundation is also an underwriter of the NewsHour.