doi:10.1038/nindia.2017.57 Published online 26 May 2017
Pulverizing electronic printed circuit boards in specialized mills at ultra-sub-zero temperatures creates reusable nano-sized dust, researchers from the Indian Institute of Science, Bangalore, in collaboration with the Texas Rice University in the United States, have found1.
India is the fifth largest producer of electronic waste in the world2. Of the waste generated, a considerable amount is recycled either by burning it or crushing it down into pieces. After removing reusable materials such as residual gold or silver, the waste is usually chemically treated before going to landfill.
Electronic goods like printed circuit boards are made of several toxic chemical components such as heavy metals (lead, cadmium, germanium, etc.), oxides and polymers. Burning them produces cancer-causing gases like dioxins or furans, making the recycling process an occupational and an environmental hazard. Physical crushing on the other hand does not separate the e-waste into reusable materials.
“This type of electronic waste treatment contaminates the environment and poses health risks,” says Chandrasekhar Tiwary, the lead author of the study.
To find a sustainable solution to this problem, Tiwary and colleagues developed a grinding device that is cooled down to temperatures well below zero using liquid nitrogen. The researchers used printed circuit boards from computer mice and pulverized them in the cold ‘cryo-mill’, which spat them out as packages of nano-sized dust. When the researchers dissolved the dust in water at room temperature, they got separable chemical components such as metals, polymers and oxides.
“In our method the materials do not mix, rather separate, thanks to the different thermal properties of the components. And the easiest way to separate them is to put the dust in water,” Tiwary says.
The researchers claim that the separated oxides, polymers and metals can be reused as raw materials for making paints, plastic chairs or whiteboards.
Tiwary and team have filed a patent for the cryo-mill prototype. He says that the cry-omill has already garnered interest in waste management sectors around the world.
Material scientist Srinivasa Ranganathan at the Indian Institute of Science says the method is feasible, but the researchers also need to look at cost.
“The results are promising. However, costs need to be worked out. So we are still some time away from using this approach, but it is a promising start,” he says.
Similarly, Sudhagar Pitchaimuthu at Swansea University in the United Kingdom says that it’s encouraging that the recycling process described in this study seems to significantly reduce carbon emissions compared to the conventional recycling processes.
However, he cautions that the processed water might carry traces of heavy metals. “This may create environmental issues if it discharged into the municipal waste,” he says. “The authors could take this issue into account for up-scale studies.”