Blog

May 07, 2024

Scientists design a grinder to solve the problem of E

Photo: Siddharth Kankaria/Research Matters Ever wondered what happened to that phone you discarded for a ‘smart’ one, or the desktop computer you threw away years ago? Well, you put them in the bin.

Photo: Siddharth Kankaria/Research Matters

Ever wondered what happened to that phone you discarded for a ‘smart’ one, or the desktop computer you threw away years ago? Well, you put them in the bin. And so did countless others around the world, generating a whopping 50 million tons of electronic waste in 2013 alone. By 2030, our electronic waste is expected to touch 1000 million tons per year – more than the amount of rice grown world over!

Just 12.5% of electronic waste (e-waste) generated today is recycled. Chewing on this problem, quite literally, is a recent Indo-American study that proposes an elegantly simple method to recycle e-waste: grind it into nanoparticles. Led by Prof. Kamanio Chattopadhyay and Prof. D. Roy Mahapatra at the Department of Materials Engineering and Aerospace Engineering, Indian Institute of Science, in collaboration with researchers at Rice University, USA, the study may make e-waste recycling easy, simple and complete.

The StEP initiative by the United Nations defines e-waste to cover all items of electrical and electronic equipment and its parts that have been discarded by its owner as waste, without the intent of re-use. Refrigerators, screens/monitors, lamps, washing machines, calculators, toasters, mobile phones, computers, and more eventually end up as ‘e-waste’.

A major challenge in recycling e-waste is that electronic printed circuit boards (PCBs) present in all these devices contain life-threatening heavy metals like lead, mercury and arsenic. Hence, they must be recycled through specific channels that separate these harmful chemicals by dismantling, breaking and refining them.

“The complexity in the process of recycling, and the amount of energy needed is not economically feasible or environment friendly”, points out Dr. Chandra Sekar Tiwary, a researcher and the lead author of the study.

Today, two common methods are being used to recycle e-waste. In the first method, the e-waste is burnt and crushed, which destroys the organic polymers in PCBs and leaves metals and ceramics to be recovered and recycled. The process of burning releases toxic chemicals in the air, thus polluting it. In the second method, the PCBs are crushed into tiny bits and treated with heat and chemicals to extract metals. Since the tiny bits are about a centimeter in size, the resulting metals may react with each other and hence cannot be extracted in its pure form, thus limiting recycling. The need for extreme heat and chemicals also make this process expensive.

The researchers of this study propose to crush the PCBs into nano-size particles using a cryo-mill, a low-temperature grinder that was developed in-house at IISc. Crushing it this way at low-temperatures releases no hazardous gases. It prevents any chemical reaction between metals, and also retains organic polymers, thus enabling complete separation and reuse of polymers, oxides and metals. Metals are recycled and the organic polymers are used as starting material for producing artificial material like polymer nanocomposites. “The best part about our solution is that we do not dispose anything and use 100%, which is very important for environment”, remarks Dr. Tiwary.

The study also elaborates on two methods to recycle the powdered form of PCBs. In the first method, the powder is mixed with water, which then forms two clearly separable layers—a floating layer and a sediment layer. When the floating layer, with nano-sized particles, is diluted further, the particles are evenly distributed throughout the solution forming a colloid. This colloid can be used to manufacture printing inks and polymer based paints. Oxides of manganese, silicon, lead, tin, copper, cobalt and calcium, and also metals like silver, gold, tin, lead, copper, aluminum and nickel are found in the sediment layer and can be extracted in their pure form.

In the second method of reuse, the nanosized particles could be used to strengthen polymers and improve their mechanical properties. The team demonstrated the same by adding these nanoparticles to epoxy resin, a commonly used polymer. “Mixing nanoparticles improved the strength”, says Dr. Tiwary.

The proposed method uses just half the energy compared to burning and crushing, takes about a third of the time compared to chemical methods of recovery and results in recovering 100% of the materials and yields zero waste.

This study is a breakthrough in our quest to find green ways to end the menace of e-waste. “The two important challenges of this decade is going to be environment and energy. Waste, especially e-waste, is going to be a big problem in the developed world that will generate a lot of e-waste. A country like India must start working on it now, else our cities will be full of such waste”, signs off Dr. Tiwary.