Closing the E-Waste Circle with Green Heat
The digital revolution has an impact on the physical world. A massive uptick in the use of electronic devices has led to high demand for critical materials and extremely resource-intensive manufacturing – for every kilogram (kg) of electronics produced, 25kg of CO2 are released into the atmosphere. Rapid shifts in consumer taste and technological performance have also led to increased electronic waste (e-waste). E-waste is the fastest-growing type of refuse in the world and one of the most toxic to individual and environmental health.
However, although the technology may grow old and outdated, individual components often retain their value long after a smartphone has gone dark, making a case for recycling. It is estimated that the total value of raw materials – like plastics, copper, iron, aluminum, cobalt, nickel, tin, lead, zinc, and precious metals gold and silver – that can be recycled from e-waste is over 54 billion Euro per year. Recycling these materials can provide a valuable economic opportunity and boost the circularity of the electronics industry, but the recycling process is also heat and energy intensive. To be truly circular and sustainable, the electronics recycling industry needs physical solutions to decarbonize its heat and energy use.
Opportunities and challenges in e-waste mining
The process of reclaiming valuable raw materials from discarded electronics is called “e-waste mining”, also known as “urban mining”. It offers a literal and proverbial gold mine for countries and industries willing to invest in making the process more efficient and environmentally friendly. Recycling e-waste is also crucial to combating the scarcity of rare earth minerals and precious metals and contributing to a circular economy – including the energy economy, which increasingly relies on these raw materials to produce technologies such as solar panels.
Currently, e-waste mining faces challenges in finding efficient, eco-friendly methods to extract the raw materials for recycling. Experimental techniques like supercritical fluid, molten salt, and bioleaching show promise, but need further development to balance cost-effectiveness with value. However, existing recycling processes like pyrometallurgy have proven to be extremely effective in recovering precious metals from e-waste. These processes currently produce high levels of greenhouse gas emissions, largely due to using fossil fuels for high-temperature heat. A new way to provide this heat carbon-free is therefore needed to make e-waste mining sustainable.
The heat needed to turn e-waste into gold (and silver, and platinum…)
In the pyrometallurgical process, e-waste is run through shredders or grinders, which break the metal by-products into smaller particles. The next step is smelting the shredded mass using either flash or batch furnaces. This process results in separated metals, leftover slag, and flue gasses. From here, pyrometallurgy becomes a more varied process depending on the facility and the primary metal makeup of the separated metals:
- Primary iron loads can be further separated by oxygen and electrical arc furnaces
- Copper and lead loads can be separated by smelting furnaces
- Aluminum loads can be separated by tilting or stationary melting furnaces
A common factor between these different separation methods is the high heat requirement. The process of pyrometallurgy, depending on the exact method, requires sustained heat between 400°C and 1200°C. For example, copper smelting, which introduces sulfides to facilitate separation, requires 1200°C, while lead smelting using blast and imperial smelting furnaces requires a lower temperature between 400°C and 800°C.
Waste not, want not: Enabling electrification and waste heat reuse with thermal storage
This heat is generated mostly by fossil fuels, partially canceling out the positive effect of recycling used materials by emitting large amounts of CO2 and other greenhouse gases (GHGs). However, there are a growing number of options to replace fossil fuels with clean energy sources in these high-temperature furnaces. The most economical option is clean electricity. To ensure availability and to acquire electricity at low prices, new storage technologies for heat meet the demand for batch furnaces better than direct electrification. A power-to-heat thermal storage system, which converts renewable electricity into heat, can operate many existing furnaces without costly infrastructure changes.
These technologies can also be used for storage and reuse of the hot flue gas to preheat scrap or furnaces. The high level of consistent heat required for pyrometallurgy in recycling e-waste is the primary obstacle to making the technique the best industry option for urban mining. Capturing heat from smelting furnaces, especially in batch processes, and storing it until the next work cycle could dramatically lower GHG emissions and save recycling plants from burning excess fossil fuels.
As the demand for precious metals increases, recycling these materials can raise potential revenues and lower GHG emissions. Electronics have become an indispensable part of everyday life; recycling the last generation’s technology is therefore necessary to curb their impact on the planet. For a sustainable digital transition – and a successful circular economy – green heat solutions for recycling should be included in e-waste mining today.
Author: Martin Schichtel, Founder and CEO Kraftblock
(Published in GLOBAL RECYCLING Magazine 3/2024, Page 5, Photo: O. Kürth)
