Enabling the recycling of E-waste

Team CORE is a student team from the Eindhoven University of Technology. By making use of a process called elementary retraction we are trying to bring us one step closer to the zero-age, a time where all waste ends up as new raw materials.

The Earth

We draw our inspiration from the earth itself. Our planet has been performing elementary retraction for as long as it exists. Waste drops to the ocean floor and sinks into the core of the earth, which is how we get our name. It is then heated up and eventually ends up on top again after millions of years trough natural processes like volcanic eruptions. The problem with this is that society progresses at such a pace that the earth can’t keep up anymore. That is why we are going to bring this technique down to an industrial scale.

The Technical Problem

In most cases elementary retraction is fairly easy to apply, since most waste streams contain closely mixed materials. However, in the case of e-waste, the stream contains a highly complex mixture of dozens of elements in a matrix of plastic and silicon. With batteries, which is what we are currently working on, it gets even worse as they contain volatile materials as well. This makes mechanical separation both hazardous and complex, and in the case of chips nearly impossible.

The Solution: Elementary Retraction

Elementary retraction avoids these issues and aims to recover these materials by heating them to fairly high temperatures in a reactor, exceeding their melting points, up to 1450 °C. This causes plastics to be incinerated and the metals to melt or vaporize (e.g. zinc and cadmium, both commonly found in batteries, have boiling points of 907 °C and 767 °C respectively). By doing this we form three layers.

Layer 1: Gases

At these temperatures organic contaminants (including toxic substances like PFOS) fall apart into their constituent elements, which are then oxidized. This process produces various gases like CO, CO2 and NOx. Plastic containing bromine-based fire retardants result in the production of Br2. Therefore, we make use of a gas washing installation. We, for instance, remove CO by using catalytic converters, with the CO2 being cleaned by using an amine-installation.

Layer 2: Slag

Through the addition of sand SiO2, a slag layer is formed. This slag layer absorbs contaminants such as silicon and oxides. The viscosity of the slag is maintained through balancing between acidic and basic components – with SiO2 as an acidic and CaO as a basic component for example. This slag viscosity is a crucial factor within our process and is carefully maintained to allow slag to flow freely and to improve exchange speeds between the 3 layers. After cooling down rapidly, the slag remains amorphous resulting in a glassy black substance: obsidian. This can be used for construction projects; in roads and buildings.

Layer 3: Metals

The metals, after melting, combine into a third layer below the slag, since they are heavier. Various alloys are then formed, depending on the phase compositions. These are analyzed using thermodynamics software. After melting and separation, the metal layer can be poured off. The different elements can be separated using hydrometallurgical processes, for example by dissolving them, and then applying electrolysis or precipitation to separate specific elements.

Temperature and Energy

To reach these temperatures, the mixture is initially heated up electrically or with burners. Once a certain temperature is reached, the organic compounds (other waste) that we add to the mix will start reacting as well, producing additional heat. The goal of the mixture is then to have the right ratio of exothermic to endothermic components. At the same time the mixture also has to have enough carbon present to avoid oxidizing the metals at any particular temperature. We like to call this mixture the “smart mix”. This smart mix reduces the amount of consumed energy significantly, while also presenting the possibility to process other waste streams together with e-waste, making it not only a very sustainable solution but also financially interesting.

Model

As the specific composition of the different e-waste streams can vary, we are working on a procedure for determining the right amount of slag, the optimal temperature, viscosity and so on. This includes mass balances, energy balances, separation rates, thermodynamic models on the alloying, slag-forming and oxidation behaviors and viscosity predictions

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