Physical / mechanical separation

Most batteries consist of the same 5 types of material – an electrolyte (often part of the liquid removed in the previous step), plastics, papers, ferrous metals which are generally magnetic, and non-ferrous metals which do not contain iron and are not magnetic. Many batteries also contain carbon and oxygen.

It is relatively easy to separate these 5 groups as they have significantly different properties, such as their density, magnetic susceptibility, conductivity, and so on. The most common output streams of this initial separation phase are papers and plastics, ferrous metals, and non-ferrous metals. This is achieved through a variety of processes, combined together depending on the particular details of the batteries being recycled:

1. Magnetic

The output from the comminution stage runs along a conveyor belt while a second, magnetised conveyor belt runs overhead, attracting any magnetic material (ferrous metals) and separating it from the rest. These two streams run off their respective conveyor belts into different containers for further processing.

Outputs:

Ferrous metal particles
Non-ferrous particles

2. Electrodynamic

Electrodynamic separation utilises the triboelectric properties of different materials to separate them out. The triboelectric effect is a natural phenomenon whereby some materials take on a positive or negative electric charge after being in contact with other materials. For example, rubbing a balloon on your hair makes it negatively charged, allowing it to then stick to neutral or positively charged surfaces, such as a wall.

Outputs:

Usually 3 streams; ferrous metals, non-ferrous metals, and nonmetals.

A closer look at triboelectricity

The triboelectric effect happens because the balloon and your hair (which are neutrally charged in normal circumstances) exchange electrons when rubbed together, making your hair positively charged, and the balloon negatively charged. The electrons in the balloon are then attracted to the protons of other neutral objects, such as the wall. The force of this attraction causes the balloon to stick to the wall.

During triboelectric interactions, some materials become either positively charged, neutral or negatively charged to various degrees. This is known as the triboelectric series, and it explains how different materials will react under such conditions. Electrodynamic separation takes advantage of this effect, using the attraction, repulsion, or neutral reactions of different materials to separate them into various output streams.

There are a few other separation techniques that similarly use electromagnetic fields to separate various materials. For example, electrostatic separation, where a charge is applied along the conveyor belt with a cathode and anode end to separate conductive and non-conductive materials. Another common method is eddy current separation, which uses rapidly changing magnetic fields to induce currents in non-ferrous metals, causing them to be repelled and separated from the rest of the material

3. Sieving

Sieving is exactly what it sounds like. Materials are separated through a series of fine meshes that allow small particles through and leave larger particles behind. This depends on how comminution was carried out and how different material types break down during comminution into various sized particles.

Outputs:

Various, depending on input.
Black mass is sometimes separated out as the smallest particle in the mix (between 0.5 and 0.75mm), while 2 or 3 other streams are produced based on particle sizes (up to >2mm) and then further treated to separate out copper, aluminium, graphite (found in the black mass), and other potential contents.

It requires several stages of comminution to get materials down to a fine diameter, at which point black mass can be separated out as the smallest grains (with a diameter of between 0.5 and 0.75mm).

4. Density / buoyancy separation

Materials are separated based on their density or buoyancy in a particular solution, often using a zigzag separator. Some materials float while others sink depending on the density of the liquid they are submerged in.

For example, lighter elements (plastics and papers in most cases) will rise or float, while denser elements (metals and other heavy materials) will sink. Once separated in the solution, the materials are carefully collected to create different output streams.

Outputs: