Separating metals from plastics is a key stage in recycling processes, especially when the input material consists of mixed fractions that are difficult to treat with conventional systems.
To assess the real separation potential, Stokkermill carried out a series of tests with its own laboratory electrostatic separator on PVC flakes contaminated with aluminium.
The test demonstrated the ability of the electrostatic process to concentrate the aluminium in a conductive fraction, separating it from the main PVC fraction. The tests were carried out at an operating voltage of 30 kV on two material samples with different particle sizes.
1. How does an electrostatic separator work?
An electrostatic separator exploits the different electrical properties of materials to separate conductive particles from non-conductive ones.
In the machine used for the test, the material is fed onto an earthed rotating stainless steel roller and passes through the electric field generated by the high-voltage electrode.
Aluminium, being a conductive material, quickly transfers its charge to the roller and is thrown forward by centrifugal force. PVC, on the other hand, is an insulating material: it retains its charge, stays pinned to the surface of the drum and is discharged downwards into its own collection fraction.
The system also provides an intermediate fraction (middlings), intended for particles that show intermediate behaviour during separation.
2. Electrostatic separation of aluminium and PVC
The test was carried out on PVC flakes contaminated with aluminium, containing fine metal particles and plastic fragments. Two samples were analysed:
- one sample with an estimated particle size of approximately 2–6 mm;
- a second sample with a declared particle size of 1–3 mm.
In both cases the contaminant consisted of aluminium flakes and thin aluminium foils.
The laboratory electrostatic separator divides the material into three distinct fractions:
- Conductive fraction – aluminium
- Intermediate fraction – middlings
- Non-conductive fraction – PVC
This configuration makes it possible to assess not only the ability to remove the metal, but also the behaviour of the plastic fraction during the process.
3. Test results: aluminium concentrated in the conductive fraction
In the first sample, the conductive fraction consisted of a very small quantity of material, made up mainly of thin flakes of bright aluminium with minimal plastic content. Separation of the metal proved effective.
The second sample also produced a small conductive fraction made up of aluminium flakes and thin foils. In this case, a few light-coloured fragments were observed, attributable either to entrained PVC or to painted aluminium or aluminium laminated with plastic.
4. PVC separated from aluminium
In both samples, the non-conductive fraction was the main fraction. In the first sample it consisted predominantly of fine, thin and curled PVC flakes; in the second, thin white and grey flakes prevailed.
In both cases, no aluminium was detected in the PVC fraction on visual inspection.
The result confirms the value of electrostatic separation for treating plastics contaminated with conductive metals, where the difference in the electrical properties of the materials can be exploited for targeted separation.
5. The intermediate fraction: a parameter to optimise
In addition to the aluminium and PVC fractions, the process produces an intermediate fraction.
In the first sample, this fraction was visually estimated at around 25–35% of the total material and consisted mainly of PVC with thicker, more compact flakes. In the second sample, the intermediate fraction was also made up predominantly of thicker, stiffer flakes, with a slightly lower volume than in the first.
The test therefore highlights an important aspect for process development: the yield of the PVC fraction can be optimised by adjusting the separation parameters and the preparation of the material. According to the test observations, the behaviour of the intermediate particles appears to be influenced more by the thickness and shape of the flakes than by the presence of contamination.
6. Stokkermill laboratory electrostatic separator
The separator used for the tests is a laboratory electrostatic drum machine equipped with:
- feed hopper;
- stainless steel vibrating feeder;
- electromagnetic vibrator with adjustable flow rate;
- stainless steel roller with adjustable speed;
- electrostatic generator adjustable up to 35 kV;
- adjustable-position electrode;
- material pre-heating system;
- adjustable splitters;
- three collection drawers for the conductive, intermediate and non-conductive fractions.
During the tests described, both samples were processed at an operating voltage of 30 kV.
7. Why use a laboratory electrostatic separator?
Laboratory tests make it possible to assess the behaviour of a material in advance, before developing or sizing an industrial plant. In the case of aluminium-PVC separation, the test showed:
- effective concentration of the aluminium in the conductive fraction;
- a small, visually clean conductive fraction;
- a main PVC fraction with no aluminium detectable on visual inspection;
- consistent behaviour across the two samples analysed;
- the possibility of adjusting process parameters to optimise the PVC yield.
The test concludes that electrostatic separation at 30 kV proved effective in removing aluminium from the PVC flakes in both samples analysed.
The assessments reported are based on a laboratory test and on visual examination of the output fractions. Results depend on the characteristics of the material treated and do not in themselves constitute a guarantee of performance on an industrial scale.
8. Electrostatic separation tests on real materials
The Stokkermill laboratory can carry out separation tests on real samples, to verify the behaviour of the material and identify the most suitable process parameters.
In PVC and aluminium separation applications, characterisation of the input material (particle size, shape, thickness and composition) is essential for predicting the behaviour of the different fractions.
Stokkermill develops solutions for the separation and recovery of materials in the recycling sector, with electrostatic technologies dedicated to sorting conductive and non-conductive materials.
01/10/2026