Taking Aluminium Recycling to Another Level

Eddy Current SeparationWith Novelis opening the world’s largest aluminium recycling centre in Nachterstedt, Germany in October 2014 (Anne Kane, Resource, Winter 2015, Page 23), the big question is how to keep it supplied with secondary aluminium.

The new plant is reported to be able to process 400,000 tonnes per annum from 18 different scrap streams and covers over 60,000 square metres of land.  The main feed stock is Used Beverage Cans (UBCs).  Globally Novelis reports to recycle over 42 billion aluminum UBCs annually.

In the UK, around 8 billion aluminium beverage cans are used each year with around 60% being recycled, which is lower than in may parts of Europe.  So how are the aluminium cans recovered?

1. Private Collections – Charities often arrange for aluminium can collection and then onsale, although this has dropped in recent years;

2. Pre-Sorted Refuse – With some segregation at source, councils collect and then separate materials of which one if the aluminium can;

3. Mixed refuse – This includes feedstock to incinerators with some aluminium being recovered prior and also after incineration;

In all cases, the aluminium can has a real value and as the number of aluminium cans being used increases there is money to be recovered from the waste.

One of the most common automated methods of recovering the aluminium can is using a magnetic separator called an Eddy Current Separator.  This actually propels aluminium cans out of the non-metallic waste (plastic, paper, etc) and offers to cleanest and safest separation solution.

Does the new Novelis plant in Germany mean that there has to be more automated recycling using technology like the Eddy Current Separator and, if so, will this significantly increase the recycling rate?  It will be interesting to see how this huge new plant is kept fed.

How do you separate stainless steel?

Separating and recovering stainless steel is an issue faced by many companies processing material, from the Recycling industry (where the focus is recovery or removal) to Food manufacturing (where the aim is purely removal).  So how can you do it?

Firstly, the assumption is that stainless steel is non-magnetic?  But is that actually the case?

In fact, the answer is, unfortunately, a little complicated.

As for whether they are magnetic, the answer is that it depends. There are several families of stainless steels with different physical properties. A basic stainless steel has a ‘ferritic’ structure and is magnetic. These are formed from the addition of chromium and can be hardened through the addition of carbon (making them ‘martensitic’) and are often used in cutlery. However, the most common stainless steels are ‘austenitic’ – these have a higher chromium content and nickel is also added. It is the nickel which modifies the physical structure of the steel and makes it non-magnetic.

So the answer is yes, the magnetic properties of stainless steel are very dependent on the elements added into the alloy, and specifically the addition of nickel can change the structure from magnetic to non-magnetic.  Also, it is possible for the magnetic permeability of austenitic steels to be changed during processing. For example, cold work, welding and abrasion are liable to increase the amount of martensite and ferrite respectively in the steel.

In industry, whether that is in recycling or food processing, the stainless steel has been ‘worked’ and the vast majority has a recognizable albeit low magnetic attraction.  Then it is a case of using the right technology to enable separation.  This can be achieved with:

  1. Metal Detectors
  2. Magnetic Separators

The most recent technological development in Magnetic Separation is the High Intensity Separation Conveyor, which is shown to separate stainless steel items such as razor blades.

So to answer the question, yes it is possible to separate stainless steel and the type of technology needed is very much dependent on the application.  Further information can be obtained by speaking with one of Bunting’s technical engineers.