**5. Recycling capability of magnesium alloys**

Recycling metals is critical to their overall sustainability. Magnesium retains most of the necessary physical integrity when recycled if it is not contaminated. Remelting and forming of ingots are the main energy requirement for recycling, but generally, secondary production of magnesium ingots requires substantially less energy than primary production [32]. Otherwise, this process's greenhouse gas emission mainly depends on the selected cover gas; generally, a cumulative 3.6 kgCO2eq/kg of secondary magnesium produced could be released [33].

Today the recycling of magnesium is technologically feasible. Currently, the primary source of magnesium alloy scrap comes from the magnesium die-casting industry (the most common method of fabricating new magnesium alloys parts). Die casting foundries can manage the amount of process scrap in three different ways:


On the other hand, the processing of end-of-life vehicles is today still not easily practicable and needs technological improvement. Shredded magnesium can be contaminated with iron, nickel, and copper from coatings and fasteners, all of which are detrimental to the corrosion resistance of the metal. Although the lowvalue markets mentioned above (aluminum alloys and steel desulphurization) can absorb low-quality post-consumer magnesium, options for separating it from other metals are necessary for magnesium structural alloys applications. The main viable option is melting magnesium in contact with molten salt to remove oxides from the liquid metal. This process is today not fully capable of separating magnesium from other metals. Another possibility is metal vapor distillation: due to higher vapor pressure and low boiling point of magnesium compared to aluminum and many other metals.

On the other hand, a too high magnesium-aluminum chemical affinity results in poor separation. A much more viable route is collecting and separating magnesium from the high-quality scraps made of aluminum-magnesium alloys: the beverage can stock (e.g., the aluminum 3xxx series alloys employed for the body, the aluminum 5xxxs series used for edge), and the aluminum 5xxxs series today preferred for body panels of automobiles. To separate magnesium, chlorine gas bubbling through the liquid alloyed metal can remove magnesium by reaction, but such a hydrometallurgy process requires large amounts of chlorine and energy. Further recent advancements in magnesium separation from aluminum alloy scraps focus on electrorefining. It is a process in which metals are purified in an electrolytic cell where the anode is the impure metal, and the cathode is a very pure sample of the metal [36]. To summarize, an efficient recycling route for magnesium by automotive scraps is still an issue. Broad approaches based on the design for corrosion-free assembling and easy disassembling of magnesium parts in the multi-material structure are on track.

*Magnesium Alloys for Sustainable Weight-Saving Approach: A Brief Market Overview, New… DOI: http://dx.doi.org/10.5772/intechopen.102777*
