Although thermodynamically feasible, in practice, magnesium metal is not used for the reduction of alumina in the metallurgy of auminium. Why?

Everyone knows:
$$\ce{Mg +Al2O3->MgO +Al}$$
This reaction is thermodynamically feasible.
Use can we this for reduction of Alumina. And produce Aluminium. Then why don't we not use this why?




If you compare the [magnesium price](http://www.metalprices.com/p/MagnesiumFreeChart) (about 2$ per pound)


to the [aluminum price](http://www.metalprices.com/p/AluminumFreeChart) (about $0.80 per pound)


you can see it is unprofitable. 


Even considering the elements' relative atomic weight, you would still be losing money if you did that. 


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