nikotyna1939 - 1-5-2019 at 17:03
i want to know how to separate elemental metals from alloys like brass,bronze,cupronickel,nichrome and stainless steel
j_sum1 - 1-5-2019 at 17:23
In industry this is called refining.
There are a bunch of different methods employed -- all of which require a lot of energy.
If there was one commonality to the various processes it is selective oxidation or reduction or both.
Smelting processes involve heating the metal to above melting and then performing chemistry at the interface between the liquid metal and a slag
floating on top.
Other processes involve bubbling oxygen through which reacts with the more reactive metals. (Less reactive metals are more problematic. In the steel
industry they are called tramp and are really fifficult to remove from steel: Over time they accumulate in scrap metal feeds.)
The methods you are pobably after are wet chemistry methods.
Begin by dissolving your metal in a suitable acid.
Then separate your dissolved salts by whatever means you can -- including precipitation reactions, recrystallisation or electrolysis.
Then, once separated, perform whatever reduction is necessary to get your elemental metal back.
I am currently attempting a method like this to extract vanadium from tool steel screwdriver bits (around 0.5% V). I have not been particularly
successful so far.
A third method (which is an extremely cool idea but I have not seen in practice) is called zone refining. This is used to obtain ultra high purity
metals from reasonably pure stock.
The metal being refined is cylindrical in shape. A sleeve is placed around the metal. This sleeve, which is in contact with the metal, contains a
high temperature heating element (usually via induction I believe) and a cooling unit. As the metal is passed through the sleeve it is heated to
melting and then solidified. In this way a zone of molten metal passes from one end of the cylindrical rod to the other. As solid metal crystals are
formed, they tend to expel impurities. This is because impurities lower the melting temperature of a mixture. Hence the pure metal solidifies first.
Numerous passes of the zone refiner are done to achieve the desired purity.
As you can imagine, precise control of the temperature is required over a short distance with a huge thermal gradient. And this is all happening at
high temperature in an inert environment. But if you need it, this is the way to go.