Preparation of Neodymium Sulfate From Magnets

Extracting Neodymium From Magnets
There are many types of magnets in wide use, but currently the strongest permanent magnets are neodymium magnets, which are a sintered powder of an alloy made from neodymium, iron, and boron with the formula Nd2Fe14B. Thus, this makes it a convenient source of neodymium for the amateur chemist.

Theory:
The separation of the neodymium from the iron and boron occurs in a few different steps. First, the magnet is dissolved in some dilute sulfuric acid to form iron and neodymium sulfate. Meanwhile, the elemental boron is left behind since it is not soluble in dilute acid. Then the mixture is heated to take advantage of the inverse solubility of neodymium sulfate. While most substances (including iron sulfate) are more soluble at high temperatures, neodymium sulfate is unique in that its solubility decreases with increasing temperature. As the solution of the two sulfates is heated, the neodymium sulfate crystallizes out.

Equipment:

• Hotplate 
• Electronic mass balance 
• 100ml graduated cylinder 
• 250ml beaker 
• 150mm crystallizing dish 
• Buchner funnel 
• Vacuum pump 
• Vacuum filtration flask 
• Blowtorch 
• #120 Sandpaper 

Chemicals:

• Neodymium magnet (Acid amount is given for a 50.00g magnet) 
• 300ml dilute sulfuric acid ~30% (I used battery acid)
• Distilled water

Procedure: 

1. The magnet is heated strongly with the blowtorch until the curie temperature is reached and all magnetism is destroyed. 
   
2. The Ni-Cu-Ni coating on the magnet is removed using the sandpaper in order to allow the acid to better attack the metal. 
   
3. 200ml of the sulfuric acid is measured out using the graduated cylinder and poured into the beaker.
4. The magnet was placed into the acid and immediately a vigorous reaction is observed with plenty of effervescence. 
   
5. The beaker is allowed to sit overnight for the magnet to dissolve. (The magnet can also be broken into chunks to speed up this step)
6. After sitting overnight, the liquid is poured off and another 100ml of sulfuric acid is added to the beaker to dissolve the remainder of the magnet.
7. After again sitting overnight, the entire magnet should be completely dissolved, but if this is not the case repeat the procedure of adding acid and pouring off the solution. 
8. Crystals of iron sulfate that have formed inside the beaker are dissolved using 100ml of distilled water. 
   
9. All of the solutions are combined and a vacuum filtration is performed to remove the insoluble boron particles. 
   
10. The filtrate is poured into the crystallizing dish which is evaporated on the hotplate set to 120˚C (the solution cannot be boiled since bumping is a severe issue).
    
11. After 100ml of the solution has evaporated, the solution is vacuum filtered while hot to remove the neodymium sulfate that has precipitated out. 
    
    
    
12. The neodymium sulfate is washed with some boiling water to remove the last traces of iron sulfate. 
13. The remainder of the solution is again placed onto the hotplate until a further 100ml of water has evaporated and the filtering procedure is repeated. 
    
14. A third evaporation and filtering of the solution is performed just like the previous ones to recover the remainder of the neodymium sulfate. 
15. After three crystallizations there is very little neodymium sulfate still in solution and so no further recovery is performed. 

Result:

The first crystallization yielded 6.83g of product, the second crystallization yielded 9.37 grams of product, and the third crystallization yielded 3.60g of product. This totals to 19.80 grams of product total. (Right filter paper is 1st crystallization, vial is 2nd crystallization, left filter paper is 3rd crystallization) 

According to the formula stated above, the molar mass of "neodymium magnet" is (144.24*2)+(55.85*14)+(10.81*1)=1081g/mol. Thus, the 50.00g of magnet that I used is 0.04625 moles, and since each mole of "neodymium magnet" contains 2 moles of neodymium, there should be a theoretical 0.09251 moles of neodymium in the magnet. One mole of neodymium sulfate contains 2 moles of neodymium so a maximum theoretical 0.04625 moles of neodymium sulfate could have been produced. One mole of neodymium sulfate octahydrate has a mass of 720.794 grams so the theoretical yield is 33.34 grams. The yield of this experiment is 19.80 grams which is a 59.39% yield. The reason for this mediocre yield is that at first I attempted to boil down the solution which resulted in major losses from bumping. Otherwise, the yield would probably have been higher. 

Conclusion:

I feel that this was a pretty successful extraction and that the final product is reasonably pure. However, each crop of crystals is slightly different. The first crystallization resulted in a fluffy powder that is less crystalline compared to the second crop. The second crop is the most crystalline and the densest, while the last crop seems to be a mix of the first two. This confuses me and suggests that a recrystallization may be needed.