Nitrate reduction using Devarda's Alloy and Sodium hydroxide

[Adam Wang]

Story time: So recently, I started off as a research assistant in a lab studying corals at the local university; and I was given the task of going through all of the chemicals on the shelf, labelling them and writing down their uses. That was when I came across a small bottle of Devarda's alloy powder. Upon research, I found out about some of it's nitrate reducing properties; and a pretty dumb, but interesting idea popped into my head.

Since the reaction that takes place goes along the lines of this, and the ammonia which gets produced is gaseous :

3 NO3- + 8 Al + 5 OH− + 18 H2O → 3 NH 3 + 8 [Al(OH) 4]−

Would it be possible for somebody to make a solution of Devarda's alloy, Hydrogen peroxide and DI water, which could be slowly dripped into a large system over time to export nitrates into the air? The only problems that I think arise from this is: firstly, the aluminate that gets produced; and secondly, the possibility that my sump will smell like pee due to the ammonia gas.

 

[Randy Holmes-Farley Verified Community Expert]

I think there would be all sorts of different reactions between aluminum metal and seawater that you may not want (such as conversion of bromide to toxic hypobromite), but most importantly, you are producing more potentially soluble aluminum than you are decreasing nitrate, and aluminum is toxic to corals (in my tests) at 0.5 ppm. You are also producing ammonia which will simply renitrify to nitrate.

Chemistry And The Aquarium: Aluminum In The Reef Aquarium ? Advanced Aquarist | Aquarist Magazine and Blog
http://www.advancedaquarist.com/2003/7/chemistry

 

[Adam Wang]

I think there would be all sorts of different reactions between aluminum metal and seawater that you may not want (such as conversion of bromide to toxic hypobromite), but most importantly, you are producing more potentially soluble aluminum than you are decreasing nitrate, and aluminum is toxic to corals (in my tests) at 0.5 ppm. You are also producing ammonia which will simply renitrify to nitrate.

Chemistry And The Aquarium: Aluminum In The Reef Aquarium ? Advanced Aquarist | Aquarist Magazine and Blog
http://www.advancedaquarist.com/2003/7/chemistry

Hmmmm, nevermind then; but since the ammonia is released as gas, wouldn't the ammonia be dissipated within the air?

And if I'm using this method within a FOWLR tank, do you think it's possible? Since you've stated yourself that aluminium gets removed through skimming.

 

[Randy Holmes-Farley Verified Community Expert]

Hmmmm, nevermind then; but since the ammonia is released as gas, wouldn't the ammonia be dissipated within the air?

And if I'm using this method within a FOWLR tank, do you think it's possible? Since you've stated yourself that aluminium gets removed through skimming.

With the reaction taking place in seawater, it wont' release ammonia as a gas. It will remain in the water.

I really can't see a reason to try this. Too many things to go wrong.