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Say one was to want to make struvite ( NH4MgPO4·6H2O) from humonia. If we start with the baseline premise that one litre of human urine contains 1.4 grams of phosphate salts, which should equate to 0.11 grams of pure phosphorous...

Could you show us how you'd go about figuring out how much magnesium to add to the humonia in order get the maximum amount of MgPO4 out of the deal?

M:P molar ratio 1:1.1

I'd like to have a sort of baseline numbers to work with before I start doing this, and see what pans out. As it stands, the plan is to add very small amounts of Mg and note when the precipitate stops forming, but was wondering if you could help offer something a bit more scientific.


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Well something I haven't thought of in forever until you just brought it up, but it was improperly measured ingredients for some "sparkly powder" recipe for homemade fireworks. Sulphur was the main ingredient anyway and instead of sparkling, it was a pretty explosive reaction that split a couple inch thick mortar in 2. 

Maybe its a better idea to do the calculations the right way after all. That sorta sucked thinking about it now.

So, Vlad, could you tell me how exactly you made the NH4MgPO3? Seriously, this is extremely helpful. Anyways, I think the way you could be sure what something is going to react with might be related to the bonds and such. I will take to the internet to learn about this. 

Yes I can. But first let me apologize if I wasn't clear enough in my OP. It wasn't a matter of 'how do you do this', or, will it react...just how much magnesium, minimum-maximum. Too little Mg and your not 'extracting' all the phosphates you could have, too much and your just wasting magnesium you paid for...That's why I was wondering about a ballpark amount...

First I took aged humonia, to be exact I used 1 litre in a clear measuring cup that I use for non-cooking stuff...I weighed out 4.84 grams of Epsom salt (I think I need much less, but wont know for a few days...unless you or someone can do the math), but any soluble Mg will do. I then poured the Epsom directly into the humonia and stirred. The Epsom dissolved and after a couple of minutes of stirring became cloudy with precipitates. I added another 4.84 grams of Epsom twice more, just to see if more precipitates would form (eyeballing it)...

I left it to settle, then I slowly poured off most the liquid effluent, swished around what was left because otherwise the precipitate just sorta clings to the measuring cup, and poured that through a mesh to catch the precipitate. Dried it in the sun. Whats left is a white, cakey, crumbly powder of struvite. That's it. 

I then took the liquid effluent that I poured off and added more Epsom salt just to see if any precipitates would form. None did, seems like I had 'used up' all the phosphorous already...

BTW...Just to be clear, I did not make NH4MgPO3-6H2O as you suggested, nor could I, as PO3 is rather exotic...but I did make struvite... NH4MgPO4-6H2O

Sorry, I meant PO4. Also, I just noticed something:  "If we start with the baseline premise that one litre of human urine contains 1.4 grams of phosphate salts". If we assumed that 100% of the phosphate salts are in the form of Ammonium Phosphate then we could have something to work with. I'll just need to check that Mg can synthesize with Ammonium Phosphate. 

Vlad Jovanovic said:

BTW...Just to be clear, I did not make NH4MgPO3-6H2O as you suggested, nor could I, as PO3 is rather exotic...but I did make struvite... NH4MgPO4-6H2O

I don't think that quite all the phosphates are in any one form. See your urine contains some magnesium already, so once the uerea converts to humonia (simply by storing) and the pH starts to go up, a number of different precipitates probably start to form. I believe that this would be 'the cloudy stuff' at the bottom of your humonia storage bottles...CaPO4, MgPO4 etc...

Just that these other 'micro elements'  (I'm guessing various divalent cations mostly) do not exist in your urine in enough quantities to come even close to precipitating out all that P by themselves...(hehe I couldn't resist...P meaning phosphorous not urine :)...

Vlad, let's wait for your results and see where this takes us. As of yet, the answer is "un-google-ble".

Yeah, I'll probably post all that stuff over in 'Fish-less', I know you wanted to keep this about the math/chem...

How did the results go? How much did you end up with? How much Mg did you use?

I've been interested in your struvite experiments for quite a while, but the chemistry is over my head.  It looks like you have made good progress, and are well on your way to making the nutrients you wish to make.

I'm wondering why you did not follow Hennig Brandt's method of heating the piss.

I'm also wondering if you will publish a final how to manual?  

I feel this is a very important step toward independence.  It may sound a bit pessimistic but we may not always be able to buy plant nutrients at the garden shop, and the ability to produce the chemicals we need seems like a very good way to be prepared.

I know you have figured out all your ratios, but I ran across this short article where they are using 64% MgCl with swine effluent.  You might find it interesting.

Thank you for sharing what you are doing.

Vlad Jovanovic said:

Yeah, things in everyday life are usually complexes, or complex...and rarely pure..... I imagine if we suppose for a minute we're talking about 0.11 grams of phosphorous it would be easy for you to calculate the amount of magnesium required. But that is probably not a practical way of looking at things given the 'impurity' of the materials at hand...

Basically, I was trying to avoid a Hennig Brandt type situation...but no worries as both the precipitate (struvite) as well as the effluent will be put to good use...

Man, I've only made it about a third of the way through that first link, and my head is reeling...

Hi Bob, Yeah it's been working out real well. I've streamlined the process and am pretty happy with it. 

The reason I didn't follow Hennig Brandt's method...and the "Hennig Brandt type situation" I was referring that his method was INCREDIBLY inefficient/wasteful (not to mention needlessly complicated)...we know that now.

Thanks for the article. Yeah, you can pretty much use any Mg source as long as you respect some other basic principles, you'll be alright... (sorta how you can use many different NH4 input sources in whatever version of bio-ponics (peeponics, aquaponics, vermiponics, store bought organic hydro nutes, duck-a-ponics, Ace hardware ammonia) long as you respect the basic principles and ratios, they will all result in nitrification i.e. oxidizing NH4 into NO3...

There are a bunch of struvite updates/observations and pics in the link that Chris posted over in the 'fish-less' group.

Thanks for taking an interest.


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