Mag. Nitrate vs Mag. Sulfate

[razka3]

What's the difference between Magnesium Nitrate and Magnesium Sulfate? Can they be interchanged when using to "soften" the LECA? (along with Calcium Nitrate)

[John D.]

Magnesium sulfate is easily available (epsom salts), I haven't looked for the Mg nitrate. I would reccomend that you don't use them (Ca nitrate and Mg sulfate) at the same time in any high concentration. The calcium will combine with the sulfate to form gypsum which is not very soluble and will precipitate out. At low concentrations such as the normal fertilizer dilutions it's not a problem.

[razka3]

Thanks,

Just found some epsom salt in the closet, couldn't find it earlier - but had some Mg nitrate, was going to substitute, but don't need to now. Just curious what it would of done.

[Magnus A]

Now I am confused!
Ca makes water hard and if changed to Mg its become soft. You use Magnesium sulfate to bind Ca as gypsum and therefore you get softer water when you treat it with Mg-sulfate.
Or have I lost my mind?
So if you instead use Mg-nitrate you just raise the ion-concentration of the water.
What I refere to is the part "to "soften" the LECA? (along with Calcium Nitrate)" in the question above.

/Magnus

[Ray]

I think the "softening the LECA" thing was a misstatement.

To bind the clays and hold them as balls before firing, a variety of chemicals may be used. Some can be retained as soluble mineral salts after firing. Also, when the hot pellets exit the kiln, they are sometimes quenched with non-potable water containing who-knows-what? It might even be seawater.

By soaking the LECA in calcium nitrate and/or magnesium sulfate solutions (yes, dilute so gypsum won't precipitate), you can extract the "bad" sodium salts, replacing them with the calcium and magnesium ones, which are good for the plants.

That is a great pretreatment technique for coconut husk products, too.

[goodgollymissmolly]

Well, I certainly agree that Ca and Mg are usable by plants. The problem with both is that many of their salts are insoluble in water (it is Ca and Mg that are responsible for "hard" water. Mainly as carbonate salts).

If the LECA has sodium chloride (NaCl) contaminate it should easily be removed with water. Hot water should remove it quickly and completely, but hot is not required to get the job done.

For the removal of other less soluble contaminates you can use vinegar (5% solution of acetic acid). Virtually every acetate salt is soluble. Another great choice is ammonium nitrate. Every NH4 and NO4 salt is soluble so they assist in removing both insoluble anions and cations.

In short...if its NaCl you are removing then water is all you need and adding other stuff will not improve the removal process. If it's other salts then the suggestions above are very good choices. The addition of ions known to form insoluble salts should be avoided. That includes Ca, Mg, and sulfate (SO4--).

[orchids3]

Ray,
Have read your posts refering to this in several places. My chemist contacts say it is just not true. One taught at MIT (Chemistry and the other is a very good and active research chemist). There is just no chemical reaction that will take salt out of media - the energy levels of the reactions are just too high. Leaching or washing does take out a lot of salt - washes it out. I wonder if you have some chemical formula for what happons to salt with these chemicals that these advanced chemists have not heard about. Sorry I usually like and agree with what you say - but not this time.

[razka3]

Interesting,,, now I'm really confused! I've not taken much chemistry yet, but what little I know is not helping me!

I thought I saw a thread somewhere about the chemical process that is undergone when Ca and Mg are added to LECA that is contaminated.

On a side note, is the raised ion-concentration of the water a good thing with the added Mg nitrate?

[Magnus A]

razka3

No, orchids tends to dislike high salt consentrations, especially if the salt ia accumilated in the substrate. therefore it is recommended to try to keap the ion concentration low.
This is why many orchidgrowers by equipment for reverse osmosis to take away dissolved salts from the tapwater. Some even by conductivity meters and pH meters to get total controll over the water quality.

/Magnus

[Ray]

Goodgolly, I don't recall who did the study, but it was shown experimentally that the CaNO3 & MgSO4 did accelerate the extraction, as the sodium salts are apparently not simply precipitated on the surface. The experiment was run with both LECA and CHC.

If I recall, materials were soaked for 24 hours, one in water, the other in the solution, then they were dumped and it was soaked another 24 hours in plain water, and then the TDS of the rinse water was measured. That process was repeated several times until the baseline water TDS was pretty much reached.

It took fewer rinsings to get the TDS down with the additives.