# Disposing of Magnesium nitrate?



## pureth (Jun 5, 2013)

Hello.
I've been following a tutorial/post by 4metals on disposing of wastes from silver refining: http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=47&t=1300

The process i have followed is:
1., Solution (Copper nitrate) PH raised to around 2.5 (with soda ash).
2., Iron placed in Solution (Copper Nitrate).
3., Solution filtered (Ferric Nitrate).
4., Magnesium Oxide added to Solution (Ferric Nitrate).
5., Solution filtered (Magnesium Nitrate?).

I now have a clear solution with a ph of around 2.5 (Magnesium Nitrate?).

How can i dispose of this solution (Magnesium Nitrate?) in a safe manner?
THANK YOU IN ADVANCE. THIS FORUM IS A GOLD MINE.


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## vyper (Jun 6, 2013)

Well before you raise the pH of the copper solution I hope your adding a copper bus bar to solution to drop out any possible values that may still be present in solution. Then after addition of Iron to drop copper from solution, when you add the magnesium oxide to solution do it in small incriments because the pH will change slowly and you don't want to over do it. I would suggest mixing the oxide in water first (magnesium hydroxide) but I could be wrong there as I use sodium hydroxide myself. Works faster but harder to filter. Once the solution is clear stop adding solution and check the pH. You want a pH of around 7 which is the pH of water. Filter and dispose of solution.


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## 4metals (Jun 6, 2013)

Considering your waste is from silver refining I would do it a little different, 

The copper remains the same as does the pH adjustment and the iron to drop the copper. Thus far it is just straight cementation. 

To get rid of the iron, which should be the only thing in there, I would drop it with liquid caustic. Iron drops out pretty quickly at a pH around 3.5 basically as slimy rust brown colored precipitate that does not like to be filtered. The remaining liquid should be relatively free of other metals but I would raise the pH to neutral, it shouldn't take much more caustic as the buffer strength of the acid is greatly depleted to get it up to 3.5.

The use of the Mag Ox forms a denser cake of hydroxides and the magnesium drops out as well as the solution becomes strongly alkaline with the other metals remaining in solution. The method I stated in the post you reference is usually done on spent aqua regia so the left over acid is not as high in nitrates but also may contain zinc and nickel form the alloys you started with. That is where the Mag Ox comes in. 

Straight nitric dissolves and cementation shouldn't have much more than silver, a little gold (which came out before you cemented it), and a little palladium all of which will come down with the silver. All that should remain is copper. Iron takes care of that and caustic takes care of the iron leaving you with a sodium nitrate solution. 

If you are doing this on an industrial scale I would be running the neutralized solution for metals on an AA or ICP before discharging to sewer.


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## pureth (Jun 13, 2013)

I wasn't using a bus bar but i left clean copper in solution a week or more. Will this suffice?

From your post 4metals, I find it difficult to understand the advantage of using Mag Ox vs Caustic.
I would have thought the only difference when using Caustic is that it will cement any magnesium in the solution as well as all those metals it's bellow on the reactivity chart + the different composition of the cemented material it produces that you've mentioned.
I've read your post at least 4 times! What am i missing?

Prior to posting I had already gone through the whole cementation process and added Mag Ox to my waste solution. Is it safe to neutralize and dispose of this?

Also do Mag Ox/Caustic themselves adjust the PH of solution?


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## butcher (Jun 13, 2013)

A bit off subject from your question but somewhat related.

I tend to keep my nitrate waste separate, from my other waste, copper nitrate where silver or palladium has been cemented from a silver nitrate solution is useful to me, a weak nitric acid can be made from it by evaporating it to salts, heating these strongly and bubbling the gases into water leaving copper oxide powders which are also useful, another use for the used copper nitrate is it can be used to dissolve base metals lower than copper in the reactivity series, it can also be useful in electrolytic experiments, or in the electrolytic cell with a graphite anode to plate out copper lowering the copper content to where it can be used in a impure silver cell to break down sterling silver (Laser Steve's process).

When treating waste, I tend to try and see if there is some other use, many times I see these as byproducts of reactions, and not so much as waste, many times there is a place they can be used to do more work or to make a different chemical or product, before they have to be treated as waste.

When you treat your waste, check out the reactivity series of metals, it will be helpful, depending on the waste.

Stock pots, I usually maintain a variety of stock pots, or settling jars besides a high value stock pot waste aqua regia with traces of higher value metals, or the waste silver pot, I will normally have stock pots that are for the more dirty waste, not really true stock pots but they collect any missed values before the solution is treated for waste.

We use copper to cement out values from solution, copper works well because it is just above the more precious metals in the reactivity series, this will cement our values from solution, use up free acid, and put copper into the solution (usually with the other base metals in solution), we need the solution at least a little acidic for this to occur, this is usually no problem if you keep your caustic waste separate from the acidic waste, the copper will only be consumed to replace metals lower in series and to consume free acid, after this no more copper will dissolve. 

Ammonium waste is normally kept separate from other waste because of the dangers involved with the complexes they form.

Caustic waste is also kept separate, it can be normally be used for things like solder-mask removal, and can also be used to help neutralize acid waste when it is no longer useful, note in caustic waste like acidic waste there is sometimes traces of values, and these should be watched for and collected.

After we cement values out of an acidic waste using copper, and collect the mud's formed, this mud will contain values and some copper, and may contain some other salts of metals depending on waste like silver or lead chloride... the solution is now a mix of copper and the other base metals, using Iron to cement copper out as a metal powder is what I have found to work the best, aluminum makes a goop and sludge that is so hard to dry I try to avoid it, aluminum also gives off hydrogen gas from acidic solutions, this does tend to lower the acidity but is not worth the trouble of the sludge it forms in my opinion, aluminum also drops out many other metals (as compared to iron) with your copper, for a better understanding look at your reactivity series chart, zinc works better than aluminum but also drops all of the metals in solution below it in series including iron, but is easier to dry the sludge formed later.

The copper cemented from solution with iron can be cleaned and reused, if storing copper powder or salts I normally keep them under water for storage or under a dilute solution of acid and water, air will oxidize copper powders or salts, and can form copper carbonates that do not dissolve easy later when you wish to use these powders or salts, if you do not care to reuse the copper powder or salts, drying the copper powders, the copper salts can be dried and heated to form copper oxide. 

This will leave us with an iron chloride or sulfate solution depending on our waste, or a combination of iron acids, and other base metals, (by the way sometimes I like to keep my chloride waste and sulfate or other acid wastes separate also but I will not go into that to confuse this post more), this solution too can usually be reused it is still strongly acidic and the solution of these metal salts in solution are corrosive to metals below them, Iron chlorides will dissolve an awful lot of copper when heated and concentrated with copper, this can also help to reduce the volume of your waste as it consumes metals, this thick concentrated solution when diluted will precipitate the copper back out as copper I chloride with a much reduced volume of waste than you had in the beginning.

The Iron and other base metal waste is still acidic (free acids by now have normally been consumed, but these base metal salts are still acidic and corrosive), here if we neutralize the solution we will precipitate out most of the metals, actually I normally bring the waste up towards the caustic side with a goal of around pH 9.5 this is where the most metals will drop from the solution, after letting the mud settle and decanting liquid to another bucket I will add a bit more of acidic waste to this 9.5 pH solution to bring it to a neutral of pH7, here a tiny bit of metals will precipitate but leave me with a clear salt water solution, mostly sodium chlorides, but there are a few other very reactive metals besides sodium involved, but these are normally the more soluble metals in our environment, this solution is allowed to settle well before decanting the clear salt water to be disposed of, well I have tried to condensed this solution to a thick brine and use it to make HCl by distilling it with sulfuric acid, and have tried to use it in electrolytic cells, or to lower the acidity of the next batch of waste, but I cannot say that by doing so I was not going to more trouble or using more time than it was worth. ( I Have a septic tank so it is harder for me to dispose of salt water solutions, I do not want the salt water killing my good hard working bacteria).

To neutralize your waste solution to precipitate metal hydroxides from solution, you can use quite a few different alkaline or caustic solutions or powders, sodium hydroxide is one of the stronger, potassium hydroxide will work here also but is less common and more expensive for me, so this is where I normally start to lower my acidity, but I will normally try to conserve my caustic soda, and will also use other caustic or alkaline to lower the acidity further, I generate a lot of wood ash, burning up to three cords of firewood a year to heat my home, not counting all of the slash piles of wood I burn to clean my woods, I can leach my wood ashes to make caustic soda using rain water, or use the wood ash directly to lower the acidity of my waste, backing soda also is used but can foam bad so if you use it you have to be aware of delayed foam over reactions, so I will normally just use it only after the acidity is much closer to neutral, lime also will lower the acidity and can help to make many of the metal hydroxides less soluble, it is not as strong as the caustic soda for lowering acidity so I will normally use the lime after the solutions acidity has been lowered (or pH raised closer to neutral), I have not tried but from what I understand sulfides work well to make insoluble metals and is used in waste treatment, but I will have to do a lot more study on that before trying it out.

Processing electronic scrap generates an awful lot of waste compared to higher grade scrap like karat gold, I have many 5 gallons buckets of base metal sludge, these are a big pain for me to deal with, it is very hard for me to dry it is damp here and rains all winter, having to keep my buckets covered the sludge does not dry, summer it seems they will dry but it takes a long time, especially if they are left in the bucket, spreading them out on trays in the sun helps, but I only do this with a few tray, so several buckets usually have to wait to get their turn, I have been trying to come up with a better solution to my problem of drying waste, I do have plenty of fire wood I can use for heat, but can only burn in the wet winter time summer is too dry when you live in the forest, so fire is not an option for drying in summer, electric heat or gaseous fuel are too expensive, I have also thought if I can get the sludge somewhat dry and squeeze it through a screen to make smaller pills, pellets, or spaghetti, it would have more contact with air circulation and would dry much faster, as in the bucket or larger clumps in the drying tray take way too long to dry out.

The air dried sludge from our waste is mostly metal hydroxides (some oxides and metal powders), these hydroxides can be made safer for the environment by heating them strongly to oxides, after dried a roast in air will make the hydroxides into oxides safer to dispose of, many of the metal hydroxides will become soluble in water again and can be leached into the soil and possibly into the under ground water source (depending on disposal site or method), but the oxides of these metals do not redissolve as easily, making the metal waste powders much more friendly for waste disposal and in helping to do our part in keeping our water fresh for us and future generations.

I have rambled on enough, and could bore you with more about waste, but I guess I will get back out to the lab and try to deal with some more of my 5 gallons of elephants in the lab.


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## pureth (Jun 20, 2013)

Thank you!

Is it safe to dispose of cemented copper and iron in landfill?


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## Lou (Jun 20, 2013)

As long as they can't leach out. I would still keep the copper around and accumulate and send to the copper smelter to get any trace payables, that and it's copper. Iron is environmentally good to go, but it's easier to just have the waste hauler pick up the filter press cakes of Fe(OH)2/3.


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## butcher (Jun 20, 2013)

I am no authority on waste disposal, or the laws, so my post here is just what I believe, I have no facts to support this believe.

A lot of the disposal depends laws and regulations in your area, not every land fill is the same, not every country treats their trash the same, so much depends on how the trash in your area is treated, and the laws in your area.

Dry elemental elemental copper metal even as powders, or copper oxide dry powders, would be less of a risk for our environment that the copper in acid or alkaline solution's are, the copper as elemental copper or oxide although more stable is still not totally safe, so it should not just be dumped anywhere.

The copper in solutions should be removed from solution and made into copper metal powders (cemented from solution with a metal higher in the reactivity series like iron) or at least copper oxides, and dried well before disposal, this will put them into a safer form of the metal.

I do not know anyone who will buy or take this copper waste for recycle,which to me seems such a shame, although it would be easy to recycle, and with copper being such a sought after metal and the present prices, it seems truly a waste of a good resource, personally at this point I have saved my copper powders, and have plans to use them eventually. just the though of people talking about melting penny's for copper but throwing copper in the trash seems such a waste of both of these metals or money.

Depending on the laws in your area, How you can responsibly and legally dispose of copper, would depend on your local laws and the types of landfills used, so you should check these out in your area before of acting, or disposing of your waste.

Many areas now a days have what they call secured landfills, basically landfills to help keep trash out of the water tables, so we are not drinking peoples trash, many of these sites also have recycle area where you can place goods for recycle, such as glass, metals, oil... 
You may find you can leave your copper powder in this recycle area at your dump.

Some secured land fills will let you dispose of dry copper powder metal, or copper oxide, if it is secured in a proper container which will contain it properly, check your area to find out if this is the case in your area or with your land fill.

In many areas there is also a hazardous waste amnesty day, where you can take your hazardous waste without being charged.

Basically check your local laws and with your landfill.


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## pureth (Aug 9, 2013)

So can I pour the neutralised & filtered magnesium nitrate solution down the drain?


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## butcher (Aug 9, 2013)

I would tend to try to use it.

It is hard to dry out with just trying to let it evaporate in open containers, as it will absorb water out of the air, and heating will decompose magnesium nitrate forming magnesium oxide, the nitrate will come off as nitrogen oxide gas, which if these gases are captured and bubbled into a little water will form dilute nitric acid.

2Mg(NO3)2 –heating-à 2MgO + 4NO2 + O2

3NO2 + H2O à 2HNO3 + NO

A little hydrogen peroxide in the water can help, it supply’s oxygen to help the reaction.

2NO + O2 à 2NO2
2NO2+ H2O2 à 2HNO3


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## pureth (Aug 10, 2013)

I only have a small amount and want to dispose of it, would it be safe to use the drain?


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## butcher (Aug 10, 2013)

I do not like the idea of advising people to pour any chemical down the drain, as that will eventually end up in someones water supply, many very dangerous household chemicals get poured down our drains, and the next town down river is treating this water for drinking.

If we say you can pour a little of a certain chemical down the drain, what is a little? it may not mean the same to everyone, and with many of our solutions they may not be pure substances but can be loaded with other toxic metals. 

Pure magnesium nitrate can be used as a fertilizer, but you may not have a pure magnesium nitrate solution, you could have other dangerous metals involved.

Is this solution clear? From your description above, I do not see where you raised the pH to about 9.5 and then brought it back down to neutral pH 7, (to remove many of the metals involved). without knowing what you have I have a real hard time saying you can safely dump it into a sink drain.


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