# question on electrolisys of zinc, waste and bdg



## ericrm (Aug 31, 2014)

hi there, long time no see
i didnt know where to post to avoid making tree tread for nothing.
first question is about zinc sulfate electrolisys
i have read that you can plate out zinc in an oxygen free atmosphere or if you use pt electrode. before investing money i wanted to know if it is realy doable for the small guy and if i can empty a solution of zinc sulfate by using 2 pt anode or 2 titanium anode (if i work the same)

i know ther is a lot of post on treating our waste acid to make it safe, i wanted to ask you about how sure are you about the safety of those method. when the hydroxyde have dropped ,been filtered and ph have been neutralised, would you feel safe to evaporate to salt and use it on your property this winter (this is what i intend to do depending of what the big guys think)

edit: i have removed the bdg offer.


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## butcher (Sep 1, 2014)

ericrm,
I will try to give my opinion, or answer the some of the questions as I understand them.

First question is about zinc sulfate electrolysis
I have read that you can plate out zinc in an oxygen free atmosphere or if you use Pt electrode. before investing money I wanted to know if it is really doable for the small guy and if I can empty a solution of zinc sulfate by using 2 Pt anode or 2 titanium anode (if I work the same)

As far as using an inert anode to (plate or reduce) push metals out of solution, this can be done, If you plan on doing this I do not see why you cannot use a cheaper graphite anode as it would also be inert, although it can be attacked by the action of the gases evolved from the anode.

I am unsure of your reason for asking this question, if it is that you wish to plate zinc onto some other metal. or if you just want to remove zinc and try to keep some of the acid solution.

knowing what you reason or what you are trying to do here, can help us to possibly answer the question, or maybe help point you where to study for a better answer.

Zinc sulfate can be used to remove moss from roofs or side walks, if you have a solution of zinc sulfate you can evaporate and crystallize these salts, and then dissolve them again in a warm solution of dilute sulfuric acid, and recrystallize them for a more pure zinc sulfate salt.
Before doing this or using it on your house or on your walk, let me discuss this a little more, so you get a better understanding, I have made zinc sulfate for this purpose, but I did not use a waste solution that may contain other metals or acids, although I could have, as long as I was sure what other acids or metals were involved.
I used zinc from electrical conduit fittings and dilute sulfuric acid only, to make the zinc sulfate crystals, and dried them to powders, I had no other acids or metals involved.
I would not suggest using your waste solution on your property. 

With sulfate salts the sulfate (or sulfuric acid is has the least volatility of the acids), if a little of the other acids like HCl or nitric, or salts of these acids which are involved, and more volatile than the sulfuric or sulfates, and can be removed from solution with the evaporation or distilling off of these other acids as gases from the sulfate salts, you may have to add more zinc to consume all of the acid in solution to bring the pH closer to neutral (zinc being higher than hydrogen in the reactivity series displaces the hydrogen from the acids as hydrogen gases) the other acids (being more volatile) besides sulfuric or sulfate, can be forced from solution as you concentrate with heat or evaporation, you may need to bring the solution up to a temperature where these will be forced from solution at there boiling points, as you reach the concentration that these other acids are the most volatile in solution, and with re-crystallization you can force traces of these other acids or salts out of the zinc sulfate salt for a more pure zinc sulfate salt.

Now for the metals involved, zinc is high on the electrochemical series of metals, most of the more dangerous metals we normally deal with are below zinc, (and would be replaced by dissolving metal zinc in solution), although depending on what metals we may have involved in this solution or reaction there are many metals more reactive than zinc that can still be in the solution with the zinc, and these would need to be considered depending on the use intended for the zinc sulfate if these other metals more reactive than zinc were involved,, most of these metals may not be a problem depending on our intended use for the zinc sulfate, but some could pose dangers depending on the use of the Zinc sulfate and what this other reactive metal was, many of these other reactive metals would stay in solution as we concentrated and crystallized zinc from solution, as they are more reactive, but then again much of this depends on the metal and what it is, how reactive it is in the solution and other things like how easily these may form,from drag down, or crystalize out with the zinc salt, or be precipitated by the zinc salt...
with this in mind it would not be good to use zinc sulfate made from a waste solution unless you were sure of exactly what other metals were involved, and with our waste solution most of the time we do not know what other metals, or sometimes chemicals that can be involved...

I say do not use a waste solution or byproduct on your property.
Unless you are positive of what you have, or have made.

I know there is a lot of post on treating our waste acid to make it safe, I wanted to ask you about how sure are you about the safety of those method. when the hydroxide have dropped ,been filtered and pH have been neutralized, would you feel safe to evaporate to salt and use it on your property this winter (this is what I intend to do depending of what the big guys think)




Again I would not contaminate my property with a waste solution, or a byproduct of this waste, in fact I would not even add salt to my soil even if it was pure table or rock salt, there are chemical ice melting compounds which can act somewhat as a fertilizer, if I you do use chemicals to melt snow or ice you might consider these as they will not build up in soil to kill plant life.
These store bought ice melting compounds can be fairly cheap, so making your own does not really make any sense.
Contaminating your property makes even less sense.

I shovel or plow the snow or ice, or just wait for it to melt on its own, and do not use chemicals to melt it.

When treating my waste solution I am fairly confident of its salt content and the metals involved, and what the salt may contain. and confident of how I use, or dispose of it. Again I would not put it on my snow or roof, or dump it on my property without knowing.

As far as how you treat your waste or byproducts of your reactions, and what you do with them depends much on what you have, and how you prepare it. many of these can be reused, and others can be converted to other salts for reuse, others just need to be treated properly and disposed of properly, we can spend a lot of time discussing this, I will not go into detail here but will discuss just a few examples.

As we know with common knowledge on the forum copper chloride can be reused to dissolve copper in a recovery process, until contaminated with other metals like iron, or other reactive metals.

We can also take these copper chloride salts or solutions and convert them to copper metal, and other ionic salts to reuse the copper powders, we can displace the copper with iron, and we can also make a solution of iron chloride which can then be made into another useful product ( or treated further for waste), we can make a salt like iron sulfate to precipitate gold with, or we can take the copper chloride and convert it into another useful copper salt like copper sulfate that can be used in electrolysis, or another recovery process...

copper nitrate can be used as an oxidizer in a recovery process, or made into and another copper salt, or another metal nitrate salt, we can also recover a little bit of nitric or nitrates from the solution for reuse.

Sometimes with some of our reactions we can end up with fairly pure solutions, or gases that can be reused, or they can be converted into other salts and purified by crystallization, and re-crystallization for reuse, we can distill gases and make acids for reuse, some times we can even clean up these acids up of minor contaminates to make more pure acids, clean them up for reuse, and concentrate them. or even use the impure gases in some recovery processes.

Or we can use the byproduct form the reactions as a source for chemical we may have a use for.
We can take metal salts and convert them to another form of metal salt that we can use, or even convert some of them to an oxide we can use like litharge.

For example we can have a byproduct of a silver recovery or refining and use these in another process or make a useful chemical for another process from the byproduct. 

Example: say I have (a dangerous solution of) silver in solution as a fairly pure Ag(NH3)2 (Diammine silver compound) and I acidify it with HCl to recover the silver from solution, making the remaining solution safer by removal of the silver as silver chloride, which leave me with a fairly pure ammonium chloride solution, which could become dangerous if I added it to my other general waste solution. I can take this byproduct to make a fairly pure crystal salt, by crystallization and recrystallization, of ammonium chloride salts that I can use in another recovery process.

When dealing with our byproducts or waste it is important to know what we can use them for, and to know how we can convert them to other forms, or useful products, or purify them for use, or how to convert them into a less dangerous waste products, and how to dispose of them properly, the more you understand about the chemistry involved the better you can do this. And you should not try it without understanding that chemistry, as it could prove to be dangerous or give you a lot of problems from trying to use the products.

Sometimes we can use one waste product to treat other waste products, I save my hydroxide waste solutions (or caustic or basic waste solutions) to treat my acidic waste solutions to help neutralize the pH of both...

Note: some waste solutions should not be mixed, ammonia or ammonium wastes for example can create dangerous compounds with other waste or metals in solutions, and should be treated by themselves to avoid making explosive compounds.
When mixing waste we can be mixing dangerous chemicals that can make dangerous gases or chemical reactions, with any chemistry, we need to be careful, and having an understanding of the chemistry involved can help us to be safer from those dangers.

With your general waste acidic metal solutions ( or even your hydroxide, or alkali waste solutions) removing the more dangerous metals is important, displacing the more dangerous metals from solution with a less dangerous more reactive metal, for example if we have copper ions in solution, and we use iron metal to cement out the copper, replacing copper from the solution with iron (decanting the iron solution from the copper powdered metals), this copper metal can be reused in another recovery process, or converted to another copper salt which we may have a use for.

This leave us with a solution of iron ions in an acidic solution, we can continue to treat this as waste or use it to make another iron salt which we may have a use for.

Example say we now have mostly an iron chloride solution left and a little possible possible sulfuric or sulfates form some SMB we may have added to the original waste solution, we can make a useful product from this waste, like ferrous sulfate to precipitate gold with (in a recovery or in the first refining process, or use to test for gold in solution).

Sulfuric or sulfate being less volatile than the chlorides we can evaporate the solution down in volume add some sulfuric acid and drive off the more volatile chlorides from solutions as gases (these gases can also be distilled off and be converted to acids by bubbling into water, or used in another recovery processes where impure acids are not a problem, if bubbled into an a solution we are recovering metals from, to aid in the acid content of that recovery process),
(we may need to add more iron to use up excess acid as we go, or as the acids get stronger with concentration), 
The ferrous chloride being converted to ferrous sulfate. can be crystallized out of solution, and re-crystallized, by dissolving it in a dilute sulfuric acid and re-evaporating solution, the leaving the more reactive metals from your original waste in solution as we recover the ferrous sulfate salts.

Or we can further treat this iron chloride waste, using an alkali or hydroxide solution like NaOH , to form iron hydroxides and other metal hydroxides (from the other metal ions that may have been in this solution of waste) after letting them settle well (some metals can seem to take a very long time to settle) the solution can then be carefully decanted from the hydroxide waste sludge.
Note the pH most metals are removed from solution is about pH 9.5, so bringing our waste solution up to this pH will drop most of the metals from solution with our iron hydroxide precipitant, but some metals are amphoteric, and will re-dissolve in an excess of base or alkali, so we may have some of the amphoteric metals dissolve at this pH, after decanting the solution from the iron hydroxide (and other metal hydroxide/ oxides) (or which ever alkali we used to adjust the pH with) we need to bring the pH back down to pH 7 with a little acid (in this example a little HCl) which will again precipitate those amphoteric metals as hydroxides that may have went into solution previously at pH 9.5, the salt water allowed to settle well and decanted from this hydroxide sludge, the sludge combined and dried (which can also seem to take forever), and then the hydroxides roasted to convert them to the less soluble oxides (some of these more reactive metal hydroxides would become soluble again if water or moisture was added, which can pose dangers to the environment), by roasting the hydroxide powders to oxides where they have less of a chance of becoming soluble again and become a danger to the environment or someone else. the oxide powders can be disposed of in an approved dump site or given to a Hazardous material disposal site.

Here there are amnesty days that they will take household hazardous waste for free.

The salt water can be dumped in a sewer system if you have one, the water treatment facility can treat these salts ( which are diluted with the other waste water in the sewer system.
Here I do not have a city sewer, and I will not contaminate my septic or soil with these salts, so I evaporate the salts in a large crock pot, and save them for proper disposal...

Now what do these salts solutions contain (some of the more reactive metals), that cannot be removed from solution by the previous treatments, and depending on the alkali, hydroxide or carbonate use to treat the waste, it will contain salts of these, also depending on the acids or chemicals involved in the original waste, these reactive metal salts could contain a variety of salts, reactive metals like sodium, potassium, magnesium... some salts of chlorides, sulfates, nitrates... basically what went in and did not come out with treatment...

Basically I would not want to drink this stuff, or pour it on my property where it could contaminate my soil or even wash off into someone's water supply, or leach through the soil down into my well where I drink water from.


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## ericrm (Sep 1, 2014)

thank you Butcher, 

i should say that right now im only dealing with my waste acid and stock pot precipitate that was dropped with aluminium - a personnal preference at the time

the zinc sulfate cell come from an idea about treating my stock pot precipitate wich contain a good amont of iron mixed in it. knowing that iron wont plate out, i wished to ciment it with zinc and than plate the zinc out to reuse the acid and treat all of it that way. 

keep in mind that im not very active in recovery at the moment and it seem to me wiser to not put money into more waste acid that will be even harder for me to dispose of.


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## butcher (Sep 1, 2014)

zinc will displace the hydrogen from the acid, (hydrogen is what gives acid its acidic property). basically drive of hydrogen gas from the acid as it makes the more neutral zinc salt, or zinc sulfate salt, so the electrolyte will not have that much hydrogen to make acid from, except perhaps unless you ran the cell hard enough to split the water, this would provide the sulfate or other electrolyte with hydrogen to make acid, but then again splitting the water will also form OH (hydroxides the opposite of acid), from the HOH or H2O water.

With splitting both H and OH from the water, we again form, HOH or H2O water as the cation and anion come back together, you may need a split cell with a salt bridge, or membranes to divide the cell to keep the hydrogen and hydroxides from just reforming water in solution, instead of the hydrogen forming an acid with the electrolyte.

Another possible problem with this idea is that the hydrogen cation likes to join with another hydrogen to make H2 gas and leave the solution as a hydrogen gas, (from an acid electrolyte or from splitting water), this can leave the electrolyte becoming more, and more basic, basically the opposite of the acid you plan on making.

I cannot say if your plan would work or not, without doing more study and experimenting myself, But at this point I do not see how it would work that well, or that it would be hard to do, if it would, it also sounds like it might become too much trouble for very little gain.

In our industrial world, where many of these acids are byproducts from other industrial productions, for example after they started to collect the gases SO2 and SO3 of a process to keep from polluting the environment, with the industrial waste gases they had to find a way to get rid of these byproducts, and to find a market for all of the sulfuric acid they produced as a byproduct, like drain cleaners, where they could sell this cheap acid they were making as a byproduct of control of environmental pollution.

The acids are so cheap and commonly available, making your own acid most of the time does not make sense (except for maybe nitric acid, where for many of us who have a hard time getting it, or have to pay through the nose to have it shipped, or spend a lot of money to make a trip to get it...).


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## ericrm (Sep 1, 2014)

i guess i will have to look around for pt and ti electrode and try it for myself in that case.
thank you Butcher


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## Pantherlikher (Sep 2, 2014)

Thank you very much Butcher for your answers.

Long winded it may seem to you at first glance, the tid bits of information for further research and knowledge make every post from you well worth it's weight in any PM.

B.S.


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## kurtak (Sep 2, 2014)

ericrm said:


> i have a big bucket of bdg ,that im thinking of selling or trading around 15-20l. if your interested i can look more into it as it has a good value.



what is bdg :?: 

Kurt


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## FrugalRefiner (Sep 2, 2014)

kurtak said:


> what is bdg :?:


Butyl Diglyme, aka Dibutyl Carbitol.

Dave


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## ericrm (Sep 2, 2014)

an oil used to remove gold chloride from gold bearing solution. you can than precipitate that fairly clean gold from the bdg.

edit:i removed the bdg offer


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## ericrm (Sep 2, 2014)

Lou said:


> Failing that 1L samples are available for free from BASF.



i just saw that comment from Lou on one other post. it is better for me to remove my offer for the bdg in that case.


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## goldsilverpro (Sep 3, 2014)

The majority of the pure zinc produced is purified to about 99.995% by electrowinning from a sulfate solution. It is very tricky. Due to the high position of zinc on the electromotive series, most any other metal in the solution will deposit before zinc. Therefore, as much as possible, metal contaminates must be removed from the solution before electrowinning. Metals such as Cu and Ni are precipitated by the use of zinc dust. I doubt if zinc dust will remove the iron. It will probably just reduce it from ferric to ferrous. Iron is traditionally removed by precipitation as a hydroxide by raising the pH to about 5 with zinc oxide at a temp. between 104F-185F.

Pure aluminum is used as a cathode. The zinc deposited on it is only loosely attached and is removed by mechanical means. Lead is used as the anode. To increase the life of the anode, from .25% to .75% silver is alloyed with the lead. Small amounts of MnO2 are added to the solution to help form a proper coating on the anodes. Very small amounts of things such as gelatin or glue are added to help smooth out the cathode deposit. Much hydrogen gas is generated and good exhaust is needed to prevent explosions.

Typical operating conditions:

H2SO4 --- 175-210g/l (about 110 ml of conc. H2SO4 per liter)
Zinc --- 50-60g/l
30-40C
3.4V
40-60 A/ft2

Even if you were able to meet all these requirements, I would think the presence of HCl would cause a problem. Perhaps a severe one.


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## ericrm (Sep 3, 2014)

thank you GSP,it is very helpfull. if it work, i have 2 years back of stock pot precipitate to treat and since i made so many mistake over the years i know there is a good amount of gold in it.


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## ericrm (Sep 16, 2014)

a little folow up on the post. after treating iron sulfate tetrahydrate with zinc i do get a grey, very light precipitate. i would guess it is iron. i will let it settle and do some test later on the solution.

edit : a little bird told me i was stingy with my post so... what i did was dissolving iron sulfate (fertilizer grade)in water ,than i have cemented ,what i think is , the iron out. by the redish color that the cementing powder took when left to air for a few days,i realy would guess it is iron.i dont know how much iron could be left in solution but i think that most of it should be out. it is a very long to settle powder and a very nice grey color.

i have started to clean the sulfuric cell to get ready for the next test,electrolising the zinc out and i have took a picture of the copper deposit,it is very clean sheet, the front is more rugged but does not crumble.


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## ericrm (Sep 22, 2014)

Gsp seem to be right 

from left to right
zinc dissolving in sulfuric acid, zinc in a iron sulfate solution, filtered solution of the zinc in iron sulfate
i do get a precipitate that turn red like iron oxide but by the look of the 3rd solution it clearly is a minimal amount of iron since the solution is still blue, and zinc sulfate is suposed to be clear.


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## ericrm (Sep 22, 2014)

i ask because i have just saw that iron will not cement out of sulfuric acid and im wondering if my stock pot precipitate actually contain any iron.... iron will drop as hydroxide from iron chloride solution but will it cement out from an other metal like aluminium or zinc?


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## butcher (Sep 22, 2014)

ericrm, 
I must admit without going back and rereading all of what your doing I am kind of lost now.

Iron can be cemented out of sulfuric acid, actually a better way of saying this is iron can replaced from solution (be cemented out) of an iron sulfate solution, by using a more reactive metal like zinc or aluminum.

The more reactive zinc or aluminum can be used to displace iron from this Iron sulfate solution.

Working with a green ferrous sulfate and adding zinc metal, the green solution will loose it color as zinc replaces the iron from solution. the iron metal will precipitate out of solution, and the zinc will dissolve into solution as it shoves out iron turning the solution clear, (if no other metals are involved to give color to the solution) ....

FeSO4(aq) + Zn(s) --> ZnSO4(aq) + Fe(s)

Aluminum reaction is similar:

3FeSO4(aq) + 2Al(s) --> Al2(SO4)3

The filtered solution looks like you still have iron in solution or a dilute ferrous sulfate.

Note: zinc or aluminum will also displace hydrogen (being above hydrogen in the reactivity series)removing this hydrogen as a gas from solution making your solution less acidic, as you know this will slow down the reaction, that may be what has happened you may not have enough of an acidic solution to finish the replacement iron metal from solution with the zinc, (at least in the given time frame you have allowed for the reaction to happen in)...

Try a little more zinc metal and a few drops of sulfuric acid and see if you can replace more iron from solution. Or add some heat to help speed the reaction (and concentrate the solution), the green color should go away as iron precipitates from solution, leaving you with a more clear zinc sulfate in solution...


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## ericrm (Sep 23, 2014)

butcher, i already tryed both. olution have been cemented warm for about 7 day, when is saw that iron would not drop as expected i have added a lirrle bit of sulfuric acid as you said and the reaction started to buble again but it dosent seem to have change anything for iron (for now) i have some ph strip what should be the ph for cementing iron out of the sulfate solution?


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## butcher (Sep 23, 2014)

It will need to be at least somewhat acidic, you will need free Hydrogen in solution, a slight excess of acid will not hurt.

Try adding a piece of zinc and a little sulfuric to the filtered green solution (a little heat may help to evaporate, as the solution does look to be diluted) and see if the green color does not go away, this is a replacement reaction, and the iron sulfate needs to come into contact with the zinc metal, stirring to get the contact needed (heating to stir the solution can be useful), in the dilute green solution you may have iron Cations that need to touch or come into contact with the zinc metal (in the acidic solution) to be able to transfer electrons from the zinc metal to the iron ions in solution, so that the iron gaining an electron will become an atom of metal iron, when these atoms of iron metal combine to big enough clumps, you should see the Iron precipitate from solution. you may see this as a coating onto the zinc like a loose plating, with the solution slightly acidic the hydrogen gassing from the zinc should clean the zinc when no more iron Cations remain in solution to plate onto the zinc...

What your doing here is very similar to what we do when we cement silver with copper,
or when we convert silver chloride using HCl and aluminum...
And we want it slightly acidic, but also note, here you are using a more reactive metal, above hydrogen in the reactivity series of metals, that will displace hydrogen from your solution, basically making your solution less acidic as it forms a salt solution (of zinc sulfate)...

You can test the pH to get an idea of the hydrogen or hydroxide content of the solution, but I wouldn't worry too much about having a certain pH (although there may be an ideal pH I do not know what it would be), as long as you have the solution at least somewhat acidic for the reaction to proceed.


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## solar_plasma (Sep 23, 2014)

But iron would not stay elemental in such an environment. It would oxidize. Just think about the school experiment: iron powder or wool in distilled water, in tap water and in water with NaCl.

I would rather expect it will do the electron exchange and be reduced directly from its divalent state to monovalent hydroxides/hydrates(?)

edit: funny, how things, you always have thought to be simple, suddenly can raise a lot of questions....need to find out...maybe you were right, Butcher,especially as long as there is still undissolved zinc and no oxygen dissolved or the iron has contact to the zinc.


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## butcher (Sep 23, 2014)

If the solution becomes basic, you could get hydroxides or oxides of iron.

This is less likely with a ferrous sulfate solution unless you added something like NaOH to the equation.

It would be more common in an iron chloride solution, where it becomes less acidic, (where heating the solution too strongly can give you an insoluble red rouge powder, much like jewelers use as a polishing compound, of Fe2O3 (rust) (hematite).


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