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Author Topic: Need help in miniaturizing the Bayer Process  (Read 18327 times)

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BlueTheCow

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Need help in miniaturizing the Bayer Process
« on: May 15, 2008, 08:10:40 PM »

I'm fairly new to chemistry (I'm at the high school level of chemistry education and just started reading General Chemistry by Linus Pauling), and I want to implement the Bayer Process (for extracting alumina from ore) on a small scale (not for production or anything - more for my entertainment than anything else).

Of course I don't expect a step-by-step guide on how to do this, but I'm wondering if there is some set of books that I can read to give me some basic knowledge to work from. My main problem is that I cannot find enough information about the type of equipment used, and so I cannot figure out what kind of makeshift equipment I should use.
Furthermore, I do not really know which field this concerns, so I'm not really sure which books might help.

I would really appreciate it if someone could point me in the right direction. Thanks.
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BlueTheCow

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Re: Need help in miniaturizing the Bayer Process
« Reply #1 on: May 17, 2008, 01:39:07 PM »

Hmm. If nobody has any answers to that, I'll edit the question to something a bit more specific.
I'm working on the part where I mix the ore with a sodium hydroxide solution and heat it to 175-200ºC and then filter out the solution from the mud.

My first attempt at a reaction chamber is a stainless steel teakettle with a sealed lid (which can be removed to add reactants), and a spout which is connected to galvanized steel pipe. A coffee filter is placed in the pipe such that after digestion, the kettle may be lifted and angled such that the spout is vertical and the solution pours through the spout, through the pipe, and through the coffee filter, and then gets trapped in a long portion of pipe which holds the solution while it cools (I'm considering instead using another teakettle for the cooling part).

Anyway, to test the idea I hooked up the teakettle to the pipe and put a cap on the end instead of a cooling chamber and did not insert a filter (so it's basically a teakettle with a galvanized steel spout, with a cap fitting on the end). After playing with this setup for a few minutes, I realized that at each connection between fittings there were leaks. I expected this, but I did not expect the amount of leakage that occured. At that rate, I will not be able to sustain enough pressure on the water to keep it in liquid state at the high temperatures required, due to the fact that the steam will escape through these leaks and reduce the pressure.
There are sealants specifically for these galvanized steel pipe fittings, but they are not rated for the temperatures and pressures I expect (150ºC-210ºC and around 35 atm, which is about 500 psi).

So is there some other way to seal them properly?

Also, I'm having a bit of trouble visualizing how I can monitor the internal temperature of the teakett- I mean reaction chamber ;)
I have a digital food thermometer that says it goes up to 200ºC/392ºF and has a long pointy probe that looks like it could be used to stab meat or something. I'm not entirely sure that just touching it to the side of the teakettle will get an accurate temperature (I plan on testing this tonight). Is there some more standard method I could use? Or do I need to invest in some better equipment?
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Borek

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Re: Need help in miniaturizing the Bayer Process
« Reply #2 on: May 17, 2008, 11:26:33 PM »

A coffee filter is placed in the pipe such that after digestion, the kettle may be lifted and angled such that the spout is vertical and the solution pours through the spout, through the pipe, and through the coffee filter

Solution will be so alkaline that it will probably easily eat through your coffee filter. But that's the least of your problems.

Quote
At that rate, I will not be able to sustain enough pressure on the water to keep it in liquid state at the high temperatures required, due to the fact that the steam will escape through these leaks and reduce the pressure.
There are sealants specifically for these galvanized steel pipe fittings, but they are not rated for the temperatures and pressures I expect (150ºC-210ºC and around 35 atm, which is about 500 psi).

Your teakettle is not rated for 35 atm. What you are basically planning to do is a homemade bomb, that will explode splashing everything around with hot caustic solution of NaOH. This is an interesting, but painfull aproach to suicide.

Sorry to say that, but looks like your enthusiasm pushes you outside of the boundaries of your knowledge, thats very dangerous combination.

AFAICT you don't need high pressures for that process, but even then playing with hot, concentrated NaOH is a very dangerous idea.
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BlueTheCow

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Re: Need help in miniaturizing the Bayer Process
« Reply #3 on: May 18, 2008, 07:52:30 AM »

Thank you for your reply!
Before I comment on each part, I'd just like to say that I found and acquired a tube of sealant that says it works on gases up to 3000 PSI (about 200 atm), 400ºF (around 200ºC), and higher for liquids. So aside from the probability of explosion, the setup might work.

Solution will be so alkaline that it will probably easily eat through your coffee filter. But that's the least of your problems.
Hm... any suggestions for a more stable filter?

Quote
AFAICT you don't need high pressures for that process, but even then playing with hot, concentrated NaOH is a very dangerous idea.
Well, water boils at 100ºC, and since higher temperatures are required, at atmospheric pressure it would all boil away before the reactions could take place. I figured if I heated up the solution in a sealed container, some of the water would boil, turning into steam that would expand as the temperature increases, increasing pressure. I figured the increased pressure would allow me to retain some of the water as a liquid, giving me my hot NaOH solution. I don't think it would really reach 35 atm, that was more of a max figure that I found searching through industry websites (the specific source said this approximate pressure occurred around 240ºC, and due to various limitations I only intended to reach around 200ºC).

Quote
Sorry to say that, but looks like your enthusiasm pushes you outside of the boundaries of your knowledge, thats very dangerous combination.
Exactly! That's why I came here asking for pointers on how to acquire the necessary knowledge.  ;D

Quote
Your teakettle is not rated for 35 atm. What you are basically planning to do is a homemade bomb, that will explode splashing everything around with hot caustic solution of NaOH. This is an interesting, but painfull aproach to suicide.
Oh dear.
Well, I did expect the explosion of the setup as a possibility, so I had planned on testing it with just water (no NaOH, no ore) to see if it would explode (and also to see if I could actually keep liquid water at that temperature, and for how long, given the possibility of leaks). So at worst I would have been scarred for life with ugly burns all over, damning me to a life of pathetic virginity (or, I suppose I could die from the burns...).

In any case, I thank you for the warnings and I would like to know if there's something you can suggest (other than just giving up).
From where can I acquire a digestion chamber (to replace the kettle) that can take the temperature and pressure without blowing up?

Thank you.
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Borek

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Re: Need help in miniaturizing the Bayer Process
« Reply #4 on: May 18, 2008, 09:55:03 AM »

Google boiling point eleveation. What will be the concentration of your NaOH?
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BlueTheCow

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Re: Need help in miniaturizing the Bayer Process
« Reply #5 on: May 18, 2008, 01:55:24 PM »

Google boiling point eleveation. What will be the concentration of your NaOH?

Hm. I was thinking somewhere around 12.5mol NaOH/kg H2O (500g NaOH/kg H2O).

I took a look at the equation on the wikipedia article about boiling point elevation, and even though I'm not sure what the van 't Hoff factor for NaOH is, I don't think it would be high enough to stop the water from boiling off at 175ºC. If the van 't Hoff factor is 1, the elevation would be 6.40 K. For the elevation to be high enough (40 K-100 K, to increase the boiling point to 140ºC-200ºC), the factor would have to be around 6 to 15, or I would have to increase the molality by that same amount. Due to the finite solubility of NaOH in water (111 g/100 ml at 20°C according to wikipedia), I don't think I can increase the molality by a factor more than about 2 (it might be a bit higher as I think the solubility increases with temperature). [Edit - I think the van 't Hoff factor is 2, so the elevation would be 12.8 K, and so I would need to increase the molality by around 3-8, which doesn't seem likely].

In any case, it doesn't seem likely that the boiling point elevation of the solution by the dissolved NaOH will be sufficient to allow me to reach the necessary temperatures in an open container without the water boiling off... so... what were you suggesting? Perhaps that I should use another solute to increase the boiling point? Or... what am I missing?
« Last Edit: May 18, 2008, 02:06:34 PM by BlueTheCow »
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Borek

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Re: Need help in miniaturizing the Bayer Process
« Reply #6 on: May 18, 2008, 09:09:17 PM »

Solubility goes up with temperature and boiling point elevation is not linear for high concentrations. Unfortunaltely I don't have data for NaOH at hand, but KOH at 500g/100g H2O boils over 300 deg C.

Note: this is still dangerous as hell. Even if there is no pressure and no chances of explosion, just temp makes the solution of NaOH dangerous - and it is additionally corrosive as hell, it will eat through flesh at the light speed. Well, almost light speed.
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BlueTheCow

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About the filter...
« Reply #7 on: May 28, 2008, 12:45:36 PM »

Sorry for taking so long to reply; I wanted to test a few things on my own before I asked for more help. As to the dangers, they are still present, but I ask you not to worry about that part as I am being extremely careful.

I've been working on much smaller batches than I originally hinted to with the teakettle (my largest batch was 17.0g ore), and I have found that everything so far works as planned except the filter: the mixture eats through it before the first drop goes though, just as you said.

So what other filter type could replace the coffee filters? I've been looking around, and I've found hints to the existence of such filters, but I never come up with anything substantial.

Thanks again.
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Borek

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Re: Need help in miniaturizing the Bayer Process
« Reply #8 on: May 28, 2008, 01:18:30 PM »

This is not the answer, but it may push you in the right direction:

http://www.google.com/search?rls=en&q=alkaline+resistant+filetr&num=25&ie=utf-8&oe=utf-8
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BlueTheCow

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Cannot find a cheap alkaline resistant filter for testing
« Reply #9 on: May 29, 2008, 10:55:49 AM »

Thanks, it did help me find some further information.

However, I am still a bit stumped on how to acquire the type of filter I need. All the suppliers I've found so far seem directed towards higher scale applications (industrial production, large laboratory testing etc), and sell either high qualities or high quantities, increasing cost (e.g. sterlitech.com's 0.22 micron pore size ptfe membrane disc filters cost $263.89 for the cheapest pack, which is qty 100). My budget allows the expense, but it does not allow such expenses when I'm not sure if the product will work (that is, I'm not prepared to order $200 worth of filters to find out I can't use them for whatever reason).

Is there some cheaper, smaller quantity source I can use? Perhaps something that is meant for something else that I can use for this (similar to how I can use coffee filters for other filtration needs)?

Am I missing something important? Or do I have to just bite the bullet (very hard) and shovel out the cash in the name of science?
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HighTek

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Re: Need help in miniaturizing the Bayer Process
« Reply #10 on: May 30, 2008, 03:30:48 AM »

This could very well be the worst idea that I've given, but how about a pressure cooker?
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BlueTheCow

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Re: Need help in miniaturizing the Bayer Process
« Reply #11 on: May 30, 2008, 08:43:19 AM »

Thanks for your reply.
I did think of using a pressure cooker, but as I explored this idea, I realized that a) most pressure cookers were rated for pressures much lower than the pressures experienced in the industry, and that b) a pressure cooker is essentially a container in which water and some food is heated, and as steam develops the pressure increases, increasing the temperature at which the remaining water can sustain a liquid state, until the pressure passes the desired pressure, at which point a valve is opened and steam is released, decreasing the pressure until the valve closes.

When I thought about this, I realized that all I needed was some sealed container which could remain structurally stable in the presence of such pressure (that is, a container that would not explode at the high pressures I thought would be necessary) - the valve to relieve pressure was not necessary, and thus the expense of a pressure cooker was not necessary (the presence of such a pressure-sensitive valve makes a pressure cooker a pressure cooker instead of just a pot; so if I don't need the valve, I don't really need the pressure cooker).

In fact, as I was browsing the kitchen appliances, I stumbled upon the idea that I could use a teakettle as such a container - it would allow me to fill with ore, NaOH, and water through the top, heat from the bottom, then pour through the spout into the settling chamber. The main problem with this was that I needed to seal the spout to the settling chamber somehow; I decided to use galvanized iron pipe with teflon sealant. Shortly after this, Borek informed me that the teakettle was unlikely to remain structurally stable with the pressures I described (that is, he told me it would explode, as seen above). Furthermore, he informed me that the higher pressures were not entirely necessary to the process; rather, that I could sustain the liquid state of the water using the boiling point elevation that occurs with high concentrations of solute.

Taking his advice, I increased the concentration of my NaOH solution to 4g NaOH/g water (=4kg NaOH/kg water = 100mol NaOH/kg water = 100m). I believe that this solution, heated to around 180ºC, successfully digested my ore. Granted, of course, I then poured it through the coffee filter which was eaten away by the extremely alkaline solution, and the trial failed.

In any case, as I stated in my last post, my current problem is the difficulty in acquisition of a suitable filter (capable of filtering a 100m NaOH solution at 180ºC; I expect red mud minimum particle sizes to be around 0.5 microns). At present, I'm debating with myself as to whether I should just spend the $122 and get the 0.1 micron pore size, 47 mm diameter GE Polypropylene Membrane pack of 100 (http://www.osmolabstore.com/OsmoLabPage.dll?BuildPage&1&1&402). I know, I know, it's just $122... I don't want to sound like I'm whining, but I really don't want to spend $122, figure out it doesn't work, spend another $122, and so on, until I spend a few thousand, etc.

Anyway, that's the basic summary of this thread.

[Edit- btw, your avatar is entertaining.]
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nj_bartel

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Re: Need help in miniaturizing the Bayer Process
« Reply #12 on: May 30, 2008, 01:23:40 PM »

I highly advise you find something safer to entertain yourself with before you kill yourself in an excruciatingly painful way.  I don't think you understand.  Hot, concentrated NaOH solution will rape your tissue to the bone.  I'd be less worried about ever having sex and more worried about lucking out and living if that tea kettle explodes.
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BlueTheCow

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Re: Need help in miniaturizing the Bayer Process
« Reply #13 on: May 30, 2008, 02:19:41 PM »

I highly advise you find something safer to entertain yourself with before you kill yourself in an excruciatingly painful way.  I don't think you understand.  Hot, concentrated NaOH solution will rape your tissue to the bone.  I'd be less worried about ever having sex and more worried about lucking out and living if that tea kettle explodes.

While I do thank you for your concern about someone you've never met, I must say that it is a bit unfounded.

Firstly, I would like to say that I am taking every precaution feasible (gloves, etc.), and that even though I know there is obviously a limit to the protection allowed by such precautions, they do at least allow me extra time to evacuate any valuables (hands, etc.) from areas of danger.

Secondly, the explosion of the teakettle is extremely unlikely, for two main reasons: a) I no longer need such a high pressure in the reaction chamber, due to the boiling point elevation of the solution caused by the increase in molality suggested by Borek, and b) due to the even smaller experimental batch size, I'm now using open-topped stainless steel measuring cups as reaction chambers instead of teakettles (at least for now); so nothing could explode and if it did for some reason it wouldn't be a teakettle. Also, the smaller batch size reduces the danger somewhat, just because there's less dangerous stuff.

The biggest danger I face are bubbles of steam popping out from under chunks of dirt, sending hot mud into the air at the observer (I thought this would happen due to my experience with frying food in cooking oil), which becomes less of a problem using a lid to cover the measuring cup as it is heated (interestingly enough, the lid on one of my teakettles fits one of the measuring cups pretty nicely, allowing space for steam to escape to keep the pressure around the atmospheric pressure). The chunks of dirt hit the top (which makes for constant small *thud*ing sounds around lower temperatures) and fall back down until enough water escapes as steam to increase the molality (with NaOH) enough to bring the boiling point above the reacting temperature.

The other danger I face is the possibilty that the mixture spills over the sides of the measuring cups. This would happen for two reasons: first, when pouring through the filter, it is possible (though unlikely) that I might spill it. This hasn't happened yet, but if it does, I wear gloves and have towels nearby to contain the hot mess. The other way this could happen didn't occur to me until it actually happened. I used too much of the reactants and increased the temperature past what I expected (I didn't have much experience with my electric burner before now, so my temperature controlling was flawed), and the material overflowed out of the container while it was on the burner. I quickly removed the container from the heat and killed power to the burner, which stopped the overflow, and used the towel to clean up the mess. If I had not reacted quickly, the worst that could have happened would have been damage to equipment. Luckily, everything was fine. In any case, I prevent this now by controlling the digestion more carefully, but if it did happen again I would still be able to react in a similar way.

So you see, it really isn't all that dangerous, because I take my time and take necessary precautions. I'd be more worried about the youngins that have a fascination with explosives.

And no, I'm not worried about having sex.   ;)


Post Note:
Also, even though I know it's an extremely long thread (that's my bad, by the way - I tend to ramble), and it would take a while to read it fully... I think it would prevent further lengthening of the thread to do so - I would not have to restate things so much and so my posts would be shorter and thus the thread would be shorter and thus the next person that replies would not have to skip reading, and so on. It's a vicious cycle. I don't mean to be rude, of course, just trying to help out  ;D
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eugenedakin

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Re: Need help in miniaturizing the Bayer Process
« Reply #14 on: May 30, 2008, 04:11:27 PM »

Hello BlueTheCow,

My first comment is ... WOW .. quite unsafe. I need to start this comment with a legal statement: this mechanism and reaction in the manner you are planning is extremely unsafe. Do not perform the test or reactions, please, for your own safety.

From a theoretical perspective, a really inexpensive filter can be created from various cloths ...yep, the kind that you use to clean dishes. Folding the cloth on top of itself, along with putting it on the bottom of an old soup can can form a very good filter. If the material passes through the filter with particles, add a little sand in the bottom of the filter can before pouring your ingredients into it. Finer sand = finer filter.

Here is a little information that I was able to find on the alumina process:

Quote
Aluminium oxide, also known as alumina, is the main component of bauxite, the principal ore of aluminium. The largest manufacturers in the world of alumina are Alcoa, Alcan and Rusal.[citation needed] Companies which specialise in the production of speciality aluminium oxides and aluminium hydroxides include Alcan and Almatis. The bauxite ore is made up of impure Al2O3, Fe2O3, and SiO2. Bauxite is purified by the Bayer process:

Al2O3 + 3 H2O + 2 NaOH → 2NaAl(OH)4
The Fe2O3 does not dissolve in the base. The SiO2 dissolves as silicate Si(OH)62-. Upon filtering, Fe2O3 is removed. When the Bayer liquor is cooled, Al(OH)3 precipitates, leaving the silicates in solution. The mixture is then calcined (heated strongly) to give aluminium oxide:[3]

2Al(OH)3 + heat → Al2O3 + 3H2O

The formed Al2O3 is alumina.

More details about the process can be found here:

http://en.wikipedia.org/wiki/Bayer_process

I wish you the best on understanding the theory behind your question.

Sincerely,

Eugene



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