Sciencemadness Discussion Board - Reduction of metal sulfides with carbon

Reduction of metal sulfides with carbon

Opylation - 27-10-2020 at 17:38

Hey all, so I’ve been thinking about the carbon reduction of metal oxides forming carbon dioxide and was curious if it was possible to reduce metal sulfide with carbon to form carbon disulfide? It would probably be necessary to use an inert atmosphere or maybe use a little bit of a volatile solvent in a distillation setup with a stainless steel reaction flask to remove the O2. It may not even be necessary for an inert atmosphere as the products may displace oxygen. Idk I couldn’t find anything online about it.

Opylation - 28-10-2020 at 00:40

I’ve kind of been on a CS2 prep search for a while. I like to gather many routes of synthesis for substances so that when I get around to actually preparing them I have multiple options. By the way I did find a killer looking synth of CS2 using CBr4 and S8! This reaction runs at 160°C and all reagents are liquid while CS2 is produced. The only byproducts are Br2 and S2Br2. I’ll attach the article (German) and include a translation (the google machine).

Using the attached resource:
4CBr4 + S8 ———> 4CS2 + 8Br2
Translation:
“CBr4 + S8• 16.6 g (0.05 mmol) CBr4 and 9.62 g (0.3 mols) S8 are refluxed under N2. The yellow homogeneous melt becomes darker from 120°C and brown-black at 155°C. At 160°C the reaction has ended after 10 minutes (no CBr4 no longer detectable). In addition to the bromine and CS2 formed, some S2Br2 can also be detected (IR 355 and 535 cm-1; UV λ_max 296 nm).”

Attachment: CS2 synthesis via halogenated alkanes and sulfur.pdf (525kB)
This file has been downloaded 302 times

[Edited on 28-10-2020 by Opylation]

teodor - 28-10-2020 at 01:28

I just suspect that the reaction temp. could be even higher than reaction S vapours with C directly (the sulphide route).
Do you consider the dithioformate route?

[Edited on 28-10-2020 by teodor]

Opylation - 28-10-2020 at 08:22

I haven’t heard of that route but it does sound intriguing. Like producing CO2 using for if acid. I wonder if it could be used as a formic acid substitute in certain reductions. Do you have any literature on the reaction?

teodor - 28-10-2020 at 08:47

Just look other threads about CS2 preparation here, you will be able to gather many routes and read the reports of those who tried them . The only drawback there is a lot of information already. So you can start from the wiki page on SM about carbon disulphide and then you can follow its links.

[Edited on 28-10-2020 by teodor]

Opylation - 29-10-2020 at 03:35

Yeah, I have taken a look at the CS2 info page here on SM. One thing that I missed though was the PbS reduction to CS2 using CO. Not sure how I missed it but I went back to look at the page after you mentioned it and there it was. I’m sure C can be used in its place since it’s at a lower oxidation state. The reason why I’m looking for a carbon type reduction is because all reagents would be in a solid phase making the reaction easier to perform without the issues of sulfur contam like with C + S. That and if you’re using a torch anyways it may be better to have the Metal sulfide dissociation at a high temp (to a point), with the C + S reaction if you blast the sulfur too much it can vaporize past the carbon also the sulfur has a tendency to cool the carbon after just a little bit. A lot of starting and stopping waiting for the carbon to heat back up.

teodor - 29-10-2020 at 12:05

PbS has very high melting point for using it in my lab

I would do some experiments with SnS2 first at 400-600C.

Edit: Also I found something interesting here: https://pubs.acs.org/doi/abs/10.1021/ie502343y

[Edited on 29-10-2020 by teodor]

Opylation - 29-10-2020 at 14:13

I'll take a look. One thing I wanted to mention is that reduction with carbon does not need to be done in a liquid phase. It seems that solid phase reaction of both reagents is possible, look up carbothermic reaction. If you look at the carbon reduction of zinc oxide, the reaction takes place ~1000C well below the melting, or decomposition, point.

teodor - 30-10-2020 at 02:01

Yes, and also SnS2 is an oxidiser, that's why I mentioned it.

There are 2 reason why I personally will not try that in the nearest future:
- I have no experience of simultaneous working with high flammable liquid and high temperature at the same time & space and I prefer not to get any soon;
- I have no idea/equipment how to evacuate the air except burning it

So I would prefer to do some experiments with dithioformic acid. It should has interesting properties besides of low temp decomposition to CS2.

Opylation - 30-10-2020 at 15:32

The dithioformate reaction looks like a good one, the only concern is the extremely exothermic nature. The solution to cooling the hot vapors of CS2 would be a long and thin glass tube that makes its way from the reaction vessel to a condenser. By making the tube adequately long enough the vapors have a better chance of cooling before the condenser that finished the job

teodor - 31-10-2020 at 04:02

Quote: Originally posted by Opylation

The dithioformate reaction looks like a good one, the only concern is the extremely exothermic nature.

Could you give some details on that?

Yes, a long pipe ... but practically, I would try to get more practise by generating COS first by passing CO2 over sulphide at 150-250C, don't remember this temp correctly but this reaction is used (or was used) in analytical chemistry to quantitatively convert sulphides to carbonates. The positive constant pressure of CO2 guaranties exclusion of oxygen from inside the system, also COS is much less flammable and explosive. The only problem, it seams there is no easy way to convert it to CS2, but for me it would be interesting to create some thiocarbonates and to perform some experiments with them.

About CS2 from C + sulphide. Is it possible to absorb it during the reaction to create a trithiocarbonate without need to condense/accumulate as a liquid and then release it somehow from trithiocarbonate? I did a brief search but I didn't find much information about thiocarbonates chemistry and no one example how to generate CS2 from them.

unionised - 31-10-2020 at 05:20

If carbon reduced metal sulphides the same way that it reduces metal oxides then the rather complicated process for getting copper from the (sulphide) ore wouldn't be needed.
(And they would be able to see CS2 as a by-product.)

I suspect the reaction doesn't work or, at least, doesn't work well.

Opylation - 1-11-2020 at 17:27

Quote: Originally posted by teodor

Quote: Originally posted by Opylation

The dithioformate reaction looks like a good one, the only concern is the extremely exothermic nature.

I have an article on the thermodynamics of C, O, and S. It’s a pretty good paper, they have like 12 equilibrium reactions that they look into from a range of like 500C to 1200C. I’ll attach it at the bottom

Quote:

If carbon reduced metal sulphides the same way that it reduces metal oxides then the rather complicated process for getting copper from the (sulphide) ore wouldn't be needed.
(And they would be able to see CS2 as a by-product.)

I suspect the reaction doesn't work or, at least, doesn't work well.

I don’t know the process for obtaining copper from ore, just a little bit from looking at Wikipedia. What I could find is that a majority of copper ore is naturally an oxide or sufide. Looks like they use heat with limited oxygen to oxidize sulfur and reduce copper. What ever copper also gets oxidized they just blast the living hell out of it to force dissociation (homolysis?) into O2 and Cu(0). I would assume they don’t use carbon because since they can just heat it they save money on having to pay for a large amount of essentially just another waste product that they would have to deal with. But I could be wayyy wrong.

Edit: whoops, forgot to attach the paper

[Edited on 2-11-2020 by Opylation]

Attachment: S, O, C equilibrium with CO, CO2, SO2, CS2, and COS products.pdf (1MB)
This file has been downloaded 317 times