Sciencemadness Discussion Board

Expert knowledge on Titanium dioxide needed

CuriousEngineer - 23-10-2016 at 10:28

Hi guys,

I would appreciate your thoughts regarding a newly developed process for the recovery of titanium dioxide from waste paper. It uses an aqueous non-oxidising mineral acid.

For details check out:
http://www.avalanche-research.de/projects/5768f63e63d6180300...

As you can see its a patent. So do you know if that makes sense or do you even know if this method is already in use? Thanks.

blogfast25 - 23-10-2016 at 16:11

Quote:
A process for the recovery of titanium dioxide from waste paper containing iron, after forming sheets of decorative paper, comprises using an aqueous non-oxidising mineral acid. The liquid extraction agent phase is separated and the organic residue is oxidised pyrolytically to form CO2. Extraction takes place at a temperature above 50 °C, especially above 75 °C, at the boiling point of the acid. The non-oxidising mineral acid is hydrochloric acid. Oxidation takes place at 500-850°C. After the residue is removed, the extraction agent is treated to recover the acid. The waste paper contains an impregnated resin, and is boiled with a strong base. The extraction takes place in a reactor.


Makes no sense whatsoever. Commercial TiO2 is 110 % insoluble in strong HCl, hot or cold.

Sounds like someone's trying to scam a gullible investor out of many $$$ to me.

Dwarvensilver - 23-10-2016 at 16:43

blogfast25, have you been to the site? it will be self explanatory :D

Metallus - 24-10-2016 at 04:29

It clearly states aqueous hydrochloric acid and, as blogfast25 said, TiO2 is insoluble in such medium. Maybe if it were gaseous HCl or chlorine itself, you might have formed some titanium chloride, which is volatile and very hygroscopic anyways and would have been converted back to TiO2 immediatly after.

The only way I was able to solubilize some TiO2 was with hot oleum and that's far from non-oxidising acid.

blogfast25 - 24-10-2016 at 06:46

Quote: Originally posted by Metallus  
[...] and that's far from non-oxidising acid.



Oxidising/non-oxidising is irrelevant here: in titania the Ti is already at its highest oxidation number possible, i.e. +4.

Metallus - 24-10-2016 at 07:09

Quote: Originally posted by blogfast25  
Quote: Originally posted by Metallus  
[...] and that's far from non-oxidising acid.



Oxidising/non-oxidising is irrelevant here: in titania the Ti is already at its highest oxidation number possible, i.e. +4.

Oh ye, I was talking exclusively about the acid characteristics, since in that website they specify that it is an aqueous non-oxidising acid.

Of course titania is +4 and stays +4.

Fleaker - 24-10-2016 at 08:54

Titanium metal and titanium dioxide are soluble in HCl and sulfuric acid but certainly not expediently.

Depends on the crystalline form / heat history of the titanium oxide and of course, its particle size. Same thing goes for Nb2O5 and Ta2O5...heat either of them strongly and good luck getting it to go into HF without a trip to the PTFE lined autoclave!

If you have an autoclave, titanium dioxide will leach into HCl or sulfuric.

It's often helpful to have something like metallic iron and great stirring when doing the process, for whatever reason, it seems to help. As pigment grade TiO2 is highly desired for its whiteness, the iron would have to be removed. Probably could use a cation exchanger for that.

I guess my question is why even put it into solution? Better to carbo-chlorinate and re-distill the TiCl4, then you can be sure it's free of iron and it could either go into metal or back into hydrous titania and off to the rotary kiln...

Fulmen - 24-10-2016 at 09:16

I think you're overthinking this. It's paper containing TiO2 and iron, right? The acid only needs to remove the iron before incineration.

blogfast25 - 24-10-2016 at 10:40

Quote: Originally posted by Fulmen  
I think you're overthinking this. It's paper containing TiO2 and iron, right? The acid only needs to remove the iron before incineration.


Maybe.

Good quality white paper would contain very little Fe, as Fe(+3) is the enemy of whiteness (and the enemy of pigment-quality titania!)

Fulmen - 24-10-2016 at 10:43

"A process for the recovery of titanium dioxide from waste paper containing iron"

blogfast25 - 24-10-2016 at 10:51

Quote: Originally posted by Fleaker  
Titanium metal and titanium dioxide are soluble in HCl and sulfuric acid but certainly not expediently.

If you have an autoclave, titanium dioxide will leach into HCl or sulfuric.

As pigment grade TiO2 is highly desired for its whiteness, the iron would have to be removed. Probably could use a cation exchanger for that.



Titanium metal is slowly soluble in hot 12 M HCl, to Ti(3+) (first hand experience) as it is in hot 50 % H2SO4 (ditto). In HCl titania is not soluble, unless you can provide convincing evidence/references to the contrary. Even freshly precipitated hydrated titania doesn't dissolve in HCl quickly and solubility goes down swiftly with precipitate age. Commercial pigment titania has been calcined to death.

In the presence of iron (or maybe aluminium) as a reducing agent HCl may be more effective, as any dissolved Ti would be reduced to Ti(+3), pulling the equilibrium to the right. But I've not seen any practical applications of that idea.

In the sulphuric acid process for titania, iron is removed by pH selective precipitation: "Ti(OH)4" drops out even before the iron, from the titanyl sulphate solution.


[Edited on 24-10-2016 by blogfast25]

blogfast25 - 24-10-2016 at 11:00

Quote: Originally posted by Fulmen  
"A process for the recovery of titanium dioxide from waste paper containing iron"


That says very little about the process though. It'd be nice to see the entire patent and not just the blurb...

AJKOER - 24-10-2016 at 13:52

I may have a rough idea of what is ocurring.

First, Ferrous + O2 (assumed present during the boiling part of recovery of HCl) + acid yields a basic Ferric chloride. Here is a similar reaction sequence based on copper:

R24 O2(aq) + Cu+ → Cu2+ + O2− ( k = 4.6xE05 )
R27 O2− + Cu+ + 2 H+ → Cu2+ + H2O2 ( k = 9.4xE09 )
R25 H2O2 + Cu+ → Cu2+ + .OH + OH− ( k= 7.0 xE03 )
R23 .OH + Cu+ → Cu2+ + OH− ( k = 3.0×E09 )

Net radical reaction: O2 + 4 Cu+ + 2 H+ → 4 Cu2+ + 2 OH-

The key to a working process is to make, for example, the cuprous salt soluble (which can be accomplished in hot brine). See discussion and references cited at https://www.sciencemadness.org/whisper/viewthread.php?tid=66... .

Then, the chemistry and/or product with titanium as Ti(3+), which could be converted via dioxygen similarly to Ti(4+), apparently differs significantly enough to permit separation at elevated temperature.

There is also an interesting (but likely not relevant here) compound cited in an article "Iron Oxychloride (FeOCl): An Efficient Fenton-Like Catalyst for Producing Hydroxyl Radicals in Degradation of Organic Contaminants", by Xue-jing Yang, et al, J. Am. Chem. Soc., 2013, 135 (43), pp 16058–16061, link: http://pubs.acs.org/doi/abs/10.1021/ja409130c , where organics are converted basically to CO2.

[Edited on 25-10-2016 by AJKOER]

Maroboduus - 24-10-2016 at 20:48

HI GUYS,
Do you realize Curious Engineer wants this info because the Avalanche site claims it will pay him for it?

When you're done helping him with that I'll let you whitewash my fence and I'll only charge you a nickel each for the pleasure of doing so.

[Edited on 25-10-2016 by Maroboduus]