I need some soft lead for gasket material for my HF retort, so I am getting back to my lead refining project. I just set up a lead sulfating battery
this evening; the full scale version of my prior experiments on using AC electrolysis in sulfuric acid to rapidly sulfate lead scrap in order to
separate and purify the main metals contained therein.
The sulfates of lead, tin, and antimony are easily separated from one another due to their solubility characteristics. The final step in winning the
purified metals is to smelt the sulfates with coal or coke. This releases carbon monoxide or dioxide as well as sulfur dioxide according to, for
example, the reaction PbSO4 + 2C --> Pb + 2CO + SO2. Since the gas from the smelter will be extremely hot, it would be ideal to catalytically
oxidize it with the Contact Process directly as it comes out, as opposed to going through any other steps of condensing the SO2 or chemically
absorbing it as bisulfite or the like. However I am worried about the carbon monoxide or dioxide in the gas either poisoning the catalyst by reducing
it, or interfering with the SO2 --> SO3 oxidation. I'm not sure if this will be a problem at all or not.not_important - 15-7-2008 at 20:51
Don't think that will be a problem with vanadium based catalysts and an excess of oxygen.12AX7 - 15-7-2008 at 23:25
SO3 is a bit of an oxidizer, ain't it? Should be no problem to get rid of the CO quite rapidly then. Just use more O2.
TimShadowWarrior4444 - 16-7-2008 at 01:22
It certainly doesn’t seem that any troublesome C-S compounds can form--far too much oxygen around.
You may want to check whether your catalyst has any incompatibilities with CO or more prevalently CO2 at high temperature.
Naturally I shouldn't need to mention having adequate ventilation, gas-pressure controls, and condensation apparatus.kilowatt - 22-7-2008 at 18:35
I have collected some lead salt from my sulfating battery and have been assembling the process reactors. I have the V2O5 reactor tube more or less
assembled, and am using the same steel retort that I made for HF production as the smelter. The lead salt I have obtained appears to be a mixture of
lead dioxide and lead sulfate. It is light grey in color overall, and contains dark colored flakes of lead dioxide. With the lead dioxide content
the heat of the smelting should release some oxygen, but this will likely oxidize carbon or CO before it ever makes it to the catalyst tube, plus the
rate at which oxygen is released will not be uniform for the duration of the process.
I am concerned with how I'm going to control the air feed rate since I don't know at all what rate the smelting gas will come off. I realize that
excess air is not a problem for the reaction, but a great deal of excess air will dilute the already diluted smelt gas and this will slow the SO2
--> SO3 oxidation possibly to a point where the yield is very poor. A great excess of air would also carry away a lot of heat and make the process
less efficient.
Another possibility is to use the pressure of the feed air (up to 100psi) to liquefy the SO2 with a condenser and separate it from CO2 and CO. The
SO2 would be collected in a reservoir as CO and CO2 are vented out with a needle valve. The SO2 could then be released later to the catalyst at a
more controlled rate with a needle valve. This would effectively waste all the heat carried over from the smelter as the SO2 would need cooled down
to near room temperature before it would liquefy. It would however allow SO2 to be used in other processes.watson.fawkes - 21-8-2008 at 05:50
Quote:
kilowatt said:
I am worried about the carbon monoxide or dioxide in the gas either poisoning the catalyst by reducing it
and then later said:
Another possibility is to ... liquefy the SO2 with a condenser and separate it from CO2 and CO
Carbon
monoxide is a pretty effective reducing agent. Its action on iron oxides is one of the reasons you can smelt iron in a cupola, which is charged with
alternating layers of coke and iron. If not, you'd get huge oxidation losses. Now granted it's pretty hard to push straight air hard enough through
the stack to get to this regime, but when you use oxygen injection to raise the melt temperature, you do get higher losses.
So, I'd guess that the action of CO in vanadium oxide would lead to greatly reduced catalyst life. With a sensitive-enough balance, a large-enough
charge, and an encapsulated catalyst cell, you could just measure the mass loss by running hot CO through it. For such an analytical test, though,
don't include SO<sub>2</sub> because adsorption will interfere.
You likely will have to separate out the CO. In addition to refrigeration, you could also use a scrubbing stack with a sacrificial reductant, like,
say, iron oxide. This way you can keep the stack insulated and not lose the exhaust heat. The problem with designing such a stack is how to get the
material in intimate contact with the gas. Solids are problematic from a surface-area vs. dust-entrainment tradoff. A spray tower might be useful.
