Sparging into a slurry

[robot6]

What are the difficulties in sparging air into the cyanide detoxification (INCO) process,

CN- + H[sub]2[/sub]O + O[sub]2[/sub] + SO[sub]2[/sub] -> OCN- + H[sub]2[/sub]SO[sub]4[/sub] ?

Typically the "substrate" is some kind of slurry ... how does this affect sparger selection? That is, the tank is vigorously agitated, so does the sparger have special material to protect against erosion? Do you think it's possible to use a fused metal sparger for this application, or will it be rather rapidly eronded? What about the tank walls? In a typical application, what do you think the apparent density of the fluid is?

 

[georgeverghese]

Though I know next to nothing about the kinetics of this reaction, it does look severely limited by the dissolution of O2 into water at low pH, which may in turn be more or less insensitive to turbulence / agitation you have in this slurry, given the info posted so far.

Some chemical to improve O2 uptake into this slurry may be required before you can see the benefit of increasing turbulence / agitation to enable this reaction to approach equilibrium.

 

[robot6]

Yes, it is severely limited by O2 uptake, that is correct. The reaction is "catalyzed" by Cu(II). (I put that in quotes because I wonder whether the Cu(II) is really catalyzing the reaction, since there are some reports of it going without the Cu(II), but Cu, being a transition element, may assist the oxygen uptake.)

However, this reaction is usually done on such a grand scale that an uptake chemical (Are you thinking of something like iron, when I've got a solution of cyanide?) would be prohibited by cost. The Cu(II) works because it's usually already in the slurry.

And it is well known that the turbulence and agitation of the solution assists in O2 uptake: as O2 is consumed by the reaction, more is taken up, so long as the gas film layer and the liquid film layers can be thinned through agitation.

So this is a really old reaction and pretty well-understood. Any idea about spargers in a severely agitated slurry?

 

[georgeverghese]

In what may appear to me as a similar service in my experience on a hydromet design project for Ni/Co extraction, NiS and CoS in an alkaline slurry are converted into soluble sulphates with amm. sulphate in a pure O2 blanket at high pressure with several motorised impeller-agitators in each vessel to provide turbulence. No spargers.

In my days as an operations engineer at an ASU, a manual method for O2 purity estimation was to bubble O2 into an ammonical solution of CuSO4 to produce cuprammonium hydroxide( may perhaps work just as well with NaOH?). But this solution you have is acidic, and O2 partial press is very low also..

 

[robot6]

This reaction is kept going by the addition of lime to eat up the sulfuric acid... LeChatelier's...

 

[georgeverghese]

Hope the super chemists at INCO havent left you out on the window ledge on this with no guidance - they must have done some pilot tests on this to arrive at a workable unit configuration which gives acceptable conversion rates. Must say dumping cyanides tailings into the ocean is a frightening proposition, so would assume acceptable conversion rate must be close to 100% ? Is this plant some where in SE Asia / PNG?