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Preventing air pollution from gold purification


What are all the chemicals that can be used for scrubbing NOX, SO2? that is in gold purification plant. How to find out the quantity of scrubbing liquor?.

Rajamanickam Mathivanan
Pollution control Board(Govt) - Coimbatore, Tamil Nadu, India


Hi Rajanamickam

You pose a problem ... not so much with SO2 but with nitric. For SO2 I've seen NaOH used with good effect ... but nitric, ie. some of the many NOX variants, some you can clean up easily but for the others, it's a LONG retention time particularly when the fumes are hot.

There is an Italian Company called A.J.M. Vieri (I think that's the right spelling) who had a design which I liked.

From the retorts or cupolas (i.e., heated vessels) they had, say, a 2" dia outlet ... this was sleeved somewhat in the way that A.A. absorption columns ventilation works ... a wide tapered sleeved, adjustable, so that one can balance the extraction rather than just suck up all the fumes negatively.

This and other 2" dia outlets then connected to a 3" or 4" (I forget) header. Now comes the interesting part. The header pipe is joined to a 12" dia (30 mm) column at the top. The column is at least 10 feet long. It has about 3 or 4 little bleed screws to allow air to be sucked in.

This is connected to another 12" column and this repeated 6 times ... then to a conventional scrubber.

In other words, a LONG retention time with fresh air amounts (i.e., oxygen) being intimately mixed as the mini airflow proceeds through the remaining 5 (or was it 7?) 12" columns.

This, THIS is the way to treat max NOX airflows ... and the final scrubber was ? I forget .... maybe only 10" dia, ergo the proponents of mass transfer scrubbers would have said that the velocity be, say, 300 fpm and the NaOH rate around 5 gallons/l,000 cfm.

Personally I'm not pro mass transfer but specialized in low micron scrubbers ... and using air atomized sprays, Noranda in Pointe Clair, Que., achieved some very interesting and good results with SO2 using Na0H with a so-called LMITS PVC scrubber ... but this was in the mid 70's.

freeman newton portrait
Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

December 12, 2009

actually , to neutralise nitric acid fumes, you don't need a lot of equipment. just the nitric fumes are to be passed through a glass pipe, of nearly 2 feet long, and the other end is connected to a rubber pipe. just the rubber pipe may be some 5 mts long, and the pipe immersed in cold water in a drum or plastic barrel. the fumes coming out are neutralised in water , the water to be changed in regular intervals or if it gets warm.
simple way.

maheshkumar mane
- coimbatore, India

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