You have two options, the first is to oxidize with H2O2, then drying or if you don't have much concern about chloride, you can oxixdize with sodium hypochlorite.  Before doing this you need to determine sulfite to add the equivalent oxidizing agent.   

Thank you Taha.  I believe the H2O2 oxidization would require the material to be in an aqueous form possibly with a acidic ph in order to introduce the H202 in relevant quantities to allow for oxidation to occur.  Does this sound correct?  Chlorides would be an issue in the resultant gypsum matrix.

Oxidization can be realized by air, see http://www.google.com/patents/US4976936

or

http://nepis.epa.gov/Exe/ZyNET.exe/20006ML1.TXT?ZyActionD=ZyDocument&Client=EPA&Index=1976+Thru+1980&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5Czyfiles%5CIndex%20Data%5C76thru80%5CTxt%5C00000002%5C20006ML1.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C-&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=p%7Cf&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=1&SeekPage=x&ZyPURL

or www.cimprogetti.com/environmental.PDF 

Thank you Pavel.  Simply leaving the sulfite exposed to air will cause it to oxidize and turn into sulfate over time.  In this particular case the generator does not  / did not include any equipment for oxidizing the sulfite as it was being generated.  We are trying to find a solution for the conversion after the sulfite has already been produced.  High temperatures combined with air flow , airflow exposure over time, and solubilizing the material combined with a aeration are the only methods I have come across so far for converting material which has already been produced.  Any further comments or ideas are welcome.

A can agree with air oxidation, but the question is how fast is such reaction and to what extent this option is satisfying? also, another question may arise, Is it important to spread calcium sulfite over an appreciable area? or can it  be piled up? what about pumping air through the pile!!

The air oxidation process takes quite a bit of time and only impacts the material on the surface that is exposed.  Not very economical from a processing aspect. - Cheers

Hi Poling, does the problem solved yet?

We also faced similar problem. The calcium sulfite rich powder produce from a dry desulfurization project. did you have any suggestion?

I am also working on the project utilizing the FGD gypsum in cement.

Using FGD Gypsum in cement is relatively common in the states if anyone would like details please send me a message. For converting Sulfite into Sulfate we have not yet found economical and rapid method to accomplish this. Oxidation of course is key and we are working on a solution using vapor pressure as a first step

Hi Poling, I can't agree you more.

In china, there are tens of millions FGD gypsum and other kind of gypsum used in cement industry, there is not doult that it is feasible.

However, calcium sulfite rich byproduct seems much difficult try to used in cement industry. There is one high temperature forced oxidation produce line in the northeast of china, and operating for more than 1 year, and there may be more in the future. However, I guess the cost is still too high.

Hope you have a good progress on oxidation with vapor pressure.