Usually a phosphoric acid based liquid or gel such as Naval Jelly.

Dear Mrs. Mirsafaei,

For remove rusty iron except wet blasting method you can use and laser removal of rusty.

For anti corossion protection  before painting you can use following procedures detail explanationed in links and articles bellow.

Most comon procedures are :

• Burnishing
• Phosphatising, 
• and I am recommending also WS2 nano protection

Best regards,

Dragan Vuksanović

https://www.youtube.com/watch?v=CLaBFkeHG0A

http://www.wurth-industrie.fr/web/media/pictures/wif/download_centre/chapitre_5_EN.pdf

https://www.youtube.com/watch?v=6TN9WNgxsmo

https://www.youtube.com/watch?v=1qUT9d9PfV4

http://www.nanotehnologije.com/wp-content/uploads/2016/05/NANOTECHNOLOGY.compressed.pdf

https://www.youtube.com/watch?v=cGX2gHlUnug

Hi,

I think it really depends on your application. If you want to keep it simple and if its possible, you can just remove the iron oxide by grinding. Theerby you should choose as final grinding step a fine grinding paper. After grinding the surface should be cleaned with ethanol and any contact with water should be prevented. In the end the time between removing iron oxide and painting the surface should be as short as possible. For sure the surface will not be 100% free of iron oxide (in the microscopic scale you will find oxide), but the question is how "oxide-free" the surfaces have to be?

If the surface is coated, oxides have to be removed as well and than you will have the same issue as I desribed above - thus limited time between removing oxide and coating/painting.

The use of phosphoric acid can be of course another option beside grinding. It depends on your component/sample and the requirements.

Best regards

Immediately after high pressure/ultra high pressure water-jetting use a phosphate pre-treatment to prevent excessive flash rusting.  A good-quality primer, build and top coat then can be applied for long-term protection.  The choice of coating will depend, as Martin Scheik has responded, on the service environment, required service life expectancy and aesthetic considerations.  You should source all of the components from one of the major coating manufacturers to ensure compatibility and assured long-term performance and carry out independent third-party inspection while the work is being done to ensure that the application contractor adheres rigorously to the specified coating procedure.

One thought that has occurred to me is that after the surfaces have been cleaned in the appropriate manners suggested above (sandblasting + phosphoric acid treatment is common), then they could be fully protected with a layer of epoxy powder coating.