Hi Ged,
Effloresense(calcium carbonate) is a naturally occurring phenomena found usually in concrete products but has been known to appear on clay pavers as well. You could acid wash it but you run the risk of discolouration if your acid solution is too strong. Any use of acid should be applied with caution. Pressure washing sometimes accelerates the chemical reaction that causes effloresense and in most cases it is unavoidable. Sometimes doing nothing and allowing it to gradually disappear is an option or the old fashioned but safe method of clean water, stiff brush and loads of elbow grease will remove the bulk of it.
If you are going to seal the drive, the effloresense must be removed, as all you will be doing is sealing it in permanately. Also, allow it dry properly, applying a sealer on wet or damp pavers will cause them to go milky white.
Good Luck
Paul