Can be chemically removed by a Concrete Contractor, but usually sandblasting is used - by a sandblasting specialty contractor or some concrete contractors. Some Masonry contractors also do this.
Generally, outdoor pavers should not be sealed - commonly you get moisture migration from the ground up into the pavers that accumulates white lime deposits under the sealer, which is likely what you are seeing.
Here is a link to a similar question with answer FYI too -
https://answers.angieslist.com/can-cu...
