I don't think you will be able to remove the ink without chemicals; and even if you were willing to use chemicals, it seems the cost and trouble would erase any savings in using your junk mail this way. I don't know about your junk mail; but I know most of mine is printed with colored ink on coated paper; and I don't think you'd be able to re-use that for the printer, at all. You can easily re-use flat paper that only has print on one side, just put that in your printer, so that it will feed with the blank side for printing.
You can recycle junk mail in making homemade paper; but it is not generally suitable for printers, though it is a lot of fun to make and use.
To save money and resources when printing: set your printer to default to "draft" mode, you will save a lot of ink; and also set the default to black and white. (You can choose color or high quality for those occasions when you need it.) Purchase the least expensive printer paper you can, and be sure to print both sides. If your printer cannot do this automatically, only feed one sheet at a time, so you can reverse it and run it through the next page.
Lastly, and maybe most importantly, think twice before printing. Can you save the page to your hard drive instead? Can you copy the information (by hand) onto scrap paper? Do a "print preview" before printing from the internet. Very often, you only want one or two pages, but with all the ads and comments, you get six or eight! If all you want is 2 pages, or specific pages, only print those!
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