A process for preparing an aluminum-free boron containing zeolitic material comprising the framework structure MWW (BMWW), comprising (a) hydrothermally synthesizing the BMWW from a synthesis mixture containing water, a silicon source, a boron source, and an MWW template compound obtaining the BMWW in its mother liquor, the mother liquor having a pH above 9; (b) adjusting the pH of the mother liquor, obtained in (a) and containing the BMWW, to a value in the range of from 6 to 9; (c) separating the BMWW from the pH-adjusted mother liquor obtained in (b) by filtration in a filtration device.