Two Polish lignites (grain size 0.2-1.0 mm) were extd. with aq. soln. of NaOH (1-5% by mass) at 20-100 degrees C for 1-24 h (lignite:NaOH mass ratio 1:40 to 1:5) to sep. the humic acids as Na huminates, pptd. with HCl, demineralized with aq. HCl at 100 degrees C and dried at 80 degrees C. Under the optimum conditions (concn. of NaOH soln. 5% by mass, extn. temp. 100 degrees C, extn. time 1 h, lignite:NaOH ratio 1:20), the yield of humic acids was 69.1-70.9% by mass and ash content 3.5 or 6.6% by mass. The products were considered as adsorbents.