To study the sorption of fulvic acids (FA) from aq. solns. on a MnO2-modified zeolite ("Diapar") in relation to salt (metal cation M2+) type, and to elucidate the mechanism of FA removal by sorption and filtration, salts (Cu sulfate, nitrate, or chloride, Ca nitrate, Fe chloride, etc.) were added (to a total of 0.5 meq M2+/l.) to 200 ml of a 20-mg TOC/l FA soln. (FA concn. expressed as total org. carbon, mg TOC/l). The soln. was rotated 200 rpm with 0-10 g zeolite/l. and centrifuged 10 min/4500 rpm. The FA contg. C 45.894, N 2.56, H 4.958, S 0.402, O 46.187, and ash 3.891%, were extd. from the Kolobrzeg (PL) mud deposits and ion-exchanged into the Na form. The zeolite contg. clinoptilolite 55, montmorillonite 13, ash 26, and quartz 6%, was treated with Mn2+ to ppt. MnO2 on the zeolite surface. Over pH 3-11, zeolite's zeta-potential varied from -6 to -35 mV In 20 hrs., 4 g zeolite/l. removed only 1 mg TOC/l.; with Mg2+ and/or Cu2+ added, only 2 mg TOC/l.. With 0.5 meq Fe3+/l. at pH 3-5, 0-1 g zeolite/l. removed 13-15 mg TOC/l. At pH 6-8 (Fe(OH)(5)(2-)) and pH > 8 (Fe(OH)(6)(3-)), sorption was slight and nil, resp. The neg. charges present in excess and the resulting electrostatic repulsion disabled sorption, even if the complex-forming Fe cations were present.