Adsorption of humic acid onto pillared bentonite

Pillared bentonite, a clean and cost-effective adsorbent with high specific areas of 111.3 m2/g and high basal spacing of 1.98 nm, was prepared for the removal of humic acid from water. It is effective for the removal of humic acid with a high adsorption capacity of 537 mg/g, and adsorption is favored under acid conditions. Adsorption is dependent on ionic strength and dissolved NaCl enhanced adsorption. Over 97% removal was observed under natural pH conditions from humic acid solutions containing 10 mg/L Ca2+ or Mg2+, which suggests that pillared bentonite can be an effective adsorbent for the removal of humic acid for drinking water purification. Pillared bentonite can be regenerated with NaOH, and the regeneration efficiency reaches 83% and 85% when the concentration of NaOH reaches 0.025 and 0.05 mol/L. The mechanism for adsorption of humic acid to pillared bentonite is discussed.

Aluminum polycation PB was successfully prepared and is reported to be an effective adsorbent for the removal of humic acid from water. It has much higher zeta potential than raw bentonite and Na-bentonite. The specific area and basal spacing reaches 111.3 m2/g and 1.98 nm, respectively, which indicates the formation of a microporous system in the interlayer spaces of the PB. The adsorption properties of PB for humic acid depend on pH values. Adsorption is favored under acid conditions. PB is effective for the removal of humic acid with a high adsorption capacity of 537 mg/g. It has a much higher adsorption capacity than Na-bentonite because it has a higher zeta potential and specific area and the introduced Al2O3 pillars between the layers are effective adsorption sites for humic acid. Adsorption is dependent on ionic strength and dissolved NaCl enhanced adsorption. Ca2+ and Mg2+ in the solution significantly enhanced the adsorption. When Ca2+ and Mg2+ reach 10 mg/L, over 97% removal of humic acid was observed under natural pH conditions, which suggest that PB can be an effective adsorbent for the removal of humic acid in drinking water purification. The increase of adsorption with the increase of ionic strength and dissolved salt is probably due to the compression of the diffuse double layer and charge neutralization, the compression of the molecular volume of humic acid and the screen- ing of the surface charge of both adsorbent and adsorbate by the added salt. Otherwise, interactions in solution between salts and organics to produce a change in the properties of organics and the formation of a clay–metal–humic acid complex or clay–metal–H2O–humic acid complex can also contribute to increased adsorption with the addition of Ca2+ and Mg2+. PB can be regenerated with NaOH. The regeneration efficiency reaches 83% and 85% when the concentration of NaOH reaches 0.025 and 0.05 mol/L.