Adsorption properties of soil humic and fulvic acids by hematite

Abstract

The adsorption isotherms and their size fractionations of soil humic and fulvic acids (HA and FA, respectively) were determined at pH 7, 9.2 and 11, where the surfaces of the hematite are positively, neutrally and negatively charged, respectively. The M w , M n and polydispersity in the solution after adsorption were measured in order to investigate the preferential adsorption trend of the HA and FA. The measured adsorption was consistent with the adsorption from Langmuir isotherm fitting. The adsorption of HA onto the hematite was more favorable than that of FA due to the preferential adsorption of high molecular weight fractions and the greater hydrophobicity. As the solution pH increased, the preferential adsorption for the high molecular weight fractions partially deviated with higher polydispersity. This indicates that the adsorption of the HA and FA onto hematite was affected by the molecular conformation, and the electrostatic repulsion between the HA and FA and the hematite lead to the kinetically sluggish adsorption. Further, it implies that the adsorption properties of soil organic matter may affect the adsorption of metal and metalloid onto the adsorbent like iron-oxide in the geochemical environments.

The influence of pH on iron speciation in podzol extracts: Iron complexes with natural organic matter, and iron mineral nanoparticles

“…This effect, however, does not necessarily account for all the iron (oxy)hydroxides that were observed in the extracts since iron (oxy)hydroxides could also be mobilized from the native soil. Humic acids adsorb to Fe mineral surfaces to a greater extent than fulvic acids (Ko et al, 2005;Weng et al, 2006), and humic acids were only present in soil extracts with pH ≥ 7. Co-mobilization of iron (oxy)hydroxide nanoparticles from the native soil, together with their humic acid coatings, could therefore occur in the extracts with pH ≥ 7.…”

Effect of contact order on the adsorption of inorganic arsenic species onto hematite in the presence of humic acid

“…Soil HA was extracted from non-contaminated forest soils (Jangsung, Jeolanamdo, Korea) following the standard procedure recommended by the International Humic Substances Society [21,22]. Electrolyte-free HA was prepared using a cation-anion-exchange resin column and stored at 4 • C in the dark.…”

Interaction between beet vinasse and iron fertilisers in the prevention of iron deficiency in lupins

“…These results regarding vivianite suggest a reduction in the solubility likely due to the adsorption of organic matter on Fe‐rich particles (vivianite or oxides formed from it). The adsorption of components of DBV, such as fulvic acids,4 on Fe oxides is well documented 42. This adsorption may decrease Fe extractability and availability to plants,43, 44 because ligand‐controlled Fe dissolution requires the adsorption of the ligand on the surface of the Fe‐rich particle,45 and this adsorption can be decreased if organic compounds present in DBV are previously adsorbed on the sorption sites.…”