Adsorption Of Fulvic Acid Research Articles

Effects of salts on activated carbon adsorption of fulvic acids

Calcium, magnesium, and sodium significantly influenced the adsorptive capacity of activated carbon for fulvic acids from three sources, including a natural groundwater supply. Adsorptive capacity was evaluated as a function of salt type, salt concentration, and pH and was most sensitive to changes in low concentrations of salt. Chloride, sulfate, bicarbonate, and phosphate exhibited no observable effect on the adsorption of fulvic acid. Calcium significantly influenced the adsorption of peat fulvic acid by an activated carbon column, the addition of calcium greatly enhanced adsorption, and the withdrawal of calcium from a loaded column resulted in substantial desorption. Salts enhanced the adsorption of dihydroxybenzoic acid but had variable effects on the adsorption of EDTA, citric acid, and aspartic acid.

Characterization and activated carbon adsorption of several humic substances

A commercially supplied humic acid, extracts of a Michigan Finch soil, and extracts of leaves from a hardwood forest were characterized by molecular size fractionation, functional group analysis, and haloform formation potential. The haloform formation potential was dependent on the source of the material; differences could not be correlated with the amounts of oxygen-containing functional groups in each substance. A bituminous-base activated carbon adsorbed each humic substance with the adsorption capacity at seven days being source-dependent. The extent of adsorption of humic material from various sources was inversely related to the number of carboxyl groups per unit weight of the substance. The lower molecular weight species of a given humic or fulvic acid was more adsorbable, presumably because more surface area was accessible to these species. Soil fulvic acid adsorption increased with decreasing solution pH and increasing phosphate buffer concentration. Due to the variability of haloform formation potential and adsorbability of humic substances from different sources, treatment performance to remove these materials should be evaluated using the specific water to be treated.

Voltammetric study of humic and fulvic substances: Part I. Study of the factors influencing the measurement of their complexing properties with lead

A detailed, qualitative, investigation of the behaviour of lead complexes with fulvic substances has been carried out using several polarographic techniques, e.g d.c. polarography, a.c. polarography, normal and differential pulse polarography and cyclic voltammetry. The mercury drop electrode was used for this study. It is shown that under the conditions used (pH∼6) the charge transfer process is reversible, the complexes are labile and the adsorption of fulvic acids and fulvic complexes occurs on the electrode. The implications of these results, with regard to the use of the various amperometric titrations for the measurement of the complexing capacity of natural waters, are discussed.

Effect of Fulvic Acid on Adsorption of Methyl Parathion and Parathion by Ca2+ − and Fe3+‐Montmorillonite Suspensions.

AbstractA study was conducted to examine the effect of fulvic acid (FA) on the adsorption of methyl parathion and parathion by Ca2+ − and Fe3+‐montmorillonite suspensions, and to determine whether FA in solution could alter the water solubility of these insecticides. FA, in the 10‐ to 100‐mg/liter range, did not affect the water solubility of the two insecticides. In Ca2+‐montmorillonite suspensions, increasing FA concentrations first enhanced methyl parathion adsorption, followed by adsorption decrease at higher FA levels. Methyl parathion adsorption in Fe3+‐montmorillonite suspensions decreased, with increasing FA levels. Parathion adsorption was not significantly altered in either clay suspension. The order in which the FA, clay, and insecticide were mixed affected methyl parathion adsorption. The greatest effects were observed where FA was adsorbed by the clay before the insecticide solutions were added. FA adsorption by Ca2+‐montmorillonite fitted the Freundlich isotherm, whereas the much greater adsorption by Fe3+‐montmorillonite fitted the Langmuir isotherm. Although both CaCl2 and FeCl3 solutions greatly enhanced FA removal by their respective clay suspensions (even at low concentrations), parathion adsorption was not affected. The presence of FA in the FeCl3‐Fe3+‐montmorillonite suspensions appeared to prevent parathion degradation.

Reactions between Fulvic Acid, a Soil Humic Compound and Inorganic Soil Constituents

AbstractThe order of stabilities at pH 5.0 of complexes formed between a water‐soluble Podzol fulvic acid and nine divalent metal ions was Cu > Pb > Fe > Ni > Mn > Co > Ca > Zn > Mg. Log K (stability constant) values ranged from 8.69 for the Cu‐complex to 2.09 for the Mg‐complex and were higher at pH 5.0 than at pH 3.5. The Irving‐Williams series was not followed. Provisional results indicated that log K values for Fe3+‐ and Al3+‐fulvic acid complexes were higher than those for divalent metal‐fulvic acid complexes. Two types of reactions occurred between fulvic acid and metal ions and hydrous oxides: a major one in which both COOH and phenolic OH groups reacted simultaneously, and a minor one involving less acidic COOH groups only. To develop analytical methods for investigating metal‐organic matter complexes occurring in soils, model compounds, containing varying metal to fulvic acid ratios, were prepared. The methods so developed were later used as diagnostic tools for the characterization of metal‐organic matter complexes extracted from natural soils or occurring as distinct horizons in soil profiles.In contrast to unreacted fulvic acid, metal fulvic acid complexes reacted with phosphate via the metal to form fulvic acidmetal‐phosphate. The interlamellar adsorption of fulvic acid by montmorillonite depended on the pH of the medium, the fulvic acid concentration and the type of cation with which the clay was saturated. Fulvic acid was found to have a positive effect on root initiation, which appeared to be related to its metal complexing ability.

Reactions Between a Podzol Fulvic Acid and Na-montmorillonite

The interlamellar adsorption of fulvic acid by Na-montmorillonite was pH-dependent and decreased with increase in pH. At pH 2.5, 40 mg of clay adsorbed 33.2 mg of fulvic acid. Interlamellar adsorption was rapid and increased with increasing fulvic acid concentration until approximately 100 mg of the latter had been added to 40 mg of clay. While distilled water desorbed only 24% of the fulvic acid in the organic matter-clay complex, O.1N NaOH solution desorbed 93% of the adsorbed fulvic acid. From the experimental data it appeared that fulvic acid was adsorbed in and on the clay mainly in the undissociated or slightly dissociated form and, to a minor extent, as Na-salt. Desorption experiments showed that a decrease in interlamellar spacing of 1A was associated with the expulsion of approximately 3.0 mg of fulvic acid. It was estimated that slightly more than one-half of the fulvic acid was adsorbed in the interlamellar spaces of the clay. The controversy in the literature as to whether or not soil organic matter is adsorbed in the interlamellar spaces of 2:1 type expanding silicate minerals appears to a considerable extent to be related to disregard by many investigators of the effect of pH.