Gyula Szabo

Prediction of the adsorption coefficient (Koc) for soil by a chemically immobilized humic acid column using RP-HPLC.

By determination of HPLC capacity factors (k′) for a series of aromatics it has been possible to determine the soil adsorption coefficients (Koc). The effect of column type and mobile phase composition on the correlation between log Koc and log k′ has also been studied. We have prepared a new HPLC packing material which bears immobilized humic acid and from the values for Koc it appears this new HPLC phase is superior to other procedures - partition into n-octanol and retention on HPLC silica-based phases - which have been used to model the sorption of aromatic substances on soil or sediment.

Determination of the adsorption coefficient (Koc) of some aromatics for soil by RP-HPLC on two immobilized humic acid phases.

Abstract By determination of High Performance Liquid Chromatography (HPLC) capacity factors (k′), a comparison has been made of two new HPLC phases - physically and chemically immobilized humic acid - of their potential for determining soil adsorption coefficients (KOC) for organic pollutants. Log KOC values were estimated from log KOC versus log k′ calibration curves and were determined by using k′ and the humic acid content of the HPLC phases. These calculated log KOC values were compared with log KOC values taken from the literature.

Complexation parameters for the actinides(IV)-humic acid system: a search for consistency and application to laboratory and field observations

Summary The coherence of actinide(IV) complexation by humic substances (HS) is reviewed and new data are proposed. In a first attempt, the values of independent data from literature on Th(IV), U(IV), and Pu(IV) are collected, selected, and compiled. The data obtained follow the “classical” trend of increasing conditional formation “constants” with pH, led both by the increasing ionisation of HS and by the extensive hydrolysis of the tetravalent actinides. Even though a fair agreement is evident, the experimental uncertainties do not permit a full analogy between the actinides(IV) to be ascertained. In a second attempt, the experiments from which the original data are available were reinterpreted using only one hydrolysis constant set for U(IV) as an example, considering that all actinides(IV) have analogous humic complexation behaviour. Hence, the obtained evolution of conditional formation “constants” is much more coherent and the uncertainties do not permit to distinguish an actinide(IV) from one another. The obtained data are then applied to independent laboratory and in situ experiments in order to delimit the domain of possible applicability. This exercise demonstrates the treatment of data through analogy in the case of actinides(IV) and would permit to limit and orientate the number of necessary, but difficult, experiment with redox sensitive elements like U, Np, or Pu. It also demonstrates that complexation-only mechanisms may not be sufficient to understand field observations.

Evaluation of silica-humate and alumina-humate HPLC stationary phases for estimation of the adsorption coefficient, Koc, of soil for some aromatics☆

Abstract Two novel stationary phases have been prepared by immobilizing humic acid on aminopropylsilica and alumina and used to study, by reverse-phased high performance liquid chromatography (RP-HPLC), the contribution of the mineral phase upon the sorptive properties of soil humates for organic pollutants. By determination of K oc , the adsorption coefficient for the organic carbon of soil, for a series of aromatic hydrocarbons it has been shown that the mineral phase has little influence upon their sorption by humic acid, the principal organic component of soil.

Investigations of the uptake of transuranic radionuclides by humic and fulvic acids chemically immobilized on silica gel and their competitive release by complexing agents

The chemistry of the interactions of transuranic elements (TUs) with humic substances needs to be understood so that humate-mediated movement of transuranic radionuclides through the environment can be predicted. This paper reports the chemical immobilization on silica gel of humic and fulvic acids and evaluates the potential of these new materials for the retention of Pu and Am. In addition to the preparation of the foregoing immobilized humic substances, other low molecular weight metal-binding ligands have also been immobilized on silica gel to investigate the binding sites for transuranic elements (TUs) in humic substances. The X-ray photoelectron spectra (XPS) of Th(IV) complexed by humic acid and the immobilized humic acid are similar thus it appears that immobilization of humic acid does not generate any configurational changes in the Th(IV)-binding sites of the macromolecule. A variety of chelating agents partly mobilize these TUs sorbed on the solid phases. A batch method was used to determine the distribution coefficients (Rd) of Pu and Am between the silica gels and aqueous solutions of phosphate and citrate. The effects of the immobilized ligands, the anions and pH in the solution on sorption were assessed. Distribution coefficients (Rd) for the uptake of Pu and Am by these prepared solid phases are, in some cases, of a similar order of magnitude as those determined for soil and particles suspended in terrestrial surface waters.

Comparison of different HPLC stationary phases for determination of soil-water distribution coefficient, KOC values of organic chemicals in RP-HPLC system

The application of a HPLC-screening method for determination of soil sorption constants (KOC) was tested on five different stationary phases use of a large set of reference substances from different chemical classes Cyanopropyl and chemically bound humic acid stationary phases turned out to be the two most promising candidate for development of HPLC-screening method. The results show that the investigated HPLC method provides a quick and reliable method to determine the sorption coefficient of chemicals in soil system.

Effect of ionic strength on complexation of Pu(IV) with humic acid

Abstract Successful geochemical modelling of the migration of radioactive materials, such as the transuranic elements, from nuclear waste repositories is dependent upon an understanding of their interaction with biogeopolymers such as humic acids, the most likely complexing agents in groundwaters. An established silica/humic acid composite has been evaluated as a model substrate for naturally occurring humate-coated minerals that are likely to be present in the vicinity of the repositories. The binding of Pu(IV), the highly likely oxidation station, by the silica/humic substrate was examined at pH 4 in the range 0.02 to 3.00 M NaClO4 by the titration method. Pu(IV)-humate conditional stability constants have been evaluated from data obtained from these experiments by using non-linear regression of binding isotherms. The results have been interpreted in terms of complexes of 1:1 stoichiometry. Analysis of the complex formation dependency with ionic strength shows that the effect of ionic strength on humate complexation of Pu(IV) is not dramatically pronounced. The complexation constants are evaluated for the humate interaction with Pu4+ and Pu(OH)3+ at pH 4. The complexation constants are found, respectively, to be logHAβ0(Pu4+)=16.6±0.3 and logβ01.3.1=46.6±2.3. The estimations through analogy from previous results are in agreement with these new experimental data.

Examination of silica-salicylic acid and silica-8-hydroxyquinoline HPLC stationary phases for estimation of the adsorption coefficient of soil for some aromatic hydrocarbons

As part of the development of a liquid chromatographic procedure for predicting the environmental fate of organic pollutants, we have evaluated silica-derivatized stationary phases as models for the organic constituents of soils. These silica-derivatized phases, formed by immobilizing salicylic acid and 8-hydroxyquinoline on silica, have been evaluated by estimating the soil partition coefficients (Koc) for a series of organic chemicals and comparing them with values reported in the literature.

Investigations into the chemical forms of 239Pu in a West Cumbrian saltmarsh soil radiolabelled by an environmental process

New procedures have been developed to demonstrate the nature of binding of 239Pu in a saltmarsh soil. Evidence is presented which shows that there is a small 239Pu component which is present in a form which can be extracted by chelating agents which are similar to naturally occurring chelating agents. By in-situ derivatization procedures it has been possible to isolate two forms of complexed Pu. The effectiveness of humates as sinks for Pu(IV) and Am(III) have been modelled by using some novel forms of humic and fulvic acids chemically immobilized upon silica.

Investigation of the interactions of 110mAg+ and 125I− with humic acid chemically immobilized on silica gel

Silica gel bearing chemically immobilized humic acid (CBHA) has been prepared and used to model the uptake of 110m Ag + and 125 I − by humic matter. The adsorptive properties of CBHA, as judged by the uptake of these radionuclides, are quite distinct from those of the parent silica gel