James H. Ephraim

A unified physicochemical description of the protonation and metal ion complexation equilibria of natural organic acids (humic and fulvic acids). 1. Analysis of the influence of polyelectrolyte properties on protonation equilibria in ionic media: fundamental concepts.

Explication quantitative de la forte sensibilite des proprietes potentiometriques des polyelectrolytes acides faibles a la force ionique du milieu

A unified physicochemical description of the protonation and metal ion complexation equilibria of natural organic acids (humic and fulvic acids). 2. Influence of polyelectrolyte properties and functional group heterogeneity on the protonation equilibria of fulvic acid.

Potentiometric studies of the neutralization of several fulvic acid sources with standard base in aqueous and nonaqueous media have been conducted. Analysis of the results with a recently developed unified physicochemical model has shown that the protonation behavior of these fulvic acid sources is a reflection of their polyelectrolyte nature and their heterogeneity. It has been possible to ascribe the polyelectrolyte properties observed to a rather inflexible fulvic acid molecule whose variably charged surface is impermeable to simple electrolyte. 42 references, 24 figures, 4 tables.

On the composition and properties of humic substances isolated from deep groundwater and surface waters

Fulvic and humic acids were collected from groundwater and surface waters by an isolation procedure utilizing DEAE-cellulose, a weak anion exchange resin. DEAE-cellulose was selected since it can adsorb himics without any pH adjustment of the sampled water (in the pH range 4–8), thus making the method well suited for isolation of groundwater humic substances in the field. Characterization of general parameters (elemental composition, molecular weight, acidity, absorptivity, 14C-age) was performed on these humic substances as well as on humics isolated by other procedures. The humic weights and were divided into three categories on the basis of calculated atomic ratios, molecular weights and absorptivity: humic acids (high molecular weight) and fulvic acids (low molecular weight) from groundwater and surface waters, respectively. The similarities of the humics within each group, despite variations in age and origin, support the contention that humic substances have more properties in common than they have differences.

Properties of fulvic acids from deep groundwaters

Abstract Fulvic acids have been recovered from three deep groundwaters and one surface water and characterized with respect to elemental composition, molecular weight, acid capacity and 14 C-age. The corresponding waters are also characterized in detail. All of the fulvic acids, with ages varying from 0 to 5250 years, are very similar. The onlu significant difference between fresh and old materials are lower content of oxygen and nitrogen and higher COOH/OH-ratios for the materials from the old waters. Dating of the water using 14 C-analysis of the dissolved organic material is probably better than using the carbonate as the 14 C-source.

Complex-forming properties of natural organic acids: fulvic acid complexes with cobalt, zinc and europium

The complex-forming properties of a fulvic acid sample have been studied by an ion-exchange distribution method. The results have been analysed by a novel physicochemical approach which attempts to take into account complications introduced by the polyelectrolyte nature and functional heterogeneity of the fulvic acid molecule. These studies with trace level concentrations of cobalt, zinc and europium show that these metal ions are selectively complexed by the weakly acidic enol grouping of the fulvic acid molecule. The logarithms of the stability constants (beta(1)) for the cobalt, zinc and europium chelates are 6.5, 6.4 and 10.3 respectively.

Potentiometric titrations of humic substances : do ionic strength effects depend on the molecular weight ?

That the solution chemistry of humic substances is perturbed by ionic strength effects and functional group heterogeneity is now widely accepted. Application of the two-phase approach employing concepts from the Donnan equilibrium and the electrochemical unit cell had earlier postulated the ionic strength effects to be due to the presence of higher molecular weight moieties in the fulvic acid assemblage. Potentiometric titrations of a number of aquatic fulvic and humic acids (isolated by an initial preconcentration on diethylaminoethyl (DEAE) cellulose prior to their adsorption on XAD-8 resins) are presented as a function of ionic strength and their molecular weight distributions. Even though an apparent correlation between molecular weight distribution and ionic strength effects was observed, for humic substances of similar molecular weight, ionic strength effects seem to increase with an increase in the polydispersity of the molecule.

Effects of fulvic acid on the adsorption of Cd(II) on alumina

Abstract The effects of fulvic acids on the adsorption of cadmium on alumina has been studied by a batch distribution technique and with variation of pH (3 – 10), cadmium concentration (10 −4 – 10 −8 M) and fulvic acid concentration (0, 1, 10 and 50 mg/l). Two fulvic acids of different origin (surface water and deep groundwater) were used. The presence of fulvic acid generally enhanced the adsorption at pH below PZC (pH 7.8) and reduced the adsorption above this pH. Linear adsorption isotherms were obtained at cadmium concentration below 10 −6 M. The presence of fulvic acids at concentration levels representative of surface waters would be expected to have a significant impact on the distribution and mobility of cadmium in the environment.

Heterogeneity as a concept in the interpretation of metal ion binding by humic substances. The binding of zinc by an aquatic fulvic acid

Abstract Zinc binding by a well characterized fulvic acid was studied by the ion-exchange distribution technique and ultrafiltration method at 0.100 M NaClO 4 using trace amounts of zinc (≤ 10 −1 M) and two different fulvic acid concentrations (6.2 × 10 −4 and 1.2 × 10 −3 M). The results were interpreted by considering the various acidic sites envisaged from potentiometric titrations in aqueous and non-aqueous media. In addition to calculating the overall complex formation function, literature-based constants for the complexation between the metal ion and the ascribed functional group were employed to account for the observed binding patterns as a function of pH. This supported the interpretation of the functional groups assigned to the envisaged acidic sites. Results from the ultrafiltration method were in agreement with those obtained from the ion-exchange distribution technique.

Ultrafiltration as a technique for studying metal-humate interactions: studies with iron and copper.

Abstract An ultrafiltration method was employed to study Fe(II)/Fe(III) and Cu(II) binding by Armadale Horizon fulvic acid. The results of the Fe—fulvate studies indicate the formation of “aggregates” between Fe and the fulvic acid molecule. The reduction of Fe(III) to Fe(II) by fulvic acid is also observed. Results for Cu(II)—fulvate electrode method. An algorithm developed previously for the prediction of metal ion binding by fulvic acid at different pH and salt concentration levels was tested further by comparing Cu 2+ ion binding predictions with their measured values.

The Influence of a Fulvic Acid on the Adsorption of Europium and Strontium by Alumina and Quartz: Effects of pH and Ionic Strength

A batch method has been employed to study the adsorption of trace quantities of Eu and Sr on α-Α1203 and Si02 as a function of pH (3-9), ionic strength (0.10 and 0.01 M NaClOj and the presence of a well-characterized aquatic fulvic acid (FA). A comparison of Eu and Sr adsorption by alumina showed that FA could both reduce and enhance metal ion adsorption. In the absence of FA the adsorption of the metal ions onto alumina was a function of both pH and ionic strength. In the presence of FA the ionic strength effect on the Eu adsorption vanished, while the Sr adsorption showed a clear dependence on ionic strength. The adsorption of Eu and Sr on quartz was lower than the adsorption of the metals on alumina. Additionally, the adsorption of Eu and Sr on quartz was apparently lower than the adsorption on alumina in the presence of FA. For both metal ions the adsorption on quartz was higher at 0.10 M than at 0.01 M NaC104 — an observation that was reversed in the case of alumina. Increasing concentrations of FA lowered the pH at which Eu adsorption on alumina would be reduced.