Stability of Iron in Clays Under Different Leaching Conditions

Abstract

The iron chemistry of aluminosilicates can markedly affect their adsorption properties due to possible changes in surface charge upon exposure to a variety of processes in the environment. One of these processes is chemical leaching, but to date little has been reported on the susceptibility of structural Fe to chemical leaching. The purpose of the current study was to determine the effects of solution pH on the stability of structural Fe in kaolinites, illite, and bentonite and the potential for formation of ancillary (oxyhydr)oxides. Structurally bound Fe does not participate in sorption properties but Fe that is released and phase transformed during leaching could take part in adsorption processes and form complexes and/or covalent bonds via Fe ions. Five different Fe-bearing clay minerals were treated in 0.5 M and 2 M HCl, distilled H 2 O, 0.1 M KCl, and 0.5 M KHCO 3 for 24 h. The amount of Fe leached varied from 10 mg g À1 (for 0.1 M KCl) to 10 4 mg g À1 (for 2 M HCl) depending on the leaching agents. Acidic and water treatments indicated a relative independence of leached Fe on the initial Fe content in the clay and, conversely, a heavy dependence on the crystallinity of initial Fe phases. Well crystallized Fe(III) was stable during the leaching process, while poorly crystallized and amorphous Fe(III) phases were less stable, forming new ion-exchangeable Fe 3+ particles. Under alkaline conditions, no relation between Fe crystallinity and mobility was found. The structural and surface changes resulting from leaching processes were identified by equilibrium adsorption isotherms. In kaolinite, the specific surface area (S BET ) and porosity changed independently of Fe leaching due to the stability and crystallinity of Fe. In bentonite, the number of micropores was reduced by their partial saturation with Fe 3+ particles caused by poorly crystallized and more reactive Fe forms during the leaching process. Potential phase transformations of Fe were characterized by the voltammetry of microparticles; well crystallized Fe(III) oxides remained stable under leaching conditions, while poorly crystallized and amorphous Fe(III) phases were partially dissolved and transformed to reactive Fe 3+ forms.

Facile Metal Release from Pore-Lining Phases Enables Unique Carbonate Zonation in a Basalt Carbon Mineralization Demonstration

“…However, we believe it would be unlikely that leaching from these sites could occur under reservoir conditions. While acid leaching of Fe in smectites is well-documented, it generally requires much lower pH (<2) conditions than that present in the reservoir pore fluid (pH 4.5 or greater). − A second possibility could be the presence of Fe and Mn as interlayer cations since smectites are known to accommodate a variety of labile cations, such as Pb 2+ , Cs + , Hg 2+ , NH 4+ , Ca 2+ , Mg 2+ , K + , and Na + . − While such a scenario cannot be entirely neglected, the stability of Fe 2+ or Mn 2+ as hydrated interlayer cations would likely be questionable given their propensity to form hydroxides or oxyhydroxides. Therefore, we believe the source of Fe or Mn could most likely be the presence of Fe and Mn oxides or hydroxides sorbed or intercalated with smectites.…”

Poorly Crystalline Fe (III) Oxide excess can to alter the electrochemical paths of soils in the Brazilian Tropical Savannah.

“…The reducing flooded soils is characterized by an increase in pH and decrease both pH and SMB. The presence of iron oxides in the soil have the capability of charge change at dependent clays, such a kaolinite (Dousova et al, 2014), clay of this study. According Sumner (1963), iron oxides behave amphoterically in soil and contribute significantly to the buffer capacity of tropical soil.…”

Effect of carboxymethyl cellulose on dissolution kinetics of carboxymethyl cellulose-sodium carbonate two-component tablet

“…In this work, both surface reaction model and diffusion layer model [13] were used for the fitting of quantified dissolution data. For surface reaction model, the dissolution process was determined by the chemical reaction rate on the surface of tablet which is the decomposition speed of sodium carbonate into sodium and carbonate ions in this case.…”