Chromate adsorption on amorphous iron oxyhydroxide in the presence of major groundwater ions

Abstract

Chromate adsorption on amorphous iron oxyhydroxide was investigated in dilute iron suspensions as a single solute and in solutions of increasing complexity containing C02(g), SOZ-(aq), H4Si04(aq), and cations [K+, Mg2+, Ca"(aq)]. In paired-solute systems (e.g., Cr0:-H2C03*), anionic cosolutes markedly reduce Cr042-adsorption through a combination of competitive and electrostatic effects, but cations exert no appreciable influence. Additionally, H4Si04 exhibits a strong time-dependent effect: Cr0:-adsorption is greatly decreased with increasing H4Si04 contact time. In multiple-ion mixtures, each anion added to the mixture decreases Cr0:-adsorption further. Adsorption constants for the individual reactive solutes were used in the triple-layer model. The model calculations are in good agreement with the Cr042-adsorption data for paired-and multiple-solute systems. However, the model calculations underestimate Cr042-adsorption when surface site saturation is appr6ached. Questions remain regarding the surface interactions of both C02(aq) and H4Si04. The results have major implications for the adsorption behavior of Cr0:-and other oxyanions in subsurface waters.

Adsorption of Chromium (VI) on Calcium Phosphate: Mechanisms and Stability Constants of Surface Complexes

“…In general, anion adsorption is strongly dependent on the pH of the medium, exhibiting the greatest removal in acidic to neutral solution. As has been demonstrated in previous studies, optimal Cr (VI) adsorption occurs at a pH lower than 4 for various sorbents, such as some metallic (oxy)hydroxides [32][33][34] and natural bio-sorbents, for example, larch bark [35], cooked tea dust [36], papaya seeds [37], raw Bagasse [38], and activated carbon [39]. In the case where iron and aluminum oxides are used as adsorbents, an adsorption efficiency of higher than 80% was reached at a pH of 4 to 6.…”

Radionuclide-Chelating Agent Complexes in Low-Level Radioactive Decontamination Waste; Stability, Adsorption and Transport Potential

“…The iron oxyhydroxide gel was first synthesized by hydrolysis of a 0.24 mol/L solution of ferric chloride solution (Zachara et al 1987). This was accomplished by adjusting the solution pH to approximately 7.5 with C0 2 -free sodium hydroxide.…”

Assessment of co-contaminant effects on uranium and thorium speciation in freshwater using geochemical modelling

“…Parameters for carbonate binding to HFO were obtained by fitting to the data of Zachara et al (1987), which comprised two pH adsorption edges with HFO concentrations of 0.78 and 7.8 g dm -3…”

“…Figure S1. Model fits to the carbonate-HFO binding data of Zachara et al (1987). Ionic strength = 0.1 mol dm -3 , total CO3 = 4.6 × 10 -6 mol dm -3 .…”