Fate of nickel ion in (II-III) hydroxysulphate green rust synthesized by precipitation and coprecipitation

Abstract

SUMMARYIn order to investigate the efficiency of sulfate green rust (GR2) to remove Ni from solution, GR2 samples were synthesized under controlled laboratory conditions. Some GR2 samples were synthesized from Fe(II) and Fe(III) sulfate salts by precipitation. Other samples were prepared by coprecipitation, of Ni(II), Fe(II) and Fe(III) sulfate salts, i.e., in the presence of Ni. In another sample, Ni(II) sulfate salt was added to pre-formed GR2. After an initial X-ray diffraction (XRD) characterization all samples were exposed to ambient air in order to understand the role of Ni in the transformation of the GR2 samples. XRD was repeated after 45 days. The results showed that Nious GR2 prepared by coprecipitation is isomorphous to Ni-free GR2, i.e. Ni is incorporated into the crystalline structure. Fe(II) was not replaced by Ni(II) in the crystalline structure of GR2 formed prior to exposure to solution-phase Ni. This suggests Ni was adsorbed to the GR2 surface. Sulfate green rust is more efficient in removing Ni from the environment by coprecipitation.Index terms: nickel incorporation, nickel adsorption, X-ray diffraction, isomorphous substitution.(1) Part of the research developed at the University of Arizona, supported by CAPES, during the postdoctoral training period of the first author. RESUMO: ADSORÇÃO DE ÍON NÍQUEL EM (II-III) GREEN RUST HIDROXISULFATO SINTETIZADO POR PRECIPITAÇÃO E CO-PRECIPITAÇÃOCom objetivo de investigar a eficiência do "sulfate green rust" (GR2) na remoção de Ni da solução, amostras de GR2 foram sintetizadas em laboratório sob condições controladas. Algumas amostras de GR2 foram sintetizadas pela precipitação de sais de Fe(II) e de Fe(III); outras amostras, pela co-precipitação de sais de Ni(II), Fe(II) e de Fe(III); e em outras amostras, o sulfato de Ni(II) foi adicionado às amostras GR2 pré-formadas. Após caracterização inicial, por difração de raios X, todas as amostras ficaram expostas ao ar atmosférico durante 45 dias, a fim de se avaliar o papel do Ni na transformação delas. Após esse período, a difração de raios X das amostras foi repetida. Os resultados mostraram que Ni-GR2 preparado por co-precipitação é isomórfico do GR2, estando o íon Ni na estrutura cristalina deste. Fe(II) não foi substituído por Ni(II) na estrutura cristalina de GR2 formado a priori. Talvez o íon Ni tenha sido adsorvido na superfície do GR2. O sulfato "green rust" é eficiente para remover Ni do ambiente somente por co-precipitação.Termos de indexação: incorporação de níquel, adsorção de níquel, difração de raios X, substituição isomórfica.

Abiotic reduction of 2-line ferrihydrite: effects on adsorbed arsenate, molybdate, and nickel

“…This release of Ni may be attributed to the displacement of weakly bonded Ni species on the surface of FH by the Fe(II) (aq) ions. The readsorption behavior is attributed to the reattachment of the Ni released from solution to the newly formed phases (e.g., LP and/or GT and/or GR) 50,51 and unreacted FH. This Ni release and readsorption behavior was also observed at higher concentrations of 10 mM Fe(II) (aq) and a target pH of 8 (Table 1).…”

Green rust formation controls nutrient availability in a ferruginous water column

“…However, the scavenging effi ciency of Ni by GR is particularly high, and dissolved Ni 2+ is largely immobilized in response to GR formation during bacterial reduction of ferrihydrite (Parmar et al, 2001). Abiotic GR formation also effectively scavenges Ni 2+ from solution through both substitution into the mineral structure and adsorption (Chaves et al, 2007). Thus, reconstruction of Ni concentrations through time requires detailed understanding of the relative roles of ferrihydrite and GR in Ni uptake under ferruginous conditions.…”

Redox and pH gradients drive amino acid synthesis in iron oxyhydroxide mineral systems

“…One mineral type of interest that would have been abundant in the mildly acidic, iron-rich oceans of the early Earth (1-3) is the iron oxyhydroxides, which can precipitate in a variety of stable or metastable redox states (4,5). Iron oxides/oxyhydroxides are versatile reactive minerals that can drive redox reactions and concentrate phosphorus species, trace metals, organic molecules, and other anions (6)(7)(8)(9)(10)(11). On the early Earth, iron oxyhydroxides and/or green rust would likely have been present in the water column as well as seafloor sediments, playing a fundamental role in elemental cycling and redox chemistry (4,10).…”