Browsing by Author "Clark, MW"
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- ItemEffects of pH, competing ions and aging on arsenic(V) sorption and isotopic exchange in contaminated soils(Elsevier, 2019-06) Rahman, MS; Clark, MW; Yee, LH; Comarmond, MJ; Payne, TE; Burton, EDCattle tick control in Australia using arsenicals from early 1900s to 1955 has led to the existence of some 1600 contaminated sites in northern New South Wales alone. Sorption processes play key roles in controlling arsenic (As) accessibility and subsequent mobility in these dip soils. As(V) sorption and accessibility in three As-contaminated soils and two uncontaminated soil types (ferralitic and sandy soils) are investigated utilizing batch sorption experiments and isotopic exchange techniques. The aged contaminated soils displayed little or no ability to sorb additional As(V), and increasing the soil pH caused a substantial reduction in As(V)-sorption and resulting in As(V)-release. Isotope exchange experiments further supported that any further exposure of the aged-contaminated-soils to additional As(V) increased As-mobilization potential. Amendments of phosphate greatly decreased As(V) sorption in aged-contaminated-soils where As-sorption sites were more highly saturated, whereas phosphate had little effect on As(V) sorption in pristine soils. Similarly, sulfate reduced As(V) sorption, but these effects were less marked than those for phosphate, hence, the application of both PO43− and SO42− in As(V)-contaminated-soils may lead to potential As(V)- mobilization. Conversely, Ca2+ increases As(V)-sorption, which is consistent with expected changes in the surface charge characteristics from Ca2+ sorption, and/or Ca-AsO4 precipitations, consequently Ca2+ amendments may improve As-retention, thereby decreasing As accessibility from cattle dip soils. Therefore, the detailed knowledge presented here provides new insights that may be useful for the assessment and management of the As-contaminated soils. © 2019 Elsevier Ltd.
- ItemElectroacoustic isoelectric point determinations of bauxite refinery residues: different neutralisation techniques and minor mineral effects(American Chemical Society, 2012-08-14) Freire, TSS; Clark, MW; Comarmond, MJ; Payne, TE; Reichelt-Brushett, AJ; Thorogood, GJ5Bauxite refinery residue (BRR) is a highly caustic, iron hydroxide-rich byproduct from alumina production. Some chemical treatments of BRR reduce soluble alkalinity and lower residue pH (to values <10) and generate a modified BRR (MBRR). MBRR has excellent acid neutralizing (ANC) and trace-metal adsorption capacities, making it particularly useful in environmental remediation. However, soluble ANC makes standard acid-base isoelectric point (IEP) determination difficult. Consequently, the IEP of a BRR and five MBRR derivatives (sulfuric acid-, carbon dioxide-, seawater-, a hybrid neutralization, i.e, partial CO2 neutralization followed by seawater, and an activated-seawater-neutralized MBRR) were determined using electroacoustic techniques. Residues showed three significantly different groups of IEPs (p < 0.05) based around the neutralization used. Where the primary mineral assemblage is effectively unchanged, the IEPs were not significantly different from BRR (pH 6.6-6.9), However, neutralizations generating neoformational minerals (alkalinity precipitation) significantly increased the IEP to pH 8.1, whereas activation (a removal of some primary mineralogy) significantly lowered the IEP to pH 6.2. Moreover, surface charging curves show that surfaces remain in the +/-30 mV surface charge instability range, which provides an explanation as to why MBRRs remove trace metals and oxyanions over a broad pH range, often simultaneously. Importantly, this work shows that minor mineral components in complex mineral systems may have a disproportionate effect on the observable bulk IEP. Furthermore, this work shows the appropriateness of electroacoustic techniques in investigating samples with significant soluble mineral components (e.g., ANC). © 2012, American Chemical Society.
- ItemIsotope exchange studies of contaminant availability in soils and sediments(ICI7 Organizing Committee, 2011-09-04) Payne, TE; Comarmond, MJ; Harrison, JJ; Clark, MW; Collins, RN; Angove, MJ; Palmer, GNot available.
- ItemModified bauxite refinery residues for immobilizing U(VI)(Australian Nuclear Science and Technology Organisation, 2012-10-16) Clark, MW; Payne, TE; Harrison, JJ; Cormarmond, MJ; Dore, MJ; Collins, RNBauxite refinery residues (BRR) are a waste from the production of alumina using the Bayer process, which has high pH and soluble alkalinity. However, a modified BRR (MBRR) can be made using Mg and Ca to precipitate alkalinity as acid neutralizing capacity (ANC), which lowers pH from ≈13 to ≈8.5. The combined effects of a fine-grained mineral mix providing high surface area across a range of minerals for metal removal, and an ANC (3-5 mol/kg), gives MBRR potential for many environmental remediation and wastewater-treatment applications. We conducted several laboratory experiments that investigate and assess the application potential of MBRR for the environmental remediation U(VI). Isotopic exchange data show that U(IV) is, in part, irreversibly bound and that irreversibility increases with increased surface loading; it is also age- and temperature-sensitive. Synchrotron X-ray absorption techniques (EXAFS and XANES) suggest that a limited number of minerals bind U(VI), and the mechanisms and minerals involved are U(VI) concentration dependent. Data indicate that U(VI) binding is initiated by adsorption, largely to the hematite, but precipitation dominates as U(VI) concentration increases. This in turn suggests that irreversibility in the U(VI) binding is driven by precipitate re-crystallization rather than intra-particulate diffusion into adsorbing minerals. Moreover, the results of this work suggest that MBRR may well be useful in the environmental remediation of U(VI) contaminated soils and waters.
- ItemThe pH-dependence and reversibility of uranium and thorium binding on a modified bauxite refinery residue using isotopic exchange techniques(Academic Press Inc Elsevier Science, 2011-04-15) Clark, MW; Harrison, JJ; Payne, TEThe pH-dependence and reversibility of uranium and thorium binding onto a modified bauxite refinery residue (MBRR) were studied in laboratory uptake/leaching experiments. Natural (238)U and (232)Th isotopes were contacted with MBRR in an 8 day loading period (equilibrium pH approximate to 8.5) then leached in pH-dependent experiments, where the pH was decreased from 8 to 3 over several hours following addition of exchange isotopes (232)U and (229)Th. Relative concentrations of the thorium isotope pair ((232)Th and (229)Th) indicate that Th is very strongly bound to MBRR, and although at pH 3, some de-sorption is observed (232)Th (approximate to 3%) and (229)Th (approximate to 2.5%), released thorium is partially re-adsorbed during an overnight equilibration. During the initial equilibration, approximately 50% of the (238)U was adsorbed, and a U adsorption maximum occurs between pH 5 and pH 6, where <0.5% of the U remains in solution. However, at a pH between 5 and 3, some 60% of the bound U releases, hence the pH range of maximum U retention on the MBRR is relatively narrow. When equilibrated overnight, the MBRR releases additional U, suggesting a kinetically controlled de-sorption linked to mineral dissolution. Plots of U isotope exchange between (232)U and (238)U are linear, and suggest that U adsorption is mostly reversible. Data for adsorption in mixed systems of U and Th suggest that Th and U compete for similar binding sites. (C) 2011 Elsevier Inc.
- ItemRadium and strontium binding by a modified bauxite refinery residue – isotope exchange studies of pH-dependence, reversibility and ageing(Geological Society of London, 2019-07-24) Clark, MW; Harrison, JJ; Payne, TE; Comarmond, MJ; Thiruvoth, S; Mokhber-Shahin, LThe pH-dependence and reversibility of radium (Ra) and strontium (Sr) binding to a modified bauxite refinery residue (MBRR), and the effects of sample ageing, were studied in laboratory uptake/leaching experiments. Natural 226Ra and stable strontium (Srnat) were placed in contact with the MBRR for an 8-day loading period (equilibrium pH c. 8.5). Following the addition of exchange isotopes 228Ra and 85Sr, the samples were then leached in pH-dependent experiments, where the pH was decreased incrementally from 9 to 3 over 7 h. A further suite of samples was aged at 4°, 23° and 65°C for 6 months after the initial addition of 226Ra and Srnat and then studied in a similar set of pH-dependent exchange experiments. The relative concentrations of the Ra and Sr isotope pairs (226Ra/228Ra and Srnat/85Sr) provided insights into the adsorption strength, incorporation, reversibility and ageing effects. The Srnat data showed that the amount of bound Sr released from aged MBRR samples as the pH decreases is substantially lower than the unaged sample, showing that Sr has been incorporated in less accessible phases during the ageing period. It appears that the uptake of 228Ra by the higher-temperature aged samples is somewhat stronger than the unaged samples; however, Ra isotope exchange plots for aged and unaged samples are similar. Consequently, the stronger binding of 228Ra by the higher-temperature aged samples is probably driven by translocation to kinetically less-favourable surface sites rather than a significant incorporation of Ra within the mineral solids during ageing. © 2022 Geological Society of London
- ItemReversibility of uranium and thorium binding on a modified bauxite refinery residue: the effects of aging temperature(Elsevier, 2015-02) Clark, MW; Payne, TE; Harrison, JJ; Comarmond, MJ; Collins, RN; Reichelt-Brushett, AJThe effects of aging on the pH-dependence and reversibility of uranium and thorium binding by a modified bauxite refinery residue (MBRR) were studied in laboratory uptake/leaching experiments. Natural uranium and thorium isotopes (predominantly 238UVI and 232ThIV) of 0.4, and 0.2 mM were loaded for an 8-day period at the natural equilibrium pH of the MBRR (approximately 8.5) and were allowed to age for 6 months in humid sealed containers at 4, 23, and 65 °C. After aging, anthropogenic 232UVI and 229ThIV were added as exchange isotopes and the pH decreased stepwise from 8 to 3 over several hours in pH dependent experiments. The relative concentrations of the isotope pairs (i.e. 238UVI and 232UVI; 232ThIV and 229ThIV) indicated that irreversibility of UVI and ThIV binding by the MBRR increased with aging and was dependent on the aging temperature and surface actinide loading. Linear combination fitting of the EXAFS data for the uranium loaded materials indicated that at low uranium concentrations sorption to minerals (particularly hematite) was a prime uranium removal mechanism, but at higher concentrations precipitation dominated. The data suggest that increased irreversibility and incorporation of UVI during aging is associated with re-crystallisation of precipitates. © 2014 Elsevier Ltd.
- ItemSolid phases responsible for Mn II, Cr III, Co II, Ni, Cu II and Zn immobilization by a modified bauxite refinery residue (red mud) at pH 7.5(Elsevier, 2014-01-15) Collins, RN; Clark, MW; Payne, TEAlthough modified bauxite refinery residues (MBRR) immobilize trace metals, the retention mechanisms in this complex multiphase material have not been examined in detail. In this study, X-ray absorption spectroscopy was used to investigate the host minerals, and retention mechanisms, responsible for binding MnII, CrIII, CoII, Ni, Cu and Zn in MBRR. High metal loadings (∼10 mM at pH 3) in aqueous phases simulated highly contaminated mine drainage environments, whereas a final pH of 7.5 represents the typical MBRR pH buffering providing surface loadings of 1.7–2.6 wt%. Under these conditions, CrIII precipitated as a solid phase similar to γ-CrOOH and/or amorphous Cr(OH)3, regardless of host mineral, whereas MnII immobilization was associated with (partial) oxidation in all cases. Cobalt and Ni precipitated primarily as hydrotalcite-like solids when in contact with the MBRR, and sodalite, gibbsite and hydrotalcite tended to dominate this process. Cu uptake by MBRR resulted from the precipitation of Cu(OH)2 although sorption processes may have made an additional contribution, whereas Zn precipitated as a solid phase similar to that of hydrozincite. The nature of the trace metal precipitate formed was often influenced by the host mineral constituent of MBRR, indicating that specific minerals in the MBRR can be primarily responsible for its metal immobilization properties, with gibbsite, hematite and hydrotalcite featuring prominently. © 2013 Elsevier B.V.