Caroline Peacock | University of Leeds (original) (raw)

Papers by Caroline Peacock

Applied Clay Science, May 1, 2015

Radioactive caesium (chiefly 137 Cs) is a major environmental pollutant. The mobility of Cs in te... more Radioactive caesium (chiefly 137 Cs) is a major environmental pollutant. The mobility of Cs in temperate soils is primarily controlled by sorption onto clay minerals, particularly the frayed edges of illite interlayers. This paper investigates the adsorption of Cs to illite at the molecular scale, over both the short and long term. Transmission electron microscopy (TEM) images showed that after initial absorption into the frayed edges, Cs migrated into the illite interlayer becoming incorporated within the mineral structure. Caesium initially exchanged with hydrated Ca at the frayed edges, causing them to collapse. This process was irreversible as Cs held in the collapsed interlayers was not exchangeable with Ca. Over the long term Cs did not remain at the edge of the illite crystals, but diffused into the interlayers by exchange with K. Results from extended X-ray absorption fine structure spectroscopy (EXAFS) and density functional theory modelling confirmed that Cs was incorporated into the illite interlayer and revealed its bonding environment.

AGU Fall Meeting Abstracts, Dec 1, 2014

Crystal Growth & Design, Feb 1, 2017

Calcite formation via an amorphous calcium carbonate (ACC) precursor phase potentially offers a m... more Calcite formation via an amorphous calcium carbonate (ACC) precursor phase potentially offers a method for enhanced incorporation of incompatible trace metals, including Sr 2+. In batch crystallisation experiments where CaCl was rapidly mixed with Na CO 3 solutions the Sr 2+ : Me 2+ ratio was varied from 0.001 to 0.1; and, the pathway of calcite precipitation was directed by either the presence or absence of high Mg 2+ concentrations (i.e. using a Mg 2+ : total Me 2+ ratio of 0.1). In the Mg-free experiments crystallisation proceeded via ACC → vaterite → calcite and average K d Sr values were between 0.44-0.74. At low Sr 2+ concentrations (Sr 2+ : Me 2+ ratio ≤ 0.01) EXAFS analysis revealed that the Sr 2+ was incorporated into calcite in the 6 fold coordinate Ca 2+ site. However, at higher Sr 2+ concentrations (Sr 2+ : Me 2+ ratio = 0.1), Sr 2+ was incorporated into calcite in a 9-fold site with a local coordination similar to Ca 2+ in aragonite, but calcite-like at longer distances (i.e. > 3.5 Å). In the high-Mg experiments the reaction proceeded via an ACC → calcite pathway with higher K d Sr of 0.90-0.97 due to the presence of Mg 2+ stabilising the ACC phase and promoting rapid calcite nucleation in conjunction with higher Sr 2+ incorporation. Increased Sr 2+ concentrations also coincided with higher Mg 2+ uptake in these experiments. Sr 2+ was incorporated into calcite in a 9-fold coordinate site in all the high-Mg experiments regardless of initial Sr 2+ concentrations, likely as a result of very rapid crystallisation kinetics and the presence of smaller Mg 2+ ions compensating for the addition of larger Sr 2+ ions in the calcite lattice. These experiments show that the enhanced uptake of Sr 2+ ions can be achieved by calcite precipitation via ACC, and may offer a rapid, low temperature, low-cost, method for removal of several incompatible Me 2+ ions (e.g. Pb 2+ , Ba 2+ , Sr 2+) during effluent treatment.

EGU General Assembly Conference Abstracts, Apr 1, 2016

Mineralogical Magazine, Nov 1, 2015

The incorporation of pertechnetate (TcO 4-) into feldspathoids produced by alkaline alteration of... more The incorporation of pertechnetate (TcO 4-) into feldspathoids produced by alkaline alteration of aluminosilicate clays may offer a potential treatment route for 99 Tc-containing groundwater and liquors. Kaolinite was aged in NaOH to determine the effect of base concentration, temperature, and solution composition on mineral transformation and pertechnetate uptake. In all reactions, increased temperature and NaOH concentration increased the rate of kaolinite transformation to feldspathoid phases. In reactions containing only NaOH, sodalite was the dominant alteration product; however, small amounts (6-15%) of cancrinite also formed. In experiments containing NaOH/Cl and NaOH/NO 3 mixtures, sodalite and nitrate cancrinite were crystallized (at 70°C), with no reaction intermediates.The addition of SO 4 2crystallized sulfatic sodalite at 40 and 50°C, but at higher temperatures (60 and 70°C) sulfatic sodalite transforms to vishnevite (sulfatic cancrinite). In experiments where a pertechnetate tracer was added (at ∼1.5 μmol l-1), only 3-5% of the 99 Tc was incorporated into the feldspathoid phases. This suggests that the larger pertechnetate anion was unable to compete as favourably for the internal vacancies with the smaller OH-, NO 3-, SO 4 2or Clanions in solution, making this method likely to be unsuitable for groundwater treatment.

Nature Communications, May 17, 2022

Minerals are widely proposed to protect organic carbon from degradation and thus promote the pers... more Minerals are widely proposed to protect organic carbon from degradation and thus promote the persistence of organic carbon in soils and sediments, yet a direct link between mineral adsorption and retardation of microbial remineralisation is often presumed and a mechanistic understanding of the protective preservation hypothesis is lacking. We find that methylamines, the major substrates for cryptic methane production in marine surface sediment, are strongly adsorbed by marine sediment clays, and that this adsorption significantly reduces their concentrations in the dissolved pool (up to 40.2 ± 0.2%). Moreover, the presence of clay minerals slows methane production and reduces final methane produced (up to 24.9 ± 0.3%) by a typical methylotrophic methanogen-Methanococcoides methylutens TMA-10. Near edge X-ray absorption fine structure spectroscopy shows that reversible adsorption and occlusive protection of methylamines in clay interlayers are responsible for the slowdown and reduction in methane production. Here we show that mineral-OC interactions strongly control methylotrophic methanogenesis and potentially cryptic methane cycling in marine surface sediments.

EarthArXiv (California Digital Library), Aug 16, 2023

Applied and Environmental Microbiology, Nov 10, 2020

This is a repository copy of Outer membrane c-type cytochromes OmcA and MtrC play distinct roles ... more This is a repository copy of Outer membrane c-type cytochromes OmcA and MtrC play distinct roles in enhancing the attachment of Shewanella oneidensis MR-1 cells to goethite.

$Research paper thumbnail of Site-specific isotope fractionation during Zn adsorption onto birnessite: Insights from X-ray absorption spectroscopy, density functional theory and surface complexation modeling$

Geochimica et Cosmochimica Acta

Nature Geoscience

Photosynthesis produces molecular oxygen, but it is the burial of organic carbon in sediments tha... more Photosynthesis produces molecular oxygen, but it is the burial of organic carbon in sediments that has allowed this O2 to accumulate in Earth’s atmosphere. Yet many direct controls on the preservation and burial of organic carbon have not been explored in detail. For modern Earth, it is known that reactive iron phases are important for organic carbon preservation, suggesting that the availability of particulate iron could be an important factor for the oxygenation of the oceans and atmosphere over Earth history. Here we develop a theoretical model to investigate the effect of mineral–organic preservation on the oxygenation of the Earth, supported by a proxy compilation for terrigenous inputs and the burial of reactive iron phases, and find that changes to the rate of iron input to the global ocean constitute an independent control on atmosphere–ocean O2 and marine sulfate levels. We therefore suggest that increasing continental exposure and denudation may have helped fuel the rise i...

Supplementary Data for article 'Carboxyl-richness controls organic carbon preservation during... more Supplementary Data for article 'Carboxyl-richness controls organic carbon preservation during coprecipitation with iron (oxyhydr)oxides in the natural environment' by Curti et al.

Journal of Hazardous Materials, 2021

This is a repository copy of Characteristics and mechanisms of Pb(II) sorption onto Fe-rich waste... more This is a repository copy of Characteristics and mechanisms of Pb(II) sorption onto Fe-rich waste water treatment residue (WTR): A potential sustainable Pb immobilisation technology for soils.

Journal of Hazardous Materials, 2020

Geochimica et Cosmochimica Acta, 2019

Low sulfate, euxinic water-column conditions were a common feature of many Precambrian and Phaner... more Low sulfate, euxinic water-column conditions were a common feature of many Precambrian and Phanerozoic periods of ocean anoxia. The cycling of phosphorus in anoxic marine environments exerts a fundamental control on primary productivity, organic carbon production and burial, and hence ultimately oxygen production, but the dynamics of the phosphorus cycle in low sulfate, euxinic settings are largely unknown. Here, we provide a detailed geochemical investigation of phosphorus cycling in the low sulfate, euxinic Lake Cadagno, Switzerland, which is considered a prime analogue for ancient euxinic oceans. We find evidence for extensive recycling of phosphorus from the sediments back to the water column, stimulated by the microbial release of phosphorus from organic matter and Fe (oxyhydr)oxide minerals. Consistent with previous studies of modern and ancient anoxic settings, this regenerated flux maintains high concentrations of phosphorus in the water column, thus promoting a positive productivity feedback. However, the low-sulfate condition of the overlying water column, combined with the rapid removal of sulfide (as pyrite) from porewaters, promotes formation of Fe(II) phosphate minerals (e.g., vivianite) close to the sediment-water interface. This, in turn, modulates the extent of phosphorus recycling back to the water column, and contrasts with modern fully marine euxinic settings, where the higher concentrations of dissolved sulfate promote sulfide formation to greater depths, thus limiting Fe(II) phosphate formation close to the sediment-water interface. The prevalence of lowsulfate conditions during past euxinic episodes suggests that the operation of this near-surface sedimentary trap for recycled phosphorus would have limited the positive P-driven productivity feedback, promoting only a moderate degree of P recycling. Furthermore, the precise magnitude of this recycled P flux would, on a global scale, have been dependent on changes in the size of Earth's marine sulfate reservoir through time. Thus our findings have major implications for rates of P-driven productivity and organic carbon burial in ancient euxinic settings, which have not previously been factored into reconstructions of Earth's oxygenation history.

Chemical Geology, 2018

A universal adsorption behaviour for Cu uptake by iron (hydr)oxide organo-mineral composites.

Nature Nanotechnology

Artificial ocean fertilization (AOF) aims to safely stimulate phytoplankton growth in the ocean a... more Artificial ocean fertilization (AOF) aims to safely stimulate phytoplankton growth in the ocean and enhance carbon sequestration. AOF carbon sequestration efficiency appears lower than natural ocean fertilization processes due mainly to the low bioavailability of added nutrients, along with low export rates of AOF-produced biomass to the deep ocean. Here we explore the potential application of engineered nanoparticles (ENPs) to overcome these issues. Data from 123 studies show that some ENPs may enhance phytoplankton growth at concentrations below those likely to be toxic in marine ecosystems. ENPs may also increase bloom lifetime, boost phytoplankton aggregation and carbon export, and address secondary limiting factors in AOF. Life-cycle assessment and cost analyses suggest that net CO2 capture is possible for iron, SiO2 and Al2O3 ENPs with costs of 2–5 times that of conventional AOF, whereas boosting AOF efficiency by ENPs should substantially enhance net CO2 capture and reduce th...