Fossil rootlet biopores as conduits for contaminant transport through clay horizons: a case study of DNAPL behaviour in Severn alluvium, UK

This paper presents a case study of several DNAPL contaminated sites around the Severn Estuary (UK) where a combination of detailed observations, core dissections and physicochemical characterisation of alluvial clay–silt horizons have revealed the presence of fossil rootlet biopores which act and have the potential to act as conduits for contaminant migration through up to 13 m of clay–silt. The biopores are shown to penetrate the low-permeability (K ~ 10−10 m/s) clay–silt matrix throughout its entire depth (up to 13 m) and provide a preferential transport pathway for DNAPLs from near surface to the underlying aquifer, with particularly high concentrations measured in the biopores themselves. Capillary rise experiments with coal tar distillate demonstrate that DNAPLs are drawn into biopores, with values of surface interfacial tension for the system calculated as 8 × 10−2 J/m2. Wicking by residual plant fibres was demonstrated qualitatively and is thought to be an important additional transport mechanism. The DNAPL contamination below and throughout the Severn alluvial clay–silt horizons demonstrates that the assumption that these horizons act as an effective seal protecting underlying aquifers from severe pollution from the legacy sites around the Severn is flawed and highlights the failure of current protocols for sampling of clay horizons for hydraulic conductivity assessments, since current methods can destroy delicate in situ biopore structures. The study demonstrates that the interplay between ecological and the geological depositional environment can, at a regional scale, result in a network of biopores that can potentially act as conduits for contaminant transport

Sorption and fractionation of rare earth element ions onto nanoscale zerovalent iron particles

The removal behaviour of rare earth element (REE), (Sc, Y, La-Lu), ions onto nanoscale zerovalent iron (nZVI) particles has been investigated. Batch sorption isotherms were conducted using REE-bearing acid mine drainage (AMD) and a range of different synthetic REE solutions, which were exposed to nZVI at 0.1-4.0 g/L. Maximum adsorption capacity of Yb and La was 410 and 61 mg/g respectively (1000 mg/L LaCl3 and YbCl3 starting concentration, initial pH=4.5, T=294 K), the highest currently reported in the literature. Aqueous REE removal to ultratrace concentrations (99.9% removal) was also recorded after 30 min (the first sampling interval) exposure of ≥0.5 g/L nZVI to 10 mg/L aqueous REE solutions (nitrate counterion). Similar rapidity and near-total removal ability was recorded for the exposure of nZVI to the AMD, however, a greater nZVI concentration was required, with the removal of all REEs (with the exception of La, Ce, Nd and Gd) to <1 µg/L when exposed to nZVI at 4.0g/L for 30 mins. In all systems nZVI was selective for the removal of HREE ions in preference to LREE ions, with the mechanism determined using HRTEM-EDS and XPS analysis as via surface mediated precipitation. Overall the results demonstrate nZVI as exhibiting great promise as an effective and versatile agent for simultaneous REE ion recovery and fractionation

Selective formation of copper nanoparticles from acid mine drainage using nanoscale zerovalent iron particles

Nanoscale zerovalent iron (nZVI) has been investigated for the selective formation of Cu nanoparticles from acid mine drainage (AMD) taken from a legacy mine site in the UK. Batch experiments were conducted containing unbuffered (pH 2.67 at t=0) and pH buffered (pH 99.9% removal of all metals within 1 h when nZVI ≥1.0 g/L) from unbuffered AMD despite the coexistent of numerous other metals in the AMD, namely: Na, Ca, Mg, K, Mn and Zn. An acidic pH buffer enabled similarly high Cu removal but maximum removal of only <1.5% and <0.5% Cd and Al respectively. HRTEM-EDS confirmed the formation of discrete spherical nanoparticles comprised of up to 68% wt. Cu, with a relatively narrow size distribution (typically 20-100 nm diameter). XPS confirmed such nanoparticles as containing Cu0 , with the Cu removal mechanism therefore likely via cementation with Fe0 . Overall the results demonstrate nZVI as effective for the one-pot and selective formation of Cu0 -bearing nanoparticles from acidic wastewater, with the technique therefore potentially highly useful for the selective upcycling of dissolved Cu in wastewater into high value nanomaterials

Towards 'Precision Mining' of wastewater: Selective recovery of Cu from acid mine drainage onto diatomite supported nanoscale zerovalent iron particles

This paper introduces the concept of ‘Precision Mining’ of metals which can be defined as a process for the selective in situ uptake of a metal from a material or media, with subsequent retrieval and recovery of the target metal. In order to demonstrate this concept nanoscale zerovalent iron (nZVI) was loaded onto diatomaceous earth (DE) and tested for the selective uptake of Cu from acid mine drainage (AMD) and subsequent release. Batch experiments were conducted using the AMD and nZVI-DE at 4.0–16.0 g/L. Results demonstrate nZVI-DE as highly selective for Cu removal with >99% uptake recorded after 0.25 h when using nZVI-DE concentrations ≥12.0 g/L, despite appreciable concentrations of numerous other metals in the AMD, namely: Co, Ni, Mn and Zn. Cu uptake was maintained in excess of 4 and 24 h when using nZVI-DE concentrations of 12.0 and 16.0 g/L respectively. Near-total Cu release from the nZVI-DE was then recorded and attributed to the depletion of the nZVI component and the subsequent Eh, DO and pH recovery. This novel Cu uptake and release mechanism, once appropriately engineered, holds great promise as a novel ‘Precision Mining’ process for the rapid and selective Cu recovery from acidic wastewater, process effluents and leach liquors

Iron-mineral accretion from acid mine drainage and its application in passive treatment

This study demonstrates substantial removal of iron (Fe) from acid mine drainage (pH ≈3) in a passive vertical flow reactor (VFR) with an equivalent footprint of 154 m2 per L/s mine water and residence times of >23 h. Average Fe removal rate was 67% with a high of 85% over the 10-month trial. The fraction of Fe passing a 0.22 µm filter (referred to here as Fe-filt) was seen to be removed in the VFR even when Fe(II) was absent, indicating that the contribution of microbial Fe(II) oxidation and precipitation was not the dominant removal mechanism in the VFR. Removal rates of Fe-filt in the VFR were up to 70% in residence times as low as 8 h compared with laboratory experiments where much smaller changes in Fe-filt were observed over 60 h. Centrifugation indicated that 80–90% of the influent Fe had particle sizes <35 nm. Together with analyses and geochemical modelling, this suggests that the Fe-filt fraction exists as either truly aqueous (but oversaturated) Fe(III) or nanoparticulate Fe(III) and that this metastability persists. When the water was contacted with VFR sludge, the Fe-filt fraction was destabilized, leading to an appreciably higher removal of this fraction. Heterogeneous precipitation and/or aggregation of nanoparticulate Fe(III) precipitates are considered predominant removal mechanisms. Microbial analyses of the mine water revealed the abundance of extracellular polymeric substance-generating Fe-oxidizing bacterium ‘Ferrovum myxofaciens’, which may aid the removal of iron and explain the unusual appearance and physical properties of the sludge

Trend and Cycles in Coal and Oil Prices in the Long Run: A Schumpeterian Approach

We contribute to the task of identifying trends and cycles in energy prices by examining very long series of prices for coal and oil, going back to 1650 in the case of coal and 1859 in the case of oil. We find annual rates of increase in real price of greater than two percent are found for coal in one cycle, 1842 to 1897, and for oil in two cycles, 1897 to 1953 and 1953 to 2009. However, there is no noticeable change in coal prices for the earliest cycles, from 1675 to 1731 and 1731 to 1787, as well as a notable decline in the latest cycle, from 1953 to 2009. Also, oil prices decline from 1859 to 1897. Clearly, there is no unitary trend across coal and oil that would suggest a general failure of supply due to universal depletion of fossil fuels. Instead, the suggestion is that developments in technology are of critical importance. In particular, the shift in motive power from coal to oil is associated with a rise in the price of oil relative to coal and, in the most recent cycle, a trend decrease in the real coal price

Towards greener lixiviants in value recovery from mine wastes: Efficacy of organic acids for the dissolution of copper and arsenic from legacy mine tailings

This is the author accepted manuscript. The final version is freely available from MDPI via the DOI in this recordIn many cases, it may be possible to recover value (e.g. metals, land) from legacy mine wastes and tailings when applying leaching-based remediation such as dump/heap leaching or in-vessel soil washing. However, if the lixiviant used has the potential to cause environmental damage upon leakage, then this approach will have limited practicability due to actual or perceived risk. This study focused on comparing the efficacy of organic acids, namely methanesulfonic (CH3SO3H) and citric (C6H8O7) acid, with mineral acids, namely sulfuric (H2SO4) and hydrochloric (HCl) acid, for the dissolution of Cu and As from mine tailings. The advantage of the former acid type is the fact that its conjungate base is readily biodegradable which should thereby limit the environmental impact of accidental spill/leakage (particularly in non-carbonate terrain) and might also be directly useful in capture/recovery systems coupled with percolation leaching (e.g., as an electron donor in sulphate-reducing bioreactors). The operational factors acid concentration, leaching time, mixing intensity and solid–liquid ratio, were tested in order to determine the optimum conditions for metal dissolution. HCl, H2SO4, and CH3SO3H typically exhibited a relatively similar leaching ability for As despite their different pKa values, with dissolutions of 58%, 56%, 55%, and 44% recorded for H2SO4, HCl, CH3SO3H, and C6H8O7, respectively, after 48 h when using 1 M concentrations and a 10:1 L:S ratio. For the same conditions, H2SO4 was generally the most effective acid type for Cu removal with 38% compared to 32%, 29% and 22% for HCl, CH3SO3H and C6H8O7. As such, CH3SO3H and C6H8O7 demonstrated similar performances to strong mineral acids and, as such, hold great promise as environmentally compatible alternatives to conventional mineral acids for metal recovery from ores and waste.The work was financially supported by the Natural Environment Research Council (grant number: NE/L013908/1)

Assessing hydrothermal liquefaction for the production of bio-oil and enhanced metal recovery from microalgae cultivated on acid mine drainage

The hydrothermal liquefaction (HTL) of algal biomass is a promising route to viable second generation biofuels. In this investigation HTL was assessed for the valorisation of algae used in the remediation of acid mine drainage (AMD). Initially the HTL process was evaluated using Arthrospira platensis (Spirulina) with additional metal sulphates to simulate metal remediation. Optimised conditions were then used to process a natural algal community (predominantly Chlamydomonas sp.) cultivated under two scenarios: high uptake and low uptake of metals from AMD. High metal concentrations appear to catalyse the conversion to bio-oil, and do not significantly affect the heteroatom content or higher heating value of the bio-oil produced. The associated metals were found to partition almost exclusively into the solid residue, favourable for potential metal recovery. High metal loadings also caused partitioning of phosphates from the aqueous phase to the solid phase, potentially compromising attempts to recycle process water as a growth supplement. HTL was therefore found to be a suitable method of processing algae used in AMD remediation, producing a crude oil suitable for upgrading into hydrocarbon fuels, an aqueous and gas stream suitable for supplementing the algal growth and the partitioning of most contaminant metals to the solid residue where they would be readily amenable for recovery and/or disposal

Terms of trade movements and the global economic crisis: Implications for the Asia-Pacific region

Dramatic changes in the relative prices of goods in international trade have accompanied, and indeed preceded, the global crisis. These changes are reflected in the terms of trade ofindividual countries and in the relative prices of goods within those countries. Asia-Pacific countries are particularly affected by the changes in relative prices as they have been at the core of the increasing globalisation of production and distribution systems. An analysis of the causes and effects of the relative price changes is developed based on applying the analysisof business cycles developed by Joseph Schumpeter. Schumpeter's analysis emphasises innovation and structural change, particularly creative destruction, which impart uneven development on the economy and can foster financial crises. By applying Schumpeter's analysis the current crisis is put in the context of long-wave development of the capitalist system, which leads to predictions about the likely path of price and output changes over the medium term of the next decade or two