Karen L. Johnson

Oxidative Decolorization of Acid Azo Dyes by a Mn Oxide Containing Waste

A Mn oxide containing mine tailings, generated in the Kalahari Mn fields, has been shown to oxidatively breakdown acid azo dyes acid orange (AO) 7, acid red 88, acid red 151 and acid yellow 36 but not acid yellow 9. The total reducible Mn content of the tailings is 33%, of which 3% is hydroquinone extractable and thus easily reducible. The net oxidation state of the Mn within the tailings is 3+. Decolorization of AO 7 by the Mn tailings increases with decreasing pH. The decolorization mechanism is initiated on the hydroxyl group of AO 7 and proceeds via successive electron transfers from the dye molecule to the oxide surface resulting in the asymmetric cleavage of the azo bond. The reaction products have been identified as 1,2-naphthoquinone, 4-hydroxybenzenesulfonate, and coupling products involving 1,2-naphthoquinone and benzenesulfonate radicals. The AO 7: Mn(III) reaction stoichiometry has been tentatively calculated to be 1:3. The reaction shows longevity with 95% decolorization still observed after 60 days of dye replenishment. Further breakdown of 1,2-naphthoquinone and 4-hydroxybenzenesulfonate was not observed, thus these compounds are considered to be the terminal reaction products of the AO 7- Mn tailings reaction.

Towards a mechanistic understanding of carbon stabilization in manganese oxides.

Minerals stabilize organic carbon (OC) in sediments, thereby directly affecting global climate at multiple scales, but how they do it is far from understood. Here we show that manganese oxide (Mn oxide) in a water treatment works filter bed traps dissolved OC as coatings build up in layers around clean sand grains at 3%w/wC. Using spectroscopic and thermogravimetric methods, we identify two main OC fractions. One is thermally refractory (>550 °C) and the other is thermally more labile (<550 °C). We postulate that the thermal stability of the trapped OC is due to carboxylate groups within it bonding to Mn oxide surfaces coupled with physical entrapment within the layers. We identify a significant difference in the nature of the surface-bound OC and bulk OC . We speculate that polymerization reactions may be occurring at depth within the layers. We also propose that these processes must be considered in future studies of OC in natural systems.

Remediation of a historically Pb contaminated soil using a model natural Mn oxide waste

A natural Mn oxide (NMO) waste was assessed as an in situ remediation amendment for Pb contaminated sites. The viability of this was investigated using a 10 month lysimeter trial, wherein a historically Pb contaminated soil was amended with a 10% by weight model NMO. The model NMO was found to have a large Pb adsorption capacity (qmax 346±14 mg g(-1)). However, due to the heterogeneous nature of the Pb contamination in the soils (3650.54-9299.79 mg kg(-1)), no treatment related difference in Pb via geochemistry could be detected. To overcome difficulties in traditional geochemical techniques due to pollutant heterogeneity we present a new method for unequivocally proving metal sorption to in situ remediation amendments. The method combines two spectroscopic techniques; namely electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS). Using this we showed Pb immobilisation on NMO, which were Pb free prior to their addition to the soils. Amendment of the soil with exogenous Mn oxide had no effect on microbial functioning, nor did it perturb the composition of the dominant phyla. We conclude that NMOs show excellent potential as remediation amendments.

Healthy land? an examination of the area-level association between brownfield land and morbidity and mortality in England

It is increasingly understood that the physical environment remains an important determinant of area-level health and spatial and socioeconomic health inequalities. Existing research has largely focused on the health effects of differential access to green space, the proximity of waste facilities, or air pollution. The role of brownfield—or previously developed—land has been largely overlooked. This is the case even in studies that utilise multiple measures of environmental deprivation. This paper presents the results of the first national-scale empirical examination of the association between brownfield land and morbidity and mortality, using data from England. Census Area Statistical ward-level data on the relative proportion of brownfield land (calculated from the 2009 National Land Use Database), standardised morbidity (2001 Census measures of ‘not good’ general health and limiting long-term illness), and premature (aged under 75 years) all-cause mortality ratios from 1998/99 to 2002/03 were examined using linear mixed modelling (adjusting for potential environmental, socioeconomic, and demographic confounders). A significant and strong, adjusted, area-level association was found between brownfield land and morbidity: people living in wards with a high proportion of brownfield land are significantly more likely to suffer from poorer health than those living in wards with a small proportion of brownfield land. This suggests that brownfield land could potentially be an important and previously overlooked independent environmental determinant of population health in England. The remediation and redevelopment of brownfield land should therefore be considered as a public health policy issue. Keywords: regeneration, environment, deprivation, neighbourhood

Hydrogeological and geochemical consequences of the abandonment of Frazer's Grove carbonate hosted Pb/Zn fluorspar mine, North Pennines, UK.

Abstract The problems associated with predicting where mine water will emerge and what the quality will be in a post-closure situation are recognised world-wide. The closure of Frazer’s Grove, a fluorspar mine in the North Pennines in the UK has given the opportunity to study in detail the relationship between rising groundwater and the strata/mineworkings through which it is rising. Detailed sampling and surveys both above and underground were carried out before, during and after rebound. During the rebound phase the mine water was stratified. Since the mine water emerged in August 1999, stratification has broken up and reestablished itself twice to date. The possible causes of the break-up of stratification are examined with the aid of hydrogeochemical data and geophysical techniques. The main contaminants present in the mine water are zinc, manganese, iron and sulphate. A general exponential decrease in dissolved metal concentration in the mine water is seen with time. The hydrogeochemical data also establishes the origin of the contamination in the mine water discharge with zinc and manganese originating from Frazer’s Grove mine itself and iron from several sources. The Frazer’s Grove mine investigation provides insight into water quality and its likely development with time in abandoned mines.

Oxidation of anthracene using waste Mn oxide minerals : the importance of wetting and drying sequences

PAHs are a common problem in contaminated urban soils due to their recalcitrance. This study presents results on the oxidation of anthracene on synthetic and natural Mn oxide surfaces. Evaporation of anthracene spiked Mn oxide slurries in air results in the oxidation of 30% of the anthracene to anthraquinone. Control minerals, quartz and calcite, also oxidised a small but significant proportion of the anthracene (4.5% and 14% conversion, respectively) when spiked mineral slurries were evaporated in air. However, only Mn oxide minerals showed significant anthracene oxidation (5-10%) when evaporation took place in the absence of oxygen (N2 atmosphere). In the fully hydrated systems where no drying took place, natural Mn oxides showed an increase in anthracene oxidation with decreasing pH, with a conversion of 75% anthracene at pH 4. These results show both acidification and drying favor the oxidation of anthracene on Mn oxide mineral surfaces. It has also been demonstrated that non-redox active mineral surfaces, such as calcite, may play a role in contaminant breakdown during wetting and drying sequences. Given that climate changes suggest that wetting and drying sequences are likely to become more significant these results have important implications for contaminated land remediation technologies.

Passive Treatment of Mn-Rich Mine Water: Using Fluorescence to Observe Microbiological Activity

Abstract Conventionally, limestones have been used in passive mine water treatment systems. Limestones with the highest proportion of calcite are recommended since they have the greatest long-term alkalinity generating potential. Manganese is present in mine waters and needs to be removed in order to comply with environmental quality standards. This paper compares seven different Permian carbonate rocks, both limestone and dolomite, in their ability to promote manganese oxidation in real mine waters over an 8-h period. The substrates are characterised using thermogravimetric analysis, X-Ray diffraction and scanning electron microscopy. Fluorescence spectrophotometry is used to monitor any changes in the dissolved organic matter concentration in the water as manganese is removed. We determine that there is no statistically significant correlation between manganese removal and the proportion of calcite or between manganese removal and substrate surface roughness. Fluorescence spectrophotometry demonstrates that there is a distinct change in the observed spectra in the water during manganese removal. There is a positive and statistically significant correlation between manganese removal and the production of a tyrosine-like substance (up to ∼150 ppb in 8 h), which fluoresces at 270–280 nm excitation wavelength and 300–310 nm emission wavelength, suggesting that microbial activity is an important factor in promoting manganese removal within dolomite passive treatment systems. It may be possible to use fluorescence spectrophotometry to monitor for microbial activity in passive treatment systems.

The role of water treatment abstraction in the flux and greenhouse gas emissions from organic carbon and nitrogen within UK rivers

The fate of organic matter through watersheds has been shown to be an important component of the global carbon cycle and processes in rivers can rapidly transfer carbon from the terrestrial biosphere to the atmosphere. However, the role of water abstraction in diverting organic matter from freshwater has not been considered. This study used two methods to estimate the amount of organic carbon removed by water treatment processes, firstly, by estimating the amount of carbon that has to be removed given the abstracted volumes and the freshwater composition; and, secondly, estimated from reports of the production and composition of water treatment residuals from water companies. For the UK, the median total organic carbon removed by water abstraction was 46 ktonnes C/yr, this equates to a median per capita value of 0.76 kg C/ca/yr. The median total organic nitrogen removed was 4.0 ktonnes N/yr, equivalent to 0.07 kg N/ca/yr. The removal of TOC by water abstraction represents 1.5% of the total removal rate across UK watersheds. The release of greenhouse gases from UK rivers is now estimated to be between 12754 – 32332 ktonnes CO2eq/yr equivalent to between 55 and 127 tonnes CO2eq/km2/yr with fluvial organic matter between 8800 and 15116 ktonnes CO2eq/yr in the proportion 6:86:8 N2O:CO2:CH4. The emissions factor for 1 tonne of organic carbon entering the UK fluvial network has a median value of 2.95 tonnes CO2eq/yr with a 5th to 95th percentile range of 2.55 to 3.59 tonnes CO2eq/yr. Globally, a per capita values for countries with municipal treated water supply would be 0.8 to 0.86 kg C/ca/yr. This article is protected by copyright. All rights reserved.

The importance of aeration in passive treatment schemes for manganese removal

A major breakthrough has been achieved in passive manganese treatment, since manganese can now be removed at the same time as iron, and efficient manganese removal is feasible even where land availability is limited. The active ingredients of this novel sub-surface flow gravel bed are dolomite and manganese dioxide powder. The catalytic action of these substrates combined with aeration provides the conditions required to overcome the usually slow kinetics of manganese oxidation in the presence of dissolved iron. Three small-scale (5 L containers) continuous flow systems were operated for seven months and successfully removed >95% of manganese in this period (raw water Mn concentration ~20 mg/L). The importance of aeration was successfully demonstrated, particularly when the systems were subjected to environmental stresses such as low (or non-existent) light, low temperatures (down to 4oC) and the presence of dissolved iron in the influent water. Spiking with additional iron (to an initial concentration of 5 mg/L) not only failed to significantly lessen manganese removal rates, but complete removal of the added iron itself was also observed. Since current manganese removal systems fail with iron present at such concentrations in the influent water, these results represent a significant advance in manganese removal options.

In situ arsenic oxidation and sorption by a Fe-Mn binary oxide waste in soil

The ability of a Fe-Mn binary oxide waste to adsorb arsenic (As) in a historically contaminated soil was investigated. Initial laboratory sorption experiments indicated that arsenite [As(III)] was oxidized to arsenate [As(V)] by the Mn oxide component, with concurrent As(V) sorption to the Fe oxide. The binary oxide waste had As(III) and As(V) adsorption capacities of 70mgg-1 and 32mgg-1 respectively. X-ray Absorption Near-Edge Structure and Extended X-ray Absorption Fine Structure at the As K-edge confirmed that all binary oxide waste surface complexes were As(V) sorbed by mononuclear bidentate corner-sharing, with 2 Fe at ∼3.27Ǻ. The ability of the waste to perform this coupled oxidation-sorption reaction in real soils was investigated with a 10% by weight addition of the waste to an industrially As contaminated soil. Electron probe microanalysis showed As accumulation onto the Fe oxide component of the binary oxide waste, which had no As innately. The bioaccessibility of As was also significantly reduced by 7.80% (p<0.01) with binary oxide waste addition. The results indicate that Fe-Mn binary oxide wastes could provide a potential in situ remediation strategy for As and Pb immobilization in contaminated soils.