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Leaching of copper and nickel in soil-water systems contaminated by bauxite residue (red mud) from Ajka, Hungary: the importance of soil organic matter.

Lockwood CL, Stewart DI, Mortimer RJ, Mayes WM, Jarvis AP, Gruiz K, Burke IT - Environ Sci Pollut Res Int (2015)

Bottom Line: The red mud spill at Ajka, Hungary, in 2010 released 1 million m(3) of caustic red mud into the surrounding area with devastating results.In aerobic experiments, contact with the atmosphere reduced soil pH via carbonation reactions, and this reduced organic matter dissolution and thereby lowered Cu/Ni mobility.This could be especially problematic in locations where anaerobic conditions can prevail, such as wetland areas contaminated by the spill.

View Article: PubMed Central - PubMed

Affiliation: School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK.

ABSTRACT
Red mud is a highly alkaline (pH >12) waste product from bauxite ore processing. The red mud spill at Ajka, Hungary, in 2010 released 1 million m(3) of caustic red mud into the surrounding area with devastating results. Aerobic and anaerobic batch experiments and solid phase extraction techniques were used to assess the impact of red mud addition on the mobility of Cu and Ni in soils from near the Ajka spill site. Red mud addition increases aqueous dissolved organic carbon (DOC) concentrations due to soil alkalisation, and this led to increased mobility of Cu and Ni complexed to organic matter. With Ajka soils, more Cu was mobilised by contact with red mud than Ni, despite a higher overall Ni concentration in the solid phase. This is most probably because Cu has a higher affinity to form complexes with organic matter than Ni. In aerobic experiments, contact with the atmosphere reduced soil pH via carbonation reactions, and this reduced organic matter dissolution and thereby lowered Cu/Ni mobility. These data show that the mixing of red mud into organic rich soils is an area of concern, as there is a potential to mobilise Cu and Ni as organically bound complexes, via soil alkalisation. This could be especially problematic in locations where anaerobic conditions can prevail, such as wetland areas contaminated by the spill.

No MeSH data available.


Eh/pH conditions calculated for 33 % RM-amended anaerobic experiments superimposed on an Eh/pH Cu species predominance and relative mineral stability diagram calculated using Geochemists Workbench® for t = 21 °C/P = 1 at, for the system Cu-O-H-SO42− with log ∑Cu/m = −.3256, log ∑SO42−/m − .3646 and a[H2O(aq)] = 1. Points plotted show geochemical conditions at day 0 and experimental end points
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Fig5: Eh/pH conditions calculated for 33 % RM-amended anaerobic experiments superimposed on an Eh/pH Cu species predominance and relative mineral stability diagram calculated using Geochemists Workbench® for t = 21 °C/P = 1 at, for the system Cu-O-H-SO42− with log ∑Cu/m = −.3256, log ∑SO42−/m − .3646 and a[H2O(aq)] = 1. Points plotted show geochemical conditions at day 0 and experimental end points

Mentions: The aqueous Cu concentration in the OR 33 % RM experiment peaked after 15 days and then decreased with time (Fig. 4a). As the pH did not vary significantly after day 15, this decrease in aqueous Cu concentration is unlikely to be associated with humate solubility. However, the ORP decreased rapidly between 15 and 30 days (Fig. 3d), and sulphate was removed from aqueous solution (see Online Resource, Fig. D) suggesting the occurrence of sulphate reduction. Cu(II) species are the most stable Cu species under oxidising conditions, but Cu(I) and Cu(0) species are formed under more reducing conditions (Leckie and Davis 1979). Both Cu(II) and Cu(I) can form stable complexes with organic matter, but inorganic sulphide is thought to outcompete OM for Cu(I) in sulphide-rich environments (Fulda et al. 2013b). The Eh/pH diagram for relevant inorganic Cu species (Fig. 5) confirms that the anaerobic OR 33 % RM test reached an Eh/pH state where sulphide can compete for the Cu. There is also evidence for Cu removal from solution associated with the onset of sulphate reduction (see Online Resource, Fig. D) in the data from the OR 9 % RM experiment (Figs. 4a and 3d: note that the ORP for sulphate reduction is higher at pH 8 than at pH 9.5). By the end of this test, there was very little Cu in solution despite an elevated DOC in comparison with the soil-only control (i.e. the end-point of this test did not follow the trend of increasing aqueous Cu concentration with increasing DOC concentration). Thus, where the soil pH and the availability of organic matter favour sulphate reduction, the formation of sulphides can curtail Cu mobilisation by aqueous humates and therefore lower aqueous Cu concentrations.Fig. 5


Leaching of copper and nickel in soil-water systems contaminated by bauxite residue (red mud) from Ajka, Hungary: the importance of soil organic matter.

Lockwood CL, Stewart DI, Mortimer RJ, Mayes WM, Jarvis AP, Gruiz K, Burke IT - Environ Sci Pollut Res Int (2015)

Eh/pH conditions calculated for 33 % RM-amended anaerobic experiments superimposed on an Eh/pH Cu species predominance and relative mineral stability diagram calculated using Geochemists Workbench® for t = 21 °C/P = 1 at, for the system Cu-O-H-SO42− with log ∑Cu/m = −.3256, log ∑SO42−/m − .3646 and a[H2O(aq)] = 1. Points plotted show geochemical conditions at day 0 and experimental end points
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4490175&req=5

Fig5: Eh/pH conditions calculated for 33 % RM-amended anaerobic experiments superimposed on an Eh/pH Cu species predominance and relative mineral stability diagram calculated using Geochemists Workbench® for t = 21 °C/P = 1 at, for the system Cu-O-H-SO42− with log ∑Cu/m = −.3256, log ∑SO42−/m − .3646 and a[H2O(aq)] = 1. Points plotted show geochemical conditions at day 0 and experimental end points
Mentions: The aqueous Cu concentration in the OR 33 % RM experiment peaked after 15 days and then decreased with time (Fig. 4a). As the pH did not vary significantly after day 15, this decrease in aqueous Cu concentration is unlikely to be associated with humate solubility. However, the ORP decreased rapidly between 15 and 30 days (Fig. 3d), and sulphate was removed from aqueous solution (see Online Resource, Fig. D) suggesting the occurrence of sulphate reduction. Cu(II) species are the most stable Cu species under oxidising conditions, but Cu(I) and Cu(0) species are formed under more reducing conditions (Leckie and Davis 1979). Both Cu(II) and Cu(I) can form stable complexes with organic matter, but inorganic sulphide is thought to outcompete OM for Cu(I) in sulphide-rich environments (Fulda et al. 2013b). The Eh/pH diagram for relevant inorganic Cu species (Fig. 5) confirms that the anaerobic OR 33 % RM test reached an Eh/pH state where sulphide can compete for the Cu. There is also evidence for Cu removal from solution associated with the onset of sulphate reduction (see Online Resource, Fig. D) in the data from the OR 9 % RM experiment (Figs. 4a and 3d: note that the ORP for sulphate reduction is higher at pH 8 than at pH 9.5). By the end of this test, there was very little Cu in solution despite an elevated DOC in comparison with the soil-only control (i.e. the end-point of this test did not follow the trend of increasing aqueous Cu concentration with increasing DOC concentration). Thus, where the soil pH and the availability of organic matter favour sulphate reduction, the formation of sulphides can curtail Cu mobilisation by aqueous humates and therefore lower aqueous Cu concentrations.Fig. 5

Bottom Line: The red mud spill at Ajka, Hungary, in 2010 released 1 million m(3) of caustic red mud into the surrounding area with devastating results.In aerobic experiments, contact with the atmosphere reduced soil pH via carbonation reactions, and this reduced organic matter dissolution and thereby lowered Cu/Ni mobility.This could be especially problematic in locations where anaerobic conditions can prevail, such as wetland areas contaminated by the spill.

View Article: PubMed Central - PubMed

Affiliation: School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK.

ABSTRACT
Red mud is a highly alkaline (pH >12) waste product from bauxite ore processing. The red mud spill at Ajka, Hungary, in 2010 released 1 million m(3) of caustic red mud into the surrounding area with devastating results. Aerobic and anaerobic batch experiments and solid phase extraction techniques were used to assess the impact of red mud addition on the mobility of Cu and Ni in soils from near the Ajka spill site. Red mud addition increases aqueous dissolved organic carbon (DOC) concentrations due to soil alkalisation, and this led to increased mobility of Cu and Ni complexed to organic matter. With Ajka soils, more Cu was mobilised by contact with red mud than Ni, despite a higher overall Ni concentration in the solid phase. This is most probably because Cu has a higher affinity to form complexes with organic matter than Ni. In aerobic experiments, contact with the atmosphere reduced soil pH via carbonation reactions, and this reduced organic matter dissolution and thereby lowered Cu/Ni mobility. These data show that the mixing of red mud into organic rich soils is an area of concern, as there is a potential to mobilise Cu and Ni as organically bound complexes, via soil alkalisation. This could be especially problematic in locations where anaerobic conditions can prevail, such as wetland areas contaminated by the spill.

No MeSH data available.