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Minerals 2014, 4(1), 52-73; doi:10.3390/min4010052
Review

Environmental Risk of Metal Mining Contaminated River Bank Sediment at Redox-Transitional Zones

1,* , 1
 and 2
Received: 21 December 2013; in revised form: 21 January 2014 / Accepted: 22 January 2014 / Published: 29 January 2014
(This article belongs to the Special Issue Mine Waste Characterization, Management and Remediation)
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Abstract: Diffuse metal pollution from mining impacted sediment is widely recognised as a potential source of contamination to river systems and may significantly hinder the achievement of European Union Water Framework Directive objectives. Redox-transitional zones that form along metal contaminated river banks as a result of flood and drought cycles could cause biogeochemical changes that alter the behaviour of polyvalent metals iron and manganese and anions such as sulphur. Trace metals are often partitioned with iron, manganese and sulphur minerals in mining-contaminated sediment, therefore the dissolution and precipitation of these minerals may influence the mobility of potentially toxic trace metals. Research indicates that freshly precipitated metal oxides and sulphides may be more “reactive” (more adsorbent and prone to dissolution when conditions change) than older crystalline forms. Fluctuations at the oxic-anoxic interface brought about through changes in the frequency and duration of flood and drought episodes may therefore influence the reactivity of secondary minerals that form in the sediment and the flux of dissolved trace metal release. UK climate change models predict longer dry periods for some regions, interspersed with higher magnitude flood events. If we are to fully comprehend the future environmental risk these climate change events pose to mining impacted river systems it is recommended that research efforts focus on identifying the primary controls on trace metal release at the oxic-anoxic interface for flood and drought cycles of different duration and frequency. This paper critically reviews the literature regarding biogeochemical processes that occur at different temporal scales during oxic, reducing and dry periods and focuses on how iron and sulphur based minerals may alter in form and reactivity and influence the mobility of trace metal contaminants. It is clear that changes in redox potential can alter the composition of secondary iron and sulphur minerals and influence the sorption of toxic trace metals and susceptibility to dissolution when further redox potential changes occur. However further work is needed to determine: (i) The extent to which different duration and frequency of wet and dry cycles influences the dissolution and precipitation of iron and sulphur minerals in mining contaminated river bank sediment; (ii) The temporal effects on mineral reactivity (sorption capacity and susceptibility to dissolution); (iii) The key biogeochemical processes that control the mobility of contaminant trace metals under these dynamic redox potential conditions.
Keywords: diffuse pollution; sediment contamination; redox transitional zone; metal mine; oxic-anoxic interface; ferrihydrite; sulphide; sulphate; flood; drought diffuse pollution; sediment contamination; redox transitional zone; metal mine; oxic-anoxic interface; ferrihydrite; sulphide; sulphate; flood; drought
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Lynch, S.F.L.; Batty, L.C.; Byrne, P. Environmental Risk of Metal Mining Contaminated River Bank Sediment at Redox-Transitional Zones. Minerals 2014, 4, 52-73.

AMA Style

Lynch SFL, Batty LC, Byrne P. Environmental Risk of Metal Mining Contaminated River Bank Sediment at Redox-Transitional Zones. Minerals. 2014; 4(1):52-73.

Chicago/Turabian Style

Lynch, Sarah F.L.; Batty, Lesley C.; Byrne, Patrick. 2014. "Environmental Risk of Metal Mining Contaminated River Bank Sediment at Redox-Transitional Zones." Minerals 4, no. 1: 52-73.


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