In-situ electrochemical measurements of total concentration and speciation of heavy metals in acid mine drainage (AMD): assessment of the use of anodic stripping voltammetry

Abstract

We assessed the use of anodic stripping voltammetry (ASV) for in-situ determinations of both total concentration and speciation of dissolved heavy metals (Cd, Cu, Pb and Zn) in acid mine drainage (AMD). In the Kwangyang Au-Ag mine area of South Korea, different sites with varying water chemistry within an AMD were studied with a field portable anodic stripping voltammeter. Anodic stripping voltammetry after wet oxidation (acidification) was very sensitive enough to determine total concentration of dissolved Cd because Cd was dominantly present as 'labile' species, whilst the technique was not so effective for determining total Cu especially in the downstream sites from the retention pond, due to its complexation with organic matter. For dissolved Pb, the concentrations determined by ASV after wet oxidation generally agreed with those by ICP-AES. In the downstream samples (pH>5), however, ASV data after wet oxidation were lower than ICP-AES data because a significant fraction of dissolved Pb was present in those samples as 'inert' species associated with colloidal iron oxide particles. The determination of total dissolved Zn by ASV after wet oxidation appeared to be unsatisfactory for the samples with high Cu content, possibly due to the interference by the formation of Zn-Cu intermetallic compounds on the mercury coated electrode. In AMD samples with high dissolved iron, use of ultraviolet irradiation was not effective for determining total concentrations because humate destruction by UV irradiation possibly resulted in the removal of a part of dissolved heavy metals from waters through the precipitation of iron hydroxides.

Role of iron colloids in copper speciation during neutralization in a coastal acid mine drainage, South Korea: Insight from voltammetric analyses and surface complexation modeling

“…The ASV measurements of Chonam-ri Creek water samples under natural pH ranging from 3 to 7 suggest that pH is a crucial factor for the speciation of Cu and Pb, while pH has little effect on labile concentrations of Cd and Zn (Jung et al, 2006;Yun et al, 2001). Consistent with the field observation, the labile fractions of Cd and Zn remained high even after an artificial pH adjustment from natural pH (Fig.…”

“…Total and labile concentrations of dissolved trace metals, the total concentrations of dissolved major cations and anions, dissolved organic carbon (DOC), pH, dissolved oxygen (DO) and electrical conductivity (EC) in Chonam-ri Creek reported in Yun et al (2001) and Jung et al (2006). The physicochemical parameters as well as cations and anions in the table were used for VMINTEQ modeling.…”

“…1) was selected for a field investigation (Yun et al, 2001), as well as laboratory and modeling studies. Not only total concentrations but also labile fractions of Cu and Pb were found to decrease downstream as pH of the water increased due to the neutralizing retention pond (Jung et al, 2006). Because the mechanism governing the metal speciation during neutralization in Chonam-ri Creek before discharging to Kwangyang Bay was not well understood from field investigations, two sets of laboratory experiments and geochemical modeling were conducted.…”

“…The study area and the chemistry of the creek water have been previously described in detail (Jung et al, 2006;Yun et al, 2001). Briefly, the Kwangyang Au-Ag mine ( Fig.…”

Mine Wastes

“…The different size of the metal species and the common procedure to filter water prior to chemical analysis have a distinct implication on the analytical result. If detailed information on the speciation and bioavailability of metals is needed, other analytical methods need to be performed, including ultrafiltration and the use of exchange resins or Diffusive Gradients in Thin Films (DGTs) (Balistrieri et al 2007;Casiot et al 2009;Jung et al 2006;Søndergaard 2007). Such filters will allow significant amounts of colloidal material to pass through, and analyses of these samples will reflect dissolved and colloidal constituents (Brownlow 1996;Ranville and Schmiermund 1999).…”