Mobility and natural attenuation of metals and arsenic in acidic waters of the drainage system of Timok River from Bor copper mines (Serbia) to Danube River

Aquatic photochemistry of Cu(II) in the presence of As(III): Mechanistic insights from Cu(III) production and As(III) oxidation under neutral pH conditions

Surface complexation between arsenite (As(III)) and colloidal metal hydroxides plays an important role not only in the immobilization and oxidation of As(III) but also in the cycle of the metal and the fate of their ligands. However, the photochemical processes between Cu(II) and As(III) are not sufficiently understood. In this work, the photooxidation of As(III) in the presence of Cu(II) under neutral pH conditions was investigated in water containing 200 μM Cu(II) and 5 μM As(III) under simulated solar irradiation consisting of UVB light. The results confirmed the complexation between As(III) and Cu(II) hydroxides, and the photooxidation of As(III) is attributed to the ligand-to-metal charge transfer (LMCT) process and Cu(III) oxidation. The light-induced LMCT process results in simultaneous As(III) oxidation and Cu(II) reduction, then produced Cu(I) undergoes autooxidation with O₂ to produce O₂^•⁻ and H₂O₂, and further the Cu(I)-Fenton reaction produces Cu(III) that can oxidize As(III) efficiently (k_{Cu(III)+As(III)} = 1.02 × 10⁹ M^-1 s^-1). The contributions from each pathway (ρ_{rCu(II)-As(III)+hv} = 0.62, ρ_{rCu(III)+As(III)} = 0.38) were obtained using kinetic analysis and simulation. Sunlight experiments showed that the pH range of As(III) oxidation could be extended to weak acidic conditions in downstream water from acid mine drainage (AMD). This work helps to understand the environmental chemistry of Cu(II) and As(III) regarding their interaction and photo-induced redox reactions.

Application of microbial fuel cell for simultaneous treatment of metallurgical and municipal wastewater - а laboratory study

Microbial fuel cell (MFC) is a hybrid technology that produces electricity and recovers resources from wastewater through biocatalytic and electrochemical reactions. Metallurgical facilities in Bor, Serbia, are a source of copper-rich metallurgical wastewater, and the Town of Bor is a source of municipal wastewater rich in organic matter. The aim of this paper is to investigate the possibility of application of MFC for the treatment of metallurgical and municipal wastewater that are released into the Bor River in Serbia. A prototype of MFC was constructed for this study, and 3 sets of experiments were performed using model solutions and real wastewater. Copper was successfully removed from the treated model solution with 99.42 % efficiency. Solid copper particles were obtained with a particle size of about 1 ?m. Maxi-mum chemical oxygen demand (COD) removal rate of 191.7 mg L-1 h-1 was observed in the anodic compartment. The impact of this study is significant because MFC was implemented for the simultaneous treatment of two types of wastewaters, one containing metals and the other containing organic matter, and both types of wastewater are released into the same river.

Chemometric characterization of heavy metals in soils and shoots of the two pioneer species sampled near the polluted water bodies in the close vicinity of the copper mining and metallurgical complex in Bor (Serbia): Phytoextraction and biomonitoring contexts

In terms of investigating the authentic plant biomonitoring and phytoextraction potentials, the samples of soils and shoots of the sun spurge (SS) and common nettle (CN), were collected near several polluted water bodies in the close vicinity of the copper mining/metallurgical complex in Bor (Serbia) and characterized with regard to the content of heavy metal(oid)s: As, Cd, Pb, Cu, and Zn. The methods applied in this work such as inductively coupled plasma-mass spectrometry, one-way analysis of variance, Pearson's correlation study, hierarchical cluster analysis, and the calculation of bioaccumulation rates (expressed through the so called mobility ratios, MRs), provided very informative data on the potentials of both investigated pioneer species. The most important findings were: 1) In most cases, SS was more effective in metal extraction/translocation/bioaccumulation than CN, and especially with regard to Cu; in this particular case, extremely high concentrations were recorded and also, some significant MRs were calculated, which may be a signal of its promising potential for Cu-phytoremediation, practically, Cu-phytoextraction; however, generally, the values of most calculated MRs were very low (<1, for both plants); 2) The shoots of both plants reflected soundly the current status of metal presence in the studied environment and they can be recommended for seasonal screenings of a general level of metal pollution in the areas of interest; however, specifically, they cannot reflect quite correctly the level of soil pollution; 3) Soil Cu, and As were detected in alarming concentrations.

Effect of pH to the surface precipitation mechanisms of arsenate and cadmium on TiO2

Much attention has focused on the mutual effect of oxyanions and cations on surfaces, however, there is still a lack of knowledge on the molecular-level surface precipitation mechanisms for As(V) and Cd(II) on surfaces under different pH conditions in acid metallurgical industrial wastewater. The results of in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy show that different As(V) and Cd(II) surface precipitation mechanisms take effect at pH 5.0 and 7.0. Under acidic conditions, As(V) was preferentially adsorbed on TiO₂ rather than Cd(II). Thus, a Cd(II)-As(V)-TiO₂ ternary surface complex was formed with the adsorbed As(V) as the bridging molecule, and the subsequent layer-by-layer surface precipitate was generated. Under neutral conditions, the Cd(II)-As(V) surface precipitates were directly formed by using the aqueous Cd(II)-As(V) complex as a "seed", which took approximately 10 times longer than the acidic conditions to reach the adsorption equilibrium. Our findings provide spectroscopic evidence and elucidate the different simultaneous removal mechanisms of As(V) and Cd(II) on TiO₂ under acidic and neutral conditions, which will further our understanding and application of the immobilization of multiple pollutants in industrial wastewaters.