Svetlana Bortnikova

Leaching experiments on trace element release from the arsenic-bearing tailings of Khovu–Aksy (Tuva Republic, Russia)

Abstract The study of inactive As-bearing tailings impoundments at the Khovu-Aksy mine-site (Russia) revealed high concentrations of As in the porewater of tailings solids and in their aqueous extracts, as well as in adjacent soils. In these investigations, experimental leaching of As-containing tailings was performed in the laboratory. The three types of solutions which were used in the leach experiments to model natural waters and waters of anthropogenic origin were H2O, HNO3 and NH4HCO3, and during leaching with these solutions As concentrations were maintained at 10±2, 16±1 and ∼20 mg/l. No low-pH waters were observed at the end of the leach experiments, where pH varied between 8.3 and 9.1. These alkaline pH conditions are attributed to the effect of acid consuming carbonate mineral dissolution reactions, which are also indicated by increased concentrations of Mg and Ca. Also, the solution of certain heavy metals (Co, Ni, Fe) was negligible compared to that of As, and these metals were assumed to have been conserved in the solid phase. Analysis of the leach solutions, and modeling of the results showed that As could be removed from the surface of different particles where it had been adsorbed, and also its concentration could increase with time from the breakdown of Ca(Mg)- and Ni(Co)-arsenate phases. In the absence of an effective remediation program, As release will continue to be an environmental problem.

The use of magnetic methods in an environmental study of areas polluted with non-magnetic wastes of the mining industry (Salair region, Western Siberia, Russia)

Results obtained by combined geochemical and rock-magnetic studies of environment pollution are presented. The study area falls into a new special class of objects that has not been investigated earlier by magnetic methods: tailings of primary non-magnetic ores within an active geochemical environment and the absence of high-temperature processes in the technology of Pb–Zn ore recovery. Here an inverse correlation between metal (Pb, Zn, recovered from the ore) contents in the upper ground layer around the collection pond (highly polluted zone) and concentration-dependent magnetic characteristics (magnetic susceptibility, magnetic remanences) was found. This result conflicts with previous studies that focused on industrial and urban regions where enhanced magnetic properties of the environment (soils, sediments etc.) correspond to higher degrees of its pollution. In our case, the relationship between changes in magnetic properties and metal content variation is less pronounced but the overlap of geochemical and rock-magnetic anomalies over the study area is clear. The resulting maps confirm the advantage of magnetic methods as a proxy, rapid and inexpensive technique to measure pollution.

The Combination of Geoelectrical Measurements and Hydro-Geochemical Studies for the Evaluation of Groundwater Pollution in Mining Tailings Areas

Sulfide-bearing mill wastes of the Salair Ore Processing Plant situated in the Kemerovo region (Russia) were investigated in the time period 1999–2011. Multipurpose studies of the Talmovskie mining tailings allowed the determination of the composition of the wastes, the acid mine drainages, and the affected groundwater. Geophysical sounding techniques (frequency sounding and electrical tomography) were used to trace the geoelectric zoning of the wastes, expressed as a consistent change of the electrical resistivity specific electrical resistance (SER) from zone to zone. Layers with low resistivity indicate areas with pore spaces filled by highly mineralized solutions. These layers extend to depths of 4–5 m, indicating the penetration of toxicants into the groundwater horizon. The pollution of groundwater was confirmed by chemical analysis, according to which the concentrations of Zn, Pb, and Cd in water samples from the wells are two to three orders of magnitude higher than the maximum permissible concentration (MPC). The authors provide an attempt to identify the correlation and quantitative relationships between SER and the total amount of various metal species present in the wastes and water extracts. The proposed approach permitted to estimate the amount of accumulated tailings, in order to predict changes in the total concentrations of Mn, Al, Fe, Cu, Zn, Cd, and Pb in waste and water extracts to a depth of 30 m.

Geophysical investigations for evaluation of environmental pollution in a mine tailings area

ABSTRACT Sulfide-containing mill wastes of the Komsomolsk ore processing plant situated in the Kemerovo region (Russia) were examined in 2013–2015. Multipurpose studies of the mine tailings determined the composition of waste, pore water, mine drainages, and affected groundwater. Electrical resistivity tomography was used to trace the geoelectric zoning of the waste samples. Layers with low resistivity indicated areas with pore spaces filled with highly mineralized solutions with Fe, Cu, Zn, Cd, As, and Sb at total concentrations of up to 50 g/L. Anomalous zones can be specified as ‘geochemical barriers’ – specific layers where the mobility of the elements is reduced due to pH conditions, redox potential, and Fe(III) hydroxide precipitation. The zones of increased conductivity in oxidized mine tailings indicated local areas with high acid production potential and coexisting acidic pore solution. In non-oxidized tailings, high conductivity of the mineral skeleton was observed. There was a migration of drainage outside the tailings, its direction monitored by geophysical data. Chemical analysis confirmed that the concentrations of As in groundwater samples were higher than the maximum permissible concentration.

Mechanisms of low-temperature vapor-gas streams formation from sulfide mine waste

This paper presents experimental data that revealed the potential for chemical element transport by low-temperature vapor-gas streams. The study was conducted on sulfide waste heap sites located in the Kemerovo region, Russia. Condensates of vapor-gas streams were collected and analyzed in the air above the waste heaps and during laboratory experiments using samplers specially designed for this purpose. The gas streams from a waste heaps are complex mixtures consisting of water vapor, sulfur- and selenium-containing compounds (sulfur dioxide SO2, dimethyl sulfide C2H6S, carbon disulfide CS2, dimethyl disulfide C2H6S2, dimethyl selenide C2H6Se, and dimethyl diselenide C2H6Se2), elemental sulfur (S6, S7, and S8) and various chemical elements, including rock-forming elements (Ca, Mg, Na, K, Si, Fe, Al, and Mn), metals (Cu, Zn, Pb, Ni, and Sn), and metalloids (As, Te, and Sb). The main sources of chemical elements in the gas streams are unstable secondary minerals associated with crystalline hydrates: gypsum CaSO4 × 0.5H2O, sideronatrite Na2Fe(SO4)2(OH) × 3H2O, serpierite CaCu3Zn(SO4)2(OH)6 × 3H2O, and copiapite (Mg,Zn,Fe2+Fe3+)4(SO4)6(OH)2 × 20H2O that formed during the oxidation of sulfide minerals. Some of the elements come from pore waters that are acidic, highly mineralized solutions. The mechanism of element migration from the pore waters is as follow: the water vapor phase transports elements in the form of aqueous ions, but complexed species (such as MeSO4(aq), MeCl(aq), Me(OH)+, etc.) remain in the salt residue. A significant contribution to the processes of transformation and transport of elements is made by biochemical methylation reactions, which occur in the presence of bacteria producers of methyl groups and are accompanied by the formation of volatile compounds of arsenic, selenium, sulfur, and tellurium.

Geochemistry of surface waters in the vicinity of open pit mines at the Cay Cham deposit, Thai Nguyen province, northern Vietnam

This study provides an assessment of the environmental impact of open pit mining operations at the Cay Cham titanomagnetite-ilmenite deposit (northern Vietnam). The results of surface water sampling indicate the formation of acid mine drainage and contamination of adjacent areas by heavy metals (Cu, Zn, Ni, and Mn). The acid mine drainage is produced by oxidation leaching of sulfide minerals associated with primary mineralization owing to the low neutralization potential of the natural waters in the humid environment of tropical rainforest. The study showed that alternating dry and wet seasons typical of this climatic region promote the generation of stored acidity leading to a sharp decrease in pH of drainage water during the wet season and result in the negative impacts of this mine on both flowing and stagnant surface waters.