Tailing dumps of the tyrnyauz tungsten–molybdenum mining and processing complex: Current state and outlooks

The Tyrnyauz W–Mo deposit was developed by opencast and underground mines until 2003. The assets of the Tyrnyauz Tungsten–Molybdenum Mining and Processing Complex (TTMC) include two tailing dumps: Tailing 2 (housed on the left-hand side of the Baksan River valley, 2 km south of the settlement of Bylym) and Supertailing 2 (a superdump housed in the valley of the Gizhgit River, a left-hand tributary of the Baksan River). The height of the rock-fi lling dam of Supertailing 1 reaches 160 m. A pond on its top protects the ecosystems from the wind erosion of the dumped industrial wastes. The protecting pond is equipped with a tunnel drainage system, which is used to discharge excess water to the Baksan River, to a certain technological water level in the pond. Shallow-focus earthquakes (with M = 5–7) and/or debris and mud fl ows are able to destroy the dam, and this will result in the transfer of toxic compounds to the Baksan River and water-bearing Quaternary alluvial rocks in the foredeep, where the river fl ows into the plain. The following soil contamination sources were identifi ed: (1) Winds continuously blowing along the Baksan valley erode fi nes where the recultivation layer of Tailing 2 is disturbed and in the beach parts of Supertailing 1; the extent of this contamination varies from hundreds of meters to a few kilometers; (2) Massive blasting operations at the opencast mines before 2003 resulted in atmospheric emissions of dust clouds with ore minerals; this pollutions extends for dozens of kilometers (along the valleys of the Baksan River and its tributaries). The most ecologically hazardous emissions are those of quartz dust and dust with heavy-metal minerals, including sulfi des. A method for utilizing TTMC wastes was engineered and patented. The results provide a basis for designing measures aimed at decreasing the adverse load on the ecosystems in the Elbrus area, which is highly attractive to tourists. Mini Review Tailing dumps of the tyrnyauz tungsten–molybdenum mining and processing complex: Current state and outlooks NS Bortnikov, AG Gurbanov and Alexander Y Dokuchaev* Ore and Petrographic Museum, Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry RAS, Moscow, Russia Received: 05 October, 2020 Accepted: 22 October, 2020 Published: 23 October, 2020 *Corresponding author: Alexander Y Dokuchaev, Ore and petrographic Museum, Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry RAS, Moscow, Russia, E-mail: ORCID: https://orcid.org/0000-0001-6552-3847 https://www.peertechz.com


Introduction
The Tyrnyauz W-Mo deposit was commissioned in 1940. When the risk emerged that the German Wehrmacht may occupy the Elbrus area in the Caucasus in 1942, the processing mill, the entrances to the adits, and some ropeway stations were blasted. After the reconstruction of the facilities in 1945, the annual production (which was then conducted only in underground workings) and processing of W and Mo ores was within 1 Mt.
Until 1992, the deposit was developed by both opencast and underground mines, and the maximum production and processing rate amounted to 8 Mt ore per a year. The enterprise then produced 55-60% W and 15% Mo of the total USSR production of the metals at that time. However, when the energy price jumped in 1992, the ore mining and processing cost (i.e., the primecost of the metal heads) became higher than the factory-gate prices of the manufactured concentrate.

Sources of soil contamination
The following sources of soil contamination were identifi ed: The soil sample from a natural grassland on the left-hand fl ank of the Baksan valley (180 m northeast of Supertailing 1) contained higher (than in BS) concentrations of Na 2 O, Fe 2 O 3 , Cu, Ba, Pb, Rb, Cr, V, Со, Pb, Sc, and Cs (1.5-2 times higher), MnO (2 times higher), As (3 times higher), Zn (4 times higher), Sn (7 times higher), Sb and Mo (~9.5 times higher), and W (50 times higher).
Modern soils at the grasslands and farmlands of the settlement of Belym near TTMC tailings were thus proved to be contaminated with ecologically hazardous metals.

Contamination sources of the baksan water
Surface waters in the TTMC area and adjacent territories were sampled in 2014-2016 and analyzed by iCAP 6500 Duo, and ICP-MS. Elevated concentrations (dozens of times higher than MPC) were detected for Mo (up to 11 mg/L), W (4.4 mg/L), As (1.5 mg/L), Mn (8.4 mg/L), and Tl (up to 3.3 mg/L) in the water of Bolshoy Mukulan Stream, which fl ows across opencast ore mines and waste-rock dumps, in which fi ne ore material settled from the dust clouds (produced by intense blasting operations at TTMC opencast mines) and was accumulated.
The dominant contamination source of the Baksan water was proved to be Bolshoy Mukulan Stream but not the tailings.
Analysis of concentrations of major and trace elements in surface waters in the basin of the Baksan River led us to the following conclusions: (1) The water of the Baksan River where the river fl ows into the piedmont plain contains Al, Fe, Mn, Be, Si, Ti, Tl, and Hg concentrations that are notably higher than MPC in summertime and Si, Ti, Hg, and Tl concentrations that are lower than MPC in spring. (2) Bolshoy Mukulan Stream has the highest fl ow rate among other streams fl owing through the opencast mines and bear the highest concentrations of Al, Si, Fe, Mn, Ti, V, Ni, As, Li, Be, Mo, Cd, and Tl concentrations, which are one to two orders of magnitude higher than the MPC in summer. (3) Elevated concentrations of the same elements, as well as B, Hg, Sb, and W, are typical of the water of Maloe protecting pond (which is not running), whereas the water of Bolshoy pond (which is running) of Supertiling 1 contains elevated (higher than MPC) concentration only of As and W.

Utilization of dumped TTMC wastes
To minimize the material damage from natural and anthropogenic processes and decrease the adverse load on the ecosystems and human health, it is obviously necessary to completely utilize the industrial wastes stored in TTMC tailings and recover all economically valuable and ecologically hazardous metals from these tailings. The application of acid leaching techniques is a complicated academic and applied problem, which implies that the following two major tasks shall be fulfi lled. First, it is necessary to principally decrease the concentrations of the major complex of elements and thus produce ecologically safe solid materials suitable for further usage as starting products for manufactuting construction materials. Second, the above complex of elements shall be concentrated and subsequently subdivided into ecologically hazardous (As, Tl, and others), which require specialized dumping technique and methods, and economically valuable (W, Mo, Cu, Re, etc.) elements. The selective extraction of the latter will, perhaps, be able to compensate the operation costs, provided that the extraction and isolation of ecologically hazardous elements is a top-priority task. This problem can be solved using physical separation techniques (such as gravitational, magnetic, etc.), which were suggested over the past 25 years to produce W and The experiments were conducted at 100ºC and yielded the best results when conducted with HCl and H 2 SO 4 , with the addition of Н 2 О 2 as an oxidizer, at temperatures of 60-80ºC for 2 h.
The recovery of the metals (in relative %) was as follows: Mo 70-75, Cu 40-60, W and as 40-50, and Pb 20-60. This allowed us to identify the conditions of the suffi cient levels of acid treatment. These data can be utilized to develop a low-cost technique for leaching dumped wastes with regard to (a) the production of an ecologically safe solid phase (precipitate) that can be later used in construction operations, and (b) obtaining working solution with relatively high concentrations of valuable (Mo, W, and Cu) and ecologically hazardous (Hg etc.) elements. These concentrations shall be high enough to enable adsorption concentrating of the metals and their subsequent separation. Comparable results were obtained with a sample 10 kg in mass (i.e., the mass of the wastes was 1000 times higher).
Our still-scarce experiments on the deactivation of the wastes of Supertailing dump 1 have demonstrated the effi ciency of soda leaching. The developed utilization technique of TTMC wastes was patented [8].
It has been determined that contamination impacts not only soils at the farmlands and grasslands in the surroundings of the town of Tyrnyauz but also streams in the basin of the Baksan River. The contaminants contain toxic elements from industrial wastes dumped in the tailings. These elements are transferred to the waters of streams fl owing across TTMC opencast mines and out of the underground mining workings. The data thus acquired can be used as a basis for engineering measures and operations aimed at diminishing the adverse load on the ecosystems of the Elbrus area and on the health of the local human population.

Conclusions
Thus, the data obtained allow us to make the following conclusions 1. The dumped industrial wastes of the Tyrnyauz Tungsten-Molybdenum Complex (TTMC) are multicomponent anthropogenic deposit of metallic and nonmetallic minerals. TTMC had operated for decades before 2003. The ore was developed by opencast and underground mines and was processed using fl otation and chemical technologies. The industrial wastes are dumped in two tailings and partly recultivated.
2. An artifi cial pond on the top of the dam of Supertailing 1 is intended to protect against wind erosion. This pond (lake) was named Ullu Gizhgit; it gradually self-purifi es because of the infl ow of fresh water portions from the Gizhgit River and the addition of rain and spring-fl ood (melt) waters. The pond is equipped with a tunnel system for discharging excess waters into the Baksan River.
3. Based on numerous laboratory experiments, economically rational technological approaches were designed targeted at the complete utilization of the industrial wastes of TTMC, with the extraction of