Reagent Removal of Heavy Metals From Waters of Coal Mines and Spoil Tips of the Lviv-Volyn Industrial Mine Region

Journal of Ecological Engineering Volume 20, Issue 8, September 2019, pages 50–59 https://doi.org/10.12911/22998993/110829 Received: 2019.06.22 Revised: 2019.07.18 Accepted: 2019.07.30 Available online: 2019.08.05 Reagent Removal of Heavy Metals From Waters of Coal Mines and Spoil Tips of the Lviv-Volyn Industrial Mine Region Oksana Mazurak1*, Irina Solovodzinska1, Andriy Mazurak2, Nataliia Gryncyhshyn3 Department of Ecology, Lviv National Agrarian University 1, V.Velykogo St., 30831 Dubliany, Lviv region, Ukraine 2 Department of Building and Architecture, Lviv National Agrarian University 1, V.Velykogo St., 30831 Dubliany, Lviv region, Ukraine 3 Department of ecological safety, Lviv State University of Life Safety, 35, Kleparivska St., 79007, Lviv, Ukraine * Corresponding author’s e-mail: 1 ABSTRACT The article substantiates the efficiency of using chemical (reagent) technologies for the purification of industrial water from mines and spoil tips from heavy metals-toxicants and reducing their ecological hazard. The ecological risk indices of toxicants and their proportion in the overall level of ecological danger of the investigated object were presented. The results of experimental studies, interaction of comparative qualitative indicators of removal of heavy metal ions by inorganic reagents – calcium carbonate and sodium hydroxide were provided. It is shown that the solution of the ecological problem concerning the reduction of the toxicity level of subterminal waters of mines is their treatment with fine calcium carbonate CaCO3 that converts the heavy metal ions into hardly soluble basic carbonates or heavy metal hydroxides. Positive results concerning the efficiency of the subterminal water treatment of the «Velikomostovskaya» mine of the Chervonograd mining area by calcium carbonate were identified. That indicates a significant reduction of the ecological hazard indicator of the treated wastewater. The content of ions of most heavy metals, which precipitate in the form of basic carbonates at values close to pH = 8.5, was significantly reduced. Keywords: ecological hazard, heavy metals, toxicants, mine, calcium carbonate, sodium hydroxide. INTRODUCTION There is ecological problem of mine drainage and ground subsidence, especially in inhabited areas, as a result of the mining activity in the Lviv-Volyn industrial mine region (Fig. 1), and in particular, the mines of the Chervonograd region. The subsidence of the bottom surface (depth ranging from 0.6 to 3.9 m) is accompanied by processes of flooding and soils waterlogging. Every year, 5.0 to 10 million m3 of polluted mine waters is pumped from mines of the basin, the toxic effects of which appear at all local biocenoses covering area of about 90 km2, where 4770 hectares of farmland and 642 hectares of forest areas were destroyed. The territories of the city of Chervonograd, the villages of Sielets and Mezhirichchia are 50 flooded almost completely, which makes building drainage systems, pumping out of water and carrying out sand pouring of flooded territories a necessity. Highly mineralized metal-containing components of wastewaters from under spoil of mines and spoil tips of the Chervonograd region cause a significant degradation of the soil layer of surrounding territories, contamination of underground aquifers, migration and assimilation of toxic compounds of heavy metals at almost all levels of the environment [Adamenko et al. 2016; Buchatska 2009] Hence, the minimization of the role of the natural geological barrier is taking place and the natural systems are unabled to perform self-rehabilitation [Dong et al. 2011; Knysh and Karabin 2010]. The lack Journal of Ecological Engineering Vol. 20(8), 2019 of universal methods for the utilization of mine and sub-spoil waters in case of unreliability of their accounting, low efficiency of purification methods, and their selectivity necessitate conducting a study onthe chemistry of heavy metal binding reactions in order to create optimal conditions for their immobilization and reduce the level of toxicity of spoil mine waters [Dlamini at al. 2013; Myung 2008]. One of the main technogenic sources of influence on underground, surface waters, soils and natural biocenoses is the mine waters and spoil tips of «Velikomostovskaya» mine the department of «Lvivvugillya State Enterprise». The purpose of the work is to study the peculiarities, mechanisms and efficiency of the chemical processes for the chemical removal of heavy metal toxicants (Cu2+, Mn2+, Pb2+, Co2+, Cd2+, Zn2+, Cr3+, Fetotal., Hg2+) from mine waters of «Velikomostovskaya» mine and calculation of the proportion of each pollutant component in the level of environmental hazard of the investigated object. MATERIALS In order to reduce the toxicity of mine and spoil tip waters, reagents capable of converting heavy metal ions into sparingly soluble compounds were used – finely dispersed calcium carbonate (CaCO3) powder and 0.95N sodium hydroxide (NaOH) solution. Calcium carbonate is finely dispersed powder of white color, made by grinding marble crumb. Calcium carbonate (CaCO3) constitutes solid crystals of white color, practically insoluble in water (at 20oC, Ks=0.00066 g/100 g of H2O). The molar mass of CaCO3 equals 100.087 g/mol. Melting point +825°C, decomposition temperature +1300°C. The density is 2.83 g/ cm3. The mass fraction of calcium carbonate in the resulting powder is 98.6%; magnesium carbonate is 0.7% by weight, about 0.1% Fe2O3, and silicon compounds. The mass residual fraction on 200 microns sieve amounts to 0.5%, while on 45 microns – 63.0%. Inorganic and organic impurities, fibers or inclusions of other materials were not detected. It occurs in the form of mineral compounds – calcite, aragonite, and vaterite [Volkov and Zharsky 2005]. Another chemical agent – 0.95N sodium hydroxide solution was used. The molar mass of NaOH = 39.997 g/mol. Melting point +323°C. Boiling point +1388 °C. Density – 2.13 g/cm3. Solubility in water at 25°C is 108.7 g/100 g. Sodium hydroxide (caustic soda) is available in two types: solid and liquid. Solid granular caustic soda is a white solid matter with a granule size about 0.5–2 cm. The caustic soda is very hygroscopic, well soluble in water, when exposed to water, a large amount of heat is released. A solution of sodium hydroxide is a solution of the secondary standard, so the study was conducted with fresh NaOH solution. Liquid caustic soda is a colorless or colored liquid – sodium hydroxide, technical, GOST 2263–79. By degree of influence on the body, it refers to the substances of the 2nd class of danger [Nabivanets 1996; Volkov and Zharsky 2005]. METHODS AND PROCEDURE The studies on the mine water were carried out at laboratory of the State Environmental Inspection of Lviv region in the Department of instrumental-laboratory and radiation control in accordance with current methods and standards [Standard methods for the examination of water and wastewater (...truncated)