Abstract
The article considers the possibility of using the sediments from stations of biological iron removal for the biosorption of heavy metal ions (IHMs) from both natural groundwaters and washing waters of enterprises with galvanic cycles. The processes of extracting Zn 2+ ions (up to 50 mg/dm 3 ), Cu 2+ (up to 16 mg/dm 3 ), Ni 2+ (up to 1.3 mg/dm 3 ), Cr 6+ (up to 2.0 mg/dm 3 ) on the bacterial structures of iron bacteria consortia and the optimal parameters of passing this process are determined (for washing waters pH=8.5–9.0). The influence of constant magnetic field with intensity of 20–60 mT, as well as the influence of different kinds of sediments from stations of biological iron removal on the efficiency of the process of removing IHM have been investigated. A significant percentage of the removal of IHM using calcined precipitate (98 % for Cu 2+ , 97 % for Zn 2+ , 85 % for Ni 2+ ) is due to the exoeffect that occurs at a wide temperature range of 200–400 oС. In this case, there is a smooth decrease in the mass of the sediment, indicating the combustion of the organic component and the crystallization of the amorphous phase. As a result, goethite (a-FeOOH) and lepidocrocyte (g-FeOOH) are converted into hematite (a-Fe 2 O 3 ) and magnetite (g-Fe 2 O 3 ), which have magnetic properties. When using as a reagent a fresh sediment, active involvement in the process of adsorption of heavy metal ions is carried out by biominerals, cells and polymer matrices of iron bacteria that have a crystalline structure and a large specific surface. At the same time, the effectiveness of removing IHMs was, respectively: for Cu 2+ 93 %; for Zn 2+ 92 %; for Ni 2+ 70 %. The efficiency of one-, two- and three-stage water purification schemes have been investigated. It was established that using the three-stage scheme with hydromechanical mixers and water alkalinization to pH 9.0, the efficiency of IHM removal was: for Cu 2+ up to 96 %; For Zn 2+ up to 99 %; for Ni 2+ up to 85 %. The X-ray spectral microanalysis of the sediment of the surface of the Gallioella bacterium case revealed the accumulation of IHM in the structure. The process of adsorption of IHM on the bacterial structures of consortia of iron bacteria due to their electrostatic bonding with both anionic surface of cell wall and with organic polymers isolated by cells of iron bacteria is substantiated.
Highlights
Most of water intakes of underground water today are, to varying degrees, under the influence of anthropogenic load [1]
Local areas of heightened concentrations of chromium may appear in underground waters
Today the most common ways to purify the reverse effluents from galvanic production are such energy-consuming technologies as chemical and electrochemical deposition, ion exchange, reverse osmosis [2, 3]
Summary
Most of water intakes of underground water today are, to varying degrees, under the influence of anthropogenic load [1]. The main sources of environmental pollution with chromium are galvanic production, textile industry, and production of special alloys. Today the most common ways to purify the reverse effluents from galvanic production are such energy-consuming technologies as chemical and electrochemical deposition, ion exchange, reverse osmosis [2, 3]. It is emphasized in paper [4] that such biological methods as biosorption and bioaccumulation can be considered as an alternative to traditional and expensive physico-chemical methods. Research and development of new energy- and resource-saving technologies based on the processes of microbial biosorption of ions of heavy metals (IHM) from natural waters and wastewaters is a relevant task
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