Лаборатория геологии техногенных процессов
Maximovich N.G., Osovetskiy B.M., Blinov S.M. Geochemical Barriers and Environment Protection // GeoEng 2000: Conference Proceedings [ Electronic resonce ]. 19-24 November 2000. Melbourne, Australia. - Electronic optical disks (CD - ROM).
GEOCHEMICAL BARRIERS AND ENVIRONMENT PROTECTION
Maximovich N. G., Osovetskiy B. M. and Blinov S. M.
The application of geochemical barriers for improvement of ecological situation is reviewed. The tendered methods are based on a decrease of technogenic migration of polluting components by means of change them to non-migrating forms. A number of examples of their practical usage for environmental protection in Russian territory is presented. The natural materials or other materials, for example, manufacturing wastes were used for creation of artificial geochemical barriers. The application of such methods in a number of cases allows to avoid building of expensive refining objects since the present methods require considerably less costs.
In city-industrial agglomerations there is a set of contamination sources (waste water, areas with waste products, sumps, etc.). They result in local technogenic geochemical anomalies that negatively influence on an ecological situation. The formation of such anomalies is frequently connected with technogenic migration of polluting components in water flows. The limitation methods of pollution expansion are worked out for decreasing of its negative effect. One of such methods is usage of artificial geochemical barriers. The concept "technogenic geochemical barrier" is introduced by A. Perelman in 1976 for a zone where there is a sharp reduction of technogenic migration and, consequently a concentration of elements (Perelman, 1989).
The essence of environmental protection methods with the help of geochemical barriers consists in change of polluting components in non-migrating forms. Thus usage of natural materials or other matters, for example, manufacturing waste is possible. In a number of cases the localisation of contaminants may be realised due to natural geochemical features of soils. They help to select sites for keeping or waste throwing off (Sergeev, 1992). The experience has shown possibility of using of barriers in different situations.
USAGE OF GEOCHEMICAL BARRIERS FOR IMPROVEMENT OF ECOLOGICAL CONDITIONS
Refining of waste water from suspended particles
Considerable injury to environment can be caused by waste water with a great number of suspended particles. For clearing of them ground filters stacked in a channel of the river are used on the diamond deposits in the Perm Region. As a material for filters dredged ground wastes located in the river valley were used. Full-scale experiments have shown that depending on a path length of filtration the concentration of suspended particles in waste water can be reduced by tens or hundreds of times (fig.1).
Figure 1: Scheme of soil filter
Based on the conducted activities, the writers have computed optimal parameters for ground filters. The maximum initial concentration of suspended load, grain composition of used grounds, discharge of the river and work time of filters are taken into account. The applying of ground filters does not require high costs and is capable to reduce the content of suspended particles up to values close to background concentration (Maximovich and Blinov, 1997).
Neutralisation of acid waste waters
The mines of the Kizel Coal Basin in the Perm Region put practically without clearing in rivers acid (pH=2-4) highly mineralised sulphate waste waters incorporating abnormally high contents of iron, aluminium and heavy metals. The decontamination of acid mine waters is possible by means of their neutralisation with usage of alkaline composition waste. The laboratory activities have shown, that at usage of alkaline waste of soda production the pH value of mine waters can be increased with 2,5-2,7 up to values close to neutral. The content of Fe total is reduced with 240 down to 0,5 mg/l. The aluminium content after this experience is lower than the detection level (initial concentration of 98 mg/l). The content of sulphates is reduced to 300 mg/l. The reactant can be added directly to drainage without building of classic refining constructions.
Decrease of ground water pollution in regions for warehousing of mine heaps
The warehousing of coal mine wastes in Kizel Basin results in intensive impurity of underground waters. In regions of rock heaps the ground waters of upper water-bearing horizon have low pH values, heightened salinity, and also high contents of sulphates, iron, aluminium, heavy metals. For normalisation of underground water composition in areas of heaps it is offered to use of barium, compounds as a reactant and also disintegrated carbonate rocks, stacked in trenches at a zone of heap sewer. The experimental full-scale investigations have shown that the pH value of underground waters was increased with 1,8-1,9 up to 6,4 as a result of method applying on an experimental site. Salinity of water was decreased from 19-24 down to 3-4 g/l, as well as contents of the main polluting components (mg/l): sulphates - with 15000-17000 up to 1600-1800, iron - with 3900-4600 up to 1-2. The aluminium content at the end of experiment was below than the detection level of the analysis at initial concentration of 464 mg/l.
Decrease of sulphate content in service waters
On Holboldzhinsky coal open-cast arranged in Buryatia arid zone usage of service water for a watering are hindered by high contents of sulphates - up to 1200 mg/l inspite of the fact that its large reserves are massed in the carrier. The barium compounds were used according to the reduced technological scheme (fig.2) for a decrease of the sulphate contents. As a result of experiments the contents of sulphates were decreased to 440 mg/l (at maximum allowed concentration of 500 mg/l). The contents of remaining components did not exceed normative values.
Figure 2: Decrease of sulphate content in service waters of Holboldzhinsky coal open-cast (Buryatia) by barium compounds
Decrease of sulphate aggressiveness of underground waters
At planning activities on the territory of Gubakha chemical plant (Perm Region) the rocks of coal mine heaps of Kizel Basin with high contents of the different forms of sulfur were used. As a result of waterlogging in bulk grounds, on places higher than the locations of the foundations, the underground waters possessing sulphate aggressiveness to concrete were formed. The decrease of sulphate content in underground waters was conducted by applying of reactants containing barium (fig.3).
Figure 3: Decrease of underground-water sulphate aggressiveness by compounds of barium
The researches were conducted on two experimental sites. At the first one the reactant was entered into wells, at the second one - into a ditch. The overseeing for a water composition was conducted in wells arranged downstream of groundwaters. The experimental full-scale activities conducted on a site have shown that the underground waters possessing mean and strong sulphate aggressiveness became non-aggressive in relation to concrete as a result of method applying. The positive effect was saving within two years of observations. Besides the additional effect of ground stability increasing (Maximovich and Blinov, 1994) was monitored.
Protection of underground waters against pollution in slime storehouse areas
Warehousing of waste at Pashia metallurgical-cement works (Perm Region) resulted in impurity of underground waters at the territory of operational slime storehouse. In a pulp with alcaline reaction the great contents of Cu, Cd, Pb, Zn, Ni, Mo, As, Ti are detected. The metals form stable complexes with organic matters, migrating in alcaline conditions.
The pollution intensity of underground and superficial waters is conditioned by geological and hydrogeological conditions of the site of warehousing (fig.4). The underground waters are widespread in fissured karstic lime stones of Devonian which was overburdened by eluvial and deluvial clay depositions. The card of slime storehouse is located in old open-cast, where the clay soils are developed. The bottom of open-cast represents a rough surface of a roof of karstic limestones with clay sediments on it.
Figure 4: Schematic geological-hydrogeological section of the waste warehouse at metallurgical-cement works
By the writers, together with the lab of Geoenvironment Protection (the Moscow University) the complex multilayer screen is offered for a decrease of pollution intensity of underground waters (fig.5). The high layer is offered to create from local clay with gypsum component for decreasing of filtered solution alcalinity, that results in a hydrolysis and deposition of a part of heavy metals. The mean layer executing a trial function of pollution interception it is offered to create from a mixture of peat and pyrite wastes, creating anaerobic reduction conditions and linking metals in sulphides. The peat provides reactionary availability of pyrite grain surfaces. The lower layer consists of native clays and it is an additional sorbate screen. The laboratory researches have shown that the applying of a method provides protection of underground waters against the indicated contaminants on all period of scheduled exploitation (Maximovich et al., 1999).
Figure 5: Complex screens to protect groundwater at sludge sites
Usage of waste products of absorbite for removal of petroleum overflow consequences
The overflows of petroleum at emergencies on oil pipelines put essential threat to environment. The investigation of high-performance methods not requiring large financial costs is indispensable for reducing their consequences. The lab tests conducted in connection with emergency on the segment of Surgut-Polotsk oil pipeline of in the Perm Region have shown that the applying of multicomponent sorbent on the basis of waste products of absorbite the destruction of water-emulsified crude oil and deleting of oil, both in a volume, and from a surface of water, is provided. The part of sorbent will derivate a sorbing layer at the bottom after a deposition, which will work as a filter at presence of a filtration of water in a ground. The floating component of sorbent after its improvement can be removed from a surface of water. Sorbent is not toxic and can be incinerated after usage.
The experience on creation of geochemical barriers has shown, that it is necessary to conduct research of a composition and boundaries of impurity, typization of natural environments according to capabilities of their applying, estimation of a ground strata as natural chemical barrier, working out of models and computational methods of polluting components migration.
Usage of methods, tendered the writers, allows to avoid building of expensive refining constructions and to realize other nature protection measures used now. Usage of geochemical barriers demands considerably less costs by present methods.
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