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АРИДНЫЕ ЭКОСИСТЕМЫ, 2011, том 17, № 1 (46), с. 47-54
^ОТРАСЛЕВЫЕ ПРОБЛЕМЫ ОСВОЕНИЯ ЗАСУШЛИВЫХ ЗЕМЕЛЬ
УДК 551.583+586; 581.14
ЗАГРЯЗНЕНИЕ ПОЧВ ТЯЖЕЛЫМИ МЕТАЛЛАМИ ЗОЛОТО- И МЕДЕДОБЫВАЮЩИХ ПРОИЗВОДСТВ В ЮЖНОЙ АФРИКЕ
© 2011 г. К. Вайссенштайн, Т. Синкала**
*Германия, 33 775 Версмольд, ул. Веллингскамп, 41.
E-mail: [email protected] **Замбия, Кабалонга Лусака, Postnet bx. 161, P/B E835.
E-mail: [email protected]
Добывающая промышленность, особенно золота и меди, играет ведущую роль в народном хозяйстве южноафриканских стран. При оценке возможного изменения окружающей среды отходами этих предприятий необходимо учитывать их значение от загрязнения тяжелыми металлами и радиоактивными веществами, не только для воздуха, воды и почвы, но и для всей биосферы в целом. Главной целью работы являлось изучение почвенного загрязнения в окружении отвалов месторождений золота и меди.
В первом регионе - т.е. в районе медедобывающих производств в Китве (Замбия) -отходы часто сваливают в речные долины, а отвалы называют дамбами-хвостохранилищами. Эти плотины, в основном, без облицовки и, как правило, не имеют растительности. В результате водной и ветровой эрозии они являются источниками обширного загрязнения почв, воздуха, поверхностных и подземных вод. Результаты исследований кислотности и концентрации тяжелых металлов в поверхностных горизонтах почв показывают, что по мере увеличения расстояния от края отвалов (до 100 м) происходит снижение рН и максимальной концентрации тяжелых металлов (Cu, Co, Ni, As, Pb и Zn).
Структура отвалов бассейна Витватерсранд (Южная Африка) очень похожа на описанные ранее. Отличие их в том, что эти отвалы часто находятся на доломитовой породе, являющейся здесь основным водоупорным горизонтом подземных грунтовых вод. Воздействие шахтных отходов золодобывающих производств на загрязнение поверхностных почв тяжелыми металлами в регионе Дорнфонтейн в Карлетонвилле было изучено на разном удалении от границы отвалов (0 м, 50 м, 100 м, 200 м, 300 м, 500 м, 1000 м и 2000 м) и во всех главных направлениях ветрового воздействия. Почвенные образцы были изучены в лаборатории стандартным атомно-абсорбционным спектрометрическим методом. Анализировалась также кислотность почвенных образцов. Было установлено, что на самой окраине отвалов в результате эрозионной деятельности и низкой кислотности содержание тяжелых металлов оказалось минимальным. В тоже время самая высокая концентрация металлов, таких как Сг, Со, Ni, Аs, Си, Н§, U и Zn была обнаружена на расстоянии 100-200 м от края отвалов. В результате исследований авторы сумели выявить зоны негативных воздействий отвалов на загрязнение почв.
Обоснованные методы картирования ареалов загрязнения в географической информационной системе позволяют определять зоны загрязнения почв тяжелыми металлами вокруг отвалов золото и медедобывающей промышленности.
Ключевые слова: загрязнение почв, тяжелые металлы, кислотность почв, отвалы, Южная Африка, Замбия.
SOIL POLLUTION WITH HEAVY METALS OF GOLD- AND COPPER MINING
INDUSTRIES IN SOUTHERN AFRICA
© 2011. K. Weissenstein*, T. Sinkala**
*Germany, 33775 Versmold, Wellingskamp 41. E-mail: [email protected] **Zambia, Kabulonga Lusaka, Postnet bx 161, P/B E835. E-mail: [email protected]
Waste products of the mining industry are very important factors in the field of environmental pollution, soil pollution particularly. In the following case studies soil pollution with heavy metals in the surroundings of tailings dumps from gold- and copper mining industries, was investigated. In order to enhance knowledge about mine dumps and to provide relevant institutions in the region with identification methods, a GIS approach has been developed. The results of the studies made it possible to identify such surface soils of tailings dumps as had been severely polluted by heavy metals. This is demonstrated in two study areas in the SADC region.
Key words: soil pollution, gold mining, copper mining, South Africa, Zambia, tailings dumps, heavy metals.
Introduction
Wide areas of the SADC Region are affected by environmental pollution detrimental to industrial and agruicultural use as well as to the quality of nature and landscape. The sources of contamination are industrial facilities and waste sites as well as traffic, dumps and a diversity of other sources of hazardous substances. Chemicals used in agruiculture contributed heavily to soil pollution. The highest environmental risks are caused by toxic metals, polycyclic aromatic hydrocarbones, pesticides and nitrates.
Along with the development of the economies in the SADC countries, there is an increase in demands for environmental protection, especially in the mining areas. There appears to be growing confrontation among citizen groups, governmental agencies and members of the mining industry. The degree of conflict and its nature usually depends on the current land use and the estimated consequences of proposed disturbances. The conflict has centred in following issues: destruction of landscapes, degradation of the visual environment, disturbance of watercourses, destruction of agruicultural and forest lands, damage of recreational lands, noise pollution, truck traffic, sedimentation an erosion, land subsidence, vibration from blasting and air blasts, air pollution, soil pollution etc.
These impact processes require a proper study in order to appreciate the extent of environmental degradation. Using GIS as a tool in this study, it is possible to create a complete survey of mine dumps in the study areas.
In order to enhance knowledge about mine dumps and to develop and provide methods for the relevant institutions in the region, two case study areas were identified (Fig. 1):
Copperbelt Area - Zambia - copper mining;
Carletonville Area - South Africa - gold mining.
Problems associated with gold mining in South Africa - A case study in the Wonderfontein Basin (Far
West Rand)
Gold mining activities in South Africa are mainly concentrated in an area known as the Golden Crescent. It is an area stretching from the south east of Johannesburg in the vicinity of Springs, through that city further west and south west over a distance of approximately 400 kilometres to the south of Welkom.
The gold is contained within the conglomerates of the Witwatersrand Supergroup and the deposits can be dated at approximately 2,800.000 to 2,300.000 years BP (Kent, 1980). The gold bearing reefs also contain minerals such as pyrite, traces of silver and other metals including variable amounts of uranium.
This investigation will concentrate on a portion of an area known as the West Rand Goldfields. These Goldfields are situated to the west and southwest of Johannesburg and east northeast of Carletonville.
The upper Mooi River drains the present day area, particularly by the so-called Wonderfontein and Loopspruit tributaries. In the study, only problems associated with mines in the Wonderfontein tributary will
be discussed.
The gold ore is crushed and the gold and other minerals in the ore are extracted through flotation processes. The resultant slimes are then deposited in built up slime dams. The quality of extraction has improved through the years. In some of the older slime dams the amount of gold still present in the slime is enough to enable the mines to rework the slimes for the recovery of the gold still present. Most of the mines in the area are fairly deep and gold is mined at depths ranging from approximately 1 to 4 km.
Various environmental problems are caused by the mining industry in the study area. The more important problems are associated with the dumping of waste in the form of massive rock dumps and Slime dams (tailings). Not only are these dumps aesthetically unpleasing but they are also responsible for pollution plumes. Slime dams occupy an area of approximately 25 square kilometers in the Wonderfontein study area.
In order for Sidewalls of the dams to be as dry as possible, it was decided by some of the mining companies to locate the slime dams on the dolomite. This results in a fairly large amount of seepage into the underground aquifer. Not only the original moisture in the slimes, but also infiltrated rainwater can eventually land in the underground water. It is difficult to quantify the amount of water that eventually lands in the underground aquifer. Some of the slime dams were even constructed over existing sinkholes. In order to try and stabilize these dams, large amounts of slimes are pumped into existing sinkholes.
Fig. 1. The Map- scheme of researches in Southern Africa: the points designate places of sampling.
Рис. 1. Каросхема проведения исследований в Южной Африке: точками обозначены места отбора
проб.
The next environmental problem caused by the mining activities in the study area is related to the radioactive issue (Radioactive Monitoring Report, 1997). As has been mentioned in the introductionary paragraph, a significant amount of uranium is present in the ore being mined. H. Coetzee et al. (1997) had used surface radioactivity to trace radioactive precipitates in the vicinity of mining activities. Data from the Radioactive Monitoring Committee (1997) confirms that there is radioactivity present in samples obtained from localities in the study area. In 2006 a report from Coetzee H, Wind F. and Wade P.W. confirms the high risk of radioactive water pollution in the Wonderfonteinspruit Catchment.
Methodolgy and Analyses - Case Study South Africa
For the purpose of the case study soil samples were collected to identify the impact from Tailings -Dump - Carletonville - Doornfontein Mine Dump on surface soil pollution at several distances from the dump. Samples were taken from the soil surface of ca 0.25 qm at depth of 0-5 cm. To make sure that the results are comparable, all samples were taken under grassland.
Vegetation parts were removed, and samples were dried and sieved. The applied analytical technique used to determine the total concentration of specific elements in such samples was atomic absorption spectrometry. The analytical results are summarized in table 1. The measured ph (KCL) in the samples showed that the tailings material was highly acidic, with levels between 4.5 and 5.5, the acidity increased slightly with increasing distances from the edge of the dump, as follows: to 4.1 at 500 m distance, and 4.5 at 2000 m distance.
Table 1. Surface soil pollution (in ppm) by Doornfontein Mine Dump, Carletonville. Таблица 1. Загрязнение поверхностного слоя почвы (в ppm) сбросом отвала Дорнфонтейн в Карлетонвилле.
No Direction, distance in m Co As Se Au Hg Pb U pH (KCL)
1-SE edge 16 13 25 0 0 9.1 6.3 2.7
2-SE58 39 5 13 0.1 0 19.7 8.2 4.2
3-SE83 37 7 26 0.1 0 20.8 4.4 4.1
4-SE110 46 10 26 0.2 3.7 24.4 4.0 4.1
5 SE200 43 7 18 0.1 0 19.5 4.7 4.0
6-SE350 31 9 23 0.3 0 31.3 3.3 4.1
7-SE400 33 7 22 0 0 11.9 2.1 4.1
8-SE500 25 5 11 0.1 0 8.5 1.9 4.1
1-Nedge 4 23 0 0 22.9 8.9 2.3 3.6
2-N50 39 9 8 0.2 0 16.2 4.7 4.1
3-N100 41 11 20 0 0 16.3 3.7 4.3
4-N200 38 39 22 0.5 0 23.1 15.9 3.9
4a-N200 19 42 9 0.4 0 18.3 18.9 3.9
5-N300 44 23 0 0.4 0 26.0 15.4 4.0
6-N400 44 14 3 0.7 0 12.9 6.6 4.4
7-N-500 46 26 0 0.3 0 18.5 21.9 4.1
8-N-edge 51 208 35 0.6 0 55.8 57.2 2.8
9-N1000 54 6 1 0.3 1.2 13.4 31.1 6.4
P3 60-60 cm 178 8 0 0.4 0 78.5 3.3 4.3
P2 10-30 cm 81 10 32 0.8 4.4 31.7 5.2 4.1
P1 0-10 cm 12 30 19 0 1.1 9.9 12.3 3.3
10-N1500 40 10 31 1.0 0 10.0 10.9 7.1
11-N2000 33 3 3 0 0 20.1 2.0 4.5
An interesting finding was, that at the edge of the dump, the concentration of heavy metals like Cr, Co, Ni, As, Pb, Cu, Hg, U and Zn is almost lowest, and highest at 100 to 200 m Distance from the edge of the dump. The minimum level of heavy metals was measured in the dump material itself and often at the edge of the dump.
Two possible reasons are assumed. Firstly, it may be the wash out effect of the suspended solids with wind and water erosion. Since the slope of the dump is not revegetated, these processes are supported by the special climatic conditions of the tropical climate.
Secondly: the very high acidity of this soil samples increases the mobilization of heavy metals in soils
(table 2). Toxic heavy metals like As and Hg are washed out into ground and surface water starting from pH 4.5. This is a major risk for human health in the region.
Table 2. Values of pH for a starting Mobilisation of heavy metals in soils (Blume, 1992). Таблица 2. Значения pH для начала растворения тяжелых металлов в почвах (Blume, 1992).
Cd Zn Ni Co Al Cu As Cr Pb Hg
6.5 6.0-5.5 5.5 5.5 5.5 4.5 4.5-4.0 4.5-4.0 4.0 4.0
Problems associated with Copper Mining in Zambia - a case study in the Zambian Copperbelt
Mining and smelting in Zambia dates back to A.D. 650 when operations were on a village scale and were replaced by large scale operations in the first half of the 20th century. In 1928, Anglo - American Corporation initiated high level exploration and this was sustained until 1940 when concessions ended. By 1969 a combined production of 720,000 tons metal copper from discovered deposits was achieved in the Copperbelt (EMP, 1996).
The area of interest encompasses the Nkana Central, Nkana South Orebody (SOB), Mindola, Chambishi and Chibuluma mines. These mines are located in and around Kitwe, the third largest city, situated some 400 km north of Lusaka, the capital of Zambia. Kitwe and its satellite towns of Kalulushi and Chambishi have a combined population of 490,000 people.
The mines are situated on the north-eastern and south western sides of the Chambishi-Nkana Basin, which lies to the west of Kafue Anticline. The basin is traversed and drained by streams such as Mwambashi, Kitwe, Mindola, Uchi, Wusakile, Luanshimba, Kamuchanga, Mululu, Kalulushi, Kankashi and Chibuluma, which eventually flow into the Kafue River. This is not only the most impostant river as it supports about 40% of the 9 million People, but also the most polluted one in Zambia, mainly due to mining activities in the Zambian Copperbelt in the Upper Kafue and industrial and agruicultural activities in the Mazabuka and Kafue towns in the Lower Kafue.
The Nkana Mining Area is some 11217 hectares in extent and it is located west of Kitwe, which is situated approximately in the centre of the Zambian Copperbelt. The Nkana Mining Area comprises mainly the South Orebody (SOB), Nkana Central and Mindola Underground Mines.
Metallurgical processing of ores for copper/cobalt extraction has produced, over a period of over 30 years of mining, tailings dams covering a significant surface area. Tailings dumps, most of which are not operational, exist in the Nkana Division area covering a total surface area of 1579.9 ha and contain a total of 224.82 million tones of sulphide ore waste.
Methodolgy and Analyses - Case Study Zambia
Surface soil samples were collected to identify the impact of pollution by tailings dumps 52 and 60 on surface soil at several distances from the dumps (The Soils of the Copperbelt Province,1992). Samples were taken from the soil surface of about 0.25 qm at depth 0-0.5 cm. To make sure that the results were comparable, all samples were taken under grassland.
Vegetation parts were removed, and samples dried and sieved. The applied analytical technique used to determine the total concentration of specific elements in such samples was atomic absorption spectrometry. The analytical results are summarized in table 3. The measured ph (KCL) in the samples showed that the tailings material was alkaline with pH 7.2-8.3. Since the pH of the neutral soils in the area was quite acidic, with levels between 4.1 and 5.5 (Chirwa, Sichinga, 1996) the acidity was higher with increasing distances from the edge of the dump.
An interesting finding is that in our case the concentration of copper heavy metals like Cu, Co, Ni, As, Pb and Zn is almost highest in 100 m distance from the edge of the dump. The minimum level of heavy metals was measured in the dump material itself and often at the edge of the dump. A possible reason may be the washout effect of the suspended solids with wind and water erosion. Since the slope of the dump is not
revegetated, these processes are supported by the special climatic conditions of the tropical climate. Since in the Copperbelt these dumps are often situated in the flood plains of the river basin, there are high inputs of suspended solids like toxic heavy metals into the streams. The increase in siltation processes is a known fact of environmental degradation due to water erosion of mine dumps since there are sensitive landuses such as townships, in the impact area - the effect on human health should be considered in further investigations.
Table 3. Surface soil pollution of heavy metals (in ppm) of a tailings dump Kitwe (Zambia). Таблица 3. Загрязнение почв тяжелыми металлами от сбросов отвалов в Китве (Замбия).
Direction and distance in m Pb Cu As Ni Zn Co pH (KCL)
TD 52 6 3380 13 19 26 405 8.3
N 77 14436 22 29 152 983 6.8
N50 50 9372 60 42 269 1722 7.5
N100 87 21433 24 25 105 454 5.7
W 20 3255 15 21 55 530 7.4
W50 60 13392 26 32 119 797 6.6
W100 45 10294 16 22 80 519 6.7
S 12 3094 9 19 38 332 7.4
S50 45 9245 17 27 134 664 6.7
S100 32 9045 11 22 66 389 6.4
TD60 0 3437 3 14 4 147 7.2
S 16 3185 4 20 41 316 6.9
S50 - - - - - - 5.2
S100 44 7339 13 61 84 286 4.0
W50 9 1332 5 54 29 74 5.3
W100 434 11833 20 50 1312 631 4.2
N 6 1627 4 63 24 333 6.3
N50 7 1402 5 83 20 122 5.1
N100 13 1935 5 92 30 115 4.9
Reference soil 10 885 3 16 16 33 4.2
Description of a GIS approach - mapping the pollution level in the vicinity of tailings dumps in
the selected mining area
The main aim of the case studies is to develop modules in environmental analysis of tailings dumps, methods of identification and evaluation of environmental impacts of dumps within a GIS-based environmental management system. In this regard, the experience with the KatBo System (Zierdt, 1996), which was developed and used for monitoring and studying environmental problems related to copper mining activities of the Mansfeld Region in East Germany, has been integrated in the project. (Weissenstein et. al, 2000).
How are Mine Dump integrated in the GIS - System?
Several steps to inventories impact zones of mine dumps are shown in Figure 2, Table 4. As usual data collection is necessary, at first one need to define the input criteria - there can be anthropogenic and natural criteria. To specify the type and size of the tailings dump - it is important to analyse topographical maps, aerophotos or to do field mapping. Natural input criteria are information about type of relief, main wind direction, vegetation and soil. These main factors influence the distribution of pollution in soils. Two types of migration of pollution can be distinguished - pollution areas of large dumps and areas of dumps from
small scale mining. The last ones are often situated in agricultural areas and have short distances between themselves. There often is a high content of ore in the surrounds of the dump. The areas of these dumps will be mapped as small mine dump fields with a maximum impact area from the edge up to 250 m.
Large Dumps Small Scale Mine dumps
Fig. 2. Overview of phases to inventories environmental impact zones of mine dumps.
Рис. 2. Совокупная зона воздействия на окружающую среду нескольких источников загрязнения.
Table 4. Manual for implementation in a GIS. Таблица 4. Руководство для работы в ГИС.
Input Criteria Anthropogenic Criteria Natural Criteria
Type and size of Mine Dumps Type of Mine Dumps Large Dumps (more than 1 ha) Dumps from Small Scale Mining Relief Vegetation Soil Type
Data Source Data Collection Topographical Maps, aerophotos Field Mapping Environmental Agency Data Collection
Migration of Pollution Large Dumps Wind Erosion Pollution with heavy metals Dumps from Small Scale Mining High contents of ore in the surrounds of the dump Often situated in agruicultural areas Short distances between different dumps
Identification of the Impact Area from the edge of the Dump The pollution impact from large dumps can be predicted at 500 m from the edge of the dump. The areas of this dumps will be mapped as small mine dump fields with a maximum impact area from the edge up to 250 m.
Manual for implementation in a GIS See figure below
Risk Assessment For example: Reference concentration of heavy metals (Cu) in soils in the Kitwe Study Area -Zambia: 0-10 m 15000 ppm 10-100 m 10000 ppm 100-500 m 1000 ppm
The material of larger dumps (tailings) is very fine und is migrating with wind and water erosion. The main pollution impact of these dumps can be predicted at 500 m from the edge of the dump. For further risk
assessment analysis a reference concentration of heavy metals in soils should be measured in 1500- 2000 m from the edge of the dump. For implementation of zones of impact of dumps into a GIS typical dumps should be selected and soil pollution further investigated. These results should be applied on similar dumps in the study area.
Conclusions and Outlook
The present results represent part of the study as has been carried out only. For the purpose of evaluating any impacts of tailings in terms of heavy metal pollution of surface soils, different zones of pollution around the sources have been distinguished - such as can be used in similar areas elsewhere, as a without-sampling-method in order to map the pollution level in the vicinity of tailings. The material of larger tailings dumps is very fine und is subject to migration with wind and water. The main impact of these dumps in terms of surface soil pollution can be predicted at 500 m from the edge of a dump. For further risk assessment analysis a reference concentration of heavy metals in soils should be measured at 1500 - 2000 m from the edge of the dump. For the implementation of zones of impact of dumps into a GIS, typical dumps should be selected and soil pollution further investigated. This method can be used for mapping and for tracing back soil pollution trajectories to their original sources.
It is clear from the above discussion that there are indeed several environmental problems in the study areas due to mining activities (past and present). When comparing the studied area to the total area where gold mining occurs in South Africa and the whole of the Copperbelt of Zambia, one realizes that the extent of the problems is potentially larger still. Solutions to these problems can only be achieved through concerted research efforts.
During the last 10 years a lot of research work has been carried out in both study areas - in the South African case study area particularly, data have been integrated in a GIS and an EMS. The experience of national as well as international agencies concerned with environmental problems as described is indeed of prime importance.
Literature
Blume H.P. 1992. Handbuch des Bodenschutzes. Ecomed Verlag, Germany. Pp. 277-303.
Chirwa S. Sichinga A. 1996. Status of Vegetation and Wildlife at Nkana Mine. Division of Forestry
Research. Kitwe, Zambia. Pp. 12-16. Coetzee H, Wind F., Wade P.W. 2006. An Assessment of Sources, Pathways, Mechanisms and Risks of current and potential future pollution of water and sediments in gold mining areas of the Wonderfonteinspruit Catchment. WRC Report 1214/06. Pp. 23-54. Coetzee H., Terblanche O., Stettler R. 1997. Electromagnetic and gravity investigation of a suspected pollution plume at Doornfontein Gold Mine. Council for Geoscience-Geological Survey Report No. 1997-0239. Pretoria. Pp. 105-106. Environmental Management Plan - EMP. 1996. Nkana Division. SRK Report 229803, ZCCM. Pp. 23-24. Kent L.E. 1980. Stratigraphy of South Africa // Handbook 8. Part 1. Department of Mineral and Energy
Affairs. Geological Survey, Government Printer Pretoria. Pp. 31-32. Radioactive Monitoring Report. 1997. Radio Activity measurements in the Mooi River Basin. Unpublished report. Pretoria Pp. 19-24.
The Soils of the Copperbelt Province. 1992. Memoir accompanying the 1,000.000 Soil Map, Soil Survey
Report 153 by L. Chileshe. Pp. 21-32. Weissenstein K., de Villiers A.B., Fruehauf M., Sinkala T., Coetzee H., Freyer K., König W., Warthemann G. 2000. Mapping and Evaluation of Pollution in Mine Environments in Southern Africa using GIS and EMS // Computer science for Environmental protection 2000, 12 th International Symposium. Bonn (Germany). Vol. 1. Pp. 103-113. Zierdt K. 1996. Darstellung der Methodik zur beprobungslosen Ausgliederung von Verdachtsflächen großräumiger Bodenkontaminationen am Beispiel des Landkreises „Mansfelder Land" // Hercynia. 1969. No. 1. Pp. 117-124.
APHflHBIE ЭКОСHCTEМBI, 2011, tom 17, № 1 (46)
