Monday, 1 December 2008

GREENING OF COPPER MINING AND ORE DRESSING

A CASE STUDY OF COPPER MINE IN BUCHIM, R. OF MACEDONIA



S. Hadzi Jordanov, A. Dimitrov, D. Slavkov, P. Paunovic and Z. Tasev

Faculty of Technology and Metallurgy, University UKIM, 1000 Skopje, R. of Macedonia

shj@tmf.ukim.edu. mk






Abstract




Copper mining, ore dressing and flotation in Buchim's mine (South-East part of the R. of Macedonia) in the past 28 years resulted in:

1. Production of one million tons of Cu-concentrate and two hundred thousand tons of copper respectively,

2. Production of twenty tons of gold and twenty tons of silver,

3. Employment of more than one thousand workers and other staff that did contributed significantly to the improvement of the economical situation of the region, traditionally oriented towards agriculture.




Besides the social impact, the intensive activities of mining, ore dressing and ore flotation in such a long period produced as well an visible environmental impact, i.e.:

1. Natural landscape was degraded by the open pit mine, as well as by the growth up of enormous heaps (some 120 million tons) of overburden tailings, as well as an pond (artificial lake) were flotation tailings (totaling some 100 million tons) are discharged permanently, while flotation process water is recycled between the flotation unit and the pond in open concrete canalette.

2. Flotation solid tailings from the dam's crown are spread over the nearby villages and agriculture areas by the blowing wind.

3. Wastewaters, both surface and underground, from flotation, acid mine drainage etc. did contaminate the local watercourses and aquifers. The contamination was further spread to the next watersheds, and finally ends in the Aegean See, thus causing transboundary pollution.




In order to prevent further environmental deterioration the following actions were taken out or are planned to be soon realized:

1. Identification and risk assessment of the pollution generated by mines operation,

2. Remediation of the past and prevention of future contamination,

3. Complex and maximum exhaustive and or immobilizing treatment of mining and flotation tailings; creation of a closed loop production practice; possible use of overburden tailings as raw material instead of their discharge as waste.




Key words: Copper, mining, flotation, contaminated wastewaters, solid pollutants, prevention, remediation





Introduction


In general, copper mining and ore enrichment is accompanied by generation of significant quantities of waste. In case of open pit mining large volumes of tailings (overburden) are generated and dumped, that further increases the total quantity of solid waste. It is no wonder that mining activities are listed as the major generator of solid waste.



According to some recent analysis, plants where copper was mined and further treated did accumulate such volumes of waste and effluents that their environment is recognized as the most contaminated worldwide. All of them are situated in underdeveloped countries.



Exploitation of complex sulfide ores in the case of Buchim mine (in the South-East part of the R. of Macedonia) in the past 28 years resulted in production of more than one million tons of Cu-concentrate and two hundred thousand tons of copper metal, respectively. As a by-product some twenty tons of gold were extracted and nearly the same quantity of silver. About one thousand of workers and other staff were employed in the mine. For a small country as the R. of Macedonia is, this is significant contribution to improvement of the economical situation in this, traditionally agriculture region.



This production was accomplished by a complex treatment that, besides open pit mining and ore dressing, includes also flotation. All of these activities, besides their economical and social impact, had their pronounced environmental impact, as expressed by (i) degradation of natural landscape by both open pit mine hole and the formed enormous heaps (containing

some 120 million tons of mining tailings), (ii) degradation of landscape by the erected dam and pollution of nearby villages and agriculture areas by solid particulates (flotation tailings, totaling some 100 million tones) blown up from dam's crown and wall, (iii) degradation of landscape by the concrete canalette that connects the flotation unit with the artificial pond and (iv) contamination of local watercourses and aquifers by wastewaters generated from flotation unit, open pit hole and acid mine drainage that occurs in the heap. When dealing with such enormous volumes of water, leakage is inevitable. Atmospheric precipitations further contribute to the formation of wastewaters.



The origin of pollution


Enrichment by flotation of low-grade ore (typically 0.2 - 0,25 % copper only) is achieved by removal of copper bearing fine particles from the rest of mixed sulfide ore, so that copper concentrate is produced that contains some 20% of copper. In order to perform this enrichment enormous quantity of water is needed. Water economy imposes multiply use of water, so that water is recycled between the flotation unit and a pond of adequate capacity. The pond was formed by construction of a dam. Practically all segments of the enrichment process are accomplished in one water circulation cycle, such as (i) separation of copper sulfide minerals and their collection into a concentrate, (ii) gravitational transportation back to the dam of flotation tailings suspended in water, (iii) settling down of suspended particles and (iv) pumping of the clarified water again back to the flotation unit.



From the environmental point of view, such an intensive and spread over a significant land area water handling process inherently has some negative consequences. Recycled water accumulates residues of both treated ore and used flotation agents.



Other wastewaters are formed as a result of occasional leaching of copper ore in the open pit and in the overburden and waste rock dumps. The main source for the generation of acid mine drainage is the natural oxidation of sulfide minerals exposed to the combined action of water and oxygen, accompanied by bacterial action. A quantity of some 150 million tones of open pit overburden and waste rock material accumulated during the past mine operation. It contains up to 0.12% Cu that is continuously oxidized and leached with the rainfalls. This wastewater appears to be the most contaminated with Cu2+ ions of all hot spots, as shown later.



Part of these contaminated wastewaters escapes or is disposed into nearby rivers without any treatment, and finally reaches the Vardar River. After some 100 km all the contamination ends in the Aegean See, near the Gulf of Thessalonica.




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