PROCEEDING OF THE INTERNATIONAL CONFERENCE ON

EUROPEAN ENVIRONMENTAL POLICY

AND THE CASE OF CYPRUS MINES

ENVIRONMENTAL RISKS OF MINING USING CYANIDES AND ACIDS

Emur Henden

Ege University, Faculty of Science, Department of Chemistry, 35100 Bornova, Izmir, Turkey

ABSTRACT

Mines are wealth of a country beneath the soil and mining adds a lot to a country economy when done properly. However, until nineteen seventies understanding our environment and impact of environmental pollution on life was not enough. Most of the detailed standards on environmental pollution have been introduced in the last 30 year.  So, most of the earlier miners did not bother about environmental pollution. We can ,therefore , see several deserted mining area left unprotected causing serious risk for the environment and life.  CMC mine remains in Gemikonagi and Karadag regions of Lefke  are of the most serious examples of such cases.

Mining when realized  by physical means , example; crushing, grinding and water extraction and so on, does not usually increase the risk  of chemical pollution significantly. However , when chemicals are introduced  at the mining or mine processing process the risk of  chemical pollution also increases drastically. In such cases, nowadays, very strict  measures are required by the regulations to be taken. Such mining and mine processing plants are better be considered as chemical plants rather than  simple mining.

ACIDS AND CYANIDES IN MINING

Acids are used for extraction of metals from minerals  like copper as in the CMC case and sodium cyanide is used  for the extraction of gold and silver. Because of  these extractions processes environmental pollutions with heavy metals and cyanides  are usually observed if strict measures are not taken. It is well known that cyanides are of the very fast acting toxic substances known and great care are to be taken when used.

Cyanides may cause water air and soil pollution. Some of the metals are toxic even when enters into body at trace level. They show acute toxicity when taken at relatively larger amounts and chronic effect when taken slowly at smaller amounts.   They deposit in the body mainly in liver, kidney  and cause liver deformation, renal failure and many other deficiencies. They cause their harm in a very long period and ,therefore, are usually not detected.  Some of the metals are even accepted to be carcinogenic.eg., selenium and arsenic. Of these toxic metals lead, cadmium, mercury, arsenic, antimony, nickel, copper and berillium take more attention. However, some of the metals which are  normally accepted as nontoxic may become very toxic when converted to some of its other chemical forms in the environment usually by the effect of some specific bacteria, eg.,inorganic tin compounds are not toxic, but may be converted to tributyltin in the environment and becomes very toxic. Moreover, some metals even when present at very high concentration in soil may not be bioavailable for the plants. Toxic metals in such chemical forms are much less dangerous for the plants and thus animal life  compared to their bioavailable forms. Therefore, for soil pollution testing total and bioavailable metal contents are both need be measured.

KARADAG MINING AREA

In this area remains of underground mining shafts, leaching ponds, and contaminated soil piles exist.  These  wastes may contain various metal sulphides  and metal sulphates incluiding that of toxic metals , eg; copper, arsenic, mercury . The soil pH is very low and, therefore, can be defined as hazardous. Leaching of the toxic metals contaminates the water reservoir in the region. Unacceptably high concentrations of aluminium, iron and manganese were reported (1). These type of mine wastes may form natural acid leach by a chemical reaction.

  FeS₂   + 3.5 O₂  +  H₂ O  ®  Fe²⁺  +  2SO₄ ^2-  +  2H⁺

Similar chemical reaction takes place with copper, lead and other metal sulphides, releasing water or acid leachable iron, copper, lead and other metal salts. Moreover ,the sulphuric  acid  formed reduces the soil pH and dissolves  also other minerals  causing toxic metal contamination of soil, water and ,thus plants .

GEMİKONAĞI AREA

During the time of mining,1913-1974, raw ore was brought to Gemikonagi mine processing area. At present, unattended and unprotected contaminated wastes  are located in this area, including several tailing ponds, waste water clarifiers, row copper ore piles, waste piles, and remains of mine acid processing plant. Another serious  waste is the possible cyanide containing yellow waste pile.

Chemical reactions are still going on in some of the waste ponds. Acid generation and reaction of acids with wastes are visible. The solid and liquid wastes are very highly polluted and acidic. Liquid draining to sea has a pH as low as 2 and contained at one time 121- 149 mg/L copper, and its electrical conductivity was very high, 8 mmho/cm (Henden, 1999). These waste water drains from the polluted area are serious sources of sea water and sediment pollution.

The yellow waste piles are known to be the wastes of gold extraction process with cyanide. Gold is usually extracted from powdered minerals using about  800-1000mg/ L  sodium cyanide solution  at pH  10-11, as gold cyanide  complex ion. However, other cyanide complexing metals are  also converted to their water soluble cyanide complexes during the gold extraction. These include zinc, nickel, copper, silver, iron,  mercury, cobalt..etc., according to the following chemical reactions:

4 Au_(s)   + 8 CN₍^-_aq)     +  O₂  + 2H ₂O   Û   4[ Au(CN)₂ ] ^- _(aq) +  4OH^-_(aq)

                         Fe(OH)_{2 (s)} +  6CN_(aq)^-  Û      Fe(CN)₆⁴_(aq)^-    + 2 OH^-_(aq)

                        Cu(OH)_{2 (s)} +   4CN_(aq)^-  Û   Cu(CN)₄²_(aq)^-  +   2OH^-_(aq)

Moreover, because of the high pH used for gold extraction other toxic metals like

arsenic and antimony are also extracted  mainly as AsO₄^3-  and SbO₄^3-. Inside the yellow waste piles   all these highly toxic water soluble metal complex ions may exist at untolerable levels.  All these metals exist originally in the minerals ,but they are either stable  or blocked within the mineral structure so that they are not dissolved in water under environmental  conditions . However, when minerals are treated with cyanide at high pH  solutions, all these heavy metals are converted into their water soluble compounds, thus become bioavailable and toxic to life. Free cyanide like sodium cyanide, is not very stable in the environment under unprotected conditions and decompose by the effect of air. However, heavy metal  cyanide complexes are much more stable and may exist for years. Since gold in minerals is extracted with very  high concentration of cyanide all the natural bacteria  in the soil die and, therefore, biodecomposition of cyanides in the wastes do not take place. Taking into consideration of  the possible existence of  the  high concentration of  cyanides inside the yellow piles ,these piles should  not be  destroyed until careful analyses are carried out. If destroyed without taking any care, water pollution with cyanides and toxic metals , and air pollution with very toxic HCN and dicyan,(CN)₂, gases may take place. Therefore, these yellow piles should be analysed for cyanides and if cyanides are present, the waste soil should be treated  to destroy cyanides and to stabilize  the heavy metals.

REFERENCES

1. It is clear that both Karadag and Gemikonagi regions are very heavily polluted and need to be cleaned as soon as possible.

2. Dangerous  pollution exist in soil, surface and possibly ground water, in sea water and sediments and in air, at least, in the mine processing area and the ponds.

3. The Gemikonagi mine processing area is highly dangerous  even to walk inside. This area should be protected and free walking  inside should be forbidden.

4. Before beginning reclamation of the area, soil, surface and underground water and  plants around  and sediments should be analysed in details. Types and concentrations  and even, in some cases , chemical species of the toxic metals are to be determined in order to decide the measures to be taken for treatment and reclamation.

5. Economically valuable wastes or mineral remains are to be determined , and if present  sent to appropriate plants for use.

6. Waste water should be avoided  to reach the sea and fishing in the close area should be forbidden.

7. Further pollution of water in the Water reservoir should  be avoided. For these purpose acid drain to the reservoir can be avoided. However, if the present sediments in the reservoir continue to contaminate the water they may be cleaned out from the bottom.  Water quality at present is not good enough for irrigation. If necessary, simple chemical measures  can be taken to clean and obtain a much better quality water for irrigation if the reservoir protection delays.

8. Methods of treatments of such wastes are well known. However, since the capital required for all these analyses  and treatments are very high, supports of international organizations and CMC need to be search for.