Lance ConnellAddias Mervin

Monique M. Nurse

There are two methods of extracting gold from oreVat leaching involves mixing extracted

ore with a CN solution in large vats.Heap leaching involves piling ore into

large heaps and then spraying a CN solution on the heap and allowing the CN solution to trickle through, stripping the gold from the ore.

Gold is readily dissolved by cyanide. Most the world’s gold supply is found in low

concentrations in nature and must be dissolved from ore to be acquired. Less than 10 grams/ton of ore excavated.

NaCN is typically used as a solvent and diluted to a concentration of 0.015 – 0.035% NaCN.

Gold extraction in the Aurul plant was approximately 700 mg/liter of slurry.

Most gold mines are often found near water sources since water is used to dilute the NaCN to acceptable levels for mining.

Having a readily available supply of water cuts down on transportation and other costs associated with water needs.

In the case of Baia Mare, the tailings from the old Meda ponds, used for gold extraction are combined with water to form a slurry that was pumped to a processing plant where more CN is added if needed. Then the slurry is pumped the rest of the 6.5 km to the new Aurul gold mining site.

The processing plant was in charge of receiving the slurry from the chronically leaking Meda ponds, assessing the level of cyanide in the slurry and adding more if needed.

Cyanide levels were monitored and if needed brought to an acceptable range of 0.015 – 0.035% NaCN within the slurry and then pumped into the new tailing dams.

Extraction of gold as well as other precious metals were done at this site and remaining tailings were then pumped to the dams.

To maximize gold extraction, tailings from the new dam were pumped back to the plant for further extraction of extremely low levels of gold and were then pumped back to the tailing dam.

Tailing dams hold CN treated ore wastes from which gold has been removed.

The Aurul tailings contained concentrations of 400 mg/liter of CN and concentrations of free CN of 120 mg/liter.

Tailings typically contain 0.60 g/ton of recoverable gold.

The Aurul tailings also contained high concentrations of heavy metals such as: iron, cooper, arsenic, cadmium, lead, nickel, and manganese.

The new Aurul tailing dams were built to replace the chronically leaking Meda ponds located near Baia Mare.

The dam covered 93 hectares and was 20 meters high.

The dam was built to take advantage of the sloping hills in the area.

Lining the dam was a plastic liner that afforded 0% discharge into the surrounding area.

The dam wall was constructed on top of a starter dam, with the new dam wall added as more slurry was pumped in. The idea was to have the tailings form the wall as more and more slurry was deposited into the dam. Hydrocyclones were added to assist in lining the dam wall with the tailings.

The dam wall was constructed so that the dam could deal with storm run-off up to 118 mm.

A decanting well was fitted in the center of the dam so that the slurry could be re-circulated back to the processing plant.

Drains were also created as additional protection against seepage into the environment.

Large businesses often find it beneficial to found operations in areas where governmental regulations may not be up to par.

Many environmental organizations have pointed this out as a major contribution to the cyanide spill in Baia Mare.

The Serbian Minister of Environment announced that he will be suing the company responsible and asks for an international trial to be held.

The Baia Mare area received approximately 120 mm of snowfall and 40 mm of rain from mid-December until the end of January.

The dam was only able to accommodate storm run-off up to 118 mm.

On January 30, 2000, due to the precipitation in the area the dam crest was flooded and over 25 meters of the dam wall was washed away.

•Marine Life•Plant Life•Water compositional change

Estimated 80% of all fish in the Tisza River died.Thousands of tons of fish died.Some fish were found to contain 2.6 mg of cyanide per kilogram of weight.

Extensive damage done to the river’s ecosystems and its fauna, affecting birds, and carnivores.The Cyanide plume that traveled through the rivers was 100 times more concentrated than the limit value for drinking water in the region.30%-60% plankton killed

The initial affect of the high Cyanide concentrations on the ecosystem was devastating, however due to Cyanide’s short lived presence in the water the environment was able to begin recovery.

Heavy metals persist in the environment and bioaccumulate in living organisms.

Since the incident the heavy metals have accumulated in the sediments are collecting 6-10km downstream of Baia Mare. They will continue to be washed downstream and spread throughout the river system.

The rivers that fed or were fed into the Tisza river, have very high heavy metal concentrations, and the concentration is increasing over time.

The plume traveled down the length of the river, into the Danube river and then into the Black Sea by which time it had significantly diluted .

The waters pH would have changed from the chemical reactions taking place within it.

Cyanide comes in many formsThe most lethal being that of Hydrogen cyanide , HCN, which is lethal to humans at 1.1 mg/kg in the blood.In the plume that sweeped through the river, Cyanide most likely formed complexes with heavy metals associated with it.Even though free floating Cyanide is readily degradable when it forms into a complex ,dilution and degradation become complicated.

Complexes: Ferrous ferrocyanide (Fe[FeCN6]) and ferric ferrocyanide (Fe4[FeCN6]3). And Copper ferrocyanide (Cu2[Fe(CN)6])

Cyanide in nature Time in the environment Reactions in the water, and wildlife Forms of cyanide.

The behavior of heavy metals in nature

What is difficult about removing these contaminants?

Where does it collect?

The Cyanide plume was measured for 2000km from the point of origin to the Danube delta.

Free Cyanide is biodegradable, and as it continued downstream it was easily diluted, this made the ongoing effects of the plume short lived.

The oxidation of cyanide, can produce cyanate which is less toxic, and readily hydrolyzes to ammonia and carbon dioxide.Cyanide also reacts to Sulfur which is found in the ore and also in the wastewater from the tailings dam. Cyanide and sulfur react to produce thiocyanate, which degrades into cyanate and sulfuric acid.

The sulfuric acid would create Hydronium ions which would allow for the further degradation of the cyanate.

Hydrogen cyanide gas which has the ability to form during these reactions does not occur, because hydrogen cyanide ionizes in water. Forming CN- anions which contribute to the reaction

The heavy metals that were included in the plume consisted of copper, iron, zinc, and lead.

The high levels of these heavy metals discharged into the rivers, would cause long term affects in the ecosystem, because they are not readily degradable.

This discharge creates a chronic pollution whose damage is harder to estimate.

These heavy metals mix with the sediments at the water bed, are bioaccumulated from plant and animal life and enter into the ecosystems food chain.

If the wastewater had any treatment beforehand, the damage would have been lessened. Normally heavy metals can be removed from wastewater through flocculation, but this is in a controlled setting.

The heavy metals will continue to be pushed and accumulated throughout the entire region by the physical forces of the water current.

New exfilitration and tailings dams were built to collect these moving heavy metals.

The heavy metal contaminants are pumped into an exfiltration pond where the heavy metals settle and water is drained back into the main pond.

Cyanide breakdown quickly in sunlight Into less toxic but longer-lasting forms, such

as cyanate and cyanogen Free cyanide breakdown slowly when

water is covered by iceProtected from direct sun

Sodium hypochlorite was poured into the spill in an attempt to neutralize the cyanide. Turns cyanide into a less toxic compound The remaining water in the containment pool

was diverted into a nearby tailing dam. Sediments from other tailing deposits

Were used to seal the breach Reinforce other parts of the dam

A limited outflow of 40-50 liters per second continued and was treated with sodium hypochlorite until February 2.

The cyanide was biologically degraded and diluted as it moved along the length of the river.

Water samples from surface water were taken by three teams from the 21 sampling stations.

Typically, the water sampling locations were identical with those for the sediment sampling.

The UN sampling took place about three weeks after the plume had passed Could not validate any of the results obtained by

the Romanian, Hungarian or Yugoslavian experts.

Very high concentrations of heavy metals were detected Copper (total concentration 412.3 mg/L) Iron (total concentration 31.3 mg/L)Manganese (total concentration

18.0 mg/L) Zinc (total concentration 14.5 mg/L).

UNEP prepared new guidelines for mining UNEP joined with ICOLD to produce two

Technical Bulletins for laying down design requirements and providing lessons from past incidents as a guide to designers.

International Council for Metals and the Environment, a multi-stakeholder process was launched to develop a management code for cyanide

Short term regulations : Each site will be inspected by suitably qualified

personnel and a safety/risk assessment made Hydro-meteorological data for each site will be re-

evaluated in order to ensure that tailings ponds and lagoons are designed to cope with extreme weather events

Assessments will be made of the structural capacity of the tailings dams and impoundments to withstand extreme precipitation and snowmelt events

Immediate steps to improve safety will be carried out where these are deemed necessary

Operational and accident/emergency procedures will be reviewed and improved where necessary at both a facility and local administration level

All sites, will immediately be placed under regular surveillance Abandoned sites Daily inspection and tests in times of adverse weather

conditions

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