an evaluation of taling dam in gold mining within the eia

AN EVALUATION OF “TALING DAM” in GOLD MINING WITHIN THE EIA

Ilhan Talinli & Aysun KabilIstanbul Technical University, Faculty of Civil Engineering,

Department of Environmental Engineering

Montreal, 2003

Scope of The Work : “Ovacik Gold Mine-Turkey” is selected as a case study

and its hazardous waste management is investigated. "Storage into Tailing Dam" and it has serious

environmental concerns about the method For this aim

gold production process are examined hazardous wastes are defined influential mechanism of environmental risk and impact

assessment studies are determined recommendations for hazardous wastes generated from

Ovacik Gold Mine are introduced

What is Hazardous Waste? a hazardous substance that has been discarded or

otherwise designated as a waste material or one that may become hazardous by interaction with other substances

Hazardous waste may either be in the formform of solid, liquid, semi-solid or contained gaseous material (UNEP , WHO 1982 ).

Hazardous waste generated from gold mining processes must be managed in respect of "Cradle to Grave Control System" principles.

Relationship between Environmental Risk and Impact Assessment

Engineering Risk Assessment Impact Assessment

1.Conceptual Investigation Design

2. Gaining Rights Pre-operation and Monitoring

3. Ultimate Design

4.Construction Construction Effect Monitoring

5.Preparation Preparation Tests Monitoring

6. Operation Short-term Effect Monitoring

7.. Sustainable Long-term Effect Rehabilitation Rehabilitation

8. Temporary Elimination Rehabilitation- Monitoring

9. Ultimate Elimination Ultimate Recovery and and Rehabilitation Rehabilitation Monitoring

Interdisciplinary Organization for Environmental Risk Estimating and Impact Assessment

TolarableActivities EffectDevelopments

Regulations Impact Permissions Assessment

Engineering Ecosystem testsDesign InvestigationOperation MonitoringRehabilitation

Process Survey Two basic sectors in gold mining;

Mining Primary production of gold extraction

Mining process includes slackening soil taking up mineral and its transportation to extraction site

This activity is realized by opening gallery blasting and transportation sub-processes.

Mixed CN leaching is mostly used method of %64 %64 all around the worldall around the world in all extraction methods (EIA, Ovacik, 1991).

In this method, dissolution reaction of gold with cyanide and its mechanisms

4Au + 8 KCN + O2 + 2H2O 4K[Au (CN)2] + 4KOH

Main processes of Au production

From mine Ore Pleating – Grinding-Classification

Cyanide Leaching Adsorption (CIP , CIL)

Desorption Elution of Gold by Electrolysis Au

Waste Survey Waste types obtained from process survey for

gold extraction wastewater solid waste air emission hazardous waste sludge and noise

Wastes from Processes of Gold MiningWaste Processes Pollutants, Effects Form of

WasteWastewater All leaching

processes and Carbonmethods

Heavy metals,sulfide, flouride, SS,pH, CN, As, sulfide,alcalinity

Liquid

Solid waste Blasting, Excavation,Decupage

Dust, Particules Solid

Airemissions

Blasting, Excavation,Leaching, Carbonmethods and Carbonregeneration ,Smelting

HCN, Particules,Dust, CO2, SO2

Gas andsolid

Waste Processes Pollutants, Effects Form ofWaste

Hazardouswaste

Leach process,Carbon methods

CN, Heavy metals, Toxicity,Carcinogenic, Teratogenic,Corrosivity, Mutagenity

Liquid andsolid

Sludges Leach processes,Carbon methods

CN, Heavy metals, Toxicity,Carcinogenic, Teratogenic,Corrosivity, Mutagenity

Sludge

Noise Blasting, allprocessequipments

Noise emissions Noise

Waste of leaching –cyanide process should be considered as the most important problem in the general waste research

Main environmental effect of cyanide and heavy metals is acute toxicity

This waste must be considered as a hazardous waste in form of sludge including %50 of solid matter .

For this reason, first an environmental risk assessment should be made to solve storage and disposal problems of this waste

Practices, which will lead to environmental protection legislation, have to be based on political proposals project planning as well as legal alterations for their ease of applicability.

Management strategies also play an important role in defining a hazardous waste. These steps may include: Definition of the hazardous waste Determination of the hazardous waste Listing of the hazardous waste T/S/D facilities (Treatment, Storage, Disposal )

T/S/D Facilities in Hazardous Waste Sites

T/S/D T (treatment) : removing of the hazardous

characteristics of the waste. S (storage) : isolating of the hazardous

waste in appropriate construction for certain period.

D (disposal) : ultimate disposal of treated or stored hazardous waste in a hazardous waste side

The problem of tailing dam :they are not suitable for the T/S/D facilities They can not be a storage system because

of being inappropriately designed for hazardous waste management system

A tailing dam for each gold mining site should not be installed as a hazardous waste site.

Cyanide Removal Methods

Biological treatment/ oxidation

Chemical oxidation alkaline chlorination sodium hypochlorite chlorine calcium hypochlorite

Activated carbon adsorption

Reverse osmosis Ion exchange Wet-air oxidation Ozonation, UV/O3 Castone process Inco process

various removal methods in literature:

Treatment methods CostAlkaline Chlorination

Chlorine (Cl2) Sodium Hypochlorite

(NaOCl) Calsium Hypochlorite

(Ca(OCl)2)

0.20 $/lb removed CN 1,40 $/lb removed CN 1,90 $/lb removed CN

Catalytic Cyanide Oxidation withActivated Carbon

1,36 $/kg removed CN

SO2/Air Oxidation 11,95 $/kg removed CNKastone Process 0,41 $/lb removed CNElectrolysis 0,082 $/lb removed CNOzonation 0,14 – 0,64 $/lb removed CN

Comparison of Cyanide Removal Methods’ Costs*

*(Johannes et al., 1989)

Comparison of Capital and Operating Costs of Cyanide Removal Method

Methods Capital Costs,$Annual Operatingand Maintanence

costs ,$Total

Ion exchange(a)

UV/O3 (a)

PolysulfideTreatment (a)

(Wong and Maroney 1990)

4.000.000.-6.000.000.-

600.000.-

170.000.-590.000.-

35.000.-

- -

-

OzoneAlkalineChlorination(Mudder and Whitlock 1983 )

-

-

-

-

490.850.-$/year

63.600.- $/year

GM – IX Process AlkalineChlorination(Semmens 1989)

-

- -

164.700.-$/year

276.650.-$/yearOzonation

Chlorination(Stopka 1980)

-

-

0.34 $/h

2.44 $/h

18.500.-$ (3.78 1/h)27.500.-$ (7.57 1/h)47.088.-$ (3.78 1/h)55.566.-$ (7.57 1/h)

The result of this economical analysis shows that usage of UV/ozone method for especially high concentrations of cyanide is the most economic one.

TREATMENT PROCESS OF THE CYANIDE BY INCO PROCESS

Process steps of the Proposed treatment method of the Cyanide is INCO process for Bergama Gold mine tailings in Turkey Waste in slurry form is continuously pumped into two-

stage destruction tank set-up via a downcomer. SO2 presented as liquid form and air are injected into

the waste effluent to oxidize soluble cyanide. Reactor has a bottom impeller to ensure rapid dispersion and to promote the O2 gas transfer to the solution.

Lime slurry (%10 solid) is continuously added to maintain a pH of 8.7.

Retention time of the slurry is 60 minutes in first tank.

Cu+2 and Fe+3 are added to remove complex cyanides (ferrous and ferric cyanide), arsenic and antimony. This tank retention time is 30 minutes.

Effluent from second tank flows to the settling tank to permit settling of the precipitates.

Additional Sb is removed in third tank.

Typical operating conditions in mass balance 83000 kg/h slurry including %45 solids is fed to

reactor SO2 21 kg/h, Cu+2 8 kg/h, Fe+3 37 kg/h, lime slurry

187 kg/h are fed to reactor. Effluent contains 83000 kg/h slurry, 46000 kg/h

solution and 37000 kg/h solids. When cyanide (CNT) concentration is reduced

from 6.1 kg/h to 0.1 kg/h, Cu+2 and OCN¯ concentrations increase to 0.5 kg/h and 9.6 kg/h respectively.

Influent and effluent specific gravity is 1.396.

Reactions of the cyanide in this processCN¯ + SO2 + O2 + Cu +2 + H2O CNO¯ + Cu + H2SO4

The oxidation of thiocyanide and the hydrolysis of cyanideSCN¯ + 4SO2 + 4O2 +5 H2O CNO¯ + 5 H2SO4CNO¯ + 2H2O OH¯ + NH3 + CO2

According to INCO, iron cyanide removal is initiated by reduction of iron from to ferric to the ferrousstate2Fe+3 + SO2 + 2H2O Fe+2 +4H+ + SO4

-2

2Fe (CN)6-3 + SO2 + 2H2O 4Fe(CN)-

64 + 4H+ + SO4

-2

The ferrous cyanide complex is then removed through precipitation with either copper, zinc or nickel2 M+2 + Fe (CN)6

-4+ H2O M2 Fe (CN)6. H2O (M+2 is Cu, Ni, or Zn)

These residual metals remaining in solution are precipitated as their hydroxides:2Cu+2 + SO3

-2 + O2 + H2O + 2OH¯ 2Cu (OH)2 + SO4-2

Ni +2 + 2OH¯ Ni(OH)2

Zn + 2OH¯ Zn (OH)2

RESULTS AND DISCUSSIONS

Specific Cyanide utilization will be 0.35-1.76 kg NaCN/ton mineral (used 1.5 kg NaCN/ton)

Water content of slurry is %52 by weight and 2.083 ton slurry occurs with ratio of 1.083 m3 water/ton mineral

Specific gravity of the slurry is 1.43 ton/m3 so waste volume is 1.457 m3

Cyanide concentration : 1.5 kg NaCN /1.457 m3 = 1030 g CNT / m3

%0.035 NaCN concentration is desired in leaching tank. (0.035/100) * 1083 * 1000/1.457 = 260 g NaCN / m3 slurry and 1030 - 260 = 770 g/ m3 NaCN is utilized by other metals in

slurry.

Acid rains may cause decrease of pH in tailing dam and accumulated free CN¯ may change in form of HCN to atmosphere.

In volume of three times rain water at 3.5 pH will decrease water pH from 9 to pH 8.3. If 16000 m2 surface area and water in 0.5 m

height in tailing dam, 8000 kg cyanide may accumulate due to 100 g/ m3 concentration and this amount may transfer to atmosphere by change of pH.

Tailing Dam hazardous wastes and slurries are collected in tailing dam

which is designed 15 ha in surface area and 2 million m3 volume has also been predicted in Bergama Gold mine.

Storage of the hazardous wastes is notis not an ultimate solution in management facilities

Tailing dam is used as a storage tank in gold mining for removed cyanide slurries whereas, various wastes from extraction processes are collected

in Tailing dam is considered as an ultimate disposal areaconsidered as an ultimate disposal area

Cost to Western Europan Chemical Industry for treating and disposing of waste

Methods Cost Range US $ /tonnes

Simple Disposal to land 1-20Disposal to land in a site lined with plastic sheet 10-50Underground disposal to dropping into old wells or mines 20-150Land disposal after encapsulation either by mixing the waste 10-100with cement or other agent or by incarcerating whole drums in cement

Coastal sea dumping from ships or 5-15 Deep-ocean dumping beyond the continental shelf 10-150Simple incineration (without significant heat recovery) 30-150Incineration with alkaline stack scrubbing 100-350Incineration onboard ship at sea 50-350All types of chemical treatment and, in particular :Destruction of cyanide by hypochlorite 300-500Reduction of chromic acid 100-300Destruction of cyanide (catalytic) 200-500

Economical Analysis of Tailings in Gold Mine Suggested treatment and disposal cost of stored hazardous

waste in tailing dam as average 200 $/ton Volume of tailing dam in gold mine : 2 million m3

specific gravity of slurry is 1.43 tons /m3 Waste amount of the waste in tailing dam :2.106 m3 * 1043 tons/ m3 = 2.860.000 tons and total cost

for treatment and disposal is;

2.860.000 tons * 200 $/ton = 572.10572.1066 US$ US$

economical table of the project

Initial Investment Cost = 46. 106 US$ Production Income per year = 40 106 US$ Production Outcome = 21. 106 US$ Rant per year = (40-21) 106.= 19 106 US$ Rant of investment per 8 years = 8* 19.106

=152. 106 US$ %10 of this rant remain for Turkey = 152.

106 * 0.1 = 15.2. 106 US$

When 2.860.000 tons hazardous waste is required about 572. 106 US$ treatment and disposal cost, rehabilitation of tailing dam can not be a solution for this problem.

Benefit/cost ratio is very low. Whereas environmentally minimal hazard and impact is aimed in EIA concept.

Existing methods for removing of cyanide are appropriate to solutions. Cyanide is main pollutant in waste slurry however overall

waste can not be treated in based on individual parameters such as cyanide, copper, zinc etc.

Precipitation of heavy metals in coagulation is impossible because of being high ionic strength in slurry.

Tailing from gold extraction processes is hazardous waste in slurry form and its main characteristic is toxicity. Therefore it should be managed by T/S/D facilities such as detoxification, solidification, deep well injection, disposal to spent mining after solidification and controlled land- filling for treated waste.

Tailing dam should not be a storage or disposal method . It may be a temporary store for hazardous waste but never to forever.