cyanide clean-up at chumbwe gold mine in zambia

8/14/2019 Cyanide clean-up at Chumbwe Gold Mine in Zambia

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REPORT ON THE DISPOSAL OF SODIUM CYANIDE

AT CHUMBWE GOLD MINE

1 INTRODUCTION

A request was made by the Executive Director of the National EnvironmentalCouncil to the Chief Executive of ZCCM for assistance in the disposal of

approximately nine tonnes of sodium cyanide at Chumbwe mine. Through the

Technical Directorate, Kalulushi, the offices of the Manager Safety and the

Industry Environmental Advisor were charged with the responsibility of co-

coordinating the activities for:

* the safe removal of the cyanide

* detoxification of all residue, and

* making safe the area affected by cyanide.

Sodium Cyanide is used at Luanshya Division as a cobalt depressant on the

Baluba differential flotation circuit. Over the past seventeen years, a considerableamount of expertise had been gained by plant operators on the handling, storage

and detoxification of cyanide. As a result of this experience, Luanshya Division

was asked to play a prominent role in the Chumbwe mine exercise.

2 CHUMBWE MINE2.1 LOCATION

Chumbwe gold mine is situated in Lusaka province approximately 60

kilometres south-east of the city and 40 kilometres south-west of Chongwe

Boma. The property is located on the north bank of the Chibombe river.

The mine is privately owned and ceased production in 1987.

2.2 MINING/PROCESSINGGold mineralisation is intimately associated with pyrite and pyrrhotite, with

several outcrops on the property. Mining was carried out manually by open

pit method. Since the gold particles are finely disseminated in the sulphide

matrix, recovery by amalgamation was lower than expected. An attempt was

made at vat leaching of gravity concentration middlings, using sodium

cyanide as the lixiviant, followed by precipitation on zinc shavings

(Figure 1). These processes are represented thus:-

leaching 4AuO

+ 8NaCN + O2 + 2H2O 4Na[Au(CN)2 ] + 4NaOH

precipitation 2Na[Au(CN)2] + ZnO Na [Zn(CN)4 ] +2AuOCyanidation proved to be successful and several concrete vats were

constructed to expand the leaching section. Ten tonnes of sodium cyanide

were purchased in 1976 in preparation for enhanced leaching activity. In

1977 the mine changed ownership and the cyanidation process was shelved.

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2.3 THE HAZARD

Since 1976 the cyanide has been in storage in an insecure shed. Over theintervening years, the roof caved in and parts of the side wall collapsed

(Figure 2). Due to lack of security, several drums were stolen and their

contents dumped on the floor (Figure 3). With torrential summer rains,

cyanide solution seeped through the northern and western walls of the shed

(Figure 4), eventually leading to the death of some species (Figure 5).

After several heads of cattle were suspected of being killed by cyanide

poisoning, the local residents lobbied the National Environmental Council.

The assistance of ZCCM was requested by the council to dispose of the

cyanide safely and make safe the surroundings.

3 DISPOSAL AND DETOXIFICATION3.1 LOGISTICAL PLANNING

A meeting was held in Luanshya on 09 October 1992 between the author

and the Industry Environmental Advisor, who had visited Chumbwe mine

the previous week, to plan logistics for the cleaning up exercise. A list of

required resources was drawn up (Appendix I). It was decided that clean

cyanide will be used on the Baluba plant and contaminated spillage will be

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buried in the depository of Musi tailings dam. All personnel responsible

for organising those resources were in regular telephone contact with the

author throughout the week end to ensure that the plan was progressing

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according to schedule. All personnel to be involved in the exercise were

issued with "safety guide for handling cyanide" (Appendix II).

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3.2 IMPLEMENTATION

3.2.1 Day 1 October 12

The team, headed by the author, arrived on site and conducted a

reconnaissance survey. It was decided that throughout the exercise:* All work in the cyanide shed should be carried out upwind of the

loose cyanide pile.

* Wind direction and hydrogen cyanide gas concentration should be

monitored regularly so as not to jeopardise the safety of team

members.

* A medical doctor, equipped with all necessary first aid equipment,

should be strategically located for rapid reaction.

* At the commencement of each day's operation, team members

should be briefed on the hazards of cyanide, before task allocation.

* At the end of each day, each team member must have a steaming-

hot bath after showering.* After offloading the cyanide at Luanshya, trucks and tarpaulins

should be thoroughly washed and neutralised.


The team was enhanced by five members of the Kabwe Division

Proto team. After barricading the area and posting warning signs, the

roof of the cyanide shed was removed to improve ventilation.

Wearing breathing apparatus, the Proto team was utilised to remove

all intact drums of cyanide. The outside of each drum was thoroughly

cleaned prior to loading on a flat truck (Figure 6). After securing the

cargo and attaching the necessary warning signs to the truck

(Figure 7), it was despatched to Luanshya Division accompanied by a"competent person".

To minimise the effect of skin contact with cyanide, all personnel

working with the hazardous chemical were encouraged to wash as

frequently as possible (Figure 8).


The Kabwe Proto team was utilised in loading loose cyanide into

empty drums. The Manager Safety arranged for two additional flat

trucks and one extra Proto team to be made available.

3.2.4 Day 4 October 15The Kabwe Proto team was complemented by a seven-man Proto

team from Mufulira Division. All remaining loose cyanide briquettes

were loaded into empty drums. After sealing the drums and thoroughly

cleaning the outside of each, they were loaded in the three flat trucks.

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Five drums were found to contain saturated cyanide solution from

previous rainy seasons. These drums warranted special treatment to

facilitate safe handling and minimise the likelihood of a spill. The

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drums were punctured as close to the base as possible and tilted

slightly to ensure effective drainage onto the floor of the cyanide shed.

One of the trucks was specifically prepared to accommodate the

leaking drums in the following manner:

* A section of the pan was covered in Hessian sacks.

* A layer of river sand 50mm thick was placed on the sacks.* A plasticated tarpaulin, larger than the area covered in sand was

used as an overlay.

* Another layer of river sand, 100mm thick was placed on the

tarpaulin.

Should any cyanide solution leak out of the drums during

transportation, the river sand would have contained it. Sand, tarpaulin

and sacks were to be safely disposed of at Luanshya Division. In

retrospect, an epoxy resin would have been ideal for sealing the

perforations in the drums after draining.

After securing the cargo, the trucks were despatched to Luanshya

accompanied by a "competent person" and carrying one drum ofcalcium hypochlorite (HTH) as insurance in the event of a spill.

Neutralisation of the remaining cyanide in and around the cyanide

shed using HTH commenced (Figures 9 and 10). The neutered

cyanide was left to stand overnight.


The cyanide shed was thoroughly washed down both internally and

externally. Excess HTH was sprinkled over the neutralised areas to

ensure that detoxification was complete and that the HTH was slightly

in excess of the quantity stoichiometrically required for neutralisation.

Remnants such as empty sacks, drum covers and sealing rings were

neutralised then buried in a pit dug in plant tailings. An insurance dose

of HTH was added prior to infilling of the pit.

Because of the porous nature of the foundation slab of the shed,

cyanide could have contaminated sub-slab soil. The author expressed

his concern to the Manager Safety. The inspectors from the National

Environmental Council were briefed and the team departed for the

Copperbelt.

3.2.6 Day 6 October 17The author/team leader carried out an audit at Luanshya Division to

verify that all despatches from Chumbwe mine were accounted for and

to ensure that storage was safe.

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4 DISCUSSION4.1 NEUTRALISATION

The standard method of neutralising cyanide by alkaline chlorination

using hypochlorite was employed, as represented by the following

equation:

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CN-

+ OCl- CNO- + Cl-

Free cyanide + Hypochlorite Oxidised cyanide + Chlorine Gas

Or more specifically:

NaCN + 2NaOH + Cl2 NaCNO +2NaCl + H2O2NaCNO + 4NaOH + 3Cl2 2CO2 + 6NaCl + N2 + 2H2O

After the reaction was completed, excess hypochlorite was sprinkled over

the area and left to stand overnight. The following morning, after

ascertaining that neutralisation was complete, final washing down was

carried out. Figure 11 shows the inside of the cyanide shed after cleaning

up.

4.2 CYANIDE SHED

The cyanide shed was constructed of a single layer of porous concrete

blocks with no plastering. Because of the seepage of cyanide solution

through the northern and western walls of the building that occurred overseveral rainy seasons (Figure 4), it is inevitable that cyanide would have

remained in the interstices of the concrete blocks. As the walls were

neutralised, the chlorine gas generated forced the HTH solution out of the

pores thus preventing complete neutralisation of the walls. With this in

mind, it was decided to demolish the cyanide shed and bury the blocks,

together with all other components, to a depth of two metres in the driest

part of a tailings depository, such as the northern end of Musi dam,

Luanshya. Because of the poor state of the concrete making up the

foundation slab, it was also decided to break a portion of the slab and

examine the sub-soil.

4.3 ENVIRONMENTAL DAMAGE - LOCALISEDThe soil adjacent to northern and western walls of the cyanide shed was

contaminated through seepage of cyanide solution over a long period of

time. It was decided to break the soil to a width of two metres from the

building and to a depth of at least 500mm, neutralise with HTH and mix

with lime to provide protective alkalinity then finally cover with 500mm

of river sand. Bacterial action on vegetation and sulphide minerals results

in the formation of acids that could react with cyanide in the contaminated

soil to produce hydrogen cyanide gas, protective alkalinity prevents this.

4.4 ENVIRONMENTAL DAMAGE - LARGE SCALE

Since the cyanide shed was located on an elevated area, dissolved cyanide

could have migrated into the Chibombe river valley. Monitoring of water

quality in the Chibombe and Luimba rivers had therefore become

imperative.

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5 DEMOLITION OF CYANIDE SHED

The demolition squad comprising members of the Proto teams from Mufulira,

Kabwe and Nampundwe went to Chumbwe mine on 27 October with the primary

objective of demolishing the cyanide shed and despatching the components of the

building to Luanshya for burial in Musi tailings dam.

After the shed was demolished, the composition of the foundation slab was foundto be a mixture of laterite and Portland cement. Such a foundation, being very

porous, allowed a considerable amount of cyanide solution to seep through to the

underlying soil. It was also discovered that approximately half of the soil on which

the foundation was cast was brought-in material while the remaining half was

natural in-situ soil (Figure 12). Because of its high porosity, the brought-in soil in

the north-western corner of the shed was found to be the most contaminated.

It was decided to demolish two square metres of foundation at the western end

and inspect the underlying soil (Figure 12). The soil was noticeably contaminated

to a depth of 500mm with dissolved cyanide recrystallising on gravel particles

(Figure 13). At this depth, a strong smell of ammonia gas was detected. This wasprobably produced by the action of anaerobic bacteria on cyanide, represented as:

HCN + 3H2 CH4 + NH3The broken foundation and the excavated foundation soil were loaded together

with the building components into two trucks and despatched to Luanshya.

Further qualitative testing using HTH indicated that the soil was contaminated at

even greater depth. The extent of the contamination was so pervasive that a

decision was taken to demolish the entire foundation slab and excavate down to

the subsoil horizon (Figure 14), at a later date. As a temporary measure, theexcavated area was dosed with HTH and lime at the rates of 20 kg/m2 and

10 kg/m2 respectively then in filled with river sand.

Demolition of the remainder of the foundation and subsequent excavation down

to the subsoil commenced on 02 November and was undertaken by the

Nampundwe Proto team. All demolished/excavated material was loaded in 35 kg

sacks and stored under cover until transported to Luanshya.

A site inspection was made on 10 November and qualitative tests were conducted

on the uppermost layer of subsoil, reached after excavating 1500mm below slab.

Material extracted from this layer did not react with HTH, this could have resultedfrom the action of sunlight in complexing the free cyanide. However, soil samples

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taken from a depth of 100mm into the subsoil reacted slightly as shown below.

Having been satisfied that as much of the contaminated soil as was practically

possible had been removed, the author, in consultation with the Senior Inspector

from the National Environmental Council decided on the following line of action.

The side walls of the excavation was trimmed as shown in Figure 15, the base

of the excavation limed at a dosage of 10 kg/m2 and the entire area in filled with

river sand. This was carried out on 11 November using the Nampundwe team.

6 DISPOSAL OF CONTAMINATED MATERIALS AT MUSIThe highest point of tailings within the Musi dam repository was chosen as the

Disposal site for the contaminated building materials and soil. In so doing, the

advantages were several:

* This was the remotest part of the tailings repository.

* This was the driest part of the tailings dam.

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* The lake level at the time was 800m away and 25m below the burial pit

bottom.

* With the lake so far away and well below burial point, in the unlikely event of

leached cyanide reaching the phreatic surface, it would emerge as a spring

along the sloping blanket of tailings leading to the lake. This will facilitate the

breakdown of free cyanides to complexes by the action of sunlight.* In the most unlikely event of cyanide reaching the lake, the discharge will flow

through a bed of reeds in the Musi valley before reaching the Luanshya dam.

Water from Luanshya dam is not discharged into the natural river system but is

pumped to the Luanshya concentrator where it is used as process water.

Figures 16 and 17 show the burial and precautionary neutralisation of

contaminated soil, an exercise which was witnessed by two Inspectors

from the Mines Safety Inspectorate (Figure 18).

7 RECOMMENDATIONS7.1 During the rainy season, the National Environmental Council should conduct

weekly sampling exercises along the Chibombe and Luimba rivers todetermine the cyanide content of the rivers water.

7.2 After the river sand covering the former cyanide slab has consolidated, it

should be capped with a layer of impervious material, such as ant hill clay.

7.3 An audit of all registered gold mines in Zambia should be conducted by a

competent person to ascertain whether similar hazards exist.

7.4 The National Environmental Council should educate all users of cyanide on

the hazards associated with this poisonous chemical.

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8 ACKNOWLEDGEMENTSThe team is highly indebted to the Technical Directorate for the logistical, material

and moral support provided, without which accomplishing the task would have

been extremely difficult. The co-operation of the management of Kabwe Division

is acknowledged for providing the services of the Divisional Proto team on three

consecutive days and for providing accommodation for the Mufulira Proto team.Without the assistance of the management of Nkana Division in providing a water

bowser throughout the exercise, the detoxification process would have been

impossible. Appreciation is also shown to Mufulira and Power Divisions for

providing a Proto team and two flat trucks respectively, at very short notice. The

service provided by the Industry Mine Rescue Training Co-ordinator in

marshalling the activities of the various Proto teams is also acknowledged.

Gratitude is expressed to the management of Luanshya Division for releasing

members of the team to conduct the exercise, for providing transportation and

safety equipment and for arranging accommodation. Finally, the guidance

provided by the Inspectors from the National Environmental Council assisted in

accomplishing the task in a safe and timely manner.

9 BIBLIOGRAPHY9.1 Anon, "Gold extraction for the small operator," - Imperial Chemical

Industries, 1936, pp 94,95.

9.2 Seecharran K R, "Handling Of Sodium Cyanide", - ZCCM, Luanshya

Division, Concentrator Department, Feb 1990.

9.3 Pretorius C, "Cyanide Safety", - South African Mining World, June 1991,

pp 38-43.

KENNETH R SEECHARRANTEAM LEADER 20 11 92

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APPENDIX I - RESOURCES UTILISED

1 HUMAN

1.1 Manager Safety

1.2 Concentrator Superintendent Luanshya Division (Team Leader)

1.3 Team Medical Doctor

1.4 Industry Environmental Advisor

1.5 Assistant Industry Environmental Advisor

1.6 Senior Assistant Metallurgical Engineer

1.7 Experienced Reagent Mixer

1.8 Experienced Laboratory Assistant

1.9 Kabwe Division Proto Team

1.10 Mufulira Division Proto Team

1.11 Nampundwe Mine Proto Team

1.12 4 x Truck Drivers

2 TRANSPORTATION

2.1 3 x Flat Trucks

2.2 1 x Water Bowser

2.3 3 x Mini Buses - for Proto teams

2.4 3 x Light Vehicles

3 SAFETY AND DETOXIFICATION EQUIPMENT

3.1 First aid kit complete with cyanide antidote and vomit mixture3.2 Oxygen resuscitator

3.3 Breathing apparatus for each member of Proto team

3.4 First aid stretcher

3.5 6 x Auer-type masks complete with face shields

3.6 6 x PVC Gauntlets

3.7 6 x PVC Jackets This was in addition to the kit issued

3.8 6 x PVC Trousers to each member of the Proto teams

3.9 6 x Pairs of rubber boots

3.10 1 x Roll of mutton cloth

3.11 Draeger gas sampling apparatus

3.12 Aluminium dust for checking wind direction3.13 2 x Pinch bars

3.14 4 x Shovels

3.15 3 x Picks

3.16 1 x Chain block

3.17 8 x Large tarpaulins

3.18 4 x Long pieces of rope

3.19 4 x Medium sized buckets

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3.20 Several danger warning signs

3.21 1 x Large ball of string

3.22 1 x 10m Measuring tape

3.23 1 x Penknife

3.24 1 x Waterproof marker

3.25 5 litres of liquid soap3.26 500g Powdered milk - for treatment of hypochlorite ingestion

3.27 1 x Dry-powder fire extinguisher

3.28 20m of 18mm Rubber hosepipe

3.29 10 x 50kg Drums of calcium hypochlorite (HTH)

3.30 500kg Hydrated lime

3.31 25 x Empty reagent drums

3.32 100 x Hessian sacks

3.33 100kg Fondu cement

3.34 Copious supply of potable and industrial water

APPENDIX IIBRIEF TO ALL PERSONNEL ON CYANIDE CLEAN-UP TEAM

The necessity to handle such a large quantity of exposed sodium cyanide in a safe,efficient and environmentally responsible manner will be of paramount

importance throughout the exercise.

The cyanide ion is an extremely potent and rapidly-acting poison, but one forwhich specific and effective antidotal treatment is available. Cyanide poisoning is

a true medical emergency and treatment is highly effective if given immediately.

THE ANTIDOTES MUST BE MADE AVAILABLE BEFORE THE EXERCISECOMMENCES.

Cyanide exerts its effect by interfering with the ability of the cells to useoxygen. Although oxygen is carried by the red corpuscles of the blood to the

tissues, the cyanide blocks the respiratory enzymes. It prevents the cells from

functioning normally and the result is the same as if no oxygen is available.

The victim of cyanide poisoning is suffering from asphyxia at the cellular

level as the cells and, therefore the organism as a whole, are being deprived

of the oxygen required by the life process. This results in quick death if the

number of cells affected is great or if the cells are in a vital area.

The following procedure will be adopted to deal with the spill:* Secure the area

* Wear protective clothing and respiratory equipment

* Take immediate action to prevent further spillage

* Isolate the spill to minimise danger

* Confine the spillage to as small an area as possible and make every effort

to keep the cyanide dry

* Clean up as much of the spillage as possible, WORKING FROM THE

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UPWIND DIRECTION

* Neutralise any remains which cannot be cleaned up

* Rehabilitate the area ensuring that protective alkalinity has been provided

* Transport sealed bags of residue back to Luanshya for safe disposal

If water is flowing out of the area, or if cyanide has spilled into a nearby ditch, thecontaminated water should be confined by dykes or dams to prevent it fromentering the watercourse, downstream users of the water must be warned

immediately not to use it. Simultaneously, a sampling exercise must be carried

out to monitor the extent of the pollution.

CONTACT WITH CYANIDE CAN RESULT IN POISONING THROUGH THESKIN EVEN IF THE SKIN IS UNBROKEN!

Fire extinguishers should be of the dry-powder type. DO NOT USE WATER! Inthe event of a fire, the fire fighters should approach from the upwind side using

full protective gear. If exposed to water, acetylene is produced due to a small

quantity of residual calcium carbide in the cyanide.

BECAUSE OF THE EXPLOSIVE HAZARD POSED BY THEGENERATION OF ACETYLENE, NO SMOKING OR NAKEDFLAME SHOULD BE ALLOWED WITHIN THE SPILLAGE AREA!

Toxic symptoms occur if cyanide is absorbed through the skin, swallowed orinhaled. Liquid cyanide can be readily absorbed by the skin. In the presence of

sweat on the skin, which is usually acidic, cyanide may react to produce hydrogen

cyanide which is readily absorbed through the skin. On an empty stomach, in the

presence of high acid content, absorption will be expected to proceed rapidly.

CYANIDE POISONING SYMPTOMS - learn to recognise them* Headache

* Dizziness

* Laboured breathing

* Racing pulse* Nausea

* Weakness of the limbs

* Disorientation

* Profuse sweating

* Unconsciousness

KENNETH R SEECHARRANCONCENTRATOR SUPERINTENDENT (TEAM LEADER)

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cyanide clean-up at chumbwe gold mine in zambia

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