Cyanide Clean-up At Chumbwe Gold Mine In Zambia

REPORT ON THE DISPOSAL OF SODIUM CYANIDE AT CHUMBWE GOLD MINE 1 INTRODUCTION A request was made by the Executive Director of the National Environmental Council 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 cocoordinating 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 considerable amount 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 MINE 2.1 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/PROCESSING Gold 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 Æ 4Na[Au(CN)2 ] + 4NaOH

precipitation

2Na[Au(CN)2] + ZnO Æ Na [Zn(CN)4 ] +2AuO

Cyanidation 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 the intervening 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 DETOXIFICATION 3.1 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 steaminghot bath after showering. * After offloading the cyanide at Luanshya, trucks and tarpaulins should be thoroughly washed and neutralised. 3.2.2 Day 2 October 13 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). 3.2.3

Day 3 October 14 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 15 The 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 7

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 of calcium 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. 3.2.5

Day 5 October 16 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 17 The 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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DISCUSSION 4.1 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- Æ CNO- + ClFree cyanide + Hypochlorite Æ Oxidised cyanide + Chlorine Gas

Or more specifically: NaCN + 2NaOH + Cl2 Æ NaCNO +2NaCl + H2O 2NaCNO + 4NaOH + 3Cl2 Æ 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 over several 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 - LOCALISED The 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 found to 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 was probably produced by the action of anaerobic bacteria on cyanide, represented as: HCN + 3H2 Æ CH4 + NH3 The 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, the excavated 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 resulted from 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 MUSI The 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 RECOMMENDATIONS 7.1 During the rainy season, the National Environmental Council should conduct weekly sampling exercises along the Chibombe and Luimba rivers to determine 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 ACKNOWLEDGEMENTS The 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 BIBLIOGRAPHY 9.1 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 SEECHARRAN TEAM LEADER

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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 mixture 3.2 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 direction 3.13 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 3.21 3.22 3.23 3.24 3.25 3.26 3.27 3.28 3.29 3.30 3.31 3.32 3.33 3.34

Several danger warning signs 1 x Large ball of string 1 x 10m Measuring tape 1 x Penknife 1 x Waterproof marker 5 litres of liquid soap 500g Powdered milk - for treatment of hypochlorite ingestion 1 x Dry-powder fire extinguisher 20m of 18mm Rubber hosepipe 10 x 50kg Drums of calcium hypochlorite (HTH) 500kg Hydrated lime 25 x Empty reagent drums 100 x Hessian sacks 100kg Fondu cement Copious supply of potable and industrial water

APPENDIX II BRIEF TO ALL PERSONNEL ON CYANIDE CLEAN-UP TEAM • •

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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 for which 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 EXERCISE COMMENCES. Cyanide exerts its effect by interfering with the ability of the cells to use oxygen. 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, the contaminated water should be confined by dykes or dams to prevent it from entering 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 THE SKIN EVEN IF THE SKIN IS UNBROKEN! Fire extinguishers should be of the dry-powder type. DO NOT USE WATER! In the 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 THE GENERATION OF ACETYLENE, NO SMOKING OR NAKED FLAME SHOULD BE ALLOWED WITHIN THE SPILLAGE AREA! Toxic symptoms occur if cyanide is absorbed through the skin, swallowed or inhaled. 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 SEECHARRAN CONCENTRATOR SUPERINTENDENT (TEAM LEADER)

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