35 YEARS OF PROGRESS IN ENVIRONMENTAL STRATEGY AND TECHNOLOGY IN NON FERROUS METALS MINING AND SMELTING INDUSTRY. Björn Lindquist

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1 1 35 YEARS OF PROGRESS IN ENVIRONMENTAL STRATEGY AND TECHNOLOGY IN NON FERROUS METALS MINING AND SMELTING INDUSTRY Björn Lindquist Tilek AB, Fasanvägen 1, S , Gräddö, Sweden, Telephone , Fax , ABSTRACT In the paper different cases from solving environmental problems in mines and smelters are presented. Three of these cases will more in detail give examples of successful solutions to following problem areas: 1. Waste disposal and rehabilitation of tailing dams 2. Pyrometallurgical processes environmentally cleaner 3. Effluent treatment The cases will be based on experiences from the Boliden Mining and Smelting Company. Some general comments to strategy in environmental work will additionally be given. INTRODUCTION Boliden is one of the leading mining and smelting companies in Europe with operations in Sweden, Finland, Norway and Ireland. Boliden s main products are copper, zinc, lead and gold and silver. The number of employees is approximately and the turnover amounts to approximately EUR 3.8 billion annually. Boliden s Production Entities Aitik (Sweden) Copper mine Boliden Area (Sweden) Zinc mines Rönnskär Boliden (Sweden) Copper smelter Harjavalta/Pori (Finland) Copper smelter Garpenberg (Sweden) Zinc mines Tara (Ireland) Zinc mine Kokkola (Finland) Zinc smelter Odda (Norway) Zinc smelter Smelters Mines Bergsöe (Sweden) Lead smelter Figure 1. Map of actual Boliden operations.

2 2 The size of the company has increased over the years and in order to be able to follow the progress over a long period of time only the Swedish operations are discussed. The 35 years of time span coincides roughly with the duration of an effective environmental legislation supported by corresponding authorities. WASTE DISPOSAL AND REHABILITATION OF TAILING PONDS Many problems facing the company in the past has now been solved in such a way that they are not seen as problems any longer. They are summarized in table 1. Table 1. Problems Emissions to air from drying of concentrate Emissions to water from tailing ponds Emissions to water from mines Transportation of concentrates Solutions Replacement of driers with press filters ph-control, water circulation to concentrators Water treatment in tailing ponds or in separate effluent treatment plants Closed transportation systems The implementation of environmental control measures has dramatically reduced emissions to air and water from the Boliden mining activities though at the same time production has increased. This is shown in figure 2. Mines, Production and Emissions Production (Cu+Pb+Zn) ktonnes/yr Metals to water (Cu+Pb+Zn) tonnes/yr Dust to air (Cu+Pb+Zn) tonnes/yr Year Figure 2. Development of mine production and emissions to air and water from mines and concentrators

3 3 The main environmental problem facing the company nowadays is to foresee how big quantities of waste materials should be handled in order to be able to leave the mining site the day when the operations have come to an end. In Swedish Legislation a Decommissioning Plan is part of the approval process for mining activities. The main waste material from Boliden mines are the tailings. There are at present three ways to avoid formation of sulphuric acid with metals ions from the tailings: 1. To cover with water, wet cover 2. To cover with solid materials, dry cover 3. To remove sulphide materials prior to its storage The first two methods prevent the oxygen access to the solid waste and thereby oxidation and acid formation is limited. Either water or a clay material is used for sealing. Both these methods have been used at several mine sites and are constantly followed up and improved. The tendency is that water cover gives, so far, a better protection. A typical wet cover project is the reclamation of the Stekenjokk mine with flooding of the tailings pond. The metal content in outgoing water is now one tenth of what was predicted in the design. A typical dry cover project is the one used at the Saxberget tailings pond as shown in Figure 3. Figure 3. Dry cover at the Saxberget tailings pond The conclusions from the project shows that The cover reduces the oxygen inflow and water infiltration as predicted Slow improvement of drainage water quality Significant reduction in mass transport from the area Relocated oxide smelter waste a significant pollution source in the pond area Cover is sensitive to erosion Sewage sludge as sealing layer ( test plot ) well functioning

4 4 In the third method the sulphide content is removed from the tailings to such a low content that just a limited oxidation will occur which can be neutralized by other minerals in the tailings. This method has been chosen for the big open pit at Aitik. The sulphides in the tailings, in the form of a pyrite concentrate, will be stored separately and can in this way in the future be subject to an engineered way of cover. The main part of the tailings can be stored safely without sealing from oxygen supply and just be covered in order to prepare for vegetation. Such a cover has already started, even though the mine is expected to be in operation for many years to come, and is based on ash and sewage sludge. GENERAL INFORMATION OF THE RÖNNSKÄR SMELTER The Rönnskär smelter in Skelleftehamn in northern Sweden extracts metals and manufactures chemical products from mineral concentrates and recycling materials. The main products are copper, lead, gold, silver and zinc clinker. Examples of by-products are liquid sulphur dioxide, sulphuric acid, selenium and nickel sulphate. The process flow sheet is presented in Figure no 4. Figure 4. Process flow sheet at the Rönnskär smelter Table 2. Annual production for various products at the Boliden Rönnskär smelter Copper tonne Lead tonne Gold kg Silver kg Zinc clinker tonne Sulphuric acid tonne Liquid sulphur dioxide tonne

5 5 PYROMETALLURGICAL PROCESSES ENVIRONMENTALLY CLEANER General The integration with Boliden s own mines ensures daily arrivals of concentrates. A daily train shuttle transports concentrates from Boliden s Aitik mine in the Arctic Circle. Concentrates from Boliden s concentrator in the vicinity arrive by truck. Rönnskär is a world leader in the recycling of base metals. Values are extracted from scrap and other waste containing metal such as copper ashes from the brass industry, scraped printed circuit boards, sorted metal fractions from dismantlers and shredders and copper cables. Zinc is recovered from slags and ashes as well as from EAF-dust. Materials are sampled and verified on arrival to define metal values and checked for unwanted impurities that may disrupt the processes. Sampling is based on proven methods, well-defined routines and experienced personnel. Sampling is of utmost importance to the profitability of recycling. Technology introduced with environmental impact The Rönnskär smelter plant comprises today a multitude of different process equipments which meet high environmental standards. Some examples of such technologies which have been applied in the last decades are: fluidized bed roasting of concentrates with oxygen enrichment slag fuming for recovery of zinc from slag and secondary material Kaldo technology for electronic scarp recycling and autogenous lead smelting conventional converting, spectroscopic process control upgraded electric smelting, new cooling system enlarged electro refinery, converted to ISA technology new precious metals plant including Kaldo technology upgraded infra structure: expanded harbour with a closed belt conveyor system for copper-concentrates in order to reduce diffuse dust emission new sulphuric acid plant new oxygen plant, operated by Air Liquide New flash furnace and modernized process units Management of emissions to air The result in emissions decrease to air over a long period of time is shown in Figure 5. Figure 5. Development of emissions of SO 2 and dust from the Rönnskär smelter

6 6 A comprehensive control program is carried out by a special sampling team. 37 textile filters are supervised. The total filter area of the filters is 31000m 2 and the volume of filtered air is about 2 Mm 3 per hour. The dust content in cleaned air after textile filters must be kept under 5mg/m 3. To keep a good filter performance it is crucial that supervision and maintenance is performed in accordance to established routines. Modern textile filters are effective and can clean the dust content in filtrated air below 1mg/m 3. Sulphur fixation rate is 99% which is the result of an effective ventilation system, good process control and best available proven technique at the sulphuric acid/sulphur dioxide plant. The technique at the sulphur plant includes double absorption, mercury cleaning and polishing off-gases by selenium and carbon filters. Looking back at the emissions to air substantial reductions have been achieved. This is the result of large investments in filter equipment, new processes, closure of some plants, improved maintenance and education of process operators. During the last two decades ( ) the total dust discharge to the air has been reduced from 1000 tonnes per year to 32 tonnes per year which is equal to a reduction by 97%. WATER AND SEWAGE MANAGEMENT In 1975 a water strategy was established which was based on separate treatment of discharged water containing different levels of contamination. The Rönnskär smelter has four separated piping systems for the effluent water. Water with high metal content is pumped to the water treatment plant at Rönnskär. Cooling water with low metal content is discharged to the sea. The sewage water is pumped to a treatment plant. The four water systems and flow rates are described in Table 3. Table 3. Water treatment for effluent water. Water type Flow Metal content Pumped to (m 3 /h) Process water 150 High Rönnskärs treatment plant Rain & wash water 50 Varying Rönnskärs treatment plant Cooling water 5000 Low The recipient Sewage water 10 Low The sewage treatment plant of the smelter In 1978 the water treatment plant was taken into operation at Rönnskär. The capacity of the plant is 200m 3 /h. The technique is based on metal precipitation with sulphide followed by precipitation with lime. The metal rich sulphide sludge is recirculated to the process. The lime sludge which has low metal content is land filled. The process is very effective and has gradually been optimized. The process control was further improved by the installation of an on-stream x-ray analyzer equipment in As a precipitation agent green liquor containing sulphide from the pulp and paper industry is used. The assays of cleaned water are displayed in table 4. In the same table the assays of discharged cooling water is presented. The flow sheet of the water treatment plant is described in figure 6.

7 7 Figure 6. Flow sheet of the effluent waters treatment plant. Table 4. Assays of discharged water 2001 from Rönnskär. Parameter Cu Pb Zn Cd As Hg Ni COD Cleaned water na Cooling water * ) Guidance value for cleaned water accord. to permit HELCOM recommendation * ) Cleaned water is mixed w. cooling water before effluent sampling The assays of discharged water does not exceed the HELCOM recommendations HELCOM is the governing body of the Convention on the Protection of the Marine Environment of the Baltic Sea Area more usually known as the Helsinki Convention. Since 1970 the metal discharges has been reduced by 99.8%. This is demonstrated in Figure 7.

8 8 Figure 7. Emissions to water from the Rönnslär smelter ENVIRONMENTAL MONITORING Emission control Rönnskär is operated in accordance with a permit from the Swedish Licensing Board for Environmental Protection. The permit includes overall regulations and limit values for emissions into air and water. The emissions of the smelter and their impact on the environment are monitored in accordance with a detailed programme. On a monthly basis, emission reports are sent to the County Administrative Board, which is the supervisory agency. In addition, the performance of approximately 35 filters and scrubbers is monitored. Every year 600 water samples, dust samples and 50 calibration samples for SO 2 are taken. Seven major sources for emissions of sulphur dioxide are recorded continuously. The emission control is conducted by a four member sampling team. Local studies About 60 investigations have been performed in the surroundings of the Rönnskär smelter in order to study concentrations and effects on different forms of life, including on humans. Just a few examples will be given in the following.

9 9 The sulphur dioxide content in ambient air has been measured 3 km west of Rönnskär. The average content is about 4µg/m 3, which is well below the current environmental quality norm, 20µg/m 3. Samples of the mollusc Lymnea Palustris has been taken in 5 year intervals on 13 locations at the coast of Bothnia from 33 km north of Rönnskär to 90 km south. The assays show elevated grades around the smelter but the affected area is decreasing. A gradual recovery can be observed and elevated grades were 1999 found in a limited area from 3km north to 7 km south of the smelter. The results are shown in figure Norr North Hg mg/ kg 33 km, Bredviken 22 km, Herrudden 3 km, Gråsidan 2 km, Gåsören 0,8 km, Näsudden, Rö 3 km, Långskuttun 7 km, Tällön 12,5 km Skallön 25 km, Bjuröklubb 44 km, Brännögrund 8 km, Snusan 1,4 66 km, Näsudden, Gr 90 km, Ratan Hg-89 Hg-94 Hg-99 "Background" South Figure 8. Hg assays of Lymnea Palustris 1989, 1994 and Numerous studies on humans have been carried out on humans in Rönnskärs surroundings In an extensive study of metal exposure on pregnant women living in the vicinity of Rönnskär was carried out in co-operation with the University of Umeå. Approximately 500 women participated. As a reference location Holmsund 130 km south Rönnskär was chosen. Assays carried out were: Pb and Cd in blood, As in urine and Hg in hair. The results were presented in a report by Västerbottens Läns Landsting in The results showed no difference in pregnancy outcome or metal concentrations between the Rönnskär area and Holmsund. This study was followed up in 2001 when the babies from the study had been born and reached ages between 10 and 12 years. It could then be stated that they, 153 children, did not have higher concentrations of lead or cadmium in their blood than children from other places in Sweden and lower concentrations in comparison with international studies. The Rönnskär smelter has carried out substantial environmental improvements during the last 35 years. The Rönnskär smelter today is a world-class plant which comprises a high degree of environmentally adapted processes. The radically reduced emissions have given positive environmental effects in the surroundings including the Bothnian Bay. Local studies show that the recovery process is in progress. CONCLUSIONS AND COMMENTS

10 10 Sometimes it is astonishing how fast nature recovers once emissions come to an end or are radically reduced. Metals are present in nature and particularly at mining sites. If mining activities do not influence the natural concentrations of metals the need for environmental control measures should be limited. The relationship between the environmental authorities and the Boliden Company has generally been characterized by openness to the arguments of other parties and a mutual interest to solve the problems. Another conclusion is that it pays off for the mining and smelting company to take every potential environmental problem seriously, it means to investigate on its size and possible ways to eliminate it and to inform all parties involved. ACKNOWLEDGEMENTS The author thanks Boliden for its support and comments to this paper. It should also be informed that in 2009 an environmentally oriented conference for the mining and metallurgical industry will take place in Skelleftå, Sweden. On behalf of the organizers I greet you there when the sun is shining practically all night. Further information on