Good achievements in water management in 2016
Good progress was made with regards to water management during the year under review. The construction of the new centralised water treatment plant was completed and the amount of water stored at the mining area nearly reached the target level. The water discharged from the site clearly fulfilled the conditions set in the environmental permit.
The total size of the areas allocated for production and water treatment at Terrafame's site is approximately 16 square kilometres. Approximately 6 million cubic metres of water falls as precipitation annually at the mining area, and that water needs to be purified before releasing it from the mining area.
Accurate measurement of precipitation has been carried out at the mining area since summer 2013. During the last three years, rainfall has been higher than the average in the Kainuu region. The annual average rainfall (mm/year) measured at the mining area in 2014–2016 was 847 mm, while the corresponding figure for the Kainuu region as a whole was 650 mm. Terrafame's mine is thus located in an area where it is likely to rain more than in the Kainuu region on average.
The rainfall measured at the mining area in 2015 – 1,042 mm – was exceptionally high. In 2016, the measured rainfall 701 mm at the mining site was lower than in the previous year, which is likely to be close to the long-term average for the region.
Figure 1: Rainfall measured at the mining area in 2014–2016.
Trial use of centralised water treatment plant began in late 2016
Terrafame's water purification process includes the purification of process waters and the purification of collected rainwater.
The company's metals production plant plays a key role in the purification of process water, as most of the precious metals are removed from the solution at the plant. Since the autumn of 2013, water has been directed from the metals production plant to a reverse osmosis (RO) plant, which produces water for the most demanding water usage applications at the metals production plant. Up to March 2016, the RO plant's reject water, which contains sulphate, was discharged to a gypsum pond, from where part of the sulphate ended up in the water treatment process. Since March 2016, the RO plant's reject water has been discharged to the bioleaching solution circulation in which sodium sulphate precipitates as sodium jarosite in the leaching heaps.
During 2016, Terrafame used field treatment plants based on lime neutralisation to manage collected rainwater. A centralised water treatment plant was built in 2016. The plant was in trial use in November and December and was taken into actual use at the beginning of 2017.
Both the old field treatment plants and the new centralised facility are based on lime neutralisation. Using lime neutralisation to purify water is very common in Finland and elsewhere in the world. In neutralisation, the pH of water is raised to approximately 10 by feeding lime milk to the water, which will cause the metals to precipitate. The precipitation generated in field treatment plant processes has been stored in geotubes and in intermediary storage ponds to await final disposal. With the new centralised water treatment plant, precipitation will be generated in one location and can be placed into the gypsum ponds.
The water treatment plants have functioned very well: the effectiveness of purification has typically fluctuated between 95 and 99 per cent. During 2016, for example, the waters run through the discharge pipe contained on average 0.024 milligrams of nickel per litre (mg/l), when the limit set in the permit was 0.3 mg/l. The average concentration of sulphate in 2016 was 1,917 mg/l, when the limit set in the permit was 4,000 mg/l.
Figure 2 shows the main substance concentrations in the water run through the discharge points in 2015 and 2016 compared to the permit limits. Figure 3 presents the average substance concentrations in the water directed into the discharge pipe as compared to the permit conditions. As shown in figures 2 and 3, in both years, the water discharged from the mining area met the conditions set in the environmental permit for all substances. The concentrations have remained virtually unchanged in 2016.
Figure 2: Concentrations measured from water run through all discharge points in 2015 and 2016 in relation to the limits set in the permit. Despite Terrafame having a partial year of operation – from 15 August to 31 December – the 2015 concentration data is presented for the whole year.
Figure 3: Concentrations measured from water run through the discharge pipe in 2015 and 2016 in relation to the limits set in the permit. The trial run of the discharge pipe began in September 2015, and the discharge pipe was taken into use in November 2015.
Ariel – a development and pilot project at the mine
Efficient water management at the mine is a common goal for Terrafame and its owners. In November 2015, the Terrafame Group launched a development and pilot project Ariel, seeking to identify new technological solutions for purifying mine waters and reducing their sulphate levels. Terrafame Group invested two million euros in this project.
The project reached the test run phase in the spring of 2016, during which the proposed solutions were tested in practice at Terrafame's mine. The project's steering group comprised Finland's leading water specialists from organisations such as VTT Technical Research Centre of Finland, the Geological Survey of Finland (GTK), the Finnish Water Forum, Aalto University, Lappeenranta University of Technology and the University of Oulu.
Significant reduction in the amount of water stored at the mine
In January–April 2016, Terrafame discharged a total of 670,000 cubic metres of water through the old discharge routes in accordance with the environmental permit. This was not sufficient to ensure that the water melting in the spring would fit in the storage ponds. For this reason, in April–May 2016, the company had to resort to additional discharges of approximately 1.9 million cubic meters of water.
Additional discharges were used to release purified water that met all the concentration limits set in the environmental permit through the old discharge routes and the Nuasjärvi discharge pipe. Due to the discharges, the sulphate concentration of the old routes exceeded the maximum limit set in the environment permit by 2,605.9 tonnes. Despite the additional discharges, the amount of water stored at the mining area at the end of the spring flood (8.4 million cubic meters) was very close to the maximum limit.
On 28 April 2016, the Vaasa Administrative Court issued a final decision regarding the Nuasjärvi discharge pipe and water emissions along the old discharge routes (concerning the permit issued in 2013). In its decision, the Court defined essentially stricter annual sulphate quotas (15,000 tonnes per year) for the Nuasjärvi discharge pipe than in the original permit decision of the Regional State Administrative Agency for Northern Finland (24,000 tonnes per year). On the other hand, the monthly load limit set in the interim decision issued by the Vaasa Administrative Court for the melting season was raised to 2,000 tonnes a month, thus making it possible to use the discharge pipe at its full capacity during the open water season.
After the additional discharges that ended in the spring of 2016, purified waters have been run through the Nuasjärvi discharge pipe only in accordance with the quotas set in the decision of the Vaasa Administrative Court. The amount of water stored at the mining area dropped rapidly during the summer and autumn of 2016. This was mainly due to the use of the Nuasjärvi discharge pipe at full capacity, the binding of water to stacked ore, the efficient use of the reverse osmosis plant, and the additional evaporation caused by bioleaching.
Since March 2016, the reject water generated by the RO plant has been discharged to the circulating bioleaching solution. The total amount of reject water discharged to the circulating solution during 2016 is approximately 0.5 million cubic metres, including 5,700 tonnes of sulphate going back to the leaching heaps. The sodium sulphate in the reject water precipitates as sodium jarosite in the leaching heaps. In addition to reject water, 1.9 million cubic metres of additional water was discharged from the quarry to the circulating bioleaching solution, including approximately 16,000 tonnes of sulphate.
In total, 7.1 million cubic metres of water was directed through the discharge pipes and 2.5 million cubic metres through the old discharge routes in 2016, the amount of discharged water thus totalling 9.6 million cubic metres. The amount of water at the mine continued to decrease throughout the summer and autumn of 2016, so that at the end of 2016, the amount of water stored at the mining area was down to 3.8 million cubic metres, which was very close to the target level.
|Pond||Volume of water, m3|
|31 Dec. 2015||31 Dec. 2016|
|Contaminated waters in total**||7,000,244||2,672,859|
|Purified waters in total**||3,066,045||1,161,871|
|Total volume of water in the area||10,066,289||3,834,730|
|* Including the Urkki pond|
|** Excluding the water in the gypsum ponds|
Water stored at the mining area at the end of 2016.