Ramp-up year in production
During the operational year 2016, Terrafame continued its strong ramp-up in production. Nickel and zinc stacking and leaching quantities grew during every quarter. Production also increased at the metals production plant from one quarter to the next.
Terrafame continued to increase the production volumes of metals throughout 2016 and the production year was successful. The zinc production was in line with the company's annual production plan and the nickel and cobalt production somewhat behind the plan.
Ore mining and stacking to the primary leaching heap totalled 14.2 million tonnes during the year. Primary heaps 2 and 3 were completed, and heap 4 was built for the most part. By the end of the year, 75 per cent of the primary leaching area was taken into production.
New layers to secondary leaching
In the secondary leaching area, a second ore layer was completed during the year to heap 2, as well as a third layer to heap 1. Approximately 13.5 million tonnes of ore stacked by the previous operator was reclaimed and transferred to the secondary leaching heap during the year.
One of Terrafame's largest investments in 2016 was the construction of the foundations for secondary leaching heaps 3 and 4. These new leaching areas will double the secondary leaching area and are due to be commissioned in 2017 and 2018.
Bioleaching worked as planned
The primary and secondary bioleaching performance was in line with the plan throughout the year. As an exothermic process, bioleaching can be successfully carried out also in the winter. The primary leaching heaps stacked by Terrafame generated substantial heat during the year as a whole. As a result, the company's chemical production efficiency improved and brought significant savings over the course of the year.
In metals recovery, metal sulphides – i.e., metal and sulphur compounds – are separated from the process solution with chemicals. In Terrafame's production, copper is first extracted from the solution, then zinc, and finally nickel and cobalt. Copper leaches from the ore at a later stage than zinc, and nickel and copper production is planned to begin in 2017.
Both lines at the metals production plant deployed
The production speed at the metals production plant was adjusted to the production of bioleaching heaps. The plant was first run at an unhurried pace, using only one of the two production lines. With the increase in bioleaching heap production volumes, the second production line was taken into use in October. By the end of the year, the cost-efficiency improved significantly as the production volume increased. During the operational year, the plant produced 9,554 tonnes of nickel and 22,575 tonnes of zinc.
In 2016, both lines at the metals production plant were stopped on 16–31 December, due to a fire in a hydrogen sulphide reactor. During this unplanned shutdown, the bioleaching continued and the metals production was moved to 2017.
Centralised water treatment plant completed at end of year
The new centralised water treatment plant was completed in late 2016, and the trial was started in November. The centralised water treatment plant simplifies the site's water purification process leading to a more cost-efficient purification as well as further improved consistency of purification results.
At the centralised water treatment plant, the same best available technology is utilised as has been in use until now in the field purification units. The cleaning process is now concentrated into one automated production unit. The cleaning capacity is 1,400 cubic metres of purified water per hour.
The new plant was taken into use in early 2017 based on the environmental permit.
Reverse osmosis plant is a key step in sulphate management
In March 2016, a reverse osmosis plant reject was for the first time pumped into the leaching process. With this method, approximately 5,700 tonnes of sulphate accumulated into the process water was returned and led to the bioleaching heaps in March–December. This had a significant impact on the adequacy of Terrafame's sulphate quota and the water balance at the site.
Reverse osmosis has been utilised in industrial use for decades, particularly in the production of clean water. Terrafame in Finland has one of the largest reverse osmosis plants at its disposal.
Picture 1. Nickel production volumes in 2016.
Picture 2. Zinc production volumes in 2016.