Issue 11, p. 161 (2022)

  Oral

Case study: improved sampling of iron sludge at Glencore Nikkelverk

  • Eirik Djuve  
  • Elke Willam Thisted
Glencore Nikkelverk AS, Vesterveien 31, P.O.boks 604, 4604 Kristiansand, Norway
[email protected]
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 Corresponding Author
Glencore Nikkelverk AS, Vesterveien 31, P.O.boks 604, 4604 Kristiansand, Norway
[email protected]
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Glencore Nikkelverk produces nickel, copper and cobalt with high purity. This demands several leaching and filtration steps removing contaminants to achieve a high-quality metal via electrolysis. In one of the process steps iron is oxidized to its trivalent state and forms a slurry precipitate, which contains different iron components described as FexOy(OH)z. The slurry is very fine-grained, corrosive and has a miry consistency resembling muddy clay. Filter presses with up to 90 frames separate the process solution from the iron slurry, which undergoes a washing cycle. Due to the slurry’s fine-grained nature, this washing cycle is challenging with uneven distribution of the washing water and results in loss of valuable dissolved Nickel chloride (NiCl2) which is left in the slurry. The slurry discharges of the filter presses are stored in Nikkelverk’s underground landfills and leads to a yearly loss of approximately 20 million Norwegian kroner. In 2017, the R&D department at Nikkelverk took spear samples for over a period of nine month to map the Nickel content in the material prone to be discharged to the underground landfill. The results showed that the Nickel lost was approximately 40% higher than reported from the samples taken directly from a frame by the operators. In 2018, a mapping of several press frames by handheld X-ray analysis showed that the Nickel content, depending on the position of the sample taken in a frame, varies. Since the physique of the operators determines where the sample is prone to be taken, this will add to the variation in the analytical result of Nickel lost. It can be assumed that this variation completely overshadows the process variation resulting in lost Nickel. In summary, the current sampling protocol gives a high variation and a wrong content of Ni in the slurry. Nikkelverk’s commitment to its business system and thereby involvement of resources on any level of the company has resulted in formations of process teams which shall approach such issues and find solutions fit-for-purpose. Therefore, a process team was initiated to develop an automatic sampler in-house for the iron slurry. Their goal was to achieve samples that are more representative as the ones retrieved by today’s protocol. There are six filter presses where slurry is separated from the filtrate. Each filter press releases its slurry on a conveyor belt, which transports the slurry to a collecting chute. The idea is to mount an automatic sample in the collecting chute prior to the slurry compiled for transport to the underground landfill. The article will describe in detail the pre-studies of the problem, the development of the automatic sampler for the collecting chute and discuss its conformity regarding the theory of sampling.

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