Electrowinning of iron

Available online at www.sciencedirect.com

Hydrometallurgy 90 (2008) 213 – 220 www.elsevier.com/locate/hydromet

Electrowinning of iron from sulphate solutions
E. Mostad a,⁎, S. Rolseth b , J. Thonstad c
c a Nervikstunet 4, NO7300 Orkanger, Norway SINTEF Materials and Chemistry, NO7465 Trondheim, Norway Department of Materials Technology, Norwegian University of Science and Technology,NO7491 Trondheim, Norway b

Received 1 September 2006; received in revised form 26 February 2007; accepted 2 July 2007 Available online 26 July 2007

Abstract During a 10 years period from 1947 to 1957, a research group at the smelter owned by Orkla Grube-Aktiebolag at Thamshavn, Norway, developed the so-called Pyror Process, the aim of which was to take care of all the valuable components in thecopper-bearing pyrite ore being produced at the nearby Lökken mine. The present paper describes pilot plant operation of the crucial step of this process, which is electrowinning of iron from a sulphuric acid solution, using iron starting sheets and lead anodes surrounded by a diaphragm. High purity iron was produced, with a current yield of 85% and a power consumption of 4.25 kWh/kg iron. © 2007Published by Elsevier B.V.
Keywords: Iron; Electrowinning; Pyrite; Sulphate solutions

1. Introduction The pyrite mining operation at Lökken Verk was started way back in 1654 and was carried on with interruptions until 1904. Since then the mine was run continuously under the ownership of Orkla GrubeAktiebolag, until it was finally closed down in 1987. The smelter at Thamshavn was based on theoperation of a unique process developed by the company, producing sulphur in elemental form and copper as a matte containing the precious metals. The pyrite smelting was started in 1931 and was discontinued in 1962 for economic reasons. The main weakness of the Orkla smelting process was its inability to take care of the iron content of the ore, which for the greater part went into the slag. Thisfact was the background for the

process idea of iron extraction that was launched and developed during the early years after World War II. In view of the present situation with the threat of global warming, alternative methods for steelmaking have been considered, (ULCOS, EU 6th Framework Programme). In order to throw some light on what has been done in the past concerning electrowinning of ironfrom aqueous solutions, the authors have collected available information about an extensive project on electrowinning of iron from sulphate solutions, that was carried out some 50 years ago in Norway. This was not a scientific study per se, but the results are deemed to be of interest for anyone contemplating similar work. By publishing this data we wish to ensure that the accumulated knowledgeis preserved. 2. The pyror process

⁎ Corresponding author. E-mail address: eigil.mostad@c2i.net (E. Mostad). 0304-386X/$ - see front matter © 2007 Published by Elsevier B.V. doi:10.1016/j.hydromet.2007.07.014

The underlying idea of the Pyror process was to bring the iron content of the pyrite (FeS2) into an acid-soluble

214

E. Mostad et al. / Hydrometallurgy 90 (2008) 213–220

form(FeS), using a heat treatment to expel the loosely bound second sulphur atom from the pyrite. The heat treatment was performed either as a calcining procedure at 800 to 900 °C under inert atmosphere or by smelting in an electric furnace. The latter may preferably be performed with the addition of an iron oxide-containing material, such as a fayalite slag. As acid for the extraction of iron we choseto work with sulphuric acid, mainly because hydrochloric acid is a more corrosive agent, thereby creating greater problems in handling. The extraction of the iron was carried out at

90 to 95 °C in a three-stage counter-current leaching system of the Dorr–Oliver type, the reaction being, FeS þ H2 SO4 ¼ FeSO4 þ H2 S ð1Þ

In Fig. 1 is shown a flow-sheet presenting the main features of the...