Electrical conductivity and density of NiSO4/H2SO4 solutions in the range of modern nickel electroreﬁning and electrowinning electrolytes
R. WU1, M. OLIAZADEH2 and A.M ALFANTAZI1,* 1 Department of Mining Engineering, Tehran University, PO Box 11365-4563, NorthernAmirabad, Tehran, Iran 2 Department of Metals and Materials Engineering, The University of British Columbia, Vancouver, BC, Canada, V6T 1Z4 (*author for correspondence, fax: þ604 822 3619, e-mail: email@example.com)
Received 30 September 2002; accepted in revised form 7 April 2003
Key words: conductivity, density, electrolyte, electroreﬁning, electrowinning, nickel
Abstract Thedensity and electrical conductivity of nickel sulfate electrolytes as a function of nickel and sulfuric acid concentration and electrolyte temperature have been experimentally measured. Models have been developed to explain the eﬀects of temperature, nickel and sulfuric acid concentration on the electrical conductivity and density. Empirical equations to mathematically quantify the reported values havealso been derived to allow reasonable extrapolation. These models maybe used to enhance the electroreﬁning and electrowinning processes.
1. Introduction Electrolytic processes are among the most important methods for the production of high-purity nickel. Nickel recovery by electroreﬁning and electrowinning accounts for close to half of the total world nickel production. In electroreﬁning, theplates of crude metal are anodically dissolved in a suitable electrolyte, while pure nickel metal is deposited on the cathodes. In the electrowinning of nickel from either the sulfate or chloride media, nickel is deposited at the cathode and either oxygen, in sulfate media, or chlorine, in chloride media, is produced at the anode. Nickel electrowinning from sulfate electrolyte has receivedconsiderable attention in recent years and it is the preferred rout for most of the new laterite processing plants in Australia. For example Cawse and Bulong, who commenced nickel production 1999, electrowin nickel metal from sulfate electrolytes, which are generated from laterite ores via solvent extraction routes . In electrowinning of nickel from sulfate electrolytes the following main reactionsoccur: Cathode : Anode : Ni2þ þ 2 eÀ ! Ni 2H2 O ! O2 þ 4Hþ þ 4eÀ ð1Þ ð2Þ
competition with nickel deposition according to following reaction, which could seriously reduce the current eﬃciency of the cell: 2Hþ þ 2eÀ ! H2 ð4Þ
The overall cell reaction is 2NiSO4 þ 2H2 O ! 2Ni þ 2H2 SO4 þ O2 ð3Þ
The cathode must be protected from the strongly acidic anolyte otherwise hydrogen gas would be formedin
The electrodeposition process can be greatly inﬂuenced by the density and electrical conductivity of the electrolytes, which can be determined by other parameters including composition, pH and temperature of the electrolyte and impurities. As indicated nickel sulfate/sulfuric acid solutions are often used as the base electrolytes in electroreﬁning and electrowinning to produce metallicnickel. Chloride based electrolytes are also commonly used in nickel electrowinning. The density and electrical conductivity of these electrolytes are of signiﬁcant importance in reducing the energy consumption, enhancing mass transfer and inﬂuencing the carry over of impure particulate into the ﬁnal nickel deposits, which are related to the rate of formation of nickel on the cathode. Although thereare some studies on the nickel electrowinning and electroreﬁning processes [1–4], review of the literature indicates that virtually no information is available on the density and electrical conductivity for nickel electrowinning and electroreﬁning sulfate electrolytes. A number of studies haves been reported for other electrowinning electrolytes such as copper [5, 6] and zinc [7, 8]. Price et al....