Anodic Dissolution of Iron in Ammoniacal Ammonium Carbonate Solution

Abstract

The electrochemical behavior of iron has been characterized in aqueous ammoniacal ammonium carbonate solution. Pure iron anodically polarized in He-or O=,-saturated 2 kmol m -'~ NH:~ + 1 kmol m -'~ (NH4)2CO:3 solutions exhibits both stable active (E = -650 to -400 mV, SHE) and passive (E = -330 to 1000 mV) regions. A cathodic loop was observed in the potential range of -380 to 100 mV. It is suggested, on the basis of cathodic polarization curves of a graphite electrode in various concentrations of ammoniacal solution, that the cathodic loop is due to oxygen discharge. The addition of CoCO:~ to the ammoniacal solution has the same effect as oxygen in that it increases the cathodic current and potential range of the cathodic loop and, as such, functions as a strong oxidant.

The electrochemistry of the leaching reactions in the Caron process II. Cathodic processes

“…This passivation occurs due to the formation of an oxide layer [8,9] at potentials which can be attained in the presence of high concentrations of dissolved oxygen and/or other oxidants such as cobalt(III) ions [10,11]. In the presence of thiosulfate, the passivation is promoted by the precipitation of a mixed cobalt/nickel sulfide layer as a result of reduction of thiosulfate in the presence of these ions [7].…”

Study of the dissolution of chalcopyrite in solutions of different ammonium salts

“…Studies have been carried out on the leaching of nickel from pre-reduced laterite ores (nickel and iron are present as reduced metallic grains and metal alloys) (Das and Anand, 1995;Jandová andPedlík, 1994, Kim et al, 1991;Lee, Osseo-Asare, and Pickering, 1985;Nikoloski, 2002;Nicol, Nikoloski, and Fittock, 2004). At a pH of about 9.8 in ammoniacal solutions, the dominant dissolved iron species is the ferrous tetra-ammine ion and the dissolution reaction has been postulated to occur according to Equation [2] (Nikoloski, 2002;D'Aloya and Nikoloski, 2012;Subrata, 2010;Nikoloski and Nicol, 2006;Osseo-Assare and Asihene, 1979):…”

An electrochemical investigation of the formation of CoSx and its effect on the anodic dissolution of iron in ammoniacal-carbonate solutions

“…It is therefore important to gain a better understanding of the factors and conditions that affect the anodic behaviour of iron, in order to have better control over it and therefore improve the overall efficiency of the process. Although the passivation of iron induced by polarisation has been consistently reported in many studies (Jandova and Pedlik, 1991;Kho et al, 1992;Kim et al, 1991;Lee et al, 1985;Nicol et al, 2004; A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT Nicol, 2006;Nikoloski et al, 2003), only a few of these have documented it taking place as a spontaneous process. Under open circuit conditions, iron has generally been found to remain in active dissolution, except in heavily aerated or oxygenated solutions (Nikoloski et al, 2003).…”

“…This is supported by measurements conducted at the QNi Caron plant in Yabulu, Australia (Nicol et al, 2004;Nikoloski et al, 2003). Although iron rejection is necessary at this stage of the process, the passivation of iron has been identified as one of the possible factors behind its relatively poor extraction efficiency, as suggested by several investigations into the active-passive behaviour of iron in ammoniacal-carbonate solutions (Jandova and Pedlik, 1991;Kho et al, 1992;Kim et al, 1991;Lee et al, 1985;Nicol et al, 2004;Nikoloski and Nicol, 2006;Nikoloski et al, 2003;OsseoAsare., 1983). It is therefore important to gain a better understanding of the factors and conditions that affect the anodic behaviour of iron, in order to have better control over it and therefore improve the overall efficiency of the process.…”