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M. J. Dias et al.
Introduction
Overall Interest on Zinc Oxidized Ores
Hydrometallurgical extraction of metals from its ore has innumerous advantages over
the pyrometalurgical route chiefly because it is more attractive economically, technically and environmentally. Additionally, it costs less and does not emit hazardous
gases such as SO 2 , for instance [1].
It is known that the production of zinc from sulfide ores has its benefits due to
its great separation from gangue as well as to easily concentrate through flotation
techniques. Nevertheless, with the decline of zinc sulfide reserves worldwide and the
restrictions on SO 2 emissions during its processing, there has been an increased interest in processing reserves of zinc oxide ores [2]. Besides, according to [3], oxidized
zinc deposits has such advantages in comparison with non-oxidized deposits:
– High zinc content when compared to sulfide zinc ores (zinc is greater than 10%);
– Low hardness type of ore which demands minor detonations;
– In general, it is exploitable in open cast mines.
Furthermore, the combination of both pyro and hydrometallurgical routes is
responsible for the main production of zinc by RLE (Roasting-Leaching-Electrolysis)
[4]. One of the oxidized ores containing zinc is named silicate (Zn 2 SiO 4 ), which is
found in nature and denominated as willemite, its mineral name given by geologists
[5]. This zinc ore is commercially treated and processed through a hydrometallurgical and solvent extraction technology in two places worldwide: Nexa Resources (in
Brazil) and Skorpion Zinc (in Namibia), respectively.
Silicate Leaching Process
Regarding silicate concentrate [6]. Três Marias zinc facility has devised an integration
of both silicate and sulfide concentrate processes. In this zinc plant, which belongs
to Nexa Resources, the silicate treated ore is received from Vazante’s mine, which
also belongs to the same company. At Vazante’s mine, the ore is extracted from
an underground mine and goes through such processes as: comminution, flotation,
thickening and filtration. The result is a concentrate with 40% zinc content and 15%
humidity, on average.
At Três Marias’ site, the concentrate is repulped with a solution containing 50 g/L
of zinc and feeds the pressure leaching process, which employs autoclaves. In this
process, the soluble zinc from the secondary solution precipitates as zinc hydroxide
and the calcium and magnesium carbonates contained in the solid are solubilized in
the form of sulfates (Eqs. 1 and 2).
MgCO 3 + ZnSO 4 + H 2 O → Zn(OH) 2 + MgSO 4 + CO 2
(1)
M. J. Dias et al.
Introduction
Overall Interest on Zinc Oxidized Ores
Hydrometallurgical extraction of metals from its ore has innumerous advantages over
the pyrometalurgical route chiefly because it is more attractive economically, technically and environmentally. Additionally, it costs less and does not emit hazardous
gases such as SO 2 , for instance [1].
It is known that the production of zinc from sulfide ores has its benefits due to
its great separation from gangue as well as to easily concentrate through flotation
techniques. Nevertheless, with the decline of zinc sulfide reserves worldwide and the
restrictions on SO 2 emissions during its processing, there has been an increased interest in processing reserves of zinc oxide ores [2]. Besides, according to [3], oxidized
zinc deposits has such advantages in comparison with non-oxidized deposits:
– High zinc content when compared to sulfide zinc ores (zinc is greater than 10%);
– Low hardness type of ore which demands minor detonations;
– In general, it is exploitable in open cast mines.
Furthermore, the combination of both pyro and hydrometallurgical routes is
responsible for the main production of zinc by RLE (Roasting-Leaching-Electrolysis)
[4]. One of the oxidized ores containing zinc is named silicate (Zn 2 SiO 4 ), which is
found in nature and denominated as willemite, its mineral name given by geologists
[5]. This zinc ore is commercially treated and processed through a hydrometallurgical and solvent extraction technology in two places worldwide: Nexa Resources (in
Brazil) and Skorpion Zinc (in Namibia), respectively.
Silicate Leaching Process
Regarding silicate concentrate [6]. Três Marias zinc facility has devised an integration
of both silicate and sulfide concentrate processes. In this zinc plant, which belongs
to Nexa Resources, the silicate treated ore is received from Vazante’s mine, which
also belongs to the same company. At Vazante’s mine, the ore is extracted from
an underground mine and goes through such processes as: comminution, flotation,
thickening and filtration. The result is a concentrate with 40% zinc content and 15%
humidity, on average.
At Três Marias’ site, the concentrate is repulped with a solution containing 50 g/L
of zinc and feeds the pressure leaching process, which employs autoclaves. In this
process, the soluble zinc from the secondary solution precipitates as zinc hydroxide
and the calcium and magnesium carbonates contained in the solid are solubilized in
the form of sulfates (Eqs. 1 and 2).
MgCO 3 + ZnSO 4 + H 2 O → Zn(OH) 2 + MgSO 4 + CO 2
(1)