Laterites and other oxidized nickel ores constitutea very important part of world-wide nickel reserves. In theconventional production of ferronickel from these ores, muchfine material is produced which cannot readily beaccommodated directly in existing three-electrode or six-in-lineAC furnaces. DC-arc furnace technology allows ore -ides lessthan 1 mm in size to be treated directly, thereby improving theoverall recovery of nickel without the need for expensiveagglomeration techniques. Because of the high moisture contentof laterites, the ores should be dried and calcined beforesmelting. In order to decrease the energy consumption further,the ores could also be pre-reduced. The CO-rich off-gas fromthe furnace could be used to supplement the energyrequirements, and is also a good reducing agent. Because fineore particles are readily treated in a Dc-arc furnace, units such asfluidized beds (which require materials of small particle size)can be used for the pre-treatment stage of the process.A process has been developed whereby nickel laterites of a widecompositional range can be smelted in a DC-are furnace, toproduce ferronickel. The flexible operation of a DC-arc furnace(especially its lower dependence on electrical properties of theslag, because of open-arc operation, in addition to the ability torun at an optimum slag temperature, due to the open-bath modeof operation) allowed for the successful treatment of ores with aSiO_2/MgO ratio between 1.2 and 3.0, as well as orescontaining up to 30 per cent by mass of iron (which tends tocause slag foaming in a conventional immersed-electrodefurnace). A frozen lining can be maintained between the moltenbath and the refractory lining, in order to minimize refractorywear (especially at high SiO_2 contents). Results of furnacetestwork at power levels up to 750 kW are presented. Tests atthe 120 kW furnace scale, together with some preheating in a300 mm diameter bubbling fluidized bed, are also described.
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