Optimum Treatment Time for Solid-State Extraction of Nickel from Nickel Sulfide Concentrates at 1073 K
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DUCTION
NICKEL
is a critical alloying element in steels,[1,2] other corrosion-resistant alloys,[3] and batteries.[4] Approximately, 60 pct of the annual Ni production worldwide is consumed in the stainless steel industry.[5,6] The conventional route to extract Ni from Ni sulfide concentrates involves smelting and refining to remove the Fe and S associated with Ni. During smelting, sulfur in the concentrate is oxidized to SO2 and reports to the off gas, while Fe is oxidized to FeO and is slagged off. When SO2 concentration in the off gas is 10 to 12 vol pct, it can be effectively captured for sulfuric acid production,[7] while more dilute gases are often vented to the atmosphere. Sulfur dioxide mitigation in Ni smelters constitutes significant operating and capital costs, sometimes greater than the smelting cost itself. Further, there are considerable environmental hazards and penalties associated with any SO2 emitted to the
FANMAO WANG, SAM MARCUSON, and MANSOOR BARATI are with the Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, Ontario M5S 3E4, Canada. LEILI TAFAGHODI KHAJAVI is with the Department of Materials Engineering, University of British Columbia, 309-6350 Stores Road, Vancouver, British Columbia V6T 1Z4, Canada. Contact e-mail: [email protected] Manuscript submitted on May 28, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS B
atmosphere. As a result, handling SO2 emissions from the smelter remains a challenge or a cost driver for the Ni industry. Through laboratory experiments, the concepts of selective oxidation-sulfation or oxidation-chlorination roasting followed by water leaching has been proposed as an alternative route for the conventional smelting process.[8 12] Yu et al. reported that oxidation-sulfation of nickel sulfide concentrate at 973 K for 150 minutes, with the addition of 10 mass pct Na2SO4 results in recovering 79, 91, and 95 pct of Ni, Cu, and Co, respectively.[11,12] Mu et al. found that under the optimum conditions of temperature (448 K), FeCl3ÆH2O addition (50 mass pct), and time (120 minutes), the maximum recoveries of Ni and Cu were 92 and 89 pct after water leaching.[9] These alternate processes have to separate Ni and Cu from the leach solution, adding an electro-winning step to the process flowsheet. Furthermore, SO2 and SO3 gases are still generated during the roasting step, and effluent treatment is a must. The presence of oxygen either in the conventional smelting or the aforementioned selective roasting inevitably leads to the generation of SO2. The concept of an oxygen-free thermal treatment process for the recovery of Ni from pyrrhotite tailings was put forward and tested by Sridhar et al.[13] In this method, the Fe/S ratio of the sulfide is increased by adding Fe or removing S, leading to precipitation of ferronickel (FeNi). Recently, this method was further developed by Liu et al.[14] and Yu et al.[15]; they confirmed that in
the presence of metallic Fe and under inert or reducing atmosphere, S in pyrrhotite is trappe
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