Thermal Upgrading of Nickeliferous Pyrrhotite Tailings for the Recovery of Nickel in the Form of Ferronickel Alloy
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INTRODUCTION
PYRRHOTITE (Pyrr, Fe1xS, x = 0 to 0.125) is ubiquitous in Ni-Cu sulfide ore deposits. In the beneficiation of Ni sulfide ores, the main Ni-bearing mineral, i.e., pentlandite (Fe,Ni)9S8, is recovered into the Ni concentrate while the bulk of the sulfidic constituents being Pyrr is rejected as tailings to improve smelting capacity and minimize SO2 emissions.[1] It has been recognized that, for the Ni sulfide ores in the Sudbury region of Ontario, Canada, appreciable amounts of pentlandite occurs as micro-sized ‘‘flames’’ finely disseminated in the Pyrr matrix[2]; as a consequence, this part of pentlandite together with Pyrr inevitably reports to the tailing stream. On the other hand, the nonstoichiometric Pyrr found in Sudbury has a dissolved Ni content in the range of 0.6 to 0.8 pct Ni, which represents more than half of the total Ni value contained in the Pyrr tailings.[3] Estimates show that in Sudbury about 75 to 100 Mt Pyrr on a dry basis has been accumulated, and fresh Pyrr tailings are being produced
DAWEI YU is with the School of Metallurgy and Environment, Central South University, 932 Lushan South Road, Changsha, Hunan 410083 P. R. China and also with the Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, ON M5S 3E4, Canada. Contact e-mail: [email protected] FENG LIU, JIAJING ZHANG, and MANSOOR BARATI are with the Department of Materials Science and Engineering, University of Toronto. Manuscript submitted March 19, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
at a rate of up to ~ 5000 tpd.[4] Given these facts, Sudbury Pyrr tailings may be regarded as a significant Ni resource, and a process for the recovery of Ni and mitigation of tailings has been of interest. Such a process could potentially be applied to Pyrr of other mines where there has been reports of high Ni contents, such as 2 to 3 pct Ni in Norilsk, Russia,[5–7] and 1 to 2 pct Ni in Jinchuan, China.[7,8] The last attempt to commercially process Sudbury Pyrr tailings for value recovery was ended by Vale (formerly known as INCO) in 1991 with the shutdown of roasters.[9] At present, impounding Pyrr tailings is practiced, which reportedly is the most effective measure to prevent the occurrence of acid mine drainage (AMD).[10] However, subaqueous deposition of Pyrr tailings requires high maintenance costs, and the sulfide oxidation in Pyrr-rich tailing impoundments is an ongoing risk.[11] In this regard, the development of economically sound and environmentally friendly technologies is still needed for processing of Sudbury Pyrr tailings to mitigate their long-term environmental impact. A thermal upgrading process to concentrate Ni in an alloy phase followed by magnetic separation was first studied by Vale in the 1970s.[12,13] The basic principle behind this process has been discussed in a previous publication.[14] As shown in the Fe-Ni-S isotherm (Figure 1), at 1173 K, a monosulfide solid solution (mss) exists between Fe1xS and Ni1xS, and the Fe-rich portion of this ternary system is dom
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