Xiong Xiaolu, Li Guangshi, Lu Xionggang, Cheng Hongwei, Xu Qian, Li Shenggang
State Key Laboratory of Advanced Special Steel & Shanghai Key Laboratory of Advances Ferrometallurgy & School of Materials Science and Engineering, Shanghai University, 99 Shangda Road, Shanghai 200444, China.
School of Physical Science and Technology, ShanghaiTech University, 100 Haike Road, Shanghai 201210, China and CAS Key Laboratory of Low-Carbon Conversion Science and Engineering, Shanghai Advanced Research Institute, Chinese Academy of Sciences, 100 Haike Road, Shanghai 201210, China.
Phys Chem Chem Phys. 2020 Feb 26;22(8):4832-4839. doi: 10.1039/d0cp00197j.
Millerite (NiS) is the main source for metallurgical production of nickel worldwide. To improve the extraction rate of nickel, chlorination is usually carried out, as the resulting nickel chloride (NiCl2) can easily dissolve in water and be separated. Although molecular chlorine (Cl2) can be used as the chlorination reagent, greener reagents such as ammonium chloride (NH4Cl) are preferable from a process design perspective. However, the efficiency of NH4Cl as a chlorination reagent must be further improved for this process to be viable for industrial applications, and mechanistic understanding is imperative to this end. Here, we performed extensive density functional theory (DFT) calculations to elucidate the chlorination mechanism of NiS by exploring three possible pathways. We first considered the direct chlorination of NiS by Cl2, which was suggested to form by the reaction between NH4Cl and SO3 catalyzed by a metal oxide. Alternatively, NH4Cl was found to react favorably with the partially or fully oxidized NiS surface in the presence of oxygen (O2). During the oxidation of NiS, sulfur dioxide (SO2) may form. Furthermore, sulfur or oxygen vacancy was predicted to form during the chlorination of NiS or NiO with NH4Cl. Based on the available experimental evidence and our computational results, three possible mechanisms for the chlorination of NiS using NH4Cl as the chlorination reagent in the presence of O2 were proposed.
针镍矿（NiS）是全球镍冶金生产的主要来源。为提高镍的提取率，通常会进行氯化处理，因为生成的氯化镍（NiCl₂）能轻易溶于水并被分离出来。虽然分子氯（Cl₂）可用作氯化试剂，但从工艺设计角度来看，氯化铵（NH₄Cl）等更环保的试剂更可取。然而，要使该工艺在工业应用中可行，必须进一步提高NH₄Cl作为氯化试剂的效率，为此对其机理的理解至关重要。在此，我们进行了广泛的密度泛函理论（DFT）计算，通过探索三种可能的途径来阐明NiS的氯化机理。我们首先考虑了Cl₂对NiS的直接氯化，这是由金属氧化物催化的NH₄Cl与SO₃之间的反应所建议形成的。另外，发现NH₄Cl在氧气（O₂）存在下能与部分或完全氧化的NiS表面发生有利反应。在NiS氧化过程中，可能会形成二氧化硫（SO₂）。此外，预计在NH₄Cl对NiS或NiO进行氯化时会形成硫或氧空位。基于现有的实验证据和我们的计算结果，提出了在O₂存在下以NH₄Cl作为氯化试剂对NiS进行氯化的三种可能机理。
