Iron extraction from copper slag by additive-free activation roasting‒magnetic separation
通过无添加活化焙烧\u2012磁选从铜渣中提取铁

Xiaoxue Zhang ¹, Hongyang Wang ^1,2*, Yuqi Zhao ², LiqunLuo^1,*
张晓雪 ¹， 王洪阳 ^1,2*， 赵玉琪 ²， 罗丽群^1，*

1.‒School of Resources and Environmental Engineering, Wuhan University of Technology, Wuhan 430070, China.
1.武汉理工大学 资源与环境工程学院，湖北 武汉 430070

2.‒School of Materials Science and Engineering, Anhui University of Science and Technology, Huainan 232001, China.
2.\u2012安徽科技大学材料科学与工程学院，中国 淮南232001

* Corresponding author: Hongyang Wang (hywang3@163.com); LiqunLuo( lqluollq@hotmail.com)
* 通讯作者：Hongyang Wang （hywang3@163.com）;罗丽群 LiqunLuo（ lqluollq@hotmail.com）

Abstract:Iron grain growth during deep reduction roasting is important for iron enrichment from copper slag (CS) through magnetic separation. In this work, a novel method of additive-free activation roasting, including oxidation and subsequent reduction roasting, was proposed to increase the iron grain size, then the iron was extracted by magnetic separation.The phase transformation of CSduring activation roasting was studied byTG, XRD, SEM, and EDS. Results showed that the main mineral of fayalite in CSwas decomposed into iron oxides and silica during oxidation roasting, and the thickness of iron oxide layer on the particle surface increased with the oxidation temperature. During reduction roasting, the CS and oxidized copper slag (OCS) were ultimately converted into metallic iron and cristobalite solid solution.In the reduced product obtained at 1150°C, the iron grain sizeswere 6.42μm and 16.62μmfrom CS and OCS-1100 °C,respectively. Furthermore, the Fe content in the magnetic concentrate was 72.86% in the reduced product of CSwhilethat was 87.85% in the reduced product of OCS-1100 °C with anFe recovery of ~85%. This study opens a new direction for iron enrichment from copper slag.
摘要：深还原焙烧过程中的 Iron 晶粒生长对于磁选从铜渣 （CS） 中富铁至关重要。在本工作中，提出了一种无 添加活化焙烧的新方法，包括氧化和随后的还原焙烧，以增加铁的晶粒尺寸，然后 通过磁选提取铁。通过TG 、 XRD 、 SEM 和 EDS 研究了活化焙烧过程中 CS的相变。 结果表明，CS中辉石的主要矿物在氧化焙烧过程中分解成氧化铁和二氧化硅，颗粒表面的氧化铁层厚度 随着氧化温度的增加而增加。在还原焙烧过程中，CS 和氧化铜渣 （OCS） 最终转化为金属铁和方石英固溶体。在 1150°C 下得到的还原产物中，铁的晶粒尺寸s 分别为 6.42μm 和 16.62μm（CS 和 OCS-1100 °C）。 此外，磁精矿中 Fe 含量为 72.86%，而 CS 还原产物为 87%。 在 OCS-1100 °C 的还原产物中 为 85%，nFe 回收率为 ~85%。本研究为铜渣富铁开辟了新的方向。

Keywords: copper slag;additive-free activation roasting;iron grain size; magnetic separation; concentrate
关键词： 无铜渣添加剂活化 焙烧铁 粒度;磁性分离浓缩液

1. Introduction
1. 介绍

Copper, whichis second only to the aluminum in the consumption of nonferrous material, has been widely used in various industries,such as construction, machinery, national defense, and electric power(Schlesinger et al., 2011). The demand of copper increased from~19.0 million tons in 2010 to ~24.0 million tons in 2020,which is expected to reach ~28.5 million tons in 2030(Elshkaki et al., 2016). Pyrometallurgy, which has the advantages of high production efficiency, low energy consumption, and high quality of electrolytic copper, is still the main method to produce copper using sulfide minerals (e.g. bornite(Cu₅FeS₄) and chalcopyrite (CuFeS₂))and accounts for more than 80% of global copper supply (Zuo et al., 2022). After the pyrometallurgical treatment of the raw material, the copper is enriched to over 99.0%.Meanwhile, the iron is separated by reacting with quartz to form molten fayaliteslag, which is known as copper slag (CS) in the industry. Approximately 2.0−3.0 tons of CS are produced for 1.0 ton of copper production, and the global generation of CS is about 40 million tons annually(Xia et al., 2022; Wan et al., 2021). Land stockpiling for CS occupies a large space, and causes severe pollution to the surrounding environment due to the presence of several elements, such as Zn, Pb, Cu, and As (Holland et al., 2019; Phiri et al., 2021; He et al., 2021). Therefore, the comprehensive utilization of CS must be realized.
铜在有色金属材料的消耗量中仅次于铝，已广泛应用于建筑、机械、国防和电力等各个行业（Schlesinger et al.， 2011）。 铜的需求从 2010 年的 ~1900 万吨增加到 2020 年的 ~2400 万吨，预计到 2030 年将达到 ~2850 万吨（Elshkaki 等人，2016 年）。 Pyrometallurgy 具有生产效率高、能耗低、电解铜质量高等优点，仍然是 使用硫化物矿物（例如斑铜矿 （Cu₅FeS₄） 和黄铜矿 （CuFeS₂）），占全球铜供应量的 80% 以上（Zuo et al.， 2022）。对原材料进行火法冶金处理后，铜的富集度达到 99.0% 以上。同时，铁通过与石英反应分离，形成熔融的 Fayalite渣，在工业上被称为铜渣 （CS）。 大约 2.0−3。1.0 吨铜产品离子生产 0 吨 CS，全球每年生产约 4 000 万吨 CS（Xia et al.，2022 年;Wan et al.， 2021）的 L和 CS 的储存占用空间很大 ，并且由于 Zn、Pb、Cu 和 As 等多种元素的存在，对周围环境造成严重污染（Holland等人，2019 年;Phiri et al.， 2021;He et al.， 2021）的 因此， 必须实现 CS 的综合利用。

Fe extraction is one of the main directions for the high-value application of CS, in which there are 35%−45% of Fe, 30−40% of SiO₂, ~0.94% of Pb, ~1.83% of Zn and so on(Goraiand Jana, 2003; Patrick et al., 2020; Zhuo et al., 2022). The main extraction methods include smelting reduction, selective oxidation−magnetic separation, and carbothermal reduction−magnetic separation processes. In the smelting reduction, the Fe in CS is reduced into liquid iron by smelting reduction at 1480 °C−1520 °C, meanwhile the other elements in CS are discarded in the form of Ca-bearing slag(Heo et al., 2013; Zhang et al., 2015). However, the high energy consumption and huge generation of slag restrict the industrialized application of smelting reduction method. In the selective oxidation‒magnetic separation,the Fe-bearing minerals in liquid CS can be oxidized into magnetite during coolingby regulating the partial pressure of oxygen. Afterward, the magnetite is selectively enriched by magnetic separation(Tsunazawa et al., 2019; Zhang et al., 2005). However, the viscosity of liquid CS rapidly increases with the precipitation of magnetite, thereby hindering the growth of magnetite particle.
Fe 提取是 CS 高价值应用 的主要方向之一，其中有 35%−45% 的 Fe、30−40% 的 SiO₂、~0.94% 的 Pb、~1.83% 的 Zn 等（Gorai和 J ana，2003 年; Patrick et al.， 2020; Zhuo 等人。， 2022）的主要提取方法包括冶炼还原、选择性氧化-磁分离和碳热还原-磁分离工艺。 在冶炼还原中， CS 中的 Fe 在 1480 °C−1520 °C 下通过冶炼还原转化为液态铁，同时 CS 中的其他元素以含钙渣的形式丢弃（Heo et al.， 2013;Zhang et al.， 2015）的 然而，高能耗和大量造渣制约了冶炼还原法的工业化应用。 在选择性氧化磁选中，液态 CS 中含铁矿物在冷却过程中通过调节氧分压被氧化成磁铁矿。病房后，磁铁矿通过磁分离选择性富集（Tsunazawa et al.， 2019;Zhang et al.， 2005）的。 然而，液体 CS 的粘度随着磁铁矿的沉淀而迅速增加，从而阻碍了磁铁矿颗粒的生长。

Carbothermal reduction−magnetic separation method is a potential method for the industrialized application of CS(Tian et al., 2021; Zhuo et al., 2019). Inthe carbothermal reduction, the Fe-bearing minerals in CS are reduced into ferromagnetic metallic iron, meanwhile Zn and Pb are enriched in the gas dust due to their volatility. The metallic iron in reduced productis then enriched by magnetic separation. When CS is directly reduced by carbothermal reduction, the metallic iron in the reduced product is difficult to be enriched by grinding−magnetic separation due to the small mean particle size of about 6μm(Kim et al., 2013; Wang and Song,2020). Therefore, large amounts of additives (e.g. calcium salts and sodium salts) are added in the CS during carbothermal reduction to increase the mean particle size of metallic iron to≥20μm for iron enrichment(Ku et al., 2019; Li et al., 2019). Considering that the additive is unrecyclable, a huge amount of magnetic tailing is generated and difficult to be disposed.
C树热还原-磁分离法是 CS（Tian et al.，2021 年;Zhuo et al.， 2019）的 在碳热还原中，CS 中含铁矿物被还原成铁磁性金属铁，同时 Zn 和 Pb 由于挥发性而富集在气体尘埃中。然后通过磁分离富集还原产物中的金属铁。当 CS 通过碳热还原直接还原时，由于平均粒径约为 6μm，还原产物中的金属铁 很难通过研磨 - 磁分离进行富集（Kim et al.，2013 年;Wang 和 Song，2020 年）。因此，在碳热还原过程中，在 CS 中添加了大量添加剂（例如钙盐和钠盐），以将 金属铁的平均粒径增加到 ≥20μm 以进行铁富集（Ku et al.， 2019;Li et al.， 2019）的。 考虑到添加剂不可回收， 会产生大量的磁性尾矿，难以处理。

If the particle size of metallic iron in the reduced productcould be increased during carbothermal reductionof CS without adding any additive,the iron can be enriched by magnetic separation and the comprehensive utilization of silica can also be achieved. Relevant studies showed that fayalite can be oxidized into silica and hematite, where hematite can be easier to be reduced into metallic iron thanfayalite(Gyurov et al., 2011). In addition, hematite whiskers can be found on the particle surface of oxidized fayalite(Gaballah et al., 1978). Therefore, a novel method of oxidation and subsequent reduction roasting to increase the particle size of metallic ironwas proposed in this work.Furthermore, the metallic iron in reduced productwas enriched by magnetic separation. The phase transformation of CS during roasting was studied bythermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersion spectrum (EDS).
如果在 不添加任何添加剂的情况下，在碳热还原CS时可以增加还原产物中 金属铁的粒径，则可以通过磁分离富集铁，也可以实现二氧化硅的综合利用。Relevant 研究表明，辉铁矿可以氧化成二氧化硅和赤铁矿，这里的赤铁矿比辉铁矿更容易还原成金属铁（Gyurov 等人，2011 年）。 此外，在氧化辉石的颗粒表面可以找到赤铁矿晶须（Gaballah et al.， 1978）。 因此，本研究提出了一种新的氧化和随后的还原焙烧方法来增加金属铁的粒度。此外，通过磁分离富集还原产物中的金属铁。通过热重分析法 （TG）、X 射线衍射 （XRD）、扫描电子显微镜 （SEM） 和能量色散谱 （EDS） 研究了 CS 在焙烧过程中的相变。

2. Experimental
2. 实验的

2.1. Materials
2.1. 材料

CS, which is a tailing of liquid CS subjected to slow cooling-flotation, was obtained from Daye Nonferrous Metals Group Holdings Co., LTD, China.Its chemical compositions were as following: 40.22% Fe, 34.62% SiO₂, 1.05% Al₂O₃, 0.51%MgO, 0.28%CaO, 0.27%CuO, 2.94%ZnO and 1.81%PbO (Table 1). The XRD pattern in Fig. 1indicated that the main mineral of CS is fayalite,with small amounts of magnetite and cristobalite. The presence of cristobalitemight be caused by the conversion of quartz during copper smelting.
CS是经过缓慢冷却浮选的液体CS的尾矿，购自中国大冶有色金属集团控股有限公司。其化学成分为：40.22% Fe、34.62% SiO₂、1.05% Al₂O₃、0.51%MgO、0.28%CaO、0.27%CuO、2.94%ZnO 和 1.81%PbO（表 1）。图 1 中的 XRD 图谱表明 CS 的主要矿物是辉长石，含有少量的磁铁矿和方石英。方石英的存在可能是由铜冶炼过程中石英的转化引起的。

Table 1 Chemical compositions of copper slag (mass fraction/%)
表 1 铜渣的化学成分（质量分数/%）

Fig.1.XRD of copper slag
图 1 铜渣的 XRD

The SEM-EDS images of CS were shown in Fig.2. Results showedthat independent silica particles presentedin the CS (point A). The main elements Fe and O in point B indicated the presence of magnetite asshown in Fig.1. A small amount of Zn, Al, and Ti existed in the magnetite. The Fe/Si/O molar ratio of 1.7:1.0:3.7 in point C was close to the theoretical value of 2.0:1.0:4.0 infayalite. This result was in agreement with Fig. 1 thatfayaltie was the main mineral in the CS. In addition, 1.73 wt.% of Zn was found in fayalite, because Zn can be dissolved in the crystal lattice of fayalite to form zinc-doped fayalite (Fe_2-xZn_xSiO₄)(Wang et al., 2019).
图 2 显示了 CS 的 SEM-EDS 图像。 结果表明，独立的二氧化硅颗粒存在于 CS （点 A） 中。 点 B 中 的主要元素 Fe 和 O 表明磁铁矿的存在， 如图 1 所示。 磁铁矿中存在少量的 Zn、Al 和 Ti。C点的Fe/Si/O摩尔比为1.7：1.0：3.7，接近Fayalite中2.0：1.0：4.0的理论值。这一结果与图 1 一致，即fayaltie 是 CS 中的主要矿物。此外，在辉石中发现了 1.73 wt.% 的 Zn，因为 Zn 可以溶解在辉石的晶格中，形成锌掺杂辉长石 （Fe_2-xZn_xSiO₄）（Wang et al.， 2019）。

Fig.2.SEM-EDS images of copper slag
图 2 铜渣的 SEM-EDS 图像

2.2. Procedures
2.2. 程序

CS was oxidized in a TL1200 horizontal tube furnace (Nanjing Boyuntong Instrument Technology Co., LTD, China). When the furnace was heated to the preset temperature, a corundum crucible with 20 g of CS was placed in the furnace and then sealed. The air with a velocity of 600 mL/min was injected into the furnace to realize the oxidation of CS. After the reaction for 60 min, the corundum crucible was taken out of the furnace and cooled to room temperature. The obtained product was named as oxidized copper slag (OCS).
CS 在 TL1200 卧式管式炉（南京博云通仪表技术有限公司，中国）中氧化。当炉子加热到预设温度时，将含有 20 g CS 的刚玉坩埚放入炉中，然后密封。将速度为 600 mL/min 的空气注入炉内，实现 CS 的氧化。 反应 60 min 后，将刚玉坩埚从炉中取出并冷却至室温。 所得产品命名为氧化铜渣 （OCS）。

OCS was also reduced in the furnace. When the oxidation roasting time of CS was reached, N₂ was injected into the furnace to remove the air and the furnace temperature was reset for the following reduction roasting. CO was used as reducing gas andinjected into the furnace. After the reaction for 120 min, the corundum crucible was taken out of the furnace and reduced productwas immediately poured in water to prevent its oxidation during cooling.
OCS 在 炉中也减少了。当达到 CS 的氧化焙烧时间 时，将 N₂ 注入炉中以去除空气，并重置炉温以进行下一次还原焙烧。 以 CO 为还原气注入炉内。 反应120 min后，将刚玉坩埚从炉中取出，立即将还原产物倒入水中，以防止其在冷却过程中氧化。

After liquid‒solid separation, the solid sample was dried in a vacuum oven(YZG-600, Nanjing Wuhuan Technology Industry Co., Ltd, China). Approximately 20 g of reduced productand 40 mL of water wereplaced in a vibrating mill (Wuhan Luoke Pulverizing Equipment Manufacturing Co., LTD, China)andgroundto the particle size of‒325mesh >90% for the liberation of iron grain.The metallic iron in the slurry was recovered by magnetic separation using a magnetic tube (XCQS-Ф50, Jiangxi Hengcheng Mineral Processing Equipment Co., LTD, China) with a magnetic intensity of 1000 Gs. The magnetic concentrate and tailing wereobtained by solid-liquid separationand dried in the vacuum oven for the following analysis.Three series of grinding-magnetic experiments were carried out for each reduced product to analysis the iron content and recovery in concentrate.
液体\u2012固体分离后，将固体样品 置于真空烘箱中干燥（YZG-600，南京万环科技实业有限公司，中国）。将大约 20 g 还原产品和 40 mL 水放入振动磨机（中国武汉罗克粉碎设备制造有限公司）中，将粒径为 325 目 >90% 的颗粒用于释放铁谷物。使用磁强为 1000 Gs 的磁管（XCQS-Ф50，江西恒诚选矿设备有限公司，中国）通过磁选回收浆料中的金属铁。经固液分离得到磁性精矿和尾矿，并在真空烘箱中干燥以进行后续分析。对每种还原产物进行了 3 个系列的研磨磁实验，分析 了精矿中的铁含量和回收率。

2.3. Analyses
2.3. 分析

X-ray diffractometer (MAX-RB, Rigaku Corporation, Japan) was used to analyze the phase composition of CS, OCS, and reduced product with the following conditions:2θof 10°−70°, scanning rate of 10°/min, and step size of 0.02.Jade 6.0 softwarewas selected to analyze the crystalline phases in the XRD patterns. SEM (JXA-8230, JEOL, Japan) and EDS (X-Act, INCA, UK) were used to determine the microstructure and compositions of CS, OCS, and reduced product. Prior toSEM-EDS analysis, the samples should be processed with the following steps: (1) mixing with epoxy resin and triethanolamine, (2) drying in an oven at 70 °C for 5 h, and (3) polishing. Afterward, C was coated on the surface of the polished samples to increase the electrical conductivity during SEM-EDS analysis. In order to guarantee the accuracy of iron grain size during calculation, four typical acquisition positions were selectedin each reduced sample.Therefore, the average of the 4 sets of data was the iron grain size. Thermal analyzer (SDTQ600, TA, USA) was used to analyze the thermogravimetry of CS under the following conditions: air velocity of 100 mL/min, heating rate of 10 °C/min, and temperature of 25 °C‒1100 °C. Atomic absorption spectrometer (TAS-990, PERSEE, China) was applied to analyze the chemical compositions of CS and magnetic concentrate. Fe recovery (η) during magnetic separationwas calculated using Formula (1).
X 射线衍射仪（MAX-RB，日本理学公司）用于分析 CS、OCS 和还原产物的物相组成，其条件如下：2θ为 10°−70°，扫描速率 为 10°/min，步长为 0.02。 选择 Jade 6.0 软件分析 XRD 图谱中的晶相。SEM （JXA-8230，JEOL，日本）和 EDS （X-Act，INCA，英国）用于测定 CS、OCS 和还原产物的微观结构和组成。 在SEM-EDS 分析之前， 应按照以下步骤处理样品：（1） 与环氧树脂和三乙醇胺混合，（2）在 70 °C 的烘箱中干燥 5 小时，以及 （3） 抛光。之后，在抛光样品的表面涂覆 C 以增加 SEM-EDS 分析过程中的电导率。 为了保证计算过程中铁晶粒尺寸的准确性，在每个还原样品中选择了 4 个典型的采集位置。因此，4 组数据的平均值是铁晶粒尺寸。 采用 Thermal 分析仪（SDTQ600，TA，USA）在以下条件下对 CS 进行热重分析 ：风速 100 mL/min，加热速率 10 °C/min，温度 25 °C\u20121100 °C。 原子吸收光谱仪 （TAS-990， PERSEE， China） 用于分析 CS 和磁精矿的化学成分。 磁性分离过程中的 Fe 回收率 （η） 使用 公式 （1） 计算。

  (1)
（1）

wherem₁ and m₂were the mass of reduced product and magnetic concentrate, respectively; Q₁ and Q₂ denoted the Fe content in reduced product and magnetic concentrate, respectively.
其中m₁ 和 m₂分别是还原产物和磁精矿的质量;Q₁ 和 Q₂ 分别表示还原产物和磁性精矿中的 Fe 含量。

3. Results and discussion
3. 结果与讨论

3.1.Reaction behaviors of CS during oxidation roasting
3.1. CS 在氧化焙烧过程中的反应行为 s

3.1.1.TG analysis
3.1.1.TG 分析

The thermal stability of CS was tested,with results shown in Fig. 3. The weight of CS slightly decreased with the increase of roasting temperature from 25°C to 300 °C due tothe dehydration. In the temperature interval of 300 °C‒800 °C, the weight of CS steadily increased with temperature and the slope of the fitting straight line was 0.0053. The slope of the fitting straight line increased to 0.0097 when oxidation temperature reached 800 °C‒1000 °C,indicating that CS oxidation became vigorous. The weight of CS slightly increased with temperature above 1000 °C. Finally, the maximum change reached4.40%,indicating that CS was efficiently oxidized.
测试了 CS 的热稳定性，结果如图 3 所示。由于脱水，随着 烘烤温度从 25°C 升高到 300 °C，CS 的重量略有下降。在 300 °C\u2012800 °C 的温度区间内，CS stea 的重量随温度的增加而增加，拟合直线的斜率为 0.0053。 当氧化温度达到 800 °C\u20121000 °C 时，拟合直线的斜率增加到 0.0097，表明 CS 氧化变得剧烈。 当温度高于 1000 °C 时，CS 的重量d 略有增加。最后，最大变化达到 ed4.40%，表明 CS 被高效氧化。

Fig.3.TG curve of copper slag
图 3铜渣的 TG 曲线

3.1.2.XRD analysis
3.1.2.XRD 分析

XRD patterns of the OCS obtained at 600°C‒1100°C with an interval of 100°C were shown in Fig. 4. Compared with XRD pattern of CS, the diffraction peak intensity of fayalite decreased and the characteristic peak of magnetite vanished in XRD pattern of OCS-600°C. In addition, the characteristic peaks of hematite remained, while those of cristobaliteshowed no notable change. Therefore, the fayalite in CS can be oxidized into hematite and amorphous silica at 600°C. With oxidation temperature increasing from 600 °C to 800 °C,the diffraction peak intensity of fayalite showed a decreasing trend,while that of hematite exhibited an increasing trend.This finding indicated that elevated temperature benefitted the decomposition of fayalite during oxidation roasting. Furthermore, the diffraction peak intensity of cristobalite increased in the OCS-800°C due tothe conversion of amorphous silica to cristobalite solid solution (Yang et al., 2022; Li et al., 2019). When the roasting temperature reached 900°C, the vanishment of characteristic peak of fayalite indicated the complete decomposition of CS. In addition to hematite, cristobalite, and cristobalite solid solution, the characteristic peaks of magnetite were detected in the XRD patterns of OCS-1000°C and OCS-1100°C. The particle surface of CS quickly oxidized into hematite and free silica at elevated temperatures,resulting in a lowair diffusion inside the particle. Therefore, the inner part of CS particle was oxidized into magnetite and free silica (Tsunazawa et al., 2019).
在 600°C\u20121100°C 下以 100°C 的间隔获得的 OCS 的 XRD 图谱如图 4 所示。与 CS 的 XRD 图谱相比，在 OCS-600°C 的 XRD 图谱中，辉石的衍射峰强度降低，磁铁矿的特征峰消失。 此外，赤铁矿的特征峰仍然存在，而 方石英的峰值没有显示出明显的变化。因此， CS 中的辉石可以在 600°C 下氧化成赤铁矿和非晶态二氧化硅。 随着氧化温度从 600 °C 升高到 800 °C，辉石的衍射峰强度呈下降趋势，而赤铁矿的衍射峰强度呈上升趋势。这一发现表明，高温有利于氧化焙烧过程中 fayalite 的分解。此外，由于无定形二氧化硅转化为方石英固溶体，方石英的衍射峰强度在 OCS-800°C 中增加（Yang等人，2022 年;Li et al.， 2019）的。当 焙烧温度达到 900°C 时，辉石特征峰的消失表明 CS完全分解。 除了赤铁矿、方石英和方石英固溶体外，在 OCS-1000°C 和 OCS-1100°C 的 XRD 图谱中还检测到了磁铁矿的特征峰。 CS的颗粒表面 在高温s 下迅速氧化成赤铁矿和游离二氧化硅，导致颗粒内部的空气扩散率低。因此，CS 颗粒的内部被氧化成磁铁矿和游离二氧化硅（Tsunazawa et al.， 2019）。

Fig.4. XRD patterns of oxidized copper slags
图 4 氧化铜渣的 XRD 图

Symbols:▽-Fayalite;△-Cristobalite;○-Hematite;☆-Magnetite;◇-Cristobalite solid solution
符号：▽-Fayalite;△-方石英;○-赤铁矿;☆-磁铁矿;◇-方石英固溶体

3.1.3.SEM-EDS analysis
3.1.3.SEM-EDS 分析

The SEM-EDS results of the OCS obtained at 600 °C, 900 °C and 1100 °C were shown in Fig. 5. Some fayalite in the CS was oxidized into hematite and amorphous silica, and cracks could be found on the particle of OCS-600 °C. Meanwhile, the distribution of Fe was consistent with that of Si and O, indicating that hematite intertwined with amorphous silica. EDS results showed that the particle containeda significantly higher Fe content than Si and O. This finding was consistent with the results that Fe had the highest weight percentage in fayalite in Fig. 2. When the oxidation temperature reached 900 °C, the element distribution and content of Fe, Si and O in the particles were almost the same.The main elements on the particle surface were Fe and O with small amounts of Si. Therefore, the Fe element in fayalite migrated to the particle surface during oxidation roasting, and a Fe oxidation film with a thickness of about 2μm was formedon the particle surface. Furthermore, the thickness of Fe oxidation film increased to about 5μm in the OCS-1100 °C, and the element content of Fe inside the particle wasclose to that of O but significantly lower than that of Si. Therefore, a relatively large amount of Fe migrated from fayaliteto the particle surface with the increase of oxidation temperature(Gaballah et al., 1978).
我们在 600 °C、900 °C 和 1100 °C 下获得的 OCS 的 SEM-EDS 结果如图 5 所示。 CS 中的 S ome fayalite 被氧化成赤铁矿和非晶态二氧化硅，在 OCS-600 °C 的颗粒中可发现裂纹 s。同时，Fe 的分布与 Si 和 O 的分布一致，表明赤铁矿与无定形二氧化硅交织在一起。 EDS 结果表明，颗粒 中 Fe 含量明显高于 Si 和 O。 这一发现与图 2 中 Fe 在 Fayalite 中具有最高重量百分比的结果一致。当 氧化温度达到 900 °C 时，颗粒 s 中元素分布和 Fe、Si 和 O 的含量几乎相同。颗粒表面的主要元素是 Fe 和 O，其中含有少量 Si。 因此，辉石中的 Fe 元素在氧化焙烧过程中迁移到颗粒表面，在颗粒表面形成了厚度约为 2μm 的 Fe 氧化膜。 此外，在 OCS-1100 °C 中，Fe 氧化膜的厚度增加到约 5μm，颗粒内部的 Fe 元素含量接近 O，但明显低于 Si。 因此，随着氧化温度的升高，相对大量的 Fe 从 fayalite迁移到颗粒表面（Gaballah et al.， 1978）。

Fig.5. SEM-EDS images of oxidized copper slags
无花果。5 氧化铜渣的 SEM-EDS 图像

(a) OCS-600 °C; (b) OCS-900 °C; (c) OCS-1100 °C
（a） OCS-600 °C;（b） OCS-900 °C;（c） OCS-1100 °C

3.2.Reaction behaviors of OCS during reduction roasting
3.2.还原烘焙过程中 OCS 的反应行为

3.2.1.XRD analysis
3.2.1.XRD 分析

XRD patterns of the reduced products from CS and OCS-1100 °C were presented in Fig. 6. In addition tofayalite and cristobalite,metallic iron was found in the reduced products obtained at 950 °C (Fig. 6(a)). When the roasting temperature increased to 1000 °C, the diffraction peak intensity of fayalite decreased while those of metallic iron and cristobalite increased. The increase in the diffraction peak intensity of cristobalite was caused by the formation of cristobalite solid solution (Wang and Song, 2020). In the reduced products obtained at ≥ 1050 °C, the characteristic peaks of fayalite vanished but those of metallic iron, cristobalite, and cristobalite solid solution were still detected. Therefore, the fayalite in CS could be fully reduced into metallic iron and cristobalite solid solution through reduction roasting.
CS 和 OCS-1100 °C 还原产物的 XRD 图谱如图 6 所示。 除了方石英和方石英外，在 950 °C 下获得的还原产物中还发现了金属铁[图 6（a）]。当 焙烧温度升高到 1000 °C 时，辉长石的衍射峰强度降低，而金属铁和方石英的衍射峰强度增加。方石英固溶体的形成导致方石英的衍射峰强度增加（Wang 和 Song，2020 年）。在 ≥ 1050 °C 下获得的还原产物中，方石英的特征峰消失了，但仍然检测到金属铁、方石英和方石英固溶体的特征峰。因此，CS 中的法亚石可以通过还原焙烧完全还原成金属铁和方石英固溶体。

Compared with the results in Fig. 4, the characteristic peaks of hematite in OCS-1100 °C vanished after reduction roasting at 950 °C.However, thepeaks of fayaliteremained. Fayalite could still be detected in the reduced products obtained at 1000 °C, but the intensity of its diffraction peak remarkably decreased. When the roasting temperature exceeded 1050 °C, only metallic iron, cristobalite, and cristobalite solid solution were found in the reduced products. Therefore, the hematite in OCS-1100 °C could be reduced to ferrous oxide at 950 °C and then reacted with cristobalite solid solution to form fayalite.Meanwhile,elevated reduction temperature (≥1050 °C) directly promoted the conversion of hematite into metallic iron, avoiding the formation of fayalite(Luo et al., 2021).
与图 4 中的结果相比，OCS-1100 °C 赤铁矿的特征峰在 950 °C 焙烧后还原后消失。然而，fayalite的 epeaks 仍然存在。在 1000 °C 下获得的还原产物中仍然可以检测到 Fayalite，但 其衍射峰的强度显着降低。 当 焙烧温度超过 1050 °C 时，还原产品中仅发现金属铁、方石英和方石英固溶体。 因此， OCS-1100 °C 中的赤铁矿可在 950 °C 下还原为氧化亚铁，然后与方石英固溶体反应生成辉长石。同时，升高的还原温度 （≥1050 °C） 直接促进了赤铁矿向金属铁的转化，避免了辉铁矿的形成（Luo et al.， 2021）。

Fig.6.XRD patterns of the reduced products fromCS (a) and OCS-1100 °C (b)
图6CS （a） 和 OCS-1100 °C 还原产物 （b） 的 XRD 图谱

Symbols:▽-Fayalite;△-Cristobalite;○-Hematite;★-Metallic iron;◇-Cristobalite solid solution
符号：▽-Fayalite;△-方石英;○-赤铁矿;★ -金属铁◇-方石英固溶体

3.2.2.SEM-EDS analysis
3.2.2.SEM-EDS 分析

SEM images of the reduced products from CS and OCS-1100 °Cwere shown in Fig. 7,with the corresponding EDS analysis results listed in Table 2. After reductively roasting at 1000 °C, a thin reaction layer was formed on the particle surface. EDS results of Point A showed the presence of unreacted fayalite in the reduced product. The reaction layer thickened when the roasting temperature was increased to 1050 °C, but unreacted fayalitewas still observed. This finding was inconsistent with the XRD results inFig. 6(a),which stated that fayalite was fully reduced into metallic iron and cristobalite solid solution at 1050 °C. This might be caused by the limited detection of XRD analysis on the inside of the particle. When the roasting temperature exceeded 1100 °C, the fayalite in the CS was fully converted into metallic iron and free silica, and the particle size of metallic increased with temperature. Apart from Si and O in Points E and G, a small amount of Fe element was detected, indicating that iron doping caused the formation of cristobalite solid solution during reduction roasting. In addition, the particle size of metallic iron wasdifficulty in the increase due to the tight wrap of silica.
CS 和 OCS-1100 °C 还原产物的 SEM 图像如图 7 所示，相应的 EDS 分析结果见表 2。在 1000 °C 下还原焙烧后，在颗粒表面形成一层薄的反应层。A 点的 EDS 结果显示 还原产物中存在未反应的 fayalite。当 焙烧温度 升高到 1050 °C 时，反应层变厚，但仍观察到未反应的法亚石。这一发现与图 6（a） 中的 XRD 结果不一致，图 6（a） 中指出，辉石在 1050 °C 时完全还原成金属铁和方石英固溶体。 这可能是由于对颗粒内部的 XRD 分析检测有限造成的。当 焙烧温度超过 1100 °C 时， CS 中的法亚石 完全转化为金属铁和游离二氧化硅，金属的粒径随温度的增加而增加。 除了 S E 点和 G 点的 Si 和 O 外，还检测到少量的 Fe 元素，表明铁掺杂导致在还原焙烧过程中形成方石英固溶体。 此外， 由于二氧化硅的紧密包裹，金属铁的粒度难以增加。

When OCS-1100 °C was reduced at 1000 °C, a reaction layer wasformed on the surface and inside of the particles. Considering that a microchannelwas generated in the OCS after oxidation roasting at 1100 °C as shown in Fig. 5, the hematite inside the OCS particles could be reduced by reacting with CO passing through the microchannel. OCS-1100 °C was almost reduced into metallic iron and free silica at 1050 °C. Furthermore, OCS-1100 °C was fully reduced when the roasting temperature exceeded 1100 °C. Comparison ofFig. 6(a4) and (b4) showed that the particle size of metallic iron in the reduced product from OCS-1100 °C was remarkably larger than that in the reduced product from CS, indicating that oxidation could promote the growth of metallic iron particle size in CS during reduction roasting.
当 OCS-1100 °C 在 1000 °C 下降低时，在颗粒表面和内部 形成反应层 。 考虑到如图 5 所示，在 1100 °C 下氧化焙烧后在 OCS 中产生微通道，OCS 颗粒内的赤铁矿可以通过与 CO 通过微通道的反应来还原.OCS-1100 °C 在 1050 °C 时几乎还原成金属铁和游离二氧化硅。 此外，当 烘烤温度超过 1100 °C 时，OCS-1100 °C 完全降低。图 6（a4） 和 （b4） 的结果表明，OCS-1100 °C 还原产物中金属铁的粒径明显大于 CS 中的还原产物，表明氧化可以促进还原焙烧过程中 CS 中金属铁粒径的增长。

Fig.7.SEM images of reduced products from CS (a) and OCS-1100 °C (b)
图 7 CS （a） 和 OCS-1100 °C （b） 还原产物s 的 SEM 图像

Reduction temperature: 1-1000 °C; 2-1050 °C; 3-1100 °C; 4-1150 °C
还原温度：1-1000°C;2-1050 °C;3-1100 °C;4-1150 °C

Table 2EDS analysis results of reduced products
表 2 还原产物s 的 EDS 分析结果

The mean particle size of metallic iron in the reduced products was measured as previous description(Zhang et al., 2020), with the results shown in Fig. 8. After the reduction roasting of the CS, the mean particle size of metallic iron in the reduced products increased with the temperature from 2.15 μm at 1000 °C to 6.42μm at 1150 °C. But the liberation of minerals with particle size of ‒10μm is still difficult to be achieved through grinding, leading to its low recovery. After oxidation roasting, the mean particle size of metallic iron in the reduced products from OCS showed a significant increase compared with that in the reduced product from CS. At 1150°C, the mean particle size of metallic iron increased from 7.27μmin the reduced product from OCS-800 °C to 16.62μmin the reduced product from OCS-1100 °C. Combined with the results in Fig. 5, this result indicated that the hematite in the particle surface of OCS was easily reduced into metallic iron during reduction roasting. The formed metallic iron exhibited a nucleating effect on the growth of metallic iron due tohematite reduction inside the OCS particles, leading to the growth of metallic iron in reduced products (Wang et al., 2021). Therefore, the iron grain in reduced product could be increased by peroxidation of CS.
如前所述（Zhang et al.， 2020）测量了还原产品中金属铁的平均粒径， 结果如图 8 所示。 CS 焙烧 还原后，还原产物中金属铁的平均粒径 随温度从 1000 °C 的 2.15 μm 增加到 1150 °C 的 6.42μm。 但通过研磨仍难以释放粒径为 \u201210μm 的矿物，导致其回收率低。 氧化焙烧后，OCS 还原产品中金属铁的平均粒径与 CS 还原产品 相比显著增加。 在1150°C 时，金属铁的平均粒径从 OCS-800 °C 还原产物的 7.27μm 增加到 OCS-1100 °C 还原产物的 16.62μm。 结合图 5 中的结果，该结果表明， OCS 颗粒表面 的赤铁矿在还原焙烧过程中很容易被还原成金属铁。 由于 OCS 颗粒侧的赤铁矿还原，形成的金属铁对金属铁的生长表现出成核作用 ，导致金属铁在还原产品中的生长（Wang et al.， 2021）。因此，CS的过氧化可以增加 还原产物中的铁粒。

Fig.8.The mean particle size of metallic iron in reduced products
图 8还原产品中金属铁的平均粒径

3.3. Iron enrichment through magnetic separation
3.3. 通过磁分离富铁

The main minerals in the reduced product were ferromagnetic metallic iron and nonmagnetic silica (i.e. cristobalite and cristobalite solid solution) as shown in Fig. 6.Therefore, the efficient separation of iron and silicon could be achieved by traditional grinding‒magnetic separation. The metallic iron in the reduced products from CS, OCS-900 °C, and OCS-1100 °C was enriched under the following magnetic conditions: particle size of ‒325 mesh >90% and magnetic intensity of 1000 Gs.
还原产物中的主要矿物是铁磁性金属铁和非磁性二氧化硅（即方石英和方石英固溶体），如图 6 所示。因此，可以通过传统的研磨\u2012磁分离来实现铁和硅的高效分离。CS、OCS-9 00 °C 和 OCS-1100 °C 还原产物中的金属铁在以下磁离子条件下富集：粒径 %3E90% 和 1000 Gs 的磁强度。

The magnetic separation results of reduced products obtained at 1150 °C were shown in Fig. 9(a). A concentrate with Fe content of 72.86% and Fe recovery of 82.57% was obtained bymagnetically separating the reduced product from CS.This result was consistent with that reported by Kim et al(Kim et al., 2013). When the CS was treated by oxidation at 900 °C and 1100 °C, the Fe content in the concentrate increased to 75.65% and 87.85%,and the Fe recovery was 82.57% and 85.84%, respectively. As shown in Fig. 7 and 8, the mean particle size of metallic iron in the reduced product from CS was 6.42μm, most of the metallic iron waswrapped by silica, leading to the difficulty in liberation during grinding and in separation during magnetic separation. When the oxidation temperature was increased from 900 °C to 1100 °C, the mean particle size of metallic iron in the reduced product increased from 9.11μm to 16.62μm. Therefore, the metallic iron in the reduced product from OCS-1100 °C was efficiently enriched by magnetic separation, and the obtained concentrate with Fe content of 87.85% could be used in the steel production.
在 1150 °C 下获得的还原产物 s 的磁分离结果如图 9（a） 所示。Fe 含量为 72.86%，Fe 回收率为 82 的精矿。57% 是通过从 CS 中磁性分离还原产物获得的。他的结果与 Kim et al.（Kim et al.， 2013）报告的结果一致。当 CS 在 900 °C 和 1100 °C 下氧化处理时，精矿中 Fe 含量增加到 75。65% 和 87.85%，且 Fe 恢复率 y w为 82。57% 和 85.84%。 如图 7 和图 8 所示，CS 还原产物中金属铁的平均粒径为 6.42μm，大部分 金属铁 w被二氧化硅包裹，导致研磨过程中难以释放，磁分离过程中难以分离。当氧化温度从 900 °C 提高到 1100 °C 时，还原产物中金属铁的平均粒径从 9.11μm 增加到 16.62 μm。 因此，OCS-1100 °C还原产物中的金属铁通过磁选高效富集，得到的Fe含量为87的精矿。85% 可用于钢铁生产。

The phase composition of magnetic concentrates was analyzed, with XRD patterns shown in Fig. 9(b). The efficient separation between metallic iron and silica in the reduced products obtained at 1150 °C was not achievedaccording to the evidence of the small amount ofcristobalite and cristobalite solid solution detected in the magnetic concentrate apart from the main mineral of metallic iron. Furthermore, the diffraction peak intensity of cristobalite and cristobalite solid solution decreased with the increase of oxidation temperature, indicatingthe decrease of silica content in the magnetic concentrate. These findings werein agreement with the separation results in Fig. 9(a), that is, the metallic iron in the reduced products can be selectively enriched by magnetic separation.
分析了磁性精矿的物相组成，XRD 图谱如图 1 所示。 9（b） 的。 根据在磁精矿中检测到的少量方石英和方石英固溶体的证据，除了金属铁的主要矿物外，在1150 °C下获得的还原产物中金属铁和二氧化硅之间的有效分离是没有实现的。 此外，方石英和方石英固溶体的衍射峰强度随着氧化温度的升高而降低，表明磁精矿中二氧化硅含量降低。这些发现与图 9（a） 中的分离结果一致，即 还原产物中的金属铁可以通过磁分离选择性富集。

SEM-EDS images of magnetic concentratewere shown in Fig. 9(c-f). In accordance with the EDS results, the white particles were metallic iron and the gray particles were silica. The efficient separation between metallic iron (mean particle size of −10 μm) and silica in the reduced product from CS and OCS-900 °C was not achieved through grinding‒magnetic separation process (Fig. 9(c) and 9(d)) as evidenced by the locked particles and independent silica particles found in the concentrate. As shown inFig. 9(e), the locked particles remarkably decreased and some independent silica particles were present in the concentrate due to the entrainment during separation. Meanwhile, the metallic iron with a particle size of 16.62μmin the reduced product from OCS-1100 °C could be efficiently liberated under the same grinding conditions (Fig. 8), thereby benefiting the following enrichment of magnetic separation. Future work would focus on the intensified magnetic separation process to further increase the Fe content in the concentrate.
磁精矿的 SEM-EDS 图像如图 1 所示。 9（c-f）。根据 EDS 结果，白色颗粒是金属铁，灰色颗粒是二氧化硅。从 CS 和 OCS-9 00 °C 中还原产物中金属铁（平均粒径为 -10 μm）和二氧化硅之间的有效分离不是通过研磨-磁分离工艺实现的（图 D）。 9（c） 和 9（d）），浓缩物中发现的锁定颗粒和独立二氧化硅颗粒证明了这一点。 如图 1 所示。 9（e） 中，由于分离过程中的夹带，锁定颗粒显着减少，浓缩液中存在一些独立的二氧化硅颗粒 。同时，在相同的研磨条件下，OCS-1100 °C 还原产物中粒径为 16.62μm 的金属铁可以有效释放（图 8），从而有利于后续磁选富集。 未来的工作将集中在强化磁选工艺上，以进一步提高精矿中 Fe 的含量。

Fig. 9. Magnetic separation results of reduced products (a) andcharacteristic of magnetic concentrates (b-f)
图 9 还原产物 s 的磁分离结果 （a） 和磁精矿特性 （b-f）

XRD patterns of magnetic concentrates (b); SEM images of magnetic concentrates of reduced products from CS (c), OCS-900 °C (d), and OCS-1100 °C (e); EDS images (f)
磁精矿的 XRD 图谱 （b）; CS （c）、OCS-9 00 °C （d） 和 OCS-1100 °C （e） 还原产物的磁精矿的 SEM i法;EDS 图像 （f）

The chemical compositions of magnetic products were listed in Table 3. In the concentrate, the main compositions were Fe and SiO₂ with corresponding contents of 87.85% and 8.12%. In addition, the metallic iron (MFe) content was 83.15%, meaning that the metallization ratio of concentrate is 94.65%. Therefore, this concentrate is a high-quality material for electric furnace steelmaking (Nakase et al., 2023). As to the tailing, the SiO₂ content reached 81.06%, and the Fe content was 14.07%. The contents of other elements, including CuO, ZnO, and PbO, were very small. So, this tailing can be used as cement raw material (Wang et al., 2020). Ultimately, the near-zero waste discharge from CS is achieved through additive-free activation roasting‒magnetic separation, and the obtained concentrate is raw material for electric furnace steelmaking and tailing for cement production.
磁性产品的化学成分见表 3。 精矿中主要成分为 Fe 和 SiO₂，相应含量为 87。85% 和 8.12%。此外，金属铁 （MFe） 含量为 83.15%，即精矿的金属化比为 94.65%。因此，这种精矿是电炉炼钢的优质材料（Nakase et al.， 2023）。尾矿中，SiO₂ 含量达到 81.06%，Fe 含量为 14.07%。其他元素（包括 CuO、ZnO 和 PbO）的含量非常少。因此，这种尾矿可以用作水泥原料（Wang et al.， 2020）。最终，通过无添加剂活化焙烧\磁选实现 CS 的近零废物排放，获得的精矿是电炉炼钢的原料和水泥生产的尾矿。

Table 3 Chemical compositions of magnetic products (mass fraction/%)
表 3 磁性产品的化学成分（质量分数/%）

* reduced products from OCS-1100 °C at 1150 °C for 120 min
* OCS-1100 °C 的还原产物在 1150 °C 下 120 分钟

3.4.Discussion on the iron extraction from CS without additive
3.4.探讨无添加剂的 CS 铁提取

Reduction roasting is an efficient method to remove Zn and Pb, and decomposesfayalite, which is the predominant mineral in the CS, into ferromagnetic metallic iron and nonmagnetic silica. However, when the CS was directly reduced at 1150 °C, the mean particle size of metallic iron in the reduced product was 6.42μm, leading to difficulty in separation between metallic iron and silica through grinding-magnetic separation(Kim et al., 2013). The fayalite in the CS could be oxidized into hematite and silica (i.e. amorphous silica and cristobalite solid solution) through oxidation roasting. Aniron oxide film was formed on the particle surface in the OCS-1100 °Cdue to the migration of Fe element and the increase in thickness up to ~5 μm with elevated oxidation temperature. During the subsequent reduction roasting, the hematite on the particle surface of OCS was easily reduced into metallic iron, which exhibited a nucleating effect on the metallic iron that grew from hematite reduction inside the OCS particles. This phenomenon led to the growth of metallic iron in the reduced products,benefitting the iron extraction through magnetic separation under the same grinding conditions. The schematic illustration of iron extraction from CS by roasting‒magnetic separation without additivewas shown in Fig. 10. The mean particle size of metallic iron in the reduced product from OCS-1100 °C reached 16.62 μm, and a concentrate with a Fe content of 87.85% and a Fe recovery of 85.84% was obtained through grinding‒magnetic separation process. Therefore, the efficient separation of iron and silicon in CS was realized throughadditive-free activation roasting‒magnetic separation. The obtained concentraterich in iron was a high-quality material for electric furnace steelmaking,while the tailing rich in silica could be used for cement production. This work realizedthe near-zero waste discharge of CS.
还原焙烧是一种去除 Zn 和 Pb 并将 CS 中的主要矿物 fayalite 分解成铁磁性金属lic 铁和非磁性二氧化硅的有效方法。然而，当 CS 在 1150 °C 下直接还原时，还原产物中金属铁的平均粒径为 6.42μm，导致难以通过研磨磁分离分离金属铁和二氧化硅（Kim et al.， 2013）。 CS c ould 中的 f亚利石通过氧化焙烧氧化成赤铁矿和二氧化硅（即无定形二氧化硅和方石英固溶体）。 由于 Fe 元素的迁移和氧化温度升高时厚度增加至 ~5 μm，在 OCS-1100 °C 中，在颗粒表面形成了尼隆氧化e 膜。 在随后的还原焙烧过程中， OCS 颗粒表面的赤铁矿 很容易被还原成金属铁，这对 OCS 颗粒内部赤铁矿还原生长的金属铁表现出成核效应。 这种现象导致还原产物中金属铁的生长，有利于在相同研磨条件下通过磁选提取铁。 通过焙烧从 CS 中提取铁的示意图\u2012 无添加剂was，如图 1 所示。 10.OCS-1100 °C 还原产物中金属铁的平均粒径达到 16.62 μm，Fe 含量为 8 7 的精矿。85% 和 85 的铁回收率。84% 是通过研磨\u2012磁分离工艺获得的。因此，CS 中铁和硅的高效分离是通过无添加活化焙烧\u2012磁分离实现的。 获得的富铁精矿是电炉炼钢的优质材料，而富含二氧化硅的尾矿 则用于 水泥生产。 这项工作实现了CS 的近零废物排放。

Fig.10.Schematic illustration of iron extraction from CS by activation roasting‒magnetic separation
无花果。10 通过活化焙烧从 CS 中提取铁的示意图\u2012磁性分离

4. Conclusions
4. 结论

The effect of oxidation on iron grain growth during reduction roasting of CS was systematically studied, and the separation between metallic iron and silica in the reduced products by magnetic separation was investigated. The main findings were as follows:
系统研究了CS还原焙烧过程中氧化对铁晶粒生长的影响，并研究了磁选法分离还原产物中金属铁和二氧化硅的分离。主要发现如下：

1) The Fe-bearing minerals in CS could be fully oxidized into iron oxide (i.e. hematite and magnetite) and silica (i.e. amorphous silica and cristobalite solid solution) by oxidation roasting. An iron oxide film was formed on the particle surface in OCS-1100 °C due to the migration of Fe element and the increase in thickness up to ~5 μm with the elevated oxidation temperature.
1） CS c中的含铁矿物 通过氧化焙烧完全氧化成氧化铁（即赤铁矿和磁铁矿）和二氧化硅（即无定形二氧化硅和方石英固溶体）。在 OCS-1100 °C 中 ，由于 Fe 元素的迁移和随着氧化温度升高而厚度 增加至 ~5 μm，在颗粒表面 形成了氧化铁膜。

2) When the CS was directly reduced at 1150 °C, the mean particle size of metallic iron in the reduced product was 6.42μm. Meanwhile, the mean particle size of metallic iron in the reduced products from OCS significantly increased compared with that in the reduced products from CS.In particular, the mean particle size was increased from 9.11μm in OCS-900 °C to 16.62μm in OCS-1100 °C.
2） 当 CS 在 1150 °C 下直接还原时，还原产物中金属铁的平均粒径为 6.42μm。同时，与 CS还原产物相比，OCS 还原产物中金属铁的平均粒径 d 显著增加。特别是，平均粒径从 OCS-9 00 °C 的 9.11 μm 增加到 OCS-1100 °C 的 16.6 2 μm。

3) After magnetic separation, a concentrate with Fe content of 72.86% and Fe recovery of 82.57% was obtained from the reduced product of CS. By comparison, a concentrate with Fe content of 87.85% and anFe recovery of 85.84% was acquired from the reduced product of OCS-1100 °C.
3） 磁选后，得到 Fe 含量为 72.86% 且 Fe 回收率为 82 的精矿。57% 从 CS的还原产物中获得。 相比之下， Fe 含量为 87.85% 和 nFe 回收率 85。84% 是从 OCS-1100 °C 的还原产物中获得的。

CRediT authorship contribution statement
CRediT 作者贡献声明

Xiaoxue Zhang: Methodology, Writing – review & editing, Formal analysis. Hongyang Wang: Writing –review & editing, Formal analysis, Funding acquisition. Yuqi Zhao: Methodology, Writing – review & editing. LiqunLuo: Formal analysis, Supervision.
张晓雪： 方法论， 写作 – 审查与编辑， 形式分析。Hongyang Wang： 写作 - 审查和编辑，正式分析，资金获取。Yuqi Zhao： 方法论，写作 - 审查和编辑。LiqunLuo： 形式分析，监督。

Declaration of Competing Interest
利益争夺声明

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
作者声明，他们没有已知的竞争性经济利益或个人关系，这些利益或个人关系似乎可能会影响本文报告的工作。

Acknowledgments
确认

This work was financially supported by the National Natural Science Foundation of China (52004194) and the Scientific Research Foundation for High-level Talents of Anhui University of Science and Technology (2022yjrc25).
这项工作得到了中国国家自然科学基金 （52004194） 和安徽科技大学高层次人才科研基金 （2022yjrc25） 的财政支持。

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