2023 Volume 64 Issue 8 Pages 1937-1945
Large amounts of solid waste-spent cathode carbon (SCC) was produced in aluminum electrolysis process. At present, landfill and storage methods are widely used, which will not only cause great harm to the environment, but also cause a lot of waste of resources. Nickel and iron were recovered from laterite nickel ore by reduction roasting-magnetic separation using SCC as reducing agent. The fluorine in SCC was fixed in roasted ore by adding CaO. The feasibility of the method was verified by thermodynamic analysis and experiments, and the optimum conditions for CaO addition were determined. The recovery of nickel and iron reached 91.23% and 89.63% respectively when the addition of SCC was 14 wt.% and CaO was 8 wt.%. Adding 8 wt.% CaO under the condition of SCC as reducing agent can change the viscosity of roasted ore and promote the aggregation of ferronickel particles. The concentration of soluble F− in roasted ore was reduced and fixed in roasted ore in the form of insoluble calcium fluoride. Under the condition of adding 8 wt.% CaO, the fluorine fixation rate was 95.99%, and the concentration of F− in roasted ore was only 31 mg·L−1.
Globally, the aluminum electrolysis industry annually produces 1–1.5 × 106 tons of SCC, of which only China’s electrolytic aluminum industry produces more than 4 × 105 tons of SCC every year.1) In recent years, more than 4 million tons of accumulated stockpiles have not been landfilled in suitable sites and are waiting for further treatment through open-air stacking.2–4) SCC contain about 60%–70% carbon, which was a secondary resource with great recycling value.5) In the production process of aluminum electrolysis, graphite cathode by electrolyte and aluminum corrosion will absorb a large amount of fluoride, near the steel rod will generate a small amount of cyanide.6) The main component of SCC in aluminum reduction cell was C, and it also contains Na3AlF6, CaF2, NaF, AlF3 and α-Al2O3.7) However, as a by-product containing large amounts of soluble fluorine (NaF, CaF2 and Na3AlF6) and cyanide (NaCN, Na4Fe (CN)6 or Na3Fe (CN6)).8) When the untreated waste cathode carbon was stacked in the open air, it will produce harmful gases after encountering water, seriously pollute the water, soil and atmospheric environment, and seriously affect the health and ecological balance of animals and plants.9–11) Therefore, SCC as hazardous solid waste.
The comprehensive utilization of SCC was mainly to recover carbonaceous materials and fluoride. The treatment methods include leaching method, high temperature method and safe landfill method.12–15) Leaching treatment of SCC was one of the more studied methods in recent years. Xiao et al.16) studied the effects of ultrasonic-assisted and traditional leaching methods on the leaching rate of fluorine and the content of residual carbon by alkali leaching of aluminum electrolysis SCC. It was found that the treatment time of ultrasonic-assisted alkali leaching of SCC was 55.6% shorter than that of traditional process, and the removal rate of impurities was higher. There are disadvantages such as complex process and high processing cost. While realizing the decomposition of cyanide, it also realizes the conversion and recovery of fluoride.17,18) Due to the problems of high energy consumption and secondary pollution in the existing treatment methods, the environmental pollution of SCC in electrolytic aluminum has not been effectively solved, resulting in the vast majority of SCC in aluminum reduction cells still being abandoned.19–21) At present, the safe landfill method with high cost was mainly used. The commonly used landfill and storage methods for the treatment of electrolytic aluminum solid waste will cause great harm to the environment. Even if the hazardous waste was completely landfilled, it will still produce persistent pollution.22)
Nickel was an important metal and has been widely used in many fields.23–25) More than 60% of nickel products are used in stainless steel production, due to the increase in stainless steel production, the global demand for nickel increased year by year. Onshore nickel ore was mainly divided into laterite nickel ore and nickel sulfide ore.26) As an important source of nickel ore, laterite nickel ore accounts for more than 70% of the world’s nickel reserves, but nickel production only accounts for about 40%.27,28) Nickel laterite ore was abundant in southwest China. Nickel reserves amount to 1.86 million tons.29) Because these laterite ores show the common characteristics of low nickel and iron content, high magnesium and silicon content. Due to the high magnesium content, nickel content was often <1%, acid consumption was very large, so this kind of ore was often treated by reduction roasting-magnetic separation process.30) Additives and reducing agents are also a research hotspot in the reduction roasting-magnetic separation process.
In this study, SCC was used as a reducing agent and CaO was used as an additive to treat laterite nickel ore by reduction roasting-magnetic separation to achieve nickel and iron enrichment and harmless treatment of SCC. The effects of additive dosage on the fixation of F−, the toxicity of roasted ore, the reduction of nickel and iron during the reduction of laterite nickel ore by SCC were studied. Finally, the optimum experimental conditions of additive dosage were determined to realize the harmless and resource utilization of SCC and the efficient enrichment of nickel and iron in laterite nickel ore.
The chemical analysis results of the laterite nickel ore used in the experiment are shown in Table 1. The nickel content was only 0.82 wt.% and the iron content was 9.67 wt.%. In our previous study, we found that laterite nickel ore was mainly composed of Lizardite, Quartz and Maghemite.29) Nickel and iron were diffusely distributed in the ore and are wrapped by Si, O and Mg elements. Ni mainly exists in the mineral in the form of replacing magnesium in magnesium silicate, while iron exists partly in the mineral in the form of oxide and partly in silicate.31)
The reducing agent SCC used in this experiment was the waste produced by aluminum electrolysis industry, which was classified as dangerous solid waste. The results of chemical analysis are shown in Table 2. The toxicity test results are shown in Table 3. The concentration of F− seriously exceeds the standard (100 mg·L−1), indicating that untreated SCC will cause serious harm to the environment and animals and plants. Through the data found that SCC contains a large amount of reducing carbon, and contains a small amount of CaO and fluoride. Fluorides mainly exist in the form of NaF, Na3AlF6 and CaF2. Analytical pure CaO was used as additive in the experiment.
The laterite nickel ore and SCC were crushed and ball milled by a grinding machine (XZM-100 vibration mill prototype) to make more than 80% of the particle size less than 74 µm. In our previous study, we found that the optimum conditions for the reduction of laterite nickel ore by spent cathode carbon were reduction temperature 1250°C and reduction time 75 min. The laterite nickel ore, SCC and CaO were mixed and put into a corundum boat using a tubular furnace (GSL-1500X) in a protective gas (N2) atmosphere to heat up to 1250°C for reduction roasting for 75 min. Each experiment was repeated at least three times under the same conditions to ensure that the error was within ±2%. The grinding machine was used for wet grinding and crushing, and the magnetic separation tube (DTCXG-ZN50 magnetic separation tube) was used for magnetic separation. The obtained magnetic material and magnetic separation tailings are filtered and dried to obtain ferronickel concentrate and magnetic separation tailings. The experimental process was shown in Fig. 1. The recovery of nickel and iron was calculated according to the principle of mass balance.
Flow chart of experiment.
A standard leaching solution for the determination of dissolved F− and CN− was prepared by dissolving 5 g of the tested solid sample (SCC and roasted ore) in 50 mL of deionized water. The content of F− in the solution was determined by fluoride ion selective electrode potential method, and the minimum detection concentration was 0.05 mg·L−1. The content of cyanide was determined by silver nitrate titration (SEPA), and the minimum detection concentration was 0.025 mg·L−1.32)
Based on the multiphase equilibrium theory, the standard Gibbs free energy of the reaction and the viscosity of the roasted ore were calculated by Factsage 7.2 software. The phase composition and microstructure of the roasted ore were characterized by X-ray diffraction and scanning electron microscopy. The effects of additive dosage on the fixation of F−, the toxicity of roasted ore, the reduction of nickel and iron during the reduction of laterite nickel ore by SCC were studied. Finally, the optimum experimental conditions of additive dosage were determined, and the harmless and resource utilization of SCC were realized. At the same time, nickel and iron in laterite nickel ore were efficiently enriched.
The reduction reaction mechanism of laterite nickel ore by SCC and CaO was as follows. The standard Gibbs free energy of the reaction was shown in Fig. 2. The reaction temperature was 700∼1400°C, atmospheric pressure. In the reduction process, SCC was used as a reducing agent to reduce nickel and iron from laterite nickel ore. The reactions occurred are as follows:
| \begin{align} &\text{NiO$_{\text{(s)}}$} + \text{C$_{\text{(s)}}$} = \text{Ni$_{\text{(s)}}$} + \text{CO$_{\text{(g)}}$};\\ & \Delta G^{0}{}_{T} = 76212-173.22T\,\text{J/mol} \end{align} | (1) |
| \begin{align} &\text{NiO$_{\text{(s)}}$} + \text{CO$_{\text{(g)}}$} = \text{Ni$_{\text{(s)}}$} + \text{CO$_{\text{2(g)}}$};\\ & \Delta G^{0}{}_{T} = -47103.92+1.63T\,\text{J/mol} \end{align} | (2) |
| \begin{align} &\text{C$_{\text{(s)}}$} + \text{CO$_{\text{2(g)}}$} = \text{2CO$_{\text{(g)}}$};\\ & \Delta G^{0}{}_{T} = 123315-174.85T\,\text{J/mol} \end{align} | (3) |
| \begin{align} &\text{3Fe$_{2}$O$_{\text{3(s)}}$} + \text{C$_{\text{(s)}}$} = \text{2Fe$_{3}$O$_{\text{4(s)}}$} + \text{CO$_{\text{(g)}}$};\\ &\Delta G^{0}{}_{T} = 71538-223.69T\,\text{J/mol} \end{align} | (4) |
| \begin{align} &\text{3Fe$_{2}$O$_{\text{3(s)}}$} + \text{CO$_{\text{(g)}}$} = \text{2Fe$_{3}$O$_{\text{4(s)}}$} + \text{CO$_{\text{2(g)}}$};\\ &\Delta G^{0}{}_{T} = -51777-48.84T\,\text{J/mol} \end{align} | (5) |
| \begin{align} &\text{Fe$_{3}$O$_{\text{4(s)}}$} + \text{C$_{\text{(s)}}$} = \text{3FeO$_{\text{(s)}}$} + \text{CO$_{\text{(g)}}$};\\ &\Delta G^{0}{}_{T} = 140582-202.77T\,\text{J/mol} \end{align} | (6) |
| \begin{align} &\text{Fe$_{3}$O$_{\text{4(s)}}$} + \text{CO$_{\text{(g)}}$} = \text{3FeO$_{\text{(s)}}$} + \text{CO$_{\text{2(g)}}$};\\ &\Delta G^{0}{}_{T} = 17267-27.93T\,\text{J/mol} \end{align} | (7) |
| \begin{align} &\text{FeO$_{\text{(s)}}$} + \text{C$_{\text{(s)}}$} = \text{[Fe]} + \text{CO$_{\text{(g)}}$};\\ &\Delta G^{0}{}_{T} = 110180-151.85T\,\text{J/mol} \end{align} | (8) |
| \begin{align} &\text{NiO$_{\text{(s)}}$} + \text{FeO$_{\text{(s)}}$} + \text{2CO$_{\text{(g)}}$} = \text{[Fe,Ni]} + \text{2CO$_{\text{2(g)}}$};\\ &\Delta G^{0}{}_{T} = -60238+24.63T\,\text{J/mol} \end{align} | (9) |
Standard Gibbs free energies of (a) and (b) reduction reactions, (c) detoxification reactions.
The reaction equation (9) (NiO + FeO + 2CO = [Fe,Ni] + 2CO2) is the main reaction in the reduction of nickel and iron. The ΔG0 value of the reduction reaction of NiO by SCC was lower than that of the reduction reaction of iron metal oxide below 1000°C. From the thermodynamic point of view, nickel oxide was easier to be reduced than iron oxide, which indicates that the recovery of iron was more difficult than that of nickel. During the reduction process, toxic components such as soluble cyanide and fluoride in SCC can be removed according to the following reaction equations.
| \begin{align} &\text{2NaF$_{\text{(l)}}$} + \text{CaO$_{\text{(s)}}$} + \text{SiO$_{\text{2(s)}}$} = \text{CaF$_{\text{2(s)}}$} + \text{Na$_{2}$SiO$_{\text{3(s)}}$}; \\ &\Delta G^{0}{}_{T} = -126270+25.01T\,\text{J/mol} \end{align} | (10) |
| \begin{align} &\text{2AlF$_{\text{3(l)}}$} + \text{3CaO$_{\text{(s)}}$} = \text{3CaF$_{\text{2(s)}}$} + \text{Al$_{2}$O$_{\text{3(s)}}$};\\ &\Delta G^{0}{}_{T} = -561892+33.69T\,\text{J/mol} \end{align} | (11) |
| \begin{align} &\text{2Na$_{3}$AlF$_{\text{6(l)}}$} + \text{6CaO$_{\text{(s)}}$} + \text{3SiO$_{\text{2(s)}}$} \\ &\quad = \text{6CaF$_{\text{2(s)}}$} + \text{Al$_{2}$O$_{\text{3(s)}}$} + \text{3Na$_{2}$SiO$_{\text{3(s)}}$}; \\ &\Delta G^{0}{}_{T} = -489948-32.65T\,\text{J/mol} \end{align} | (12) |
| \begin{align} &\text{NaCN$_{\text{(l)}}$} + \text{O$_{\text{2(g)}}$} = \text{CO$_{\text{2(g)}}$} + \text{N$_{\text{2(g)}}$} + \text{Na$_{2}$O$_{\text{(l)}}$};\\ &\Delta G^{0}{}_{T} = -2043384+186.22T\,\text{J/mol} \end{align} | (13) |
It can be seen from reaction reactions equation (10)–(12) (2NaF + CaO + SiO2 = CaF2 + Na2SiO3; 2AlF3 + 3CaO = 3CaF2 + Al2O3; 2Na3AlF6 + 6CaO + 3SiO2 = 6CaF2 + Al2O3 + 3Na2SiO3) that the addition of NaF, AlF3 and Na3AlF6 in CaO fixed slag can form CaF2 insoluble in water. CaF2 can reduce the melting point of slag, improve the fluidity of slag, accelerate the separation speed of slag and nickel iron metal particles, promote the grade and recovery rate of nickel and iron. Reaction reaction equation (13) (NaCN + O2 = CO2 + N2 + Na2O) shows that cyanide was easily decomposed into CO2 and N2 at high temperature, which eliminates the toxicity of SCC.
The thermodynamic equilibrium calculation of the composition of roasted ore obtained under the conditions of SCC addition amount of 14 wt.%, reduction temperature of 1250°C and reduction time of 75 min was carried out by Factsage software. Figure 3(a) was the formation of SiO2, CaO and Na2O in roasted ore under different CaO additions when SCC was used as reducing agent. With the increase of CaO, the reduction degree of roasted ore increases, and the content of SiO2 increases first and then decreases. SiO2 will lead to the increase of the viscosity of roasted ore. When CaO was used as an additive, F− remains in the roasted ore in the form of CaF2. With the increase of CaO addition, the content of CaF2 increases. Na2O in the roasted ore mainly comes from NaF in SCC, and Na2O increases rapidly with the increase of CaO content. The components of SiO2, CaF2, CaO and Na2O in the roasted ore have a great influence on the viscosity of the roasted ore. The results show that the increase of CaF2 and CaO significantly reduces the viscosity of roasted ore. According to the roasted ore composition with different CaO additions, the viscosity was calculated by using the viscosity database in Factsage and the modified quasi-chemical model, as shown in Fig. 3(b).33) Results show that with the increase of CaO addition, the viscosity of roasted ore decreases, mainly due to the addition of CaO to generate CaF2 to reduce the viscosity. The viscosity of roasted ore is reduced, the fluidity is improved, which is beneficial to the aggregation of ferronickel particles and greatly improves the recovery rate of nickel and iron.
The composition and viscosity of substances with different amounts of CaO, (a) SiO2, CaF2, CaO and Na2O content, (b) roasted ore viscosity.
SCC was considered to be a hazardous solid waste due to its large amount of fluoride and cyanide. Therefore, the behavior of toxic components fluoride and cyanide should be carefully considered when SCC was used as a reducing agent to extract valuable metals from laterite nickel ores. Fluoride and cyanide in SCC decompose and volatilize during the reduction process, and some of them are transferred to roasted ore. The cyanide was easily decomposed completely by high temperature treatment at 1250°C. However, a large amount of fluoride (Na3AlF6 and NaF, etc.) will enter the air in the form of gas, or remain in the roasted ore in the form of soluble fluoride, which will cause serious pollution to the environment. Therefore, a key point in the feasibility of using SCC as a reducing agent was to avoid the volatilization of fluoride into the air, so that it forms insoluble fluoride and remains in the roasted ore.
As an important fluorine-fixing agent in the process of SCC fire treatment, CaO has an important influence on the fixation of fluorine in the reaction process. When the reduction temperature was 1250°C and the reduction time was 60 min, the addition amount of SCC was 14 wt.%. The toxicity of F− and CN− in the roasted ore with different CaO additions was analyzed. The results were shown in Table 3. In the table, A was the toxicity test of the reducing agent SCC, and B, C, D, E, F and G were the roasted ore under the conditions of SCC, SCC and 2 wt.% CaO, SCC and 4 wt.% CaO, SCC and 6 wt.% CaO, SCC and 8 wt.% CaO and SCC and 10 wt.% CaO, respectively. The results are shown in Fig. 4. With the increase of CaO, the content of soluble fluoride in roasted ore gradually decreases, and meets the requirements of F− ≤ 100 mg·L−1 and CN− ≤ 5 mg·L−1.34) CN− was easily decomposed into N2 and CO2 at high temperatures (>550°C), so CN− was not detected in the leachate in all experimental cases. For F−, the content in the leaching solution during the experiment was less than 100 mg·L−1. Therefore, the product of the reduction roasting process-roasted ore meets the environmental requirements and was easy to be safely treated and directly landfilled.
F− concentration of roasted ore with different CaO amount.
Although the leaching solution of roasted ore with and without CaO can meet the requirements of hazardous waste discharge, the principle of CN− treatment was to obtain non-toxic CO2 and N2 by high temperature decomposition, but the principle of F− treatment was different. The mechanism of action was shown in Fig. 5. When CaO was not added, most of the soluble fluoride (NaF) enters the air through volatilization, leaving only a lower content of soluble fluoride and insoluble fluoride. When CaO was added, most of the soluble fluoride was fixed in the roasted ore in the form of insoluble fluoride such as CaF2, which was not volatile and insoluble. Since some fluorides volatilize into the air during the smelting process, which may cause pollution problems, the fluorine content in the roasted ore was determined to study the fixation rate of fluorine in the roasted ore. The fixed rate of fluorine η (%) was the ratio of fluorine content in roasted ore to total fluorine in SCC, expressed as formula (14). where FRO was the fluorine content in roasted ore, MRO was the mass of roasted ore, FSCC was the fluorine content in SCC, and MSCC was the mass of SCC added.
| \begin{equation} \eta = \frac{\text{F}_{\text{RO}} \times \text{M}_{\text{RO}}}{\text{F}_{\text{SCC}} \times \text{M}_{\text{SCC}}} \times 100\% \end{equation} | (14) |
Detoxification mechanism (a) with and (b) without CaO.
Figure 6 shows the effect of CaO addition on the fluorine fixation rate. It can be seen that CaO has a significant effect on the fixation of soluble F-in waste cathode carbon. With the increase of CaO addition, the fixation rate of F− in waste cathode carbon increases gradually. When CaO was not added, η was only 70%, indicating that about 30% of fluorine was volatilized into the air. Under the condition of 8 wt.% CaO, η is 95.99%, and only a small amount of fluoride is discharged through exhaust gas and absorbed by alkali solution. Toxicity testing of roasted ores revealed a leaching concentration of F− of 31 mg·L−1, with CN− not detected, well below the allowable emission standard. Considering comprehensively, 8 wt.% CaO was selected as the best fluorine fixation experimental condition.
Effect of CaO amount on fluorine fixation rate.
As an important additive in the reduction roasting treatment of laterite nickel ore, CaO has an important influence on the reduction of ferronickel. Under the conditions of reduction roasting temperature 1250°C, reduction time 60 min, grinding time 6 min, magnetic field intensity 150 mT, the addition of SCC is 14 wt.%. The effects of different CaO additions on the recovery of nickel and iron were compared, and the results are shown in Fig. 7. Formula (15) is the calculation formula of nickel iron recovery rate.
| \begin{equation} \alpha = \frac{\text{m}_{1} \times \omega_{1} + \text{m}_{2} \times \omega_{2}}{\text{m}_{1} + \text{m}_{2}} \times 100\% \end{equation} | (15) |
Effect of CaO addition on recovery of ferronickel.
In the formula, α is the theoretical maximum value of nickel/iron, m1 is the concentrate quality, ω1 is the concentrate nickel/iron grade, m2 is the magnetic separation slag quality, ω2 is the magnetic separation slag nickel/iron grade.
It is found in Fig. 7 that when SCC is used as a reducing agent, the reduction effect of laterite nickel ore increases significantly with the addition of CaO. It was found in Fig. 6 that the F− in SCC was basically fixed under the condition of 8 wt.% CaO. When CaO was added, the main factor affecting the reduction of ferronickel particles changed from fixed CaF2 in SCC to added CaO, so the recovery rate of ferronickel increased first and then tended to be gentle. The recovery rates of nickel and iron were 91.23% and 89.63% respectively when 8 wt.% CaO was added. The addition of CaO had little effect on the recovery rate of nickel and iron, and F− was basically fixed to meet the emission standards. The optimum condition for considering cost is 8 wt.% CaO.
3.5 Phase transition characteristics and mechanismXRD analysis of roasted ore with or without CaO under different reducing agents is shown in Fig. 8. Four mineral phases, Quartz, Magnesium olivine, Ni–Fe and Pyroxene, were mainly found in the roasted ore when CaO was added when the reducing agent was anthracite. When CaO is not added, it is found that the phase is similar to the original ore, and Ni–Fe and Pyroxene are not found. Pyroxene is a chain structure formed by the reaction of CaO with forsterite. When CaO is added when the reducing agent is SCC, in addition to the four mineral phases of Quartz, Magnesium olivine, Ni–Fe and Pyroxene, a new phase Tremolite is also formed in the roasted ore. Tremolite is a chain structure formed by the reaction of CaF2 with forsterite. CaF2 forms tremolite mainly by changing the viscosity and by reacting with silicates in laterite nickel ore. The tremolite exhibits a chain-like structure of silicates. Compared with the island structure of magnesium silicate, the ion accumulation mode of chain structure silicate is looser, and the ionic bond force between silicon oxygen backbone and metal cation is weaker, so the reactivity of chain structure silicate is higher than that of island structure silicate. While CaO mainly promotes the aggregation of nickel–iron particles by changing the viscosity, and reacts with silicate in laterite nickel ore to form a chain structure silicate-pyroxene, which improves the reactivity and promotes the enrichment of nickel and iron.
Comparison in XRD pattern: (a) raw ore, the roasted ore with 8 wt.% CaO (d) and without CaO (b) under anthracite conditions, and the roasted ore with 8 wt.% CaO (e) and without CaO (c) under SCC conditions.
Tremolite and Pyroxene were not found when CaO was not added. Combined with the reaction (10)–(12) (2NaF + CaO + SiO2 = CaF2 + Na2SiO3; 2AlF3 + 3CaO = 3CaF2 + Al2O3; 2Na3AlF6 + 6CaO + 3SiO2 = 6CaF2 + Al2O3 + 3Na2SiO3) in Fig. 2, the reaction of NaF, Na3AlF6 and CaO can occur at 1250°C, which further verifies that CaO reacts with NaF and Na3AlF6 to form CaF2. It is found from Fig. 6 that the content of total fluorine (including soluble fluorine and insoluble fluorine) in roasted ore increases obviously after adding CaO compared with that without CaO. Through the toxicity leaching test of roasted ore in Table 3, it was found that the soluble fluorine did not increase and decreased significantly, indicating that more fluorine was converted to CaF2 through CaO and remained in roasted ore.
From Fig. 9 that after the addition of CaO, the ferronickel particles are obviously aggregated than those without CaO. After ore crushing, due to the magnetic properties of ferronickel particles, larger ferronickel particles are more easily separated from ore by magnetic separation than smaller ferronickel particles. Through EDS analysis of ferronickel concentrate, it is found that point 1 and point 4 are the points of larger metal particles in ferronickel concentrate with and without CaO, respectively. It is found that the metal after adding CaO is a ferronickel alloy, and the metal generated without adding CaO is mainly metal iron particles. Points 3 and 6 are the points of smaller metal particles in the ferronickel concentrate with and without CaO, respectively. It was found that the main component of the fine particles after adding CaO was ferronickel alloy and wrapped by a small amount of forsterite. The main component of the fine particles without CaO was that the metal iron contained a small amount of nickel and was wrapped by a certain amount of forsterite. It shows that obvious aggregation of nickel appears after adding CaO, which improves the recovery of nickel and iron. Point 2 and point 5 are the non-metallic regions in the ferronickel concentrate with and without CaO addition, respectively. It is found that CaF2 appears in the non-metallic region after adding CaO, and the non-metallic region without CaO is mainly forsterite and a small amount of unreacted anthracite. It was further indicated that the soluble F− in SCC was fixed after adding CaO.
Comparison of SEM and EDS: the roasted ore with 8 wt.% CaO (a) and without CaO (b) under SCC conditions.
The recovery of nickel and iron from laterite nickel ore by reduction roasting-magnetic separation with SCC as reducing agent was studied. The harmless reuse of SCC and the recovery of nickel and iron from laterite nickel ore have brought great economic and environmental benefits to the nickel and aluminum industries. The main conclusions are as follows:
Financial support for this study was supplied from Innovative Research Group Project of the National Natural Science Foundation of China (Project Nos. 52074140) and the Yunnan Provincial Key Research and Development Program-International Science and Technology Cooperation Special Project (Project Nos. 2018IA055).
