Table of Content

24 August 2020, Volume 20 Issue 8

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Contents

Cover and Contents

Chin. J. Process Eng.. 2020, 20(8):  0. 

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Reviews

Current status of scandium resources and application research progress of solvent extraction in the process of scandium extraction

Shuai SUN Hongqian SUN Jing SONG Jingkui QU Tao QI

Chin. J. Process Eng.. 2020, 20(8):  877-886.  DOI: 10.12034/j.issn.1009-606X.219336

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As one of rare and precious rare earth elements, scandium is extremely dispersed in the crust and often associated with other minerals. With excellent properties of scandium and its compounds, scandium is widely used in aerospace materials, electronic information, nuclear technology and other industries. It is mainly used in aluminum?scandium alloy material, solid oxide fuel cell (SOFC), scandium sodium halogen (HID) lamp, ultralight shape memory magnesium?scandium alloy and fast storage. The technology of scandium recovery is complicated and the cost is high. Scandium is abundant in China, which accounts for 1/3 of the world. The research of scandium extraction and deep processing in China is still weak, and there is a big gap with the world advanced level. This work summarized the resource distribution, supply and demand of scandium, and introduced the technologies and examples of scandium extraction from different scandium containing materials, such as titanium dioxide waste acid, red mud, zirconium smelting materials, tungsten slag, focused on the application of solvent extraction in extracting scandium process, and analyzed the different extraction system of extraction mechanism of scandium, found that low extraction rate, emulsification and three phase problems were the common difficulties of scandium system. In addition, it was proposed that China should lead the designated product standards, focus on the study of methods to improve the recovery of scandium, improve the comprehensive extraction of scandium and symbiotic elements, and constantly develop green extraction technology.

Flow & Transfer

Numerical investigation of film flow characteristics of molten slag in air quenching dry granulation process

Lili WANG Yuzhu ZHANG Yue LONG Zibing WANG Haibin KE

Chin. J. Process Eng.. 2020, 20(8):  887-895.  DOI: 10.12034/j.issn.1009-606X.219307

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Liquid film formation is an important part of the air quenching dry slag granulation process and the granulation effect of slag depends on the film flow characteristics. To investigate the flow behavior of slag and the effects of different operating parameters and slag properties on the film flow characteristics, a three-dimensional unsteady numerical model was established using k?? based shear stress transport (k?? SST) turbulence model and the coupled level-set, and the volume of fluid (CLSVOF) method was utilized to capture the sharp air?liquid interface. The film formation mechanism and the influence of different operating parameters and slag properties on the film flow characteristics were discussed. Also, dimension analysis of the film edge thickness was conducted. The results indicate that the flat film was formed because of flow deformation due to air impingement, recirculation zone, and pressure gradients. An unstable wave appeared on the film surface owing to the gas?liquid velocity difference. The wavelength of surface wave decreased first and then increased along the axis, and the film thickness gradually decreased along the axis. The wavelength of surface wave and the film thickness decreased with the increasing airflow velocity and increased with the rise in slag mass flow rate. The wavelength of surface wave and film thickness decreased with the increasing slag density and increased with the rise in slag viscosity. A dimensionless was developed which indicates that the film thickness had exponent relation to the airflow velocity, slag mass flow rate, slag density, and viscosity.

Simulation of jet enhancement of fluid flow and heat transfer in helical coiled channel

Yaxia LI Yuan ZHANG Jing ZHANG Liping KOU Bin GONG Jianhua WU

Chin. J. Process Eng.. 2020, 20(8):  896-903.  DOI: 10.12034/j.issn.1009-606X.219331

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The CFD software was employed to study the fluid flow characteristics and heat transfer enhancement in the helical coiled channel under the action of jet. The cross-section of the helical channel was circular and the dimensionless curvature and pitch of the helical channel were 0.061 and 0.121, respectively. The simulated results were in good agreement with the existing experimental data. The structure of composite vortices and its evolution process in the channel have been discussed. The effect of jet action on heat transfer enhancement was investigated in the range of incident angle ?=π/6–π/3 and jet velocity ratio ?j=3–6. The results show that in the initial stage of jet in the helical channel, the secondary vortices induced by centrifugal force were completely suppressed by impact of the jet. And another pair of vortices named as jet induced vortices emerged under the impact and entrainment of the jet, wherein the rotating direction was opposite to that of the vortices induced by the centrifugal force. With the flow development, the structure of the jet induced vortices changed from two vortices into one vortex, and then, gradually dissipated and disappeared. The heat transfer of fluid near the inner wall of helical channel was significantly enhanced by the jet action. As ? decreased or ?j value increased, the heat transfer enhancement effect was increased. In the studied range of ?j≥4, without considering the jet flow rate increase, the comprehensive heat transfer enhancement factor JF1 was between 1.26 and 1.67, while when the jet flow rate increase was considered, JF2 was in the range of 1.008~1.19.

Fluidization characteristics of binary mixtures of iron-based oxygen carrier and dried sewage sludge

Qingchao GONG Jianqiao WANG Dongdong FANG Feng DUAN Lihui ZHANG

Chin. J. Process Eng.. 2020, 20(8):  904-911.  DOI: 10.12034/j.issn.1009-606X.219301

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Chemical looping combustion technology can effectively decrease the pollutant emissions from the dried sewage sludge incineration. The mixing and separation of binary mixtures of dried sludge and iron-based oxygen carrier are involved in the fluidized bed due to their big difference in physical properties. The fluidization experiments of binary mixtures of dried sewage sludge and iron-based oxygen carrier were carried out in a plexiglass cold fluidized bed with 100 mm inner diameter in this study. The effects of particle size, mass ratio of dried sewage sludge and oxygen carrier and operating velocity on the fluidization characteristics were investigated. The results showed that the sludge can be mixed well with the oxygen carrier with mean particle size of 0.66 mm, and the minimum fluidization velocity ( ) was equal to the minimum mixing operation velocity (Um). When the mean particle size of oxygen carrier was 1.46 mm, it gradually transited from the separated fluidization state to the mixed fluidization state as the operating velocity increased, and the Um was greater than in this condition. When the mean particle size of oxygen carrier was 2.43 mm, the separated fluidization state was always maintained. Based on a proposed dimensionless number Gd for judging the mixed/separated fluidization state of binary mixtures of dried sewage sludge and iron-based oxygen carrier, the binary mixtures were in a mixed fluidization state while 0<Gd<0.8, and the binary mixtures were in a separated fluidization state while Gd>0.8.

Reaction & Separation

Experimental study on separation of lead and zinc from tailings with high mud content in Yunnan Province

Huichao JI Quanjun LIU Xu JIANG Jingshen DONG

Chin. J. Process Eng.. 2020, 20(8):  912-920.  DOI: 10.12034/j.issn.1009-606X.219319

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The separation of lead and zinc from tailings with high mud content in Yunnan was examined, which was characterized by a fine particle size, severe argillization, and relatively complex properties. A combination of flotation and gravity separation of mud and sand was adopted to effectively separate lead and zinc and realized the comprehensive recovery and utilization of the complex tailing resources. Results revealed that the lead content was 4.29wt% and that the zinc content was 4.99wt%. Lead mainly existed as cerussite and plumbojarosite. Lead and iron metasomatize to form different wrapping forms, making separation extremely difficult. Zinc mainly existed as zinc oxide, which exhibited a high degree of oxidation. Zinc oxidation rate reached up to 99%, and it was mainly difficult to separate hemimorphite. Ultimately, the lead concentrate with a lead grade of 33.87% and a recovery rate of 62.53% were obtained by the closed-circuit beneficiation process; the silver content in the lead concentrate and its recovery rate were 142.50 g/t and 30.92%, respectively; the zinc concentrate with a zinc grade of 15.21% and a recovery rate of 47.82% were obtained.

Selective transformation and separation of rare earths from NdFeB magnet scraps based on sulfuric acid reduction

Jinliang WANG Longjun WANG Fupeng LIU

Chin. J. Process Eng.. 2020, 20(8):  921-928.  DOI: 10.12034/j.issn.1009-606X.219316

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Considering the current status associated with the difficult extraction of rare earths in NdFeB magnet scraps in terms of economy and efficiency, rare earths were selectively separated from NdFeB magnet scraps by sulfating roasting. Fe2(SO4)3 was found to induce the sulfate transformation of rare-earth oxides, significantly reducing the amount of sulfuric acid. Almost 98% of rare earth oxides were transformed to soluble rare earth sulfate by the combined action of H2SO4 and Fe2(SO4)3 under conditions of a theoretical amount of sulfuric acid of 2.0 times, a roasting temperature of 750℃, and a roasting time of 1.5 h, while less than 0.1% of iron was leached, mainly existing in the form of a residue as a hematite (Fe2O3) phase; this hematite phase can be easily smelted in iron works. As a result, the reduction of sulfuric acid and the comprehensive utilization of NdFeB magnet scraps are achieved.

Recovery of scandium and fluorine from molten salt electrolysis waste residues

Yunfeng FU Weiwei WANG

Chin. J. Process Eng.. 2020, 20(8):  929-937.  DOI: 10.12034/j.issn.1009-606X.219323

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To realize the detoxification treatment of the fluorine-containing waste residue from the production of an Al–Sc master alloy by molten salt electrolysis and recover valuable elements, based on the characteristics of a high fluoride and low scandium content in mineralogical compositions, the two-stage hydrometallurgical leaching of electrolytic slag from the Al–Sc alloy prepared by molten salt electrolysis was conducted for the recovery of fluorine and scandium. X-Ray diffraction (XRD), X-ray fluorescence (XRF), ion chromatograph (IC), inductively coupled plasma atomic emission spectrometer (ICP-OES), scanning electron microscope (SEM) were employed to investigate the trend and distribution of fluorine, scandium, and aluminum in detail. Results revealed that during the alkali leaching process, the fluorine in the molten salt slag was converted into sodium fluoride with low solubility, and almost all of the fluorine can be dissolved into the solution by washing with water. The scandium in the molten salt slag remained in the alkali leaching slag; therefore, the separation of fluorine and scandium was realized. By utilizing the insolubility of α-Al2O3 in less concentrated sulfuric acid at a low temperature, the alkali leaching slag was then leached by sulfuric acid to separate and recover scandium from α-Al2O3. Effects of the leaching agent concentration, liquid to solid ratio, leaching temperature, time, and other process parameters on the leaching rates in the alkali leaching and acid leaching processes were investigated. The optimum reaction conditions were determined to be a sodium hydroxide concentration of 100 g/L, a liquid to solid ratio of 12:1, a leaching temperature of 90℃, and a leaching time of 1.5 h for the alkali leaching process, and the sulfuric acid concentration of 1.5 mol/L, a liquid to solid ratio of 6:1, a leaching temperature of 90℃, and a leaching time of 50 min for the acid leaching process. Under the optimized parameters, the leaching rates of soluble aluminum and fluorine in the molten salt residue after alkali leaching were 97.12% and 98.71%, respectively. The purity of the sodium fluoride product reached 98.70%. Furthermore, the leaching rate of scandium reached 92.01% during the subsequent acid leaching process.

Experimental study on separation of zinc and silver flotation from a silver-rich zinc concentrate in Yunnan

Jie LI Cuicui JI Xian XIE Bowen KANG Peiqiang FAN

Chin. J. Process Eng.. 2020, 20(8):  938-946.  DOI: 10.12034/j.issn.1009-606X.219288

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Silver is a rare and precious metal with excellent performance and wide applicability, and is a dominant element in the national economy. Among the abundant silver mineral resources in China, associated silver reserves account for 88% of total silver reserves. Due to the pro-lead and pro-zinc nature of silver, associated silver is mainly hosted in deposits dominated by lead and zinc. For the comprehensive recovery of associated silver in lead-zinc ores, the traditional process mostly uses lead flotation and zinc suppression approaches to recover lead and zinc main metal minerals under high alkali, as well as enrichment of silver minerals in lead concentrates or zinc concentrates. However, the associated silver minerals in the high alkali process are easily inhibited and the losses are severe. Furthermore, the recovery rate of China's associated silver can only reach 60%~70%, while foreign countries generally reach 70%~80%. A silver-rich zinc concentrate in Yunnan mainly contains sphalerite, pyrite, galena, and cerussite; silver exists in cerussite in the form of isomorphism. According to the properties of ore samples, the technological process of lead flotation and zinc suppression was determined in a preliminary manner. Hydraulic analyses found that the highest silver content is present in particles with size –19+10 μm. On this basis, the effects of grinding fineness, inhibitors, activators, and collectors on flotation separation indexes were investigated. The results showed that the dosage of Na2SiO3, CuSO4, butyl xanthate, and terpenic oil were 2000, 200, 300, and 30 g/t, respectively. Furthermore, through a roughing, scavenging, cleaning, full-process closed-circuit experiment, it was possible to obtain a zinc concentrate with Zn grade of 61.08% and recovery rate of 95.89%, and a silver concentrate with Ag grade of 1548.32 g/t and recovery rate of 71.17%. In this way, flotation separation of zinc and silver was achieved, and the efficient enrichment of associated silver was obtained.

Process & Technology

Cooling characteristics and influencing factors of glass quenching process

Gaowei YUE Chongchong WAN Lu WANG Yanbing LI

Chin. J. Process Eng.. 2020, 20(8):  947-958.  DOI: 10.12034/j.issn.1009-606X.219337

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Cooling law of high temperature glass in air-grid plays an important role in the stress of tempered glass, and there are many factors that affect the cooling law of glass. However, because glass moves fast in air-grid, it is very difficult to test the real-time temperature change of high-temperature glass. Moreover, the test of glass cooling for each influencing factor greatly increases the workload of workers. So the physical model of glass cooling in air-grid was established to numerically simulate the cooling law, and in order to verify the reliability of the model, the cooling law of high temperature glass had been tested in air-grid with infrared thermometers under the set parameters. After the high temperature glass entered into the air-grid, the glass temperature at different times presented a strip, which reflected the nonuniformity of glass cooling, but on the whole, the glass temperature gradually decreased with the quenching time, and the glass temperature decreased with quenching time in a negative index. The numerical simulation results were in good agreement with the test results. Then the physical model was applied to simulate the cooling law of high temperature glass with the effect of wind pressure, wind temperature, distance from nozzle to glass, speed out of the heating furnace, and round-trip speed in air-grid. The results showed that the glass temperature decreased exponentially with the wind cooling time. The greater the wind pressure was and the lower the wind temperature was, the faster the glass cooling was, that was, the wind pressure and the wind temperature had a significant influence on the cooling law of glass. Secondly, the distance of the nozzle to glass had a certain effect on the glass cooling, and the effect of speed out of the heating furnace, and round-trip speed in air-grid was not obvious. This study provided important theoretical basis for setting technological parameters of tempered glass production process.

Effect mechanism of Ca²⁺ and Mg²⁺ in water on the floatability of specularite and chlorite

Mingyang LI De LIAN Junjie HAO Yiming HU Xiangpeng GAO

Chin. J. Process Eng.. 2020, 20(8):  959-969.  DOI: 10.12034/j.issn.1009-606X.220024

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In order to research the effect of water quality on the separation of specularite and chlorite, the effect and mechanism of Ca2+ and Mg2+ on the flotation behavior of specularite and chlorite using dodecylamine (DDA) as the collector were studied via micro-flotation tests, Zeta potential measurements, Boltzmann theoretical analyses, solution chemistry calculation and molecular dynamics simulation in deionized water and tap water flotation environment, respectively. The results of micro-flotation tests demonstrated that specularite and chlorite were depressed to some extent in tap water. Compared with the deionized water system, the recovery rates of specularite and chlorite decreased by 8.01 and 8.99 percent point, respectively. In simulated tap water environment, Ca2+and Mg2+ made the recovery rate of specularite decreased by 11.91 and 18.88 percent point, respectively, while decreased by 7.44 and 15.45 percent point, respectively, for chlorite. The inhibitory effect of tap water on specularite and chlorite flotation mainly caused by the existence of Ca2+ and Mg2+. The depression effect of Ca2+ and Mg2+ on specularite was stronger than that of chlorite, and the depression effect of Mg2+was more obvious than Ca2+. The results of mechanism detection indicated that the adsorption of Ca2+ and Mg2+ shifted the surface potential of the two minerals to higher values, wakened the electrostatic adsorption reaction between DDA and the two minerals, decreased the contact angle, hydrophobicity and the concentration of RNH3+ in interface layer, increased the adsorption distance between DDA and the two minerals, increased the loose degree of DDA, which in all depressed the flotation of specularite and chlorite. The research contents provide theoretical basis of disturbance law and elimination methods of water quality for iron ore flotation.

Biochemical Engineering

The effects of salinity on microbial activity and N₂O release in anoxic–aerobic sequencing batch biofilm reactor

Youkui GONG Yinglong YUE Yongzhen PENG

Chin. J. Process Eng.. 2020, 20(8):  970-978.  DOI: 10.12034/j.issn.1009-606X.219325

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Accumulation of nitrites is frequently observed in saline wastewater nitrification processes, which often results in the release of the strong greenhouse gas, nitrous oxide (N2O). This study investigated the effect of salinity on microbial activity and N2O release characteristics during the simultaneous nitrification and denitrification processes in a sequencing batch biofilm reactor (SBBR). The result showed that salinity inhibited the microbial activities of each bacterial group in increasing, sequential order as follows: nitrite oxidizing bacteria (NOB)>ammonia oxidizing bacteria (AOB)>carbon oxidizing bacteria. The effluent COD was stable at about 50.0 mg/L in the range of salinity from 0 to 20 g NaCl/L. The average NH4+ removal efficiency reduced from more than 98% to 70.5%, and TN removal efficiency reduced from 42.4% to 16.9% respectively, while the N2O yield increased from 3.9% to 13.3%. Similar to SND efficiency, the internal concentration of carbon sources (PHA and Gly) first increased and then decreased with increase in salinity. The N2O release was mainly produced in AOB aerobic and endogenous denitrification processes. The low N2O release could be ascribed to the anoxic zone deep in the SBBR at low salinity (≤10 g NaCl/L). As the salinity was increased to more than 10 g NaCl/L, there was a decrease in internal carbon source synthesis, which aggravated the electron competition between each bacterial reductases in the denitrification process. Further increase in salinity led to an increase in extracellular polymer substances (EPS) synthesis and the proportion of polysaccharides (PS) in the EPS. A decrease in the anoxic area deep in the membrane led to the inhibition of the N2O reduction.

Materials Engineering

Preparation of ultrafine copper powder by high frequency hydrogen plasma enhanced reduction

Huacheng JIN Liuyang BAI Junmei FAN Guolin HOU Fei DING Fangli YUAN

Chin. J. Process Eng.. 2020, 20(8):  979-988.  DOI: 10.12034/j.issn.1009-606X.219302

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Ultrafine copper powder is widely used in the fields of electronics, lubrication, catalysts, due to its large specific surface area, excellent thermal conductivity and high surface activity. The ultrafine copper powder?s application performance is determined by the control technology of spherical, uniform particle size, monodisperse and high purity. The ultrafine copper powder was prepared by high frequency hydrogen plasma enhanced reduction with characteristics of simple operation, high purity, controllable atmosphere and less environmental pollution. The free radicals produced by hydrogen plasma arc was helpful to control the morphology and the particle size of copper powder. The feeding rate, reducing hydrogen flow rate, hydrogen distribution position, reaction zone space, cooling temperature, and the optimal process conditions were determined, and more uniform and well dispersed ultrafine spherical particles were prepared with particle size mainly between 100 and 200 nm. The oxygen content was under 1%, bulk density was 0.502 g/cm3.

Environment & Energy

Effect of different soaking time on catalytic performance of CuO/Cu@BC electrode for CO₂ reduction

Yue ZHOU Xiaojing GUO Xuanjiang LI Lu GAO Feng HONG Jinli QIAO

Chin. J. Process Eng.. 2020, 20(8):  989-996.  DOI: 10.12034/j.issn.1009-606X.219314

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As an environmentally-friendly and cost-effective biological 3D carbon nanomaterial, bacterial cellulose (BC) has been gradually used in flexible electronics. However, the application of BC in electrochemical CO2 reduction (ECR-CO2) reactions is rare. Herein, to promote its applications in ECR-CO2, BC with a 3D network structure was used as a catalyst carrier, and a catalyst electrode (CuO/Cu@BC) supporting Cu and CuO nanocomposites was prepared by in situ chemical reduction. To investigate optimal conditions, the soaking time of the BC membrane was changed to achieve structure regulation. The results revealed that at a soaking time of 24 h, the CuO/Cu24h@BC electrode exhibited a high electroactive area (12 mF/cm2), providing a considerable increase in the number of active sites for CO2 absorption; this result was verified by investigation of the electrocatalytic activity and performance. The electrochemical impedance test revealed that the activation resistor of the electrode was small and that the activation energy was high, thereby improving the electron conductivity by building an efficient transfer highway for Cu and CuO. Scanning electron microscopy analysis of the morphology of the CuO/Cu@BC electrode revealed a uniform coverage in addition to the even decoration of nanoparticles (50~70 nm) on the top, facilitating the penetration of the electrolyte. On the other hand, the seaweed structure of the CuO/Cu8h@BC electrode and the adverse combination of the nanoparticles of the CuO/Cu16h@BC electrode were disadvantageous to the transformation of CO2. In terms of the product analysis by ECR-CO2, the CuO/Cu24h@BC electrode exhibited outstanding selectivity for CO with a faradaic efficiency of 52% at a potential of ?0.6 V vs. RHE in a 0.5 mol/L KHCO3 electrolyte. All the above results demonstrated that BC was superior as an efficient electrode substrate to support electrocatalysts for CO2 reduction and that the CuO/Cu24h@BC electrode exhibited good performance for the reduction of CO2 to CO.