•Heterogeneous grinding of binary-mineral mixture is conducted in Hardgrove machine.•Analyses of breakage behavior of the mixture and each component.•Hardness index is modeled into the breakage model.•Analyses of energy split based on the modified model and energy-size data.Complex interactions among components in the heterogeneous grinding have an influence on breakage and energy consumption characteristics of components in mixtures if compared with the single breakage. In this paper, a modified Hardgrove mill, with the addition of a power meter, is used to simulate the grinding process of vertical spindle pulverizer. Binary-component mixtures of coal and pyrite, or coal and calcite, in the size of −2.8 + 2 mm, are prepared to study the heterogeneous breakage. For the mixture A of coal and pyrite, the fineness of pyrite progeny is higher than that from single-breakage. Instead, the coal in mixture A shows the opposite trend. Because of the relatively less difference in hardness between coal and calcite, size distributions of components are environment-independent. Breakage of mixture follows the first-order kinetics, as well as each component in mixtures. In order to describe the energy-size reduction of mixture, a modified model in the form t10=A(1-e-b·ECS/Hw), has been derived from modeling the mass weighted hardness index of mixture, and its predictions are highly fitted with experimental and supplemental data. In addition, energy split phenomena of components are discussed qualitatively using the modified model. Specific energies that need to yield the same product t10 of one component both in the single and mixture breakage are compared, and the interaction of one component on the breakage of another one in mixture grinding also has been analyzed. Size distributions of ground products using t10 are well predicted, which are critical to conduct the computation of size distribution of progenies at given specific energies.Download high-res image (58KB)Download full-size image

•Waste printed circuit boards (WPCBs) have high recovery value.•Triboelectric separation can remove inorganics of WPCBs nonmetallic fraction.•The inorganics present decreasing trend from negative to positive plate.•Removing inorganics can improve the usability of WPCBs nonmetallic fraction.The recovery of metals from waste printed circuit boards (WPCBs) has been studied for a long time because of the high economic value of these metals. The low usability of the nonmetallic fraction (NMF) of WPCBs caused by inorganics makes its industrial reuse difficult. Removal of inorganics by triboelectric separation with the aim of improving the usability of NMF was investigated using a lab triboelectric separation system. After separation, a new composite was produced by compounding 20 wt% NMF and 80 wt% high-density polyethylene (HDPE). The mechanical properties of each composite were compared, and the surface morphology was analyzed with a scanning electron microscope (SEM). The separation results demonstrated that inorganics were removed and collected in a groove that was closed to a negative plate. Mechanical property testing showed that the removal of inorganics could improve the usability of NMF. Both the flexural and impact strengths of the composites that were filled by NMF without inorganics were obviously improved. The SEM image indicated that air holes and faultage caused by glass fiber agglomerations and poor compatibility between HDPE and inorganics were the main features contributing to composites with poor mechanical properties.Download high-res image (331KB)Download full-size image

•Flotation process was applied in the recycling of LiBs.•Recovered electrode materials regained their original wettability by Fenton reaction.•The mechanism of the improvement of floatability was presented.•PVDF was oxidized and decomposed by Fenton reagent.In this paper, a Fenton reagent assisted flotation process is developed to recover valuable electrode materials LiCoO2 and graphite from spent lithium-ion batteries (LiBs). At room temperature, effect of key parameters for Fenton reaction such as the ratios of H2O2/Fe2+ (40–280) and liquid-solid (25–100) are investigated to determine the most efficient conditions of surface modification of electrode materials by Fenton reagent. The modified electrode materials are separated by flotation operation to recover the cathode material and anode materials respectively. The results show that in the optimum conditions that the Fe2+/H2O2 ratio is 1:120, and the liquid-solid ratio is 75:1, most of the organic outer layer coated on the surface of electrode materials can be removed. After modified by Fenton reagent, the original wettability of LiCoO2 and graphite is regained. The −0.25 mm crushed products of spent LiBs can be separated into LiCoO2 concentrate and graphite concentrate by flotation process efficiently.

•Comparison of energy efficiency between E and MPS type vertical spindle pulverizer.•Modify the energy-size reduction model based on experimental data.•Comparison of energy efficiency by breakage model and structure parameter difference.•Relationship of product t10 linked with specific grinding energy and product tn.•Comprehensive analyses of classification and grinding to compare energy efficiency.0.5%–2% gross power generation of coal power plant is consumed by vertical spindle pulverizer (VSP), and it is essential to select a VSP with better operational performance. Simulated studies of lab-scale mills, which show the similar breakage mechanism with VSP, and industrial sampling on VSPs are conducted to compare energy efficiencies of E and MPS type VSPs (with the grinding media of balls and tread rollers, respectively). The classical energy-size reduction model is modified with the addition of particle size in the exponential form to compare the grinding energy efficiency (product fineness for the certain specific energy) of two lab-scale mills. Also, differences in structure and operational parameters of lab-scale mills are considered. For the industrial sampling tests of two VSPs, recorded data and size distribution of sampled materials are preliminarily compared. Product t10 is selected as the bridge to connect the specific grinding energy and size distribution of products. The modified breakage model is combined with the King’s equation to compare the energy efficiency on the premise of feed in the same fineness. Comprehensive comparison of the results obtained from both lab-scale and industrial-scale VSPs suggests that the MPS type VSP shows the higher grinding energy efficiency and lower total energy consumption.

•Vibrated gas-solid fluidized bed can recycle residual metals from WPCBs.•Glass fibers have bad effect on vibrated gas-solid fluidized bed segregation.•Each size fraction has its own optimum segregation parameters.•Fine size fraction has the worst segregation efficiency.Recycling of waste printed circuit boards is important for environmental protection and sustainable resource utilization. Corona electrostatic separation has been widely used to recycle metals from waste printed circuit boards, but it has poor separation efficiency for finer sized fractions. In this study, a new process of vibrated gas-solid fluidized bed was used to recycle residual metals from nonmetallic fractions, which were treated using the corona electrostatic separation technology. The effects of three main parameters, i.e., vibration frequency, superficial air flow velocity, and fluidizing time on gravity segregation, were investigated using a vibrating gas-solid fluidized bed. Each size fraction had its own optimum parameters. Corresponding to their optimal segregation performance, the products from each experiment were analyzed using an X-ray fluorescence (XRF) and a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS). From the results, it can be seen that the metal recoveries of −1 + 0.5 mm, −0.5 + 0.25 mm, and −0.25 mm size fractions were 86.39%, 82.22% and 76.63%, respectively. After separation, each metal content in the −1 + 0.5 or −0.5 + 0.25 mm size fraction reduced to 1% or less, while the Fe and Cu contents are up to 2.57% and 1.50%, respectively, in the −0.25 mm size fraction. Images of the nonmetallic fractions with a size of −0.25 mm indicated that a considerable amount of clavate glass fibers existed in these nonmetallic fractions, which may explain why fine particles had the poorest segregation performance.Download high-res image (133KB)Download full-size image

•Analyses of mineralogical characteristics to raw coal and ground products•Demonstration of mineral liberation from coal by SEM-EDX•Triboelectrostatic separation of pulverized fuel to remove mineral•Separation technology embedded in pulverizing system is benefit for energy saving.Associated minerals in the raw coal increase the energy consumption and abrasion of grinding media of vertical spindle pulverizer (VSP). Moreover, the low separating efficiency of classifier in VSP leads to the return of fines to grinding table, worsens the grinding phenomenon and make the energy-size reduction of coal complex. Beneficiation of fines rejected by classifier is helpful to save energy and decreases the air pollution caused by the combustion of minerals in fines. Aiming to evaluate the potential for beneficiating the circulating loads, multi-analytical techniques are utilized to the raw coal and ground products. Phase composition analyses of raw coal show that kaolinite is the main mineral. Comparison of scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDX) of coal before and after comminution illustrates the liberation of kaolinite from coal substance, and the measurement of charge-mass ratios indicates the opposite polarity of tribocharge between coal and minerals, which indicates the separating possibility based on difference in the electric physics. Removal results of minerals from circulating loads by the triboelectrostatic separator vary with product fineness and liberation degrees. The best separation result is obtained on the finest progenies produced with the yield and ash content of clean coal at 61.95% and 18.92%, respectively.

•New on-line sampling tools for classifier are designed and self-manufactured.•Circulating ratio and classification efficiency of classifier is calculated based on internal sampling data.•Impacts of grinding operation and coal properties on classification are considered.•Influences of coal type, air rate and roller load pressure on the classifier operation are investigated.In order to investigate the classification performance of static air classifier in an industrial Vertical Spindle Mill (VSM), sampling ports were drilled on the mill shell and new on-line sampling methods were designed. Size and density compositions of classifier feed, classifier reject and Pulverized Fuel (PF) were analyzed. Calculation was done about the circulating ratio within the VSM and classification efficiency of the classifier with several surveys. Influences of three operation variables, namely coal type, air rate and roller load pressure on the classifier performance were investigated. Result shows that circulating ratio is around 7 and 10. Yield of particles with −90 μm decreases from 32% in classifier feed to 24% in classifier reject after classification, which indicates the poor classification of classifier. Density composition of samples in classifier feed, classifier reject and pulverized fuel are quite different. Dominant density levels are −1.4 g/cm3 and +1.8 g/cm3 in pulverized fuel due to size reduction and liberation. Results of classification efficiency show that the variation of the air rate in a range between 62.8 t/h and 53.2 t/h has limited influence on the efficiency, however, classification efficiency decreases significantly when air rate is smaller than 44 t/h. In addition, both the coal type and the roller load pressure have indirectly influence on the classification efficiency by affecting the flow rate of the classifier feed.

•A laboratory roller mill to study the energy-size reduction process in VSP.•Analyses of energy and size composition of tests with different parameters.•Experimental results show the effects of multiple parameters on fineness of products.•Classical model of energy-t10 to describe energy-size reduction with fixed parameter.As an important pulverizing equipment, the vertical spindle pulverizer (VSP) is widely used in power plants to produce fines for combustion. But high temperature and pressure in VSP limit the study of grinding process. Herein, a laboratory roller mill, with the addition of a power recorder, has been designed for the simulated study. Parameters of loading force, table revolution rate and fractional filling in this device can be adjusted. Grinding tests for different combinations of these three parameters are conducted. Confidence analyses of the experimental data illustrate the reliability of results, with a 90% confidence limit being 5% of the mean measured value. Breakage characteristics of the top size show the first-order law and the initial samples of narrow size fraction are all broken and disappear with less than 20 s. Both the loading force and table revolution rate have a positive effect on t10 and the tests for condition of lower fractional fillings also generate the high value of t10. For the analyses of energy-size reduction, t10 and specific energy are conducted as the response results. The mathematical relationship between t10 and specific energy of the grinding test with fixed parameters can be described well by the classical energy-size reduction breakage model, t10=A(1-e-b·Ecs),t10=A(1-e-b·Ecs),with the R2 > 0.97. Due to the difference of values of t10 generated at the unit specific energy for the conditions of different parameter combinations, this model only can simulate the grinding process with changes of loading forces or fractional fillings. 10 Sets of additional experimental data demonstrate this conclusion. Reasons of this phenomenon are discussed.

•All the elements detected have been analyzed carefully by high resolution XPS.•Each element has been studied by XPS-peak-differentiation–imitating analysis.•Structure schematic of the fine particles is presented for the first time.•A possible reaction route of the materials during the crushing process is inferred.•The paper provides basic information for floatation.In this work, detailed surface analysis on the fine crushed products of spent lithium-ion batteries is investigated by X-ray photoelectron spectroscopy. The results showed that although LiCoO2 was a main composition of the fine crushed products, the surface atomic abundance of cobalt was only 1.69%, but the surface atomic abundance of organic compounds was more than 75%. During the crushing process, LiPF6 decomposed and harmful and toxic substances such as HF, POF3 were generated, it is necessary to take appropriate measures to avoid the secondary pollution in the crushing process of spent LiBs. Metallics such as Co, Cu, and Al were fluoridated and oxidized, and the organic compounds were oxidized and decomposed, too. The surface composition and microstructure of the fine particles were presented, which showed that the fine particles in the crushed products were lithium cobalt oxides and graphite cores coated inside by organic compounds. Flotation test pointed out that if the outer layer was removed, the flotation selectivity would be greatly improved: the enrichment ratio could be increased from 1.16 up to 3.24. Based on the surface analysis, potential ways for removal of the outer layer were proposed.

Separation of metal laden solid wastes for their recycling utilization using passive pulsed air and active pulsing air classifiers was studied. Laboratory investigation showed that the active pulsing air separator performs more efficiently than the passive pulsed air separator due to the ability to accurately control operating parameters. By studying the difference of drag coefficients of the particles moving through the airflow of varying Reynolds numbers, models of the dynamic particle motion were developed and a computer simulation was prepared. Results of the simulation were reported to predict the observed results with artificial tracing spheres being separated by the laboratory equipment. Two different, real world feed materials were separated with the laboratory scale active pulsing air classifier. The discarded catalyst consisting of precious metal components and sintered magnetic beads was separated with the separation efficiency, of 97.6 %. The second real-world feed, electronic scrap crushed to a size of 0.5 to 2 mm, showed a separation efficiency of 92.41 %. At the same time, the grade of the recovered concentrate of metals was above 98 %.

The associated minerals make coal middlings possess a relatively high ash content. Subsequent liberation through size reduction can cause recovery increase. However, effect of comminution facilities on mineral liberation of middlings was ignored. This paper studied the liberation characteristics of middlings crushed with different kinds of fragmentation forces. Middlings of −3 mm + 0.5 mm sampled from a dense medium cyclone were comminuted by a jaw crusher and a ball mill to −0.5 mm with similar size distribution respectively. The generating mechanism of fines was also analyzed. Full densimetric analyses indicate that mineral liberation of the product crushed by the jaw crusher is better than that by the ball mill at each fraction. For sizes of −0.125 mm + 0.074 mm and −0.074 mm, yields of the product with ash content 11% comminuted by jaw crusher are nearly 20% higher than that by the ball mill. Sectional micrographs observed by the scanning electron microscopy (SEM) also show the same law for these two fractions and some intergrowth particles still exist in the fraction of −0.5 mm + 0.25 mm.

Sampling ports were firstly drilled on a ZGM95 coal mill in the power plant in China, and the coal samples from various points in the pulverizer were collected under the different operation conditions. The property of the sampling material from the mill was analyzed, applying the float–sink test, size distribution analysis, proximate analysis and so on. It was indicated that the +250 μm fraction in the pulverized fuel accounted for only 0.02%, while it was 83.2% in the new feed. The circulating ratio and coal flow in the separator and the cone zone were calculated using the mass balance of the circulating load. So, the circulating ratio in the separator of the pulverizer was between 8 and 13, and the circulating ratio, the feed flow of separator and cone zone all raised with the increase of the air volume. Furthermore, the parameters of the separation functions were obtained based on the fitting method. It was shown that the mean value of the shape factor B was 0.7617, and the parameter D which is the particle size at 50% cumulative yield in the separator almost kept unchanged.

In order to reduce the energy consumption and subsequent air pollution of coal-fired power station, based on the analysis to size and density distribution of particles from the recirculating load of the classifier of pulverizer, the separation experiment on sampling material from power plant with a dilute phase fluidized bed to remove pyrite and other minerals and numerical simulation on the separation process were done. The results show that the minimum fluidization velocity is 1.62 cm/s. Pyrite and other minerals in the material are separated. Ash of the upper and bottom layer material account for 33.34% and 73.42% respectively and sulfur content occupy 1.12% and 8.96% respectively. Scanning electron microscopy and spectroscopy tests show that sulfur in the bottom material exist in the form of pyrite. Numerical simulation on the flow field form of the dilute phase separation bed with gas–solid two phase and particle motion verifies the experimental results.

The flow field of pulsing air separation is normally in an unsteady turbulence state. With the application of the basic principles of multiphase turbulent flows, we established the dynamical computational model, which shows a remarkable variation of the unstable pulsing air flow field. CFD (computational fluid dynamics) was used to conduct the numerical simulation of the actual geometric model of the classifier. The inside velocity of the flowing fields was analyzed later. The simulation results indicate that the designed structure of the active pulsing air classifier provided a favorable environment for the separation of the particles with different physical characters by density. We shot the movement behaviors of the typical tracer grains in the active pulsing flow field using a high speed dynamic camera. The displacement and velocity curves of the particles in the continuous impulse periods were then analyzed. The experimental results indicate that the effective separation by density of the particles with the same settling velocity and different ranges of the density and particle size can be achieved in the active pulsing airflow field. The experimental results provide an agreement with the simulation results.

•Crushed products can be divided into three parts based on the main composition.•A certain kind of hydrocarbon is found coated on the surface of fine particles.•A flowsheet to recycle spent LiBs is proposed according to multi-analysis results.Mineral processing operation is a critical step in any recycling process to realize liberation, separation and concentration of the target parts. Developing effective recycling methods to recover all the valuable parts from spent lithium-ion batteries is in great necessity. The aim of this study is to carefully undertake chemical and process mineralogical characterizations of spent lithium-ion batteries by coupling several analytical techniques to provide basic information for the researches on effective mechanical crushing and separation methods in recycling process. The results show that the grade of Co, Cu and Al is fairly high in spent lithium ion batteries and up to 17.62 wt.%, 7.17 wt.% and 21.60 wt.%. Spent lithium-ion batteries have good selective crushing property, the crushed products could be divided into three parts, they are Al-enriched fraction (+2 mm), Cu and Al-enriched fraction (−2 + 0.25 mm) and Co and graphite-enriched fraction (−0.25 mm). The mineral phase and chemical state analysis reveal the electrode materials recovered from −0.25 mm size fraction keep the original crystal forms and chemical states in lithium-ion batteries, but the surface of the powders has been coated by a certain kind of hydrocarbon. Based on these results a flowsheet to recycle spent LiBs is proposed.

By applying co-integration analysis, the Granger causality test and an error correction model, the dependency between the energy consumption and the gross domestic product of China was examined. In a further step an analysis was done to establish a correlation between the economic growth of different industries and China's energy consumption. An evidence-based study showed that a co-integration relationship exists between the gross energy consumption and the GDP of China and that the two variables possess bi-directional causality. The energy consumption for the secondary industry has a markedly stimulative effect to the economic growth. This paper also uses an error correction model (ECM) to explain the short-term behavior of energy demands.

•Analyses and comparison of the traditional model for the energy split factor.•Interaction between components is embodied with specific energy.•Energy-size reduction model to calculate energy of component in mixture grinding.•Calcite increases grinding energy efficiency of SCAC in the mixture breakage.Interactions among components in the heterogeneous grinding would change energy consumed characteristics of components if compared with those in the single-component breakage. In this paper, energy split phenomenon for the coarse grinding of super clean anthracite coal (SCAC)/calcite mixture of 2.8–2 mm in the ball-and-race mill is investigated. Before the analysis of experimental results, accuracy of energy split function in terms of time-dependent breakage rate is first discussed. Energy consumed characteristics of grinding in the ball mill and ball-and-race mill are also compared. Breakage model of product t10 (yield of progenies in −0.237 mm) vs specific energy is used to describe the energy-size reduction of the single-component and multi-component grinding. Interaction between components is reflected by the comparison of specific energy of components in mixture and single breakage to yield the same product t10. Based on the energy balance, energy split factors of components in different time and mixed conditions are first determined. This parameter shows no change with time. Calcite increases the grinding efficiency of SCAC significantly, with the energy split factor for SCAC ranging from 0.68 to 0.73, which means less specific energy is consumed by SCAC to yield the same t10 if compared with the single breakage. As the volumetric ratio of calcite increases in mixture, grinding energy efficiency decreases and energy split factor of calcite increases from 1.70 to 1.83. Soft material reduces the grinding energy efficiency of hard one in the multi-component breakage.Download high-res image (122KB)Download full-size image