Chenlong Duan

Recovery of metals from waste printed circuit boards by a mechanical method using a water medium.

Research on the recycling of waste printed circuit boards (PCB) is at the forefront of environmental pollution prevention and resource recycling. To effectively crush waste PCB and to solve the problem of secondary pollution from fugitive odors and dust created during the crushing process, a wet impacting crusher was employed to achieve comminution liberation of the PCB in a water medium. The function of water in the crushing process was analyzed. When using slippery hammerheads, a rotation speed of 1470 rpm, a water flow of 6m(3)/h and a sieve plate aperture of 2.2mm, 95.87% of the crushed product was sized less than 1mm. 94.30% of the metal was in this grade of product. Using smashed material graded -1mm for further research, a Falcon concentrator was used to recover the metal from the waste PCB. Engineering considerations were the liberation degree, the distribution ratio of the metal and a way to simplify the technology. The separation mechanism for fine particles of different densities in a Falcon concentrator was analyzed in detail and the separation process in the segregation and separation zones was deduced. Also, the magnitude of centrifugal acceleration, the back flow water pressure and the feed slurry concentration, any of which might affect separation results, were studied. A recovery model was established using Design-Expert software. Separating waste PCB, crushed to -1mm, with the Falcon separator gave a concentrated product graded 92.36% metal with a recovery of 97.05%. To do this the reverse water pressure was 0.05 MPa, the speed transducer frequency was set at 30 Hz and the feed density was 20 g/l. A flow diagram illustrating the new technique of wet impact crushing followed by separation with a Falcon concentrator is provided. The technique will prevent environmental pollution from waste PCB and allow the effective recovery of resources. Water was used as the medium throughout the whole process.

Industrial Application of a Modularized Dry-Coal-Beneficiation Technique Based on a Novel Air Dense Medium Fluidized Bed

ABSTRACT Coal is one of the most important primary energy sources all over the world. One of the clean-coal technologies is coal preparation, and dry-coal beneficiation plays an increasingly important role with an increasing shortage of water. A novel air dense medium fluidized bed (ADMFB) separator developed by the China University of Mining and Technology, with magnetic powder and fine coal acting as the heavy medium, has the advantages of uniform and stable bed density, low cost, and high reliability. The world’s first modularized dry-coal beneficiation based on the novel ADMFB was established, realizing the industrial application of ADMFB separation technology. The industrial application showed that the ash content of coal decreased to 3.46% with an ash rejection of 85.57%, the yield of clean coal was 67.88%, the probable error (E value) was 0.055 g/cm3, the organic efficiency was 93%, and the heavy-medium loss when separating one ton of coal was 0.42 kg. Less than

Fluidization Characteristics of the Dense Gas-Solid Fluidized Bed Separator Based on the Mixed-Medium Solids of Magnetite and Paigeite Powder

2 was spent for separating one ton of raw coal.

Experimental and Numerical Simulation of Spent Catalyst Separation in an Active Pulsing Air Classifier

Fluidization characteristics of the mixed magnetite and paigeite powder were studied by the combination approach of numerical simulation and experimental verification to optimize the design of the medium solids used in the dense gas-solid fluidized bed separator (DGSFBS). The experimental results showed that the favorable fluidization performance could be achieved with the weight proportion of paigeite powder in the mixture 25% ≤ α ≤ 35%, while the relative deviation in the bed density should be Δρ ≤ 0.025 g/cm3. The corresponding simulation results were obtained by selecting suitable mathematical models and parameters. It also indicated that the fluidized bed with mixed solids could provide a good fluidization performance and stable density distribution. The laboratory-scale DGSFBS was used to conduct the separation experiments on raw coal with size range of 13–6 mm and ash content of 33.43%. With the parameter α = 30%, the experiment resulted in the coal ash content being reduced from 33.43% to 11.63% with a probable error, E P of 0.07 and a recovery efficiency of 98.59%. Utilization of either magnetite or paigeite powder alone was not effective; however, fluidization performance and separation efficiency of DGSFBS improved with the utilization of mixed solids.

Hydrodynamic characteristics of the dense medium gas–solid fluidized bed for coal beneficiation and cleaning

Research on recycling spent catalyst is at the forefront of preventing environmental pollution and recycling resources. An active pulsing air classifier is applied to recover the valuable concentrate from spent catalyst. A multi-factor separation experiment was designed using Box-Behnken module of Design-Expert software, the results show that the separation efficiency ranged from 96.26 to 99.29%. When the airflow velocity is 8.06 m/s, pulsing frequency is 3.55 Hz, feed frequency is 35 Hz, and thus 99.29% separation efficiency can be achieved. A sharp separation is achieved with a wider performance range of operation conditions. A DEM-CFD model is developed to study the gas-solid flow in a lab-scale active pulsing air classifier. In the model, the motion of particles is obtained using the Discrete Element Method facilitated with the concept of “particle-particle,” while the gas flow by Computational Fluid Dynamics based on the local averaged Navier-Stokes equations. The simulated results agree reasonably well with the experimental observation. It will provide a cost-effective way to study the gas-solid flow in the larger-scale active pulsing air classifier with different geometrical, operational and material conditions.

Pyrite enrichment in vibrated fluidized bed based on density segregation

ABSTRACT The hydrodynamic characteristics of the dense medium gas–solid (DMGS) fluidized bed for coal beneficiation and cleaning were analyzed and discussed by the experimental measurement and numerical simulation. The magnetite powder with a wide particle size of 0.3–0.15 mm was selected as the major fluidized medium in this study. The simulation and experiment results indicate that the bed pressure drop can reach stable condition in a relatively short period with the increase of superficial gas velocity. Afterwards, the bed pressure drop shows minor fluctuations within the gas velocity of 1.8Umf ≤ U ≤ 2.2Umf. Meanwhile, the bed density shows good homogeneity at various bed heights and axial directions with slight density fluctuation. Therefore, the results clearly demonstrate that the hydrodynamic characteristics of the fluidized bed, including the bed pressure drop and separating density distribution, overall maintain stable and uniform conditions without intense fluctuations. It provides favorable fluidization and separation conditions for coal beneficiation and cleaning in the three-dimensional spaces of DMGS fluidized bed.

Study on Screening Efficiency of Banana Vibrating Screen Based on 3D DEM Simulation

ABSTRACT It is of significance for the environmental protection, the shortage of water, and the economic benefits to recovering the pyrite from the gangue with high sulphur content (GHSC) by the vibrated fluidized bed. In this study, characteristics such as the sulphur form of pyrite, size distribution, and dissociation degree of sample were analysed. Based on the above analysis, a vibrated fluidized bed was first used for the pyrite enrichment from GHSC. The effect of air velocity, vibration intensity, and bed height on the separation performance was analysed by separation experiments. The results show that the separation efficiency increased firstly and then decreased with increasing gas velocity, vibration intensity, and bed height. The total sulphur contents (TSCs) of −6 + 3, −3 + 1, and −1 + 0.5 mm size fraction materials were up to 37.94%, 35.43%, and 30.61%, respectively, and the enrichment grades were 1.72, 1.90, and 2.29 times, respectively, under the optimal conditions, indicating that using a vibrated fluidized bed was efficient for the pyrite enrichment.

Effect of vibration energy on fluidization and 1–6 mm coal separation in a vibrated dense medium fluidized bed

The screening process of a banana vibrating screen was simulated based on 3D discrete element method, where Hertz-Mindlin (no-slip) Model was applied. The experiment design and data analysis were performed by Design-Expert software. The factors determining the screening efficiency and the interaction between those factors were identified. The results showed that the screening efficiency ranged from 72.6 to 92.8 %. The screening efficiency showed a Quadratic Relationship Model with gradient of sieve surface, vibrating direction angle, vibration intensity. When two of the factors were determined, the screening efficiency decreased gradually with the gradient of sieve surface and vibration intensity, but increased with the vibrating direction angle. The effects of various factors on the screening efficiency were in the following order: gradient of sieve surface, vibration intensity and vibrating direction angle. The effects of the interaction between those factors on the screening efficiency were in the following order: gradient of sieve surface × vibration intensity, vibrating direction angle × vibration intensity, and gradient of sieve surface × vibrating direction angle.

Spontaneous segregation behavior in a vibrated gas-fluidized bed for fine lignite dry cleaning

ABSTRACT In this study, a uniform and stable vibrated dense medium fluidized bed (VDMFB) with Geldart B magnetite powder was formed, where it was considered suitable for 1–6 mm coal separation. The formation mechanisms of the best separation environment including the fluidization phenomena under different vibration parameters, the transfer process of the vibration energy, the pressure drop fluctuation and particle oscillation velocity distribution at different bed heights, as well as the corresponding effect on the uniformity and stability of the bed density were investigated. Furthermore, the separation experiment was carried out, and the results exhibited an efficient dry separation performance in the VDMFB.

Development of Mineral Processing Engineering Education in China University of Mining and Technology

ABSTRACT Fine lignite dry cleaning, which has the significant advantage of without process water, is becoming increasingly important due to global water shortage. Lignite particles of various compositions were experimentally studied in a vibrated gas-fluidized bed. This is the first report of the size-based segregation of fine particles in the vibrated gas-fluidized bed. Experimental results demonstrate that the –2 +0.5 mm lignite particles play an irreplaceable role in particle fluidization and segregation. To ensure good separation performance, the minimum content of –2 +0.5 mm lignite particles should be 13%. Separation results show that for –6 +0.5 mm lignite particles, the ash contents of clean coal and tailings are 23% and 45%, with the corresponding yields of 82% and 18%, respectively, which shows good separation performance.