Research Article pubs.acs.org/journal/ascecg
Hollow Aluminum Particle in Eddy Current Separation of Recovering Waste Toner Cartridges Jie Zheng,† Jujun Ruan,*,† Lipeng Dong,† Tao Zhang,† Mingzhi Huang,*,‡ and Zhenming Xu§ †
School of Environmental Science and Engineering, Sun Yat-Sen University, 135 Xingang Xi Road, Guangzhou, 510275, People’s Republic of China ‡ School of geography and planning, Sun Yat-Sen University, 135 Xingang Xi Road, Guangzhou, 510275, People’s Republic of China § School of Environmental Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People’s Republic of China S Supporting Information *
ABSTRACT: Abundant waste toner cartridges have been generated from the use of printers. They contain aluminum, plastic, steel, and toner. Waste toner cartridges will pollute the environment if they are not properly treated. An environmentfriendly recovery line of waste toner cartridges had been constructed in our previous work. Eddy current separation was employed to separate aluminum particles from plastic particles of crushed waste toner cartridges. However, hollow aluminum particles existed in crushed waste toner cartridges, and they have a rather low separation rate from plastic particles. There was little information about hollow aluminum particles in eddy current separation. For improvement of the efficiency of eddy current separation, models of eddy current force and movement behaviors of hollow aluminum particles in eddy current separation were established. In a comparison of horizontal throws of hollow aluminum particles to solid aluminum particles, we found hollow characters greatly decreased the horizontal throw (reduced about 0.03 m) of aluminum particles and destroyed the separation rate. Therefore, a new compactor was designed to eliminate hollow aluminum particles in crushed waste toner cartridges. This paper provides models of eddy current force and movement behavior of hollow nonferrous metallic particles in eddy current separation and contributed to improvement of the efficiency of the recovery line of waste toner cartridges. KEYWORDS: Recovery, Eddy current force, Trajectory models, Improve efficiency
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INTRODUCTION
Chemical methods are always considered as the preferable methods in environmental remediation and resource recovery.11−13 Physical technologies are suitable treatment methods of recovering e-waste.14,15 Eddy current separation is a physical technology of separating nonferrous metallic particles from others.16,17 In eddy current separation, an alternating eddy current is induced in nonferrous metallic particles when meeting a variable magnetic field. The alternating eddy current causes a new magnetic field in nonferrous metallic particles. A repulsive force between the two magnetic fields changes the movement of nonferrous metallic particles and separates them from others. No pollution is generated. Eddy current separation was employed in mineral processing in past years.18,19 It was also encouraged to recover nonferrous metallic particles from crushed e-waste.20 In our constructed environmentally friendly production line of recovering waste toner cartridges, eddy
Abundant e-waste has been generated from the use of electrical and electronic equipment1 in the world. Developing and undeveloped countries have been the dump of e-waste, not only self-produced waste but also that imported from developed countries.2 These countries bear principal responsibility for treating e-waste. High-purity precious metals, nonferrous metals, and high-quality plastics are contained in e-waste.3 Recovering e-waste not only can obtain sustainable, renewable resources of metals and plastics but also lower the costs of energy and environment for producing them. Meanwhile, vast hazardous materials (polyvinyl chloride, dechlorane, etc.) also exist in e-waste.4,5 If e-waste was not properly treated, heavy metals and hazardous materials would be exposed to the environment. Due to employment of crude technologies, heavy metals and organic pollutants have polluted the local environment and human bodies.6,7 Therefore, recovering ewaste is crucial work in resource conservation, energy renewal, and environmental protection.8−10 © XXXX American Chemical Society
Received: May 27, 2016 Revised: October 24, 2016 Published: November 2, 2016 A
DOI: 10.1021/acssuschemeng.6b01168 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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ACS Sustainable Chemistry & Engineering
Figure 1. (a) Environmentally friendly production line of recovering waste toner cartridges. (b) The structure of the employed eddy current separator.
Figure 2. Hollow and solid aluminum particles collected from crushed waste toner cartridges.
particles. Additionally, irregular movement behaviors of hollow aluminum particles also destroyed the separation rate of other solid aluminum particles by impacting and changing their movement in eddy current separation. How to improve the separation rate of hollow aluminum particles has been the critical problem of enhancing the efficiency of the production line. The eddy current force and movement behavior of aluminum particles in eddy current separation need to be investigated for researching the influencing factors of separation rate. We found there was little information about the model of eddy current force of hollow nonferrous metallic particles in eddy current separation. This study provided the models of eddy current force and movement behavior of hollow aluminum particles in eddy current separation of recovering
current separation was employed to separate aluminum particles from crushed waste toner cartridges (Figure 1a).21 However, nonferrous metallic particles in e-waste have greater differences in size, shape, and purity than minerals. Traditional eddy current separators offer a low separation rate. For improving the separation rate, models of eddy current force and movement behavior of nonferrous metallic particles in eddy current separation had been established to research the influencing factors.22,23 In the production line of recovery waste toner cartridges, many hollow aluminum particles existed in crushed waste toner cartridges. The reason was that coarse crushing was employed to crush waste toner cartridges, and aluminum in toner cartridges had a tubular shape. These hollow aluminum particles had a rather low separation rate from plastic B
DOI: 10.1021/acssuschemeng.6b01168 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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drum was 0.096 m. The thickness of the magnetic field of the separator was measured with a teslameter, and the value was 0.05m. Distribution of the magnetic field flux of the eddy current separator was simulated by the COMSOL 5.1 software. The simulated result is presented as Figure 3. The magnetic flux density decreased as the distance increased from the magnet surface. Since the magnetic permeability of air is weak, the gradient of magnetic flux density was very great, and a strong magnetic flux density mainly assembled at a small distance from the separator surface. Figure 3 also showed density distribution of magnetic field was different at the same latitude of the side view of the magnetic drum. It showed that low rotation speed will provide aluminum particles a longer time with a weaker magnetic field and will decrease the eddy current force. Thus, the rotation speed of the magnetic drum should be as high as possible in the separation process.
waste toner cartridges. Then, a compactor was designed to eliminate hollow aluminum particles in crushed waste toner cartridges. This study contributes to improving the efficiency of eddy current separation in the production line of recovering waste toner cartridges.
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MATERIALS AND METHODS
Hollow Aluminum Particles. Aluminum particles employed in this study were collected from crushed waste toner cartridges. Different shapes of aluminum particles were obtained. Besides circle, rectangle, and triangle flake aluminums (reported in previous work),23 triangle hollow aluminum (T0) and rectangle hollow aluminums (R0; in Figure 2) existed in crushed aluminum material. Their sizes ranged from 15 mm to 40 mm. Their physical characters are presented in Table 1. For investigating the influence of hollow aluminum particles
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RESULTS AND DISCUSSION In eddy current separation, the aluminum particle was subjected to gravity force, eddy current force, air frication, and impact force from other particles. Air frication force will play a big role in determining the horizontal throw of aluminum particles in eddy current separation. However, because aluminum particles kept rolling in eddy current separation, air frication force was difficult to calculate. But, it will be important work in our future. Impact force from other particles will also influence the trajectory of aluminum particles. This influence also will be the subject of future work in our research. Eddy Current Force of Hollow Aluminum Particles in Eddy Current Separation. Alternating magnetic field will be produced around the magnetic drum by the rotation of eddy current separator. The magnetic flux density of the field yields to the following formula:24
Table 1. Characteristics of the Employed Aluminum Particles particles
Se (cm2)
V (cm3)
M (g)
d (cm)
δ
γ (S/m)
T0 T1 R0 R1
2.86 4.51 3.45 5.75
0.87 0.87 1.05 1.05
2.35 2.35 2.82 2.82
0.08 0.08 0.08 0.08
0.35
6.67 × 105
0.2
on separation rate, T0 and R0 were compressed to solid particles (T1 and R1 in Figure 2). Physical characters of T1 and R1 are also presented in Figure 2. Eddy Current Separator. The employed eddy current separator is presented in Figure 1b and c. Physical characters of the eddy current separator are presented in Table 2. The separator was comprised of a
Table 2. Physical Characters of Eddy Current Separator Bm Rd μ0 H k η
0.3 T 0.096 m 4π × 10−7 N/A2 0.9 m 4 pairs 0.05 m
∞
Br =
∑ bn(r /R)−(2n+ 1)k− 1 sin(2n + 1) k(α − ωmt ) n=0
(1)
The values of parameters R and k of the eddy current separator are 0.096 m and 4 pairs. Because of the big gaps of size and rotation speed between the particle and the magnetic separator in eddy current separation, alternating magnetic flux can be supposed as crossing over the aluminum flake vertically when the flake gets close to the magnet. Thus, the value of (α −
feeding conveyor and magnetic drum. The magnetic flux of the surface of the magnetic drum was 0.3 T, and the magnetic drum was comprised of four pairs of magnetic poles. The radius of the magnetic
Figure 3. (a) Side view of the magnetic field distribution of the magnetic drum. (b) 3-D view of the magnetic field distribution of the magnetic drum. C
DOI: 10.1021/acssuschemeng.6b01168 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
Research Article
ACS Sustainable Chemistry & Engineering ωmt) can be supposed as 90°. The Fourier coefficient (bn) can be obtained by measuring the magnetic flux density and the corresponding value of radial distance (r). Eddy current was induced in the aluminum particle when it met the time-dependent magnetic field. Then, an induced timedependent magnetic field was also produced in the aluminum particle immediately. The induced magnetic field in the metal had the same vector orientation of magnetic flux as that of the inducing magnet. Eddy current force will generate between aluminum particles and magnets because of having the same vector of magnetic flux. The direction of eddy current force is determined by the position of aluminum particles in the magnetic field. When the vertical component of eddy current force is greater than gravity force, the flake will leave the belt and levitate to be accelerated forward acted on by the horizontal component of eddy current force. Eddy current force makes the flake detach from the conveyor belt and determine the movement behavior. In case I of Figure 2, the aluminum particle was folded, and there was a hollow in the particle. From the lateral view of case I, when the magnetic flux crossed the solid part of the particle, magnetic flux was called effective magnetic flux. When the magnetic flux crossed the hollow part of the particle, the magnetic flux was called invalid magnetic flux. The reason was that the hollow part of the particle was closing surfaces and the total magnetic flux was 0. In case II of Figure 2, there was no hollow in the aluminum particle. Thus, all of the magnetic flux crossing the particle was effective magnetic flux. In case III of Figure 2, the whole aluminum particle became a closed surface, and all the magnetic flux crossing the particle was invalid and the magnetic flux was 0. Thus, the completely hollow aluminum particle will have the same trajectory as the plastic particle in eddy current separation. As aluminum particles move near the rotating magnetic drum, the applied alternating magnetic flux is supposed to cross the aluminum particle vertically because of the big gaps of size and speed between aluminum particle and magnetic drum. Therefore, the effective crossing areas (Se) of the aluminum particle in case I, case II, and case III were Sp − S0, Sp, and 0, respectively. According to the previous constructed models of eddy current force,20 eddy current force of hollow triangle aluminum particles in case I yielded to ⎧ B k(ωmR − v)γdSe 2SmBm δ Tτ ⎪ FT = r 16π 2R3 ⎪ ⎪ ⎨ δ T = 0.35 ⎪ 1 ⎪τ = ⎪ (sec β − 1)2 ⎩
those in the previous work. Eddy current force of solid triangle aluminum particles was presented as ⎧ B k(ωmR − v)γVSpSmBm δ Tτ ⎪ FT = r 16π 2R3 ⎪ ⎪ ⎨ δ T = 0.35 ⎪ 1 ⎪τ = ⎪ β − 1)2 (sec ⎩
Eddy current force of solid rectangle aluminum particles was expressed as ⎧ B k(ωmR − v)γVSpSmBm δ R τ ⎪ FR = r 16π 2R3 ⎪ ⎪ ⎨ δ R = 0.2 ⎪ 1 ⎪τ = ⎪ (sec β − 1)2 ⎩
(5)
Due to there being no effective magnetic flux, hollow aluminum particles of case III were subjected to no eddy current force in eddy current separation. It meant that the aluminum particle of case III cannot be separated from other particles in eddy current separation. Verification of Models of Eddy Current Force of Hollow Aluminum Particles. The constructed models for computing eddy current force of hollow aluminum particles were tested by calculation and measurement of the horizontal throws of aluminum particles in eddy current separation. Movement behavior of aluminum particles in eddy current separation was divided into three stages: (I) entering the magnetic field, (II) detaching from the conveyor belt surface, (II) exiting from the magnetic field (see Figure 1c). At the beginning of stage (I), eddy current force increased as the aluminum particle got close to the magnetic drum. The horizontal component of eddy current force was counteracted by the friction force of the conveyor belt, and no horizontal relative motion happened between the aluminum particle and belt. As eddy current force increases, the vertical component would be greater than gravity force (G), and aluminum particles will have a vertical-upward acceleration and move upward.
G = cos β × F
(6)
Meanwhile, eddy current force decreased with the upward movement of aluminum particles due to the decline of magnetic flux. When the vertical component was equal to gravity force, aluminum particles will be suspended and keep a constant radial distance to the axis (O) of the separator. Position (x, y) was called the detachment point, and β was the detachment angle. The coordinate of the detachment point (x, y) of the aluminum particle can be calculated by
(2)
Eddy current force of hollow rectangle aluminum particles in case I was given as ⎧ B k(ωmR − v)γdSe 2SmBm δ R τ ⎪ FR = r 16π 2R3 ⎪ ⎪ ⎨ δ R = 0.2 ⎪ 1 ⎪τ = ⎪ (sec β − 1)2 ⎩
(4)
x1 = Rtgβ y1 =
R cos β
(7)
(8)
Meanwhile, point (x1, y1) is supposed as the symmetry point of (x, y) on the right of the y axis (Figure 1c). The movement of aluminum particles from point (x, y) to point (x1, y1) was considered as rectilinear motion. At this rectilinear movement, magnetic fluxes of aluminum particles and the magnetic drum
(3)
Due to no hollow in the aluminum particle, models of eddy current force for aluminum particles in case II were the same as D
DOI: 10.1021/acssuschemeng.6b01168 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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Figure 4. (a) Calculation of abscissa of point (x2, y2) of T0 and T1 in eddy current separation. (b) Calculation of abscissa of point (x2, y2) of R0 and R1 in eddy current separation.
Table 3. Calculation of Horizontal Throws of Aluminum Particles and Plastic Particle with v = 0.4 m/s and ω = 800 r/min in eddy current separation D (m)
calculation results Al
β (deg)
T0 T1 R0 R1
11.08 14.97 10.62 14.51
(x1, y1) (0.0188, (0.0256, (0.0180, (0.0248,
0.0979) 0.0994) 0.0977) 0.0992)
(x2, y2) (0.1391, (0.1441, (0.1385, (0.1434,
−0.0439) −0.0233) −0.0453) −0.0241)
d (m)
vy (m/s)
calcd.
exptl.
calcd.
exptl.
calcd.
exptl.
0.568 0.614 0.562 0.609
0.893 0.859 0.893 0.858
0.291 0.322 0.287 0.320
0.289 0.318 0.286 0.316
0.172
0.167
0.119 0.15 0.115 0.148
0.122 0.151 0.119 0.149
the aluminum particle after leaving the magnetic field and the vertical height (H) from the collection position to the conveyor. Horizontal and vertical muzzle velocities (vx and vy) of the aluminum particle when leaving the magnetic field can be presented as
was considered to be parallel. The horizontal component of eddy current force can be neglected, and eddy current force was supposed as equal to gravity force. Once the aluminum particle passes over point (x1, y1), the vertical component of eddy current force was less than gravity force. The horizontal component of repulsive force can no longer be neglected because the directions of the two magnetic fluxes were not parallel. The horizontal component will accelerate the aluminum particle in the horizontal direction until it passes through the magnetic field boundary. Point (x2, y2) was supposed as the exiting position. When passing through point (x2, y2), the aluminum particle was only subjected to gravity force, and the movement was considered as horizontal projectile motion. The horizontal throw (D) of the aluminum particle in eddy current separation is comprised of two parts: one is the horizontal distance from the y axis to existing point (x2, y2); the other is the horizontal distance from point (x2, y2) to the collection position. Abscissa of point (x2, y2) can be calculated by the following equations,9 and the results were placed in Figure 4.25 ⎧ y = −(2g − g cos β) ⎪ ⎡ ⎤2 2 ⎪ ⎛ ⎞ β − x Rtg ( ) v v ⎥ ⎢ ⎪ +⎜ ⎟ − ⎢ ⎪ g sin β g sin β ⎠ g sin β ⎥ ⎝ ⎨ ⎣ ⎦ ⎪ R + ⎪ cos β ⎪ ⎪ x 2 + y 2 = (R + η)2 ⎩
D′ (m)
vx (m/s)
⎧ 4|y2 − y1| ⎪ v = v + g sin β x ⎪ 2 g (2 − sin β ) ⎪ ⎨ ⎪ 4|y2 − y1| ⎛ 2 − cos β ⎞ ⎟ ⎪ vy = g ⎜ ⎪ ⎝ ⎠ g (2 − sin β ) 2 ⎩
(10)
Movement of the aluminum particle from point (x2, y2) to the collection position can be considered as horizontal projectile motion. Thus, the horizontal throw (D) of aluminum particles in eddy current separation can be computed by D = vx
2(H − |y2 |) g
⎛ vy ⎞2 vy +⎜ ⎟ − + x2 g ⎝g⎠
(11)
The horizontal throws of T0 and R0 in the three cases were computed and measured. The results were placed in Table 3. When the calculation horizontal throws are compared to measured horizontal throws, the constructed models of eddy current force of hollow aluminum particles can accurately describe the repulsive force of the particle in eddy current separation. The horizontal throw (D′) of plastic particles is determined by feeding speed and the vertical height (H) from the collection position to the conveyor. The trajectory equation of the plastic particle in eddy current separation was expressed as
(9)
The horizontal distance from point (x2, y2) to the collection position is determined by the horizontal muzzle velocity (vx) of E
DOI: 10.1021/acssuschemeng.6b01168 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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Figure 5. Structure of the designed compactor.
D′ = v
2H g
compressing process will eliminate hollow aluminum particles in crushed waste toner cartridges and improve the separation rate of aluminum particles from plastics.
(12)
For separating aluminum particles from plastic particles, the critical separation distance should satisfy the following equation:13 d = D − D > Lmax(metal) + Lmax(plastic)
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CONCLUSION
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ASSOCIATED CONTENT
This paper discussed the eddy current force of hollow aluminum particles in eddy current separation and construction of the computing models. Horizontal throws of hollow aluminum particles and solid aluminum particles were computed and measured. The comparison results of their horizontal throws indicated that hollow character greatly decreased the horizontal throws of aluminum particles and destroyed the separation rate of eddy current separation. Then, a new compactor was designed to change hollow aluminum particles into solid particles. This paper contributed to the guidance of the eddy current separation of hollow nonferrous metallic particles and improved the efficiency of the recovering line of waste toner cartridges.
(13)
where Lmax(metal) is the maximum size of the aluminum particle and Lmax(plastic) is the maximum size of plastic particles. In a crushed waste refrigerator, horizontal throws and separation distances between aluminum particles and plastic particles were computed, measured, and placed in Table 3. In order to investigate the influence of hollowness on separation rate, T0 and R0 were compressed into solid aluminum particles (T1 and R1 in Figure 2). Then, horizontal throws of T1 and R1 were computed and measured at the same operation parameters as those of the eddy current separator. Table 3 indicated that the horizontal throw of T1 was greater than T0, about 0.031 m. The horizontal throw of R1 was greater than that of R0 by about 0.033 m. The size of the plastic particles in crushed toner cartridges ranged from 0.05 to 0.08 m. The value of Lmax(metal) + Lmax(nonmetal) was about 0.12 m. According to Table 3, T0 and R0 could not be separated from plastic particles, but T1 and R1 were successfully separated. Thus, compressing hollow aluminum particles to solid particles can greatly improve the separation rate of aluminum particles from plastic particles. The Designed Compactor for Changing Hollow Aluminum Particles to Solid Particles. According to the calculations of horizontal throws of hollow aluminum particles and solid aluminum particles, we found the character of hollowness greatly destroyed the separation rate of eddy current separation. Therefore, a compactor was designed to eliminate hollow aluminum particles in the crushed waste toner cartridges. The structure of the compactor is given in Figure 5. When the aluminum particles came out from the crusher, they were conveyed to storage tank. When the storage tank was full of aluminum particles, the sliding plate of the tank was opened, and aluminum particles were fed into the compactor. The vibration layer of the compactor caused aluminum particles to pave into a compactor monolayer. Then, the hydraumatic stick made the pressing plate squeeze the hollow aluminum particles to solid aluminum particles. After the squeezing process, one leg of the compactor was lifted and the supporting body of the compactor was inclined for transporting the solid aluminum particles from the support body of the compactor to the vibration feeding system of the eddy current separation. The
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.6b01168. Nomenclature (PDF)
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AUTHOR INFORMATION
Corresponding Authors
*Tel.: +86 20 84113620. Fax: +86 20 84113620. E-mail:
[email protected]. *Tel.: +86 20 84113620. Fax: +86 20 84113620. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
This work was supported by National Natural Science Foundation of China (51308488), Guangdong Provincial Scientific and Technological Projects (2015B020237005, 2016A020221014), Natural Science Foundation of Jiangsu province (BK20130449), and Guangdong Provincial Natural Science Foundation (2016A030306033). The authors are grateful to the reviewers who helped us improve the paper through many pertinent comments and suggestions. F
DOI: 10.1021/acssuschemeng.6b01168 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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