Article pubs.acs.org/est
Improvements of the Recovery Line of Waste Toner Cartridges on Environmental and Safety Performances Ruan Jujun,†,‡ Li Jia,† and Xu Zhenming*,† †
School of Environmental Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People’s Republic of China ‡ School of Environmental Science and Engineering, Yangzhou University, 196 West Huayang Road, Yangzhou, Jiangsu 225000, People’s Republic of China S Supporting Information *
ABSTRACT: A physical recovery line had been constructed in plant for the increasing waste toner cartridges in previous work. However, with the production, severe lacks of the line emerged: (1) there was little proper technology of treating the collected toner; (2) strong noise was produced from the line and influenced the health of worker. For disposing toner properly, a new collected system of toner was developed. An air current separator (ACS) was designed to separate organic materials from inorganic materials of toner. Then, the separated organic materials can be incinerated and the inorganic materials can be dumped. Movement behaviors of toner particles in the ACS were analyzed, and the optimized operation parameter (13.5 m/s) of air current speed was obtained by theory analysis and experiments. For controlling the noise, noise levels emitted from the different process of the line were measured. The results indicated noise levels emitted from crusher (95.2 dB(A)) and agitator/magnetic separator (AMS, 91.9 dB(A)) were greater than the permissible noise exposure level of the Occupational Safety and Health Standards (90 dB(A)). The noise levels of other processes of the line were relatively safe. An acoustic hood was developed to reduce the noise levels of the crusher and the AMS. Then, the noise levels were both decreased to 67.6 dB(A). This paper provided important data for the environment on the industrialization of waste toner cartridges recovery.
1. INTRODUCTION About 25 million tons of e-waste was produced per year. China contributed about 2.5 million tons per year, not including the shipped e-waste from the developed countries. E-waste contains both toxic and valuable materials, and it had brought heavy pressing in waste treatment.1,2 The crude technologies such as open incineration and acid washing had caused serious environmental contaminations in China.3−5 Thus, developing environment-friendly and high-efficient technology has been the urgent need for e-waste recovery.6,7 As the key components of printers and duplicators, a large number of obsolete toner cartridges has been generated. By 2010, the total number of obsolete toner cartridges had reached about 75 million units.8 Although the governments and origin entrusted manufactures made great efforts on refilling, refurbishing, and remanufacturing the obsolete toner cartridges, a quantity of waste toner cartridges was still produced. The information provided by vendors and waste recyclers indicated that only about 45% waste toner cartridges could be collected by the licensed waste treatment company (compared to the amount of annual sales of new toner cartridges). Waste toner cartridge contains 45 wt % magnet/iron, 12 wt % aluminum, 35 wt % plastics, and 8 wt % toner. Toner was comprised of polyacrylate-styrene copolymer, polyethylene/polypropylene © 2013 American Chemical Society
paraffin wax, hydroxyl-aromatic-acidand, Fe3O4, and SiO2. Toner was considered as a hazardous material. Thus, the recovery of waste toner cartridges should not only improve resource reclamation but also environmental protection. A physical recovery system of waste toner cartridges had been developed in a previous work. The recovery line of waste toner cartridges, in the scale of demonstration experiment, had been constructed in a licensed e-waste recovery plant9,10 (Yangzhou Ningda Noble Metal CO.,LTD) in Jiangsu province of China. The plant had a standard workshop, performing well in infrastructure (especial in ground hardening and air ventilation). The sketch map of the recovery line is presented in Figure S1 (Supporting Information). The production line was comprised of crusher, agitator/magnetic separator (AMS), eddy current separator (ECS), and toner collecting system. All the machines were installed on concrete ground cushioned by rubber in order to decrease mechanical vibration. The recovery capability of the line was about 500 kg/h and the recovery rate could reach 98.2%; also, little toner leaked out. The recovery Received: Revised: Accepted: Published: 6457
December 28, 2012 April 15, 2013 May 20, 2013 May 20, 2013 dx.doi.org/10.1021/es305311k | Environ. Sci. Technol. 2013, 47, 6457−6462
Environmental Science & Technology
Article
Figure 1. Toner and its comprised materials.
Figure 2. Sketch of the combined technology of air current separator and bag-type dust collector.
Why Traditional Landfill and Incineration Were Not Suitable to Dispose Waste Toner. Toner is comprised of organic materials (OMs) and inorganic materials (IMs). The comprised materials and their characters were given in Figure 1. Toner is not suitable to landfill because of the indissoluble of OMs. Meanwhile, OMs will pollute soil and groundwater in the process of landfill. Traditional incineration is not a proper technology to dispose toner. The reason is that IMs decreased the flammability of toner and brought huge resistance in combustion process. Where Was the Strong Noise From? The recovery line was comprised of mechanical equipment. Mechanical noise has aerodynamic, electromagnetic, and mechanical origins. Aerodynamic noise is a result of pressure fluctuations due to fluctuation of fluid forces. These excited forces are caused by flow fields, turbulent flow, the interaction of the gears with air and turbulent flow with inner wall of the machines. Noise of
line was considered to be environment-friendly and highefficiency. The recovered recyclable resource was sold as raw materials. The collected toner was sent to special hazardouswaste treating department for safe disposal. With the production, lacks of the line in the aspects of environment and safety were emerged in the recovery process. The main lacks included the following: (1) lots of toner was accumulated in the special hazardous-waste treatment department and there was a lack of technology for disposing toner. Traditional landfill and incineration were not suitable to treat waste toner. (2) Although vibration absorption measure (cushion rubber) had been placed during equipment installation for decreasing vibration and mechanical noise, strong noise was still emitted from the recovery line. High noise will negatively affect human health and well-being. Problems caused by noise included hearing loss, high blood pressure, and lost productivity.11,12 6458
dx.doi.org/10.1021/es305311k | Environ. Sci. Technol. 2013, 47, 6457−6462
Environmental Science & Technology
Article
πd2p, u is the air current speed provided by fan II, and k is the resistance coefficient of airflow and
electromagnetic origin is induced by vibration force, which is caused by fluctuations of magnetic flux. The vibrating force is the resultant force of Laplace, Maxwell, and Coulomb forces. Mechanical noise is aroused by vibration of bearings, pedestal, and body of the machines involving frictional force and impact force.13 This paper tried to develop the technology of disposing waste toner and controlling the measure of noise. It contributed to the recovery line of waste toner cartridges on environmental protection and life safety and provided important data to the industrialization of waste toner cartridges recovery.
k = f (Re p)
(2)
where Rep is the Reynolds number of particle. Reynolds number is computed as ud σg
Re p =
(3)
where d is the inner diameter of the ACS and σg is the kinematic viscosity of air (14.8 × 10−6 m2/s). Thus,
2. METHODS 2.1. How to Dispose of Toner. The toner collecting system of the line was comprised of bag-type dust collector and the enclosed pipes connected to crusher and AMS. Toner was liberated in the crushing process. Most of the toner was conveyed into bag-type dust collector by the fan through closed pipe. A little toner adhered to the surface of aluminum, plastic, and steel particles and moved to AMS. In the agitator, the adhered toner was stirred and detached from aluminum, plastic, and steel particles. The detached toner was also pumped in to bag-type dust collector. There was no special process for separating OMs from IMs of toner. According to the comprised materials of toner in Figure 1, OMs and IMs of toner differ in their densities (IMs > 2.66 g/ cm3; OMs Fb + Fp
(10)
For drawing OMs in to the bag−type dust collector: Fg < Fb + Fp
(11)
According to eqs 1, 8, 9, 10, and 11, the air current speed should meet the following condition. dog (ρo − ρ) 3kρ
