Study of Enhanced Gravity Separation Based on Liberation Characteristics of a Heat-Treated Circuit Board
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Study of Enhanced Gravity Separation Based on Liberation Characteristics of a Heat-Treated Circuit Board Fangyuan Ma 1,2 & Youjun Tao 1,2
&
Yushuai Xian 1,2
Received: 22 November 2019 / Accepted: 7 May 2020 # Society for Mining, Metallurgy & Exploration Inc. 2020
Abstract This study compared particle size distribution and density distribution of crushed products for waste printed circuit boards (WPCBs) before and after heat treatment. The crushing process for heat-treated WPCBs is a selective crushing process; more metal is concentrated in the coarse particle range of 1.0–0.5 mm and high density range of 2.8–2.96 g/cm3. WPCBs were separated using the Falcon separator to recycle useful metals. The Box-Behnken module of Design-Expert was used to obtain optimal separation parameters, namely, rotational frequency of 25 Hz, recoil water pressure of 0.025 Mpa and feed speed of 34 ml/s. On this basis, the separation indexes for WPCBs with and without heat treatment were compared. Experimental results show that the recovery effect is better for heat-treated WPCBs than for those without heat treatment. Compared with the non-heattreated WPCBs, the product grade of heat-treated WPCBs is 1.95% higher, and its recovery is improved by about 14%. Finally, characteristics of WPCBs before and after heat treatment were analyzed on the basis of stress experiments and scanning electron microscopy (SEM), respectively. Results of mechanical characterization indicate that the stress experiment for non-heat-treated WPCBs has a maximum pressure load of 212 N and displacement of 20 mm, but heat-treated WPCBs only need 140 N stress and 14 mm displacement. SEM shows that copper foil and fiberglass cloth are deformed in different directions and sizes after heat treatment to form gaps, which promote liberation of copper foil and fiberglass cloth. Keywords Environment pollution . Falcon . Gravity . WPCBs . Heat treatment . Stress
1 Introduction Waste printed circuit boards (WPCBs) contribute to environmental pollution, as they contain heavy metals, so it is important to recycle metals in WPCBs to improve resource utilization and reduce environmental pollution. WPCBs contain about 30% plastic, 30% inert oxide and 40% metals [1], which fall into two categories: (1) fundamental metals, such as copper, aluminum, iron, nickel and tin, and (2) precious and rare metals, such as gold, silver and platinum [2, 3]. However, the potential damage to the environment (such as soil and water
* Youjun Tao [email protected] * Yushuai Xian [email protected] 1
Key Laboratory of Coal Processing and Efficient Utilization Ministry of Education, China Univerisity of Mining & Technology, Xuzhou 221116, China
2
School of Chemical Engineering and Technology, China University of Mining & Technolog, Xuzhou 221116, Jiangsu, China
pollution) by WPCBs due to content of heavy metals (such as lead, nickel and cadmium) should not be underestimated [3, 4]. A large number of harmful substances exist in WPCBs, which have a serious impact on the environment and human hea
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