Khanna R, Ellamparuthy G, Cayumil R, Mishra S K, Mukherjee P S
School of Materials Science and Engineering, The University of New South Wales, NSW 2052, Sydney, Australia.
Institute of Minerals and Materials Technology, Advanced Materials Technology Department, Bhubaneshwar, Orissa 751013, India.
Waste Manag. 2018 Aug;78:602-610. doi: 10.1016/j.wasman.2018.06.041. Epub 2018 Jun 23.
An in-depth investigation was carried out on the recovery of rare earth elements (REEs) from a variety of waste printed circuit boards (PCBs). High temperature pyrolysis was carried out at 850 °C for 15 min using horizontal resistance and thermal plasma furnaces with different levels of turbulence. The concentration of REEs in key pyrolysis residues, namely, copper rich red metallic fraction, lead/tin rich white metallic fraction and slag rich carbonaceous residues, were determined using ICP analysis. Most of the REEs were found concentrated in the carbonaceous residue with negligible levels of REEs recovered in the two metallic fractions. Most of the recovered REEs showed a high affinity towards to refractory oxides silica and alumina, and little affinity towards metals Cu, Pb and Sn. The yield of REEs was significantly higher from the plasma furnace indicating the important role of turbulence in the dissociation & subsequent diffusion of REEs during pyrolysis. While La, Pr, Sm and Y required turbulent conditions for their recovery, Nd, Gd, Ce and Dy were relatively easy to dissociate and extract from the waste. Significant amounts of REEs could thus be recovered from waste PCBs as concentrated recyclates for further processing and extraction of individual rare earths. This study has shown that PCBs could prove to be a valuable urban mining resource of REEs. The recovery of REEs, in addition to precious and other metals, could play an important role towards enhancing the economic and environmental sustainability of e-waste recycling.
对从各种废弃印刷电路板（PCBs）中回收稀土元素（REEs）进行了深入研究。使用具有不同湍流水平的卧式电阻炉和热等离子体炉在850℃下进行15分钟的高温热解。使用电感耦合等离子体分析（ICP分析）测定关键热解残渣中稀土元素的浓度，即富铜红色金属部分、富铅/锡白色金属部分和富碳炉渣残渣。发现大多数稀土元素集中在含碳残渣中，而在两种金属部分中回收的稀土元素含量可忽略不计。大多数回收的稀土元素对难熔氧化物二氧化硅和氧化铝具有高亲和力，而对金属铜、铅和锡的亲和力很小。等离子体炉中稀土元素的回收率明显更高，这表明湍流在热解过程中稀土元素的解离和随后的扩散中起重要作用。虽然镧、镨、钐和钇的回收需要湍流条件，但钕、钆、铈和镝相对容易从废物中解离和提取。因此，可以从废弃印刷电路板中回收大量稀土元素作为浓缩回收物，用于进一步加工和提取单个稀土。这项研究表明，印刷电路板可能被证明是稀土元素的宝贵城市采矿资源。除了贵金属和其他金属之外，稀土元素的回收对于提高电子废物回收的经济和环境可持续性可能发挥重要作用。
