Recovery of Metals from Printed Circuit Boards By Means of Electrostatic Separation

Abstract

Without the use of appropriate recycling technologies, the growing amount of electronic waste in the world can be a threat to the development of new technologies, and in the case of improper waste management, may have a negative impact on the environment. This is due to the fact that this waste contains large amounts of valuable metals and toxic polymers. Therefore, it should be recycled in accordance with the assumptions of the circular economy. The methods of mechanical recovery of metals from electronic waste, including printed circuits, may be widely used in the future by waste management companies as well as metal production and processing companies. That is why, a well-known and easily applicable electrostatic separation (ES) method was used to recover metals from printed circuit boards. The grain class of 0.32 - 0.10 mm, obtained after grinding the boards, was fed to a separator. Feed and separation products were analyzed by means of ICP-AES, SEM/EDS and XRD. The concentrate yield obtained after electrostatic separation amounted to 32.3% of the feed. Its density was 11.1 g/cc. Out of the 91.44% elements identified in the concentrate, over 90% were metals. XRD, SEM observations and EDS analysis confirmed the presence of non-metallic materials in the concentrate. This relatively high content of impurities indicates the need to grind printed circuit board into grain classes smaller than 0.32-0.10 mm.

Evaluation of the efficiency of metal recovery from printed circuit boards using gravity processes

“…The separation of products into concentrate, middlings and waste resulted from the difference in the specific density of the grains. Based on previous observations (Franke et al, 2020;Suponik et al, 2021), the concentrate included products with a specific density >7.5 g/cm 3 , the middlings included grains with a density of 7.4-3.5 g/cm 3 , and waste I and II included grains with densities of 3.4-2.5 g/cm 3 and <2.4 g/cm 3 , respectively. The separation parameters were as follows: table load: 9 dm 3 /min (water with the material); the mass of material used for testing: 400 g, water flow rate of the first nozzle 5.7 dm 3 /min, a water flow rate of the second nozzle 5.4 dm 3 /min; table stroke 1.5 mm; table movement frequency 260 strokes/min; longitudinal slope angle: 1˚; transverse slope angle: 6˚; duration of separation: 3 min 45 sec.…”

“…The nonmetallic part (plastics) can then, following the principles of circular economy, be used to produce prefabricated elements, such as, for example, composite boards. The physical recovery methods include: electrostatic (Dascalescu et al, 1992;Franke et al, 2020;Jiang et al, 2009;Wu et al, 2008), magnetic (Suponik et al, 2019;Veit et al, 2005), and gravity separation in the air (Eswaraiah et al, 2008;Yoo et al, 2009) and water medium (Duan et al, 2009;Zhu et al, 2020). Metal recovery from PCBs can also be carried out by flotation using flotation reagents (Gallegos-Acevedo et al, 2014;Otunniyi et al, 2013) or without them (Ogunniyi and Vermaak, 2009).…”

Morphology, Phase and Chemical Analysis of Leachate after Bioleaching Metals from Printed Circuit Boards

“…Referring to the composition of metallic elements of the initial material (chemical composition of ground PCB after the separation of the plastic fraction (Franke et al) [12]) as well as the solutions after the bioleaching, it can be stated that the iron percentage in the specimen increased significantly, which is related to the course of the leaching process and continuous oxidation of Fe 2+ to Fe 3+ guaranteeing a transition of the metal from the solubilized material into the solution. Analyzing the obtained SEM and TEM results, we can assume that the demonstrated small differences in the chemical composition between the obtained dried specimen from the undiluted solution and that from the diluted one were mainly connected with the applied research technique (analysis in micro-areas) as well as the preparatory procedure.…”

“…Qualitative X-ray phase analysis of ground PCBs performed by Erust et al [41] and Franke et al [12] made it possible to identify mainly metallic phases (iron and copper). The investigation results presented in this article point to the presence of mostly oxides and sulfides of these metals in dried residues precipitated from solution, which is a consequence of bioleaching.…”

“…It is possible to identify the diversified element composition: Cu, Zn, Ni, Al, Fe, Si, Ca, Pb, Sn, Cr, Mn, Mo, Ti, Pd, Pt, Ag, Au, etc. In some cases, a PCB consists of even as much as 60 elements, also toxic and hazardous [3,[9][10][11][12][13]. Actions related to the recycling of WEEE and PCB protect the natural environment by limiting the use of ores, as well as reducing the amount of generated waste and pollutants (storage of heavy metals and other toxic substances).…”