Selective Milling and Elemental Assay of Printed Circuit Board Particles for Their Recycling Purpose

Abstract

Selective/preferential milling of printed circuit board (PCB) particles followed by non-destructive characterization of the mill products was performed in order to understand the effects of different feed masses into a hammer mill and different milling time on the metal recovery and enrichment ratio. Those are important variables affecting and determining the process performance and capacity. The milling tests and elemental assay characterization were conducted by using a hammer mill and a portable X-ray fluorescence analysis (XRF), respectively. The results showed the preferential metal concentration/enrichment was achieved for several elements and their degree was varied depending on the parameters. Using the experimental data, predictive models of metal recovery were developed and the global trend of metal recoveries was observed under different mill feed and milling time and discussed.

Determination of Liberation Degree of Mechanically Processed Waste Printed Circuit Boards by Using the Digital Microscope and SEM-EDS Analysis

“…Thus, the general trend will be further discussed with the summary of liberation parameters given in Table 5. Despite being more liberated in the finest fractions in general, our previous studies [12,15] also showed the metals, especially Cu, were often enriched in coarser fractions (e.g., 1-2 mm) explained by selective agglomeration. Hence, the relationship among particle agglomeration, particle liberation and metallic enrichment is aimed to further understand in this study, and should be useful for further beneficiation stages.…”

“…The above two trends were obtained with two other metal categories and other feed mass, in general, with some exceptions (e.g., Cu liberation degree decrease with size reduction with 80 g feed due to selective agglomeration, Figure 6c). operation although the highest recovery (40%) and enrichment (1.3) of Cu in that size fraction among all the milling conditions tested [15]. A further study of selective agglomeration and selective liberation will be of great interest in terms of practical use of agglomeration as a selective material recovery process.…”

“…An experimental matrix was designed to investigate the influence of two of the hammer milling parameters, feed mass (20, 40 and 80 g) and grinding time (30, 60 and 90 s) on the selective enrichment of metals from the non-metallic fractions in the milled products. The detailed milling procedure was presented in our previous report [15]. The hammer milled PCB products were then sieved to obtain the following size fractions: 1-2 mm, 0.5-1 mm, 0.25-0.5 mm, 0.125-0.25 mm, and <0.125 mm.…”

“…The chemical composition analysis of the samples has already been published in our previous reports [12,15]. The issues associated with the use of chemical composition is that it gives the average value of the samples disregarding the liberation degree of metals.…”

“…Our previous work [15] reported the selective metal enrichment and agglomeration of metallic components (e.g., Cu, Al) through the application of a hammer milling for PCBs comminution. Based on our results and abovementioned research gaps, the objective of the present study is to assess the degree of liberation of metals within the products of hammer milling process via the combination of image acquisition and analysis, in order to evaluate their selective liberation.…”