LIBS and Hyperspectral Imaging as a Real-Time Process Control Tool for Metal Recovery from E-Waste

Ferreira, Dennis S.; Pereira-Filho, Edenir R.

doi:10.21577/0103-5053.20250130

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Full Paper • J. Braz. Chem. Soc. 36 (12) • 2025 • https://doi.org/10.21577/0103-5053.20250130 linkcopy

LIBS and Hyperspectral Imaging as a Real-Time Process Control Tool for Metal Recovery from E-Waste

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

The rapid increase in e-waste creates challenges, requiring more efficient recycling methods. This study explores the application of laser-induced breakdown spectroscopy (LIBS) combined with hyperspectral imaging to monitor leaching processes of Ag, Au, Cu and Sn in e-waste recycling. The method involved the use of sequential leaching strategies of printed circuit boards (PCBs), the best strategy was applied using HNO₃ for Cu, HCl for Sn and thiourea/Fe(NO₃)₃ for Ag and Au. Inductively coupled plasma optical emission spectrometry (ICP OES) was used to validate the metal extraction efficiency, achieving recoveries of 100% for Cu and Ag, 97% for Sn and 86% for Au. LIBS spectra showed a strong correlation with the ICP OES data, revealing reductions in the emission signals corresponding to the extracted elements. Hyperspectral imaging provided an analysis of the spatial distribution of trace elements, confirming the progressive extraction of metals. The results indicate that LIBS, associated with multivariate analysis, offers a fast and economical alternative.

Keywords:
e-waste recycling; LIBS; hyperspectral imaging; sustainable recovery; ICP OES; circular economy

Emission line (relative intensity) / nm
Ag		Au		Cu		Sn
λ1	224.643 (123)	λ1	204.454 (703)	λ1	213.598 (6104)	λ1	224.605 (2545)
λ2	228.003 (281)	λ2	211.068 (2384)	λ2	224.261 (7634)	λ2	231.723 (1218)
λ3	546.550 (643)	λ3	212.529 (1078)	λ3	224.700 (8046)	λ3	249.570 (1197)
		λ4	443.511 (231)	λ4	324.754 (16256)	λ4	257.158 (1385)
		λ5	460.751 (341)	λ5	327.396 (15301)	λ5	266.124 (1110)
		λ6	481.160 (390)	λ6	515.324 (8297)	λ6	277.981 (1224)
				λ7	521.820 (12349)	λ7	285.062 (2110)
						λ8	452.474 (2741)
						λ9	579.918 (1008)

Laser pulse	RSD / %
Laser pulse	Ag (224.64 nm)	Au (211.06 nm)	Cu (521.82 nm)	Sn (303.41 nm)
1^st pulse	45.65	28.37	50.50	29.08
2^nd pulse	45.75	27.84	53.06	27.86
3^rd pulse	48.73	28.78	51.89	28.56
4^th pulse	42.24	28.70	50.95	30.99
5^th pulse	46.56	29.80	46.54	30.23
5-pulse average	45.79	28.70	50.59	29.34

Laser pulse	RSD / %
Laser pulse	Ag (224.64 nm)	Au (211.06 nm)	Cu (521.82 nm)	Sn (303.41 nm)
1^st pulse	83.37	71.86	78.67	60.48
2^nd pulse	88.91	62.17	87.03	55.48
3^rd pulse	69.34	66.28	78.97	58.28
4^th pulse	86.44	70.10	82.16	53.52
5^th pulse	86.55	71.51	72.82	62.35
5-pulse average	82.92	67.51	79.93	58.02

Leaching step	RSD / %
Leaching step	Ag	Au	Cu	Sn
Sequence (Figure 4a)
Initial	23.1	22.2	22.9	11.8
HNO₃	12.3	40.3	31.2	11.7
Thiourea/Fe(NO₃)₃	66.7	64.4	56.6	59.3
HCl	146.2	12.2	18.3	13.1
Sequence (Figure 4b)
Initial	23.1	22.2	21.3	26.8
HNO₃	12.3	40.3	21.8	6.3
I₂/I^-	78.8	17.7	19.2	14.3
HCl	47.6	10.9	8.7	8.3
Sequence (Figure 4c)
Initial	23.1	22.2	21.3	26.8
HNO₃	12.3	40.3	21.8	6.3
HCl	63.3	12.3	13.8	51.7
Thiourea/Fe(NO₃)₃	164.9	11.7	10.8	13.4
Sequence (Figure 4d)
Initial	23.1	22.2	21.3	11.8
HNO₃	12.3	40.3	21.8	11.7
H₂SO₄/CuSO₄	129.3	11.8	11.1	15.6
Thiourea/Fe(NO₃)₃	19.0	10.9	9.5	12.6

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