Improved borate fusion technique for determination of rare earth elements in electronic waste components

ABSTRACT

The information regarding the abundance of rare earth elements (REEs) in electronic waste components (EWC) helps the recycling industry. However, after the end of use, improper disposal may be detrimental to the environment by releasing toxic substances. An optimised alkaline borate fusion method for REEs determination in electronic waste (e-waste) was developed. It is divided into three phases. Firstly, the sample preparation stages were investigated. Secondly, the optimisation of experimental particulars comprises the choice of oxidiser, flux composition, non-wetting agents, fusion time, and sample to flux ratio. The third phase consists of spectroscopic determination by inductively coupled plasma optical emission spectroscopy (ICP-OES) and X-ray fluorescence (XRF) spectroscopy. The highest REEs recovery (mg/g of e-waste) were found more in fine fractions of less than 0.09 mm compared to gross fractions. The optimum and safe fusion conditions for e-waste were achieved after slow thermal decomposition up to 550°C, pulverisation to 90% of –53 µm, flux composition (90%LiBO₂ + 10% Li₂B₄O₇), 3:1 oxidant ratio of Na₂CO₃: NaNO₃, LiBr as the non-wetting agent. Also, a sample to flux ratio of 1:15 and a total fusion time of 10 min was optimised. The newly improved alkaline fusion results compared better to those obtained from classical mineral acid dissolution with at most 5% RSD on REEs studied. The alkaline borate fusion results in smartphones e-waste were at least 15% and 25% higher than in four acid digest and microwave-assisted digest techniques, respectively. The results indicated enrichment of REEs in smartphones followed by non-smartphones and computer waste.

GRAPHICAL ABSTRACT

KEYWORDS:

• Rare earth elements
• e-waste
• alkaline borate fusion
• optimisation
• spectroscopy

Acknowledgements

The authors wish to thank all who provided us with the e-waste material used in this study. This study was permitted and supported by Cape Peninsula University of Technology (CPUT), Bellville and Scientific Services Consulting Analytical Laboratory Cape Town, South Africa.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article (and /or) its supplementary materials.