Aqueous solutions containing 10-3 M luminol and varying concentrations of hydrogen peroxide are irradiated with 20 kHz ultrasound at 50 °C. The intensity of sonogenerated chemiluminescence (SCL) is shown to increase linearly with ultrasound power and to be strongly pH dependent, reaching a maximum at pH 12. For pH < 10 SCL intensity (I SCL) is independent of H2O2 concentration. For pH >10 I SCL increases monotonically with H2O2 concentration up to10-4 M but decreases as the concentration is increased further. A mechanism is proposed in which HO2 - and the luminol monoanion competitively reduce sonochemically generated HO•, producing O2 •- and luminol radical anion, respectively. Luminescence follows the decomposition of a hydroperoxide adduct formed by reaction between O2 •- and luminol radical anion. EDTA is shown to suppress the background (silent) chemiluminescence of solutions containing luminol and H2O2 without significantly affecting I SCL. Digital images of SCL emission occurring near the transducer−solution interface are analyzed to determine the spatial distribution of sonochemical activity. It is shown that, in the absence of standing waves, I SCL decays exponentially with perpendicular distance from the surface of a plane-ended ultrasound transducer horn. Spatially resolved I SCL data is used to determine the acoustic attenuation coefficient (α) in acoustically cavitating water noninvasively. It is shown that α values at the cavitation-producing frequency increase with transducer output power and may be many orders of magnitude greater than is the case for homogeneous water.

Recycling of valuable metals from secondary resources such as waste Li-ion batteries (LIBs) has recently attracted significant attention due to the depletion of high-grade natural resources and increasing interest in the circular economy of metals. In this article, the sulfuric acid leaching of industrially produced waste LIBs scraps with 23.6% cobalt (Co), 3.6% lithium (Li) and 6.2% copper (Cu) was investigated. The industrially produced LIBs scraps were shown to provide higher Li and Co leaching extractions compared to dissolution of corresponding amount of pure LiCoO. In addition, with the addition of ascorbic acid as reducing agent, copper extraction showed decrease, opposite to Co and Li. Based on this, we propose a new method for the selective leaching of battery metals Co and Li from the industrially crushed LIBs waste at high solid/liquid ratio (S/L) that leaves impurities like Cu in the solid residue. Using ascorbic acid (CHO) as reductant, the optimum conditions for LIBs leaching were found to be T = 80 °C, t = 90 min, [HSO] = 2 M, [CHO] = 0.11 M and S/L = 200 g/L. This resulted in leaching efficiencies of 95.7% for Li and 93.8% for Co, whereas in contrast, Cu extraction was only 0.7%. Consequently, the proposed leaching method produces a pregnant leach solution (PLS) with high Li (7.0 g/L) and Co (44.4 g/L) concentration as well as a leach residue rich in Cu (up to 12 wt%) that is suitable as a feed fraction for primary or secondary copper production.

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