Industrial-Scale Quantitative Oxygen Partial Pressure Measurement of the Direct-to-Blister Electric Slag Cleaning Furnace for Chemistry Control Improvement

Abstract Oxygen partial pressure (p(O 2 )) was measured in an industrial copper direct-to-blister electric slag cleaning furnace using disposable CELOX probes, aiming to provide an alternative measure of bath chemistry. Because p(O 2 ) and copper concentration in slag are strongly linked thermodynamically, p(O 2 ) can serve as a proxy for monitoring slag reduction. Measurements were conducted across multiple furnace batches using two methodologies: dip-hole and tap-hole probing. Both techniques successfully tracked the progression of slag reduction, with p(O 2 ) decreasing consistently as slag was reduced. However, tap-hole measurements gave more reliable estimates of absolute copper concentration in slag, showing stronger agreement with EPMA measurements of liquid slag composition. A persistent vertical p(O 2 ) gradient was observed within the slag layer, indicating chemical stratification. This gradient suggests that reduction is influenced by mass-transfer limitations within the slag phase, rather than solely by interfacial coke–slag reaction kinetics. Uncertainties associated with copper concentration estimation are discussed and quantified. These results demonstrate that oxygen probe measurements provide a rapid, effective tool for monitoring slag chemistry.