Phosphorus Speciation in Sludge from Nickel Electroplating

The recycling of secondary resources to close material cycle loops should reduce the consumption of natural resources and thus help to reduce the environmental impact. For recycling, it is crucial to consider not only the nickel (Ni) content in the secondary resources, such as Ni plating waste liquids and sludge, but also the impurity levels, particularly the phosphorus (P) concentration. This study characterized the P species in three sludges from Ni electroplating processes using P K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The Ni and P concentrations in the sludges ranged from 11 to 41% and 2,800 to 24,000 ppm, respectively, depending on the type of sludge. The P K-edge XANES analysis identified phosphates and organic P as the major P species in the sludges, and hypophosphite and phosphite species as minor species. These findings provide detailed knowledge that should help to control P in Ni electroplating sludge.