The Impact of Cobalt Species on the Hazardous Characteristics of Cobalt-Leaching Residue: A Case Study from Guangdong Province, China

Cobalt (Co) is a hazardous element of significant environmental concern, primarily due to its potential leaching toxicity. However, the current assessments of leached Co residues have focused solely on the total cobalt concentration, often overlooking the distinct Co species that contribute to its hazardous nature. This study attempts to determine the impact of cobalt speciation on the toxicity of cobalt and the related hazardous characteristics. The objective of this study is to enhance the understanding of how different Co species influence the environmental toxicity of leached residues. Cobalt speciation is studied by a multivariate analysis including ignitability, reactivity, corrosiveness, acute toxicity, leaching toxicity, and toxic substance concentration. The tested concentrations are compared with the identification standards and technical specifications in China. Co species, particularly cobalt oxide, are identified as the main contributors to the toxicity of the leached Co residue. It is also noted that Co occurrence significantly affects the calculation results of cumulative toxicity, thus impacting the hazard characteristics of leached cobalt residue. The findings benefit risk evaluators and decision makers by offering a new approach for managing leached Co residues and providing a scientific foundation for the development of relevant laws and regulations in China.