A Sustainable Strategy for Spent Cathode Carbon Blocks Hazardous Waste Recycling Using Binary Molten Salt Thermal Treatment

Waste-to-Energy treatment is a promising path to environment and energy management in the future. This work detailed a binary molten salt thermal treatment methodology for the detoxification of spent cathode carbon block (SCCB) waste and the recycling of carbonaceous materials. The thermal behavior of SCCB and SCCB blended with molten salts was investigated. It was found that the NaCl-Na₂CO₃ binary molten salts significantly contributed to reducing pyrolysis onset temperature by 334.3 K compared to that of SCCB itself (i.e., activation energy of pyrolysis reaction was reduced from 4.24×10⁵ to 2.30×10⁵ J/mol), thus helping to lower thermal treatment energy consumption. With the addition of binary molten salts, the residue after thermal treatment in a horizontal tube furnace experiment was separated into two layers. The bottom-layer residue was mainly composed of molten salts. The fluorine content in the form of NaF and CaF₂ of top-layer residue was reduced significantly while the carbon content remained unchanged. Specifically, the leaching concentration of fluoride ion was decreased from 4620 mg/L to 856 mg/L. It is noted that the NaF and CaF₂ can be removed through water-leaching and hydrothermal acid-leaching methods and thus the carbonaceous materials with a calorific value of 17.5 MJ/kg were obtained.