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-Na_(2)CO_(3)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 4.24×10^(5)to 2.30×10^(5)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 CaF_(2)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 CaF_(2)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.

Preparation of lithium-ion battery anode materials from graphitized spent carbon cathode derived from aluminum electrolysis

Graphitized spent carbon cathode(SCC)is a hazardous solid waste generated in the aluminum electrolysis process.In this study,a flotation-acid leaching process is proposed for the purification of graphitized SCC,and the use of the purified SCC as an anode material for lithium-ion batteries is explored.The flotation and acid leaching processes were separately optimized through one-way experiments.The maximum SCC carbon content(93wt%)was achieved at a 90%proportion of−200-mesh flotation particle size,a slurry concentration of 10wt%,a rotation speed of 1600 r/min,and an inflatable capacity of 0.2 m^(3)/h(referred to as FSCC).In the subsequent acid leaching process,the SCC carbon content reached 99.58wt%at a leaching concentration of 5 mol/L,a leaching time of 100 min,a leaching temperature of 85°C,and an HCl/FSCC volume ratio of 5:1.The purified graphitized SCC(referred to as FSCC-CL)was utilized as an anode material,and it exhibited an initial capacity of 348.2 mAh/g at 0.1 C and a reversible capacity of 347.8 mAh/g after 100 cycles.Moreover,compared with commercial graphite,FSCC-CL exhibited better reversibility and cycle stability.Thus,purified SCC is an important candidate for anode material,and the flotation-acid leaching purification method is suitable for the resourceful recycling of SCC.