The Study of Carbon Recovery from Electrolysis Aluminum Carbon Dust by Froth Flotation

Hesong Li,Tibo Xu,Benjun Cheng,Jiaoru Wang,Yuan Feng,Wenyuan Hou,Mao Li

doi:10.3390/met11010145

Abstract

A large amount of carbon dust is generated in the process of aluminum smelting by molten salt electrolysis. The carbon dust is solid hazardous waste but contains a large quantity of recyclable components such as carbon and fluoride. How to recycle carbon dust more effectively is a challenge in the aluminum electrolysis field. In this study, X-ray diffraction, scanning electron microscope, and other methods were used to analyze the phase composition of electrolytic aluminum carbon dust. The effects of particle size distribution of carbon dust, impeller speed, reagent addition, mixing time, and flotation time on the flotation recovery of carbon dust were studied. The optimal flotation conditions were obtained and the flotation products were analyzed. The results show that the optimal particle size distribution is 70% of particles below 200 mesh, corresponding to a grinding time of 11 min. The optimum speed of the flotation machine was to be between 1600 and 1800 r/min with the best slurry concentration of 20–30% and 5 min mixing time, and the collector kerosene was suitable for adding in batches. Under the above conditions, the recovered carbon powder with a carbon content of 75.6% was obtained, and the carbon recovery rate was 86.9%.

Highlights

Molten salt electrolysis is a commonly used method for industrial aluminum smelting
The accumulation of carbon dust at a certain concentration causes an increase in electrolyte voltage drop and temperature inside the electrolysis cell, which destroy the electrolysis reaction heat balance [6] and affect the stability of the electrolysis production; the generated carbon dust needs to be regularly removed and salvaged
Aluminum electrolysis carbon dust has been officially listed on the “National Catalogue of Hazardous Wastes” [7] of China due to its environmental risks

Summary

Introduction

Molten salt electrolysis is a commonly used method for industrial aluminum smelting. Its production principle is to produce high-purity primary aluminum by electrolysis reaction with an aluminum electrolysis cell as the carrier, a carbon block as the anode, cryolite as the reaction solvent, and alumina as the raw material. Walker and Wheelock [29], Harris and Thomas [30] optimized the process conditions required for effective separation of unburned carbon from fly ash by studying parameters such as collectors, pretreatment slurry, and flotation stages in foam flotation.

Results

Conclusion