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. During the production process, the highly active elements of the anode carbon block react with air [
1], and the secondary reaction of CO
2 and liquid aluminum occurs during the production process [
2] along with anode bubble erosion [
3,
4], all of which cause the carbon block components to fall out. Under the combined effect, each ton of aluminum produced by electrolysis is accompanied by 5–10 kg [
5] of carbon dust. 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; hence, 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. Stacking treatment causes fine particles to enter the atmosphere, resulting in environmental pollution, while landfill disposal causes free-fluorine pollution of groundwater resources. According to research, carbon dust contains a large quantity of carbon, electrolytes, and other recyclables. In recent years, amounts of researches has been conducted on the harmless treatment and resource utilization of carbon dust. At present, the main treatment approach of carbon dust are fire roasting, vacuum smelting, and fluidized bed combustion technology [
8]. The vacuum smelting method and fluidized bed treatment are still at the laboratory research stage due to technical limitations and cannot yet be used for large-scale industrial applications. Although fire roasting can recover cryolite and other components in carbon dust, it causes secondary pollution due to the burning of fluoride and carbonaceous components. The flotation method is an ideal method for carbon dust recovery for its good recovery effect, less equipment, and simple process flow.
The flotation method uses the difference in hydrophilicity and hydrophobicity between different mineral particles to classify [
9,
10,
11,
12,
13]. As a means of resource recovery and reutilization, the development of processes and applications has emerged in various fields [
14,
15,
16,
17]. Carbon has strong natural hydrophobicity [
18,
19], and research on the flotation of carbon materials has been increased in recent years [
20,
21]. Yang et al. [
22] studied the flotation kinetics for the removal of unburned carbon in fly ash. They found that the amount of collector and foaming agent is the key factor in the flotation of fly ash and carried out the flotation kinetics test data fitting. Derya et al. [
23] used flotation technology to separate the unburned carbon in the bottom ash of coal-fired power plants and carried out experiments where the quantity of additives, slurry concentration, pH value, particle size distribution, flotation time and temperature were variables. Under the optimal process conditions, the carbon content of the concentrate was increased from 13.85% to 51.54%, and the carbon recovery rate was 54.54%. Zhang and Honaker [
24] believes that froth flotation is the most effective separation technology for ultra-fine materials, and studied the influence of diesel fuel consumption, adjustment time and impeller speed on the performance of activated carbon flotation. Zhou et al. [
25] mixed surfactant and collector kerosene in a certain proportion to prepare an emulsion and used it as a co-catalyst to improve the hydrophobicity of unburned carbon, then studying the effect of four different surfactants on foam flotation. An et al. [
26] studied the effect of foaming agent polyglycol ether (DF-250) and its mixture on bubble size, foam stability, and unburned carbon flotation performance and found that 75% DF-250 had the best flotation performance. Yang et al. [
27] conducted a flotation kinetic test on fly ash of different particle sizes and studied the effect of particle size on the flotation behavior of fly ash. Xu et al. [
28] studied the mechanism of non-ionic surfactant Triton X-100 (C
34H
62O
11; its hydrophilic-lipophilic balance (HLB) number is 13.4) pretreatment in enhancing the flotation of fly ash and found that it can significantly improve the hydrophobicity of the unburned carbon surface, thereby increasing the recovery rate of unburned carbon. 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.
Regarding the problem of aluminum electrolysis solid waste recycling, Vasyunina et al. [
31] adopted a grinding–classification–reverse flotation–concentration process using flotation agents such as kerosene to remove silicon, iron oxide, and carbon particles, finally recovering aluminum electrolysis production sweep materials. Tropenauer et al. [
32] introduced flotation and chemical treatment technology to solve the problem of industrial waste generated in the aluminum electrolysis process. Li et al. [
33] explored a plan for recovering the waste lining of electrolytic cells by optimizing flotation conditions, including grinding particle size, slurry density, and the mixing speed of the flotation machine, and conducted a comparative experiment. The above experiments were mostly conducted to recover solid wastes such as the waste liner of aluminum electrolysis, though there are few reports on the carbon dust flotation recovery process and especially on influencing factors such as the flotation agent and process parameters. Therefore, this study conducted analysis of the main components and surface morphology characteristics of electrolytic aluminum carbon dust, studied flotation parameters and optimized in a laboratory environment. The performance of the flotation product was tested, and a suitable flotation treatment was proposed to provide a reference for application of carbon dust flotation process. Nowadays, all countries attach great importance to the sustainable development of resources and industrial clean production [
34]. As a highly polluting industry, it is even more necessary for the aluminum electrolysis industry to implement energy saving, emission reduction and clean production. For companies, reducing harmful emissions and increasing recycling rates can save costs and obtain additional benefits while also contributing to ecological protection.