Characterisation of aluminium black dross before and after stepwise salt-phase dissolution in non-aqueous solvents

Joint utilization and harmless elimination of aluminum dross and refined magnesium slag to simultaneously recover metallic aluminum and fusing agent

Refined magnesium slag and aluminum dross are two typical hazardous solid wastes that contain significant amounts of leachable fusing agent and aluminum droplets encapsulated by dense oxidized films, respectively. This study creatively proposes a safe and green method for the joint utilization of these two wastes. The interfacial reaction behavior revealed that the dense oxidized films of the aluminum droplets were significantly broken by the erosive action of the fusing agent, providing the necessary conditions for the movement of aluminum droplets. Consequently, the aluminum droplets successfully broke free from the oxidized films and separated together with the fusing agent from the dross under the force of supergravity. The recovery ratios of metallic aluminum and fusing agent reached 98.95 % and 98.13 %, while the aluminum and fusing agent contents in the tailings were reduced to 0.82 wt% and 3.71 wt%. The study also discusses the leaching characteristic of the tailings and the scalability for industrial applications of this method in detail. This study not only achieves valuable resource recovery but also reduces the leaching risk and alleviates the land occupation and ecosystem pressure caused by industrial wastes. The tailings can be harmlessly utilized in related fields through subsequent scientific treatment.

Composites of Layered Double Hydroxides and ANA-Type Zeolite Synthesized from Hazardous Secondary Aluminum Dross for Cationic Dye Wastewater Treatment

This work first transformed hazardous aluminum waste into low-cost MgAl−layered double hydroxide@ANA zeolite (LDHs@ANA) composite for dye wastewater adsorption, which was meaningful for waste recovery and pollution control. Based on this strategy, the Al(OH)3 extracted from secondary aluminum dross (a hazardous waste in the aluminum industry) was used as an aluminum source to synthesize LDHs@ANA composite, which had more excellent adsorption capacity to methylene blue than MgAl−LDHs and ANA alone. The composite consisted of spherical ANA particles uniformly covered with LDH nanosheets, which effectively avoided a large amount of aggregation between nanosheets and increased specific surface areas and pore volumes. The kinetic results indicated that the adsorption process conformed to the pseudo-second-order kinetic model, and the adsorption site was the main factor affecting the adsorption process. The equilibrium studies showed the adsorption process was exothermic, and the Langmuir model best fitted for the adsorption process, with a maximum adsorption capacity reaching 65.27 mg/g. Meanwhile, the effects of pH, adsorbent concentration, initial methylene blue concentration, and adsorption time on the LDHs@ANA were analyzed. Overall, this work provides a fresh concept for the preparation of low-cost adsorbents from aluminum waste.

Green and Efficient Utilization of Ferruginous Gibbsite Ore and Ferruginous Manganese Ore by Synergetic Carbothermic Co-Reduction–Magnetic Separation Process

The synergetic utilization of ferruginous gibbsite ores (Al-Fe ores) and ferruginous manganese ores (Mn-Fe ores) by the carbothermic co-reduction roasting–magnetic separation process was proposed as an innovative and green process for the separation and recovery of the valuable metal elements of Mn, Fe and Al from these ores. In this paper, a ferromanganese crude alloy with 72.47% Fe and 10.19% Mn and a high recovery of 85.89% Fe was prepared, which produces an acceptable feed to produce manganese steels with an electric arc furnace. The synergistic co-reduction of the two kinds of complex and refractory minerals was favored to separate Fe, Mn and Al from these ores. The influence of the operating variables on the recovery and separation of valuable metals from Mn-Fe ores and Al-Fe ores is initially studied. Then, the stepwise reduction behaviors of a composite oxide Mn1-xFexO (0 ≤ x ≤ 1) and hercynite (Mn1−yFeyAl2O4, 0 ≤ y ≤ 1) were investigated to clarify that Mn-Fe ores have a positive impact on the reduction of fayalite and hercynite in Al-Fe ores. This study reported a simple green route, the carbothermic co-reduction–magnetic separation process, to economically and effectively treat Al-Fe ores and Mn-Fe ores.

Extraction of alumina from aluminum dross by a non-hazardous alkaline sintering process: Dissolution kinetics of alumina and silica from calcined materials

The aluminum dross (AD), which causes numerous problems of its management and disposal to environment is a useful resource to extract alumina. This study explains a novel process to extract highly pure alumina (Al₂O₃) from AD at a high extraction rate without producing the residues and exhaust gases. An experimental set up was designed to perform the grinding of AD for the decomposition of aluminum nitride (AlN) and the removal of salts. Thereby, the desalted dross was used to detect the optimum alkaline (NaOH) calcination parameters and leaching conditions, as well as the dissolution kinetics of alumina and silica. The leaching residues were used to produce Ettringite mineral with calcium-based compounds (including CaO and CaSO₄) to avoid the problems of solid waste disposal from the leaching process. Moreover, to purify the alumina, slightly soluble CaSO₄ was added in leaching solution to precipitate silicate and the optimum additive/solution ratio (g/mL) was determined. The aluminum hydroxide (Al(OH)₃), precipitated after the carbonization was calcinated at 900.0 °C for 2 h to produce γ-alumina. The morphological and mineralogical characterizations of AD, γ-Al₂O₃ and the synthesized Ettringite mineral were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and X-ray fluorescence (XRF). It was observed that activation temperature of 1000.0 °C, Na₂O/Al₂O₃ molar ratio of 1.4, leaching temperature of 60.0 °C, leaching time of 40.0 min, and the leaching liquid/solid ratio (mL/g) of 25/1 were the optimal parameter conditions to extract alumina with the extraction rate at 86.7% and purity of more than 98%. The results of leaching kinetics' study showed that the dissolution of alumina and silica were both controlled by layer diffusion process with the apparent activation energy of 11.4010 kJ·mol^-1 and 2.0556 kJ·mol^-1, respectively.

Harmless disposal and resource utilization for secondary aluminum dross: A review

Secondary aluminum dross (SAD) is solid waste of primary aluminum dross extracted aluminum, which contains approximately 40-60 wt% alumina, 10-30 wt% aluminum nitride (AlN), 5-15 wt% salts and other components. The salts include sodium chloride, potassium chloride and fluorine salts. SAD has dual attributes as resource and pollutant. SAD landfill disposal has the disadvantages of occupying land, wasting resources, a high cost and great environmental impact. SAD utilization methods are currently pyrometallurgy and hydrometallurgy. In pyrometallurgy, AlN is oxidized and the salts are evaporated at high temperature. After mixing, molding and calcination, firebricks and ceramics can be manufactured from SAD. In hydrometallurgy, AlN is hydrolyzed and salts are dissolved in water. After dissolving, filtrating, precipitating, washing and calcination, γ-Al₂O₃ can be prepared from SAD. Resource consumption and emission from both utilization methods were assessed. A ton of magnesium aluminum titanate based ceramics by pyrometallurgy consumes 1043 kg raw materials and releases 69 kg of waste gas, 4.17 t of waste water and no solid waste. A ton of γ-Al₂O₃ by hydrometallurgy consumes 3389 kg raw materials and releases 111 kg of waste gas, 12.98 t of waste water and 267 kg of solid waste. Therefore, the resource consumption and emission of SAD utilization by pyrometallurgy is lower than that by hydrometallurgy. We should focus on reducing the emission of the three wastes from pyrometallurgy. We are sure that SAD can be utilized for glass ceramics by pyrometallurgy. AlN and salts can be transformed into alumina and glass phases at high temperature with no emission. We should clarify mechanisms for SAD composition adjustment to lower the glass ceramics' melting point, AlN and salts transformed into alumina and glass phases respectively, and nucleation and crystal growth of glass ceramics at high temperature.