Preparation of Sintered Brick with Aluminum Dross and Optimization of Process Parameters

Experimental Study on the Preparation of High-Purity Iron Oxide Red by Acid Leaching Iron from Coal Gangue

Aiming at the problems of the large storage, complex composition, low comprehensive utilization rate, and high environmental impact of coal gangue, this paper carried out experimental research on the preparation of iron oxide red from high-iron gangue by calcination activation, acid leaching, extraction, and the hydrothermal synthesis of coal gangue. The experimental results show that when the calcination temperature of coal gangue is 500 °C, the calcination time is 1.5 h, the optimal concentration of iron removal is 6 mol/L, the acid leaching temperature is 80 °C, the acid leaching time is 1 h, and the liquid--solid mass ratio is 4:1; the iron dissolution rate can reach 87.64%. A solvent extraction method (TBP-SK-hydrochloric acid system) was used to extract the leachate, and a solution with iron content up to 99.21% was obtained. By controlling the optimum hydrothermal conditions (pH = 9, temperature 170 °C, reaction time 5 h), high-purity iron oxide red product can be prepared; the yield is 80.07%. The red iron oxide was characterized by XRD, SEM-EDS, particle-size analysis, and ICP-OES. The results show that the red iron oxide peak has a cubic microstructure, an average particle size of 167.16 μm, and a purity of 99.16%. The quality of the prepared iron oxide red product meets the requirement of 98.5% of the "YHT4 Iron oxide Standard for ferrite". It can be used as a raw material to produce high-performance soft magnetic ferrite. In summary, this experimental study on the preparation of iron oxide red from coal gangue is of great significance for the comprehensive utilization of coal gangue to realize the sustainable development of the environment and economy.

Effects of Hydrolysis Parameters on AlN Content in Aluminum Dross and Multivariate Nonlinear Regression Analysis

Aluminum dross, as a hazardous waste product, causes harm to the environment and humans, since the AlN it contains chemically reacts with water to produce ammonia. In the present study, a formula for modifying the AlN content in aluminum dross is proposed for the first time, by investigating the components of aluminum dross and changes in their respective contents during the hydrolysis process. Meanwhile, the effects of such hydrolysis parameters as time, temperature, and rotational speed on the hydrolysis rate of aluminum dross are explored. Furthermore, regression analysis is performed on the hydrolysis parameters and objective functions. The results show that as the reaction time increases, the variation in AlN content in aluminum dross decelerates gradually after modification. The hydrolysis rate is the fastest in the initial 4 h, which essentially stagnates after 20 h. The rise in temperature can significantly accelerate the AlN hydrolysis in aluminum dross, while the rotational speed has a non-obvious effect on the hydrolysis rate of AlN in aluminum dross. Regression analysis and secondary simplification are performed on the hydrolysis parameters and the modified AlN content, revealing that the relative error between the theoretical and experimental values is ≤ ±9.34%. The findings of this study have certain guiding significance for predicting and controlling modified AlN content in aluminum dross during hydrolysis.

Formulation of Non-Fired Bricks Made from Secondary Aluminum Ash

The secondary aluminum ash is the black slag left after the primary aluminum ash is extracted from the metal aluminum. To address the environmental pollution and resource waste caused by the accumulation and landfill of aluminum ash, this study fabricated non-fired bricks by using secondary aluminum ash as the principal raw material, which was supplemented by cement, slaked lime, gypsum and engineering sand. The effects of mix proportions of various admixtures on the mechanical properties of non-fired bricks were investigated, and on this basis, the hydration mechanism was analyzed. The results showed that the mix proportions were 68.3% aluminum ash, 11.4% cement, 6.4% slaked lime, 4.2% gypsum and 9.7% engineering sand. The compressive strength of the fabricated bricks reached 22.19 MPa, and their quality indicators were in line with the MU20 requirements for Non-fired Rubbish Gangue Bricks. Evident hydration reaction occurred inside the non-fired bricks, with main products being calcium silicate hydrate (CSH), calcium aluminate hydrate (CAH) and ettringite (AFt). Besides, a dense structure was formed, which enhanced the brick strength.