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

Removal of nitrides and fluorides from secondary aluminum dross by catalytic hydrolysis and its mechanism

Secondary aluminum dross (SAD) refers to hazardous waste from secondary aluminum refinement. It contains a large amount of aluminum nitride and fluorides that cause serious environmental pollution for direct discharge and hinder the resource utilization of SAD. However, it is difficult to remove nitride and fluoride simultaneously for their complicated phases. In this paper, the catalytic hydrolysis of SAD using NaOH as a catalyst to remove nitrides and fluorides synchronously was investigated systemically through single factor and response surface experiments. In addition, the chemical speciation and transformation of nitrides and fluorides were analyzed systematically. The catalytic hydrolysis removal mechanism was summarized. The optimal conditions for catalytic hydrolysis were established as follows: reaction temperature 96.60 °C; reaction time 2.85 h; liquid-solid ratio 9.28 mL/g and catalyst addition 12.62 wt %; and removal efficiency of nitrides and fluorides reached 99.03% and 81.93%, respectively. The mechanism of nitrides removal was that aluminum nitride was hydrolyzed to Al(OH)₃ and NH₃. NaOH reacting with Al(OH)₃ covering on the surface of AlN and the rapid escape of NH₃ promoted the hydrolysis of AlN under the catalysis of NaOH. The mechanism of fluorides removal was that the encapsulated fluoride particles were opened by catalytic hydrolysis to be dissolved in the solution. In this research, nitrides and fluorides were removed efficiently and synchronously. The hydrolysis residues can be used to prepare polyaluminum chloride (PAC) and ceramic materials. The hydrolysate can be prepared NH₃·H₂O by evaporative in alkaline solution. Then the solution without NH₄ ⁺ was prepared Al(OH)₃ by precipitation of adjusting pH value using HCl. And the remained liquid after removing NaAlO₂ was used to prepare refining agent by evaporative crystallization. The work in this paper was beneficial for the utilization of SAD.

Effects of Sodium Carbonate and Calcium Oxide on Roasting Denitrification of Recycled Aluminum Dross with High Nitrogen Content

Aluminum dross is solid waste produced by the aluminum industry. It has certain toxicity and needs to be treated innocuously. The effect of sodium carbonate and calcium oxide on the denitrification efficiency of high nitrogen aluminum dross roasting was studied in this paper. By means of XRD, SEM and other characterization methods, the optimum technological parameters for calcination denitrification of the two additives were explored. The test results show that both additives can effectively improve the efficiency of aluminum dross roasting denitrification, and the effect of sodium carbonate is better. When the mass ratio of sodium carbonate to aluminum dross is 0.6, the roasting temperature is 1000 °C and the roasting time is 4 h, the denitrification rate can reach 91.32%.