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

Zhanbing Li; Huiquan Li; Xingzhong Huang; Wenfen Wu; Zhenhua Sun; Xiuwen Wu; Shaopeng Li

doi:10.1016/j.heliyon.2023.e12893

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

Heliyon. 2023 Jan 9;9(1):e12893. doi: 10.1016/j.heliyon.2023.e12893. eCollection 2023 Jan.

Authors

Zhanbing Li^{1

2}, Huiquan Li^{2

3}, Xingzhong Huang^{2

3}, Wenfen Wu², Zhenhua Sun², Xiuwen Wu¹, Shaopeng Li²

Affiliations

¹ School of Science, China University of Geosciences Beijing, Beijing 100083, China.
² National Engineering Research Center of Green Recycling for Strategic Metal Resources, CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China.
³ School of Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049, China.

Abstract

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.

Keywords: Aluminum nitride; Catalytic hydrolysis; Fluoride; Response surface experiment; Secondary aluminum dross.