Recycling of silicon from silicon cutting waste by Al-Si alloying in cryolite media and its mechanism analysis. (October 2020)

• Record Type: Journal Article
• Authors: Wei, Donghui; Kong, Jian; Gao, Shuaibo; Zhou, Shibo; Jin, Xing; Jiang, Shengnan; Zhuang, Yanxin; Du, Xinghong; Xing, Pengfei
• Is Part Of: Environmental pollution. Volume 265(2020)Part A
• Publication Date: 2020-10
• Subjects: Silicon cutting waste -- Silicon recovery -- Cryolite -- Al-Si alloying Process -- Mechanism; Pollution -- Periodicals; Pollution -- Environmental aspects -- Periodicals; Environmental Pollution -- Periodicals; Pollution -- Périodiques; Pollution -- Aspect de l'environnement -- Périodiques; Pollution -- Effets physiologiques -- Périodiques; Pollution; Pollution -- Environmental aspects; Periodicals; Electronic journals; 363.73
• DOI: 10.1016/j.envpol.2020.114892
• Languages: English
• ISSNs: 0269-7491

Abstract

Abstract: More than 40% of the crystalline silicon has been wasted as silicon cutting waste (SCW) during the wafer production process. This waste not only leads to resource wastage but also causes environmental burden. In this paper, SCW produced by the diamond-wire sawing process was recycled by Al-Si alloying process. Cryolite was introduced to the reaction system to dissolve the SiO2 layer existed on the surface of the Si particles in SCW. Alloys with 12.02 wt% of Si were prepared and the mechanism of the alloying process was investigated in detail. The Si-Al-cryolite system and SiO2 -Al-cryolite system were studied individually to analyze the reaction process and transferring behavior of Si and SiO2 in SCW. The SiO2 shell was firstly transformed into Si-O-F ions. Then the Si-O-F ions diffused to the reaction interface by the effect of the concentration gradient and were reduced to Si by the aluminothermic reduction reaction: 4Al (l) + 3SiO2 (dissolved in the melt) = 3Si (Al)+ 2Al2 O3 (dissolved in the melt). Then the internal Si particles were released into cryolite after the dissolution of SiO2 and transferred to the reaction interface by the effect of gravity. The influences of the mass ratio of Al/SCW and agitation modes on the Si content of the alloys and the Si recovery ratio in SCW were investigated. With the increase of the mass ratio of Al/SCW from 2.2 to 6.5, the Si recovery ratio in SCW increased from 44.08% to 69.05%, but the silicon content of the alloys decreased from 16.06 wt% to 8.83 wt%. Agitation can effectively improve the smelting effect during smelting by which the silicon content of the alloys and the Si recovery ratio in SCW increased from 12.02 wt% and 64.25% to 13.17 wt% and 69.46%, respectively. Graphical abstract: Image 1 Highlights: Both Si and SiO2 in SCW were recycled by a new Al-Si alloying process. Cryolite was used as a media in the alloying process. The mechanism of the alloying process was investigated in detail. The recycling process is simple, effective and environment friendly.