Dissolution and mineralization behavior of metallic impurity content in diamond wire saw silicon powder during acid leaching

Self Cite

With the shortage of high-grade silicon (Si) feedstock due to the rapid development of photovoltaic, electronic information, and organic Si industries, there is an increasing demand to recycle Si waste economically and efficiently. However, the deep removal of B and P from Si has always been a significant challenge for Si waste recycling. A novel application of electroslag remelting (ESR) refining has been developed to remove B and P for the purification and recovery of Si. In addition, industrial tests were performed to recover the diamond wire saw Si powder. The design principle is put forward for the Si alloy electroslag system. A new 35% CaO−30% CaF 2 −17.5% Al 2 O 3 −17.5% SiO 2 electroslag applicable for Si alloy ESR is designed to meet both physical and impurity removal requirements. Furthermore, the conductivity (2.67 Ω −1 •cm −1 ), density (2.97 g/cm 3 ), and viscosity (0.05 Pa•s) meet the requirements of ESR. The dynamic refining process of Si alloy passing through the slag layer in the droplet form is the core of ESR refining, and it is found that more than 80% of B and P removal is achieved in the dynamic refining process of the droplet penetration slag. In order to understand the dynamic refining process, the mathematical model of droplet movement and impurity removal model are proposed to study the droplet movement behavior in slag and the competitive influence mechanism of multiple parameters on B removal efficiency during the dynamic refining process. Mathematical models and experimental results show that there is an ultimate velocity of droplet entry into the slag, which increases linearly with the growth of droplet size under the same slag condition. In addition, the specific surface area of the droplet plays a dominant role in the removal of B. The successful industrial experiments of Si alloy ESR prove that the design principle of the Si alloy electroslag system and the size control mechanism of Si alloy are feasible in this work. The removal efficiency of B and P reached 80 and 65%, respectively, within 30 min. It is also believed that ESR will have an application in purification and recovery of Si waste.

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Novel Application of Electroslag Remelting Refining in the Removal of Boron and Phosphorus from Silicon Alloy for Silicon Recovery

Qian

Sun

Wang

et al. 2021

Self Cite

“…The second view speculates that Ni debris present in DWSSP might be buried in the oxide layer, thus making the removal of oxide necessary to dissolve the Ni impurities . Although there is no direct evidence to support this idea, acid leaching results have demonstrated that the surface oxidation of the amorphous SiO 2 layer hinders the removal of metal impurities during the acid leaching process …”

Section: Introductionmentioning

confidence: 95%

Occurrence State and Dissolution Mechanism of Metallic Impurities in Diamond Wire Saw Silicon Powder

Yang

Wan

Wei

et al. 2020

Self Cite

The facilitation of metallic impurities removal via acid leaching pretreatment plays a key role in silicon recovery from diamond wire saw silicon powder (DWSSP) waste. Disappointingly, the occurrence state and dissolution mechanism of the metallic impurities present in DWSSP have not yet been revealed. For this reason, in this study, three different kinds of raw DWSSP were used for acid leaching tests and leaching behavior verification to investigate the dissolution mechanism. After two-stage acid leaching with 4 M HCl and 2 M HCl + 2.5 M HF, the results indicate that the removal efficiency was superior to that of other previously reported leaching processes. Furthermore, two occurrence states of metallic impurities present in DWSSP were defined based on their different dissolution behaviors, and the intrinsic relationship between dissolution behavior and the thinning process of the amorphous SiO2 shell was derived. The findings indicate that the first type of impurity was more easily dissolved in HCl solution; however, the second type of retained metallic impurity was restricted by the SiO2 shell barrier and was removed by the added HF solution. For this reason, the disintegration dissolution of the amorphous SiO2 shell was found to have a significant impact on the facilitation of the removal of impurities retained in DWSSP. The findings of this study are significant for the recovery of silicon from DWSSP with an effective acid leaching flow design.

“…12 In addition, when the impurity concentration drops to a certain level, the impurity transfer and reaction driving force are small; thus, the separation efficiency would be significantly reduced. 13 Therefore, ensuring the simultaneous and efficient removal of lowconcentration impurities is the key to upgrading metallurgical purification technology.…”

Section: Introductionmentioning

confidence: 99%

“…For example, the partition coefficient of B and P in the slag refining process is usually less than 10, , and the segregation coefficient of B and P in the solidification segregation process is close to 1 . In addition, when the impurity concentration drops to a certain level, the impurity transfer and reaction driving force are small; thus, the separation efficiency would be significantly reduced . Therefore, ensuring the simultaneous and efficient removal of low-concentration impurities is the key to upgrading metallurgical purification technology.…”

Section: Introductionmentioning

confidence: 99%

Enhanced In Situ Separation of Boron at the Silicon Alloy Solidification Interface through Innovating the Impurity Chemical Reconstruction Approach for SoG-Si

Qian

Zhou

et al. 2021

Self Cite

Removal of trace impurities such as boron (B) and phosphorus (P) has always been a challenge for the preparation of solar-grade silicon (SoG-Si). Chemical reconstruction has been thought to be an effective way to remove trace impurities by changing the phase structure and location of impurities. The traditional way of the chemical reconstruction of impurities at the grain boundary after solidification inevitably relies on the subsequent separation of crystalline Si and chemical reconstruction medium. Thus, we develop a new method for the chemical reconstruction of B at the front of the solidification interface of the Si alloy, which provides advantages for the in situ separation of the reconstructed impurity phase in the supergravity filtration separation process. The chemical reconstruction of B at the solidification front of the Si alloy has been realized by adding 25–75% of the liquation agent aluminum (Al) and about 10 000 ppm of the impurity modifier agent titanium (Ti) with the help of Thermo-Calc thermodynamic calculation and experimental verification. The influence mechanism of the supergravity field on the precipitation behavior of the chemically reconstructed phase TiB2 is revealed by the derived Maxwell–Stefan (MS) equation under the action of the supergravity field. A special filter-type combined crucible is skillfully designed and strictly controlled to cool the crucible containing the alloy melt at a constant temperature gradient under the supergravity field to achieve in situ separation of impurities at the solid–liquid interface of the Si alloy. The chemical reconstruction phase TiB2 is mainly retained on the surface of crystalline Si during the process of supergravity centrifugal filtration, which is more suitable for the deep removal of the B impurity and B content in Si drops below 1.5 ppm by simple pickling. In addition, the Si–Al–(Ti) alloy with a small amount of impurities obtained after centrifugal filtration separation can be further used for the chemical reconstruction of impurities, and the recycling of chemical reconstruction medium has been achieved. The present work proposes a new idea of chemical reconstruction of impurities at the front of alloy solidification and in situ separation, which expands the way of in situ separation of trace impurities at the solid–liquid interface of the alloy.