Effect of Sodium-Based Slag Treatment on the Distribution of Impurities in Metallurgical Grade Silicon

The distribution of impurities in metallurgical grade silicon before and after slag treatment was investigated for the purpose of upgrading metallurgical grade to solar grade silicon. It was found that metal impurities co-deposited with silicon and formed different intermetallics in the precipitated phase, and these intermetallics such as Si-Fe, Si-Ni, Si-Ti-V and Si-Ca-Al-Fe were substituted by Si-Fe-Ti-V after treatment of Na2CO3-SiO2 slag. Non-metallic impurities B and P were nearly homogeneous distribution in metallurgical grade silicon before and after slag treatment. Moreover, a particular analysis of the microstructure of slag has been carried out, it was determined that metal impurities Al and Ca could easily migrate from silicon to slag phase in the refining process.

Download Full-text

Effect of Na2O-SiO2 Slag Treatment on Hydrometallurgical Purification of Metallurgical Grade Silicon

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.420.139 ◽

2013 ◽

Vol 420 ◽

pp. 139-143 ◽

Cited By ~ 1

Author(s):

M. Fang ◽

C.H. Lu ◽

H.X. Lai ◽

L.Q. Huang ◽

J. Chen ◽

...

Keyword(s):

Comparative Analysis ◽

Acid Corrosion ◽

Intermetallic Phases ◽

Leaching Behavior ◽

Metallurgical Grade Silicon ◽

Metal Impurities ◽

Precipitated Phase ◽

Slag Treatment ◽

Corrosion Experiment ◽

Grade Silicon

The effects of Na2O-SiO2slag treatment on purification of metallurgical grade silicon by leaching with hydrogen fluoride have been investigated. A comparative analysis of microstructure evolution was carried out to examine the leaching behavior of impurities from metallurgical grade silicon. It was found that the distribution of metal impurities Al, Ca, Ti and Na, which co-deposited with Si and formed different intermetallic phases at grain boundaries, had manifest distinction between precipitated phase and silicon. Moreover, acid corrosion experiment results revealed that slag treatment improved the dissolution rate of metal impurities from metallurgical grade silicon as contrasted to that without slag treatment.

Download Full-text

Ca-Si Alloy Addition Followed by Acid Leaching as a Route to Solar-Grade Silicon

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.881-883.1562 ◽

2014 ◽

Vol 881-883 ◽

pp. 1562-1567

Author(s):

Peng Zou ◽

Kui Xian Wei ◽

Wen Hui Ma ◽

Ke Qiang Xie ◽

Ji Jun Wu ◽

...

Keyword(s):

Phosphorus Content ◽

Low Cost ◽

Acid Leaching ◽

Impurity Phase ◽

Solar Grade Silicon ◽

Metallurgical Grade Silicon ◽

Before And After ◽

Alloy Addition ◽

Grade Silicon ◽

Leaching Condition

In present, refining of metallurgical grade silicon is one of the promising routes to low-cost solar grade silicon for solar cells. Alloying with Ca has shown a great potential as efficient refining method of MG-Si in combination with acid leaching. Compared with Ca metal, Ca-Si alloy is cheaper and more secure. Great removal of impurity depends on microstructure of MG-Si after alloyed with Ca-Si alloy. In the work, the change of impurity phase which was performed by the change of the microstructure of MG-Si before and after alloyed with Ca-Si alloy has been analyzed. It was determined that CaSi2phase contained significant phosphorus content after alloying with Ca-Si alloy, It also investigated the optimal acid leaching condition after leaching, which confirmed that metallurgical grade silicon with Ca-Si alloy addition followed by acid leaching could be a potential route to remove phosphorus from MG-Si.

Download Full-text

Microstructural Characterization in Metallurgical Grade Silicon after Treatment by CaO-SiO2 and Na2O-SiO2 Slags

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.815.404 ◽

2013 ◽

Vol 815 ◽

pp. 404-408

Author(s):

Ming Fang ◽

Cheng Hao Lu ◽

Liu Qing Huang ◽

Hui Xian Lai ◽

Juan Chen ◽

...

Keyword(s):

Grain Boundaries ◽

Microstructural Characterization ◽

Metallurgical Grade Silicon ◽

Low Level ◽

Precipitated Phase ◽

Slag Treatment ◽

Grade Silicon

The microstructure and impurities distribution in metallurgical grade silicon with treated by CaO-SiO2 and Na2O-SiO2 slags were investigated. An exhaustive analysis of the transformation of precipitated phase at grain boundaries has been carried out. Prior to slag treatment, Si-Fe system intermetallic was the primary precipitated phase in metalllurgical grade silicon. After treated by CaO-SiO2 slag, Si-Ca system intermetallic became the main precipitated phase, such as Si-Ca, Si-Ca-Ti, Si-Ca-Al and Si-Fe-Ca. But Na2O-SiO2 slag had another result on refining metallurgical grade silicon; only Si-Fe-Ti phase was generated in precipitated phase and the low level of sodium in treated silicon was obtained.

Download Full-text

Removal of Impurities from Metallurgical Grade Silicon by Liquation Refining Method

High Temperature Materials and Processes ◽

10.1515/htmp-2012-0157 ◽

2013 ◽

Vol 32 (5) ◽

pp. 503-510 ◽

Cited By ~ 8

Author(s):

Jing-wei Li ◽

Zhan-cheng Guo ◽

Hui-qing Tang ◽

Jun-cheng Li

Keyword(s):

Eutectic Phase ◽

Metallurgical Grade Silicon ◽

Metal Impurities ◽

Separation Ratio ◽

Before And After ◽

Mass Fractions ◽

Removal Of Impurities ◽

Grade Silicon ◽

Considerable Loss ◽

Better Than

AbstractTo develop a new method of refining silicon for use in solar cell materials, liquation refining with Al-Si alloying was proposed for purification of metallurgical grade silicon (MG-Si). The morphologies of impurities, especially for phosphorus and iron, before and after purification were analyzed. By alloying MG-Si with Al, phosphorus in MG-Si formed Al-Si-Ca-P impurity phase and iron formed skeletal-shaped α-Al8SiFe2 phase into the Al-Si eutectic phase from MG-Si with the presence of Al. It can be concluded that removal mechanism of phosphorus and iron was not only a segregating process, but also a recombining process within certain elements to form specified impurity phases. By centrifugal separation, average separation ratio was 75.73% and average recovery ratio was 82.52% for Al-45%Si system, which is better than traditional separation methods and avoids considerable loss of Al and acid. After refining for four times, mass fractions of phosphorus and boron were reduced to 0.46 × 10−6 and 0.21 × 10−6 respectively. For transition metal impurities, Fe, Ti and Mn, removal fractions of those all were more than 95%.

Download Full-text

Comparison between slag refining processes for B removal with metallurgical grade silicon and Si–Sn alloy

Metallurgical Research & Technology ◽

10.1051/metal/2018047 ◽

2018 ◽

Vol 115 (3) ◽

pp. 312 ◽

Cited By ~ 3

Author(s):

Rowaid Al-khazraji ◽

Yaqiong Li ◽

Lifeng Zhang

Keyword(s):

Removal Efficiency ◽

Acid Leaching ◽

Experimental Results ◽

Mass Ratio ◽

Metallurgical Grade Silicon ◽

Clear Effect ◽

Slag Refining ◽

Before And After ◽

Grade Silicon ◽

Refining Processes

Boron (B) removal by slag refining using CaO–SiO2–CaCl2 was investigated in metallurgical-grade silicon (MG-Si) and 75 wt% Si–Sn alloy. Experiments were conducted at 1500 °C for 15 min. The microstructure was characterized before and after refining. The effects of acid leaching, basicity, and slag/Si mass ratio on B removal were investigated. Experimental results showed that acid leaching had no effect on B removal from MG-Si but had a clear effect on the refined Si–Sn alloy after slag refining. The final B concentration was highly affected by the CaO/SiO2 mass ratio with minimum value, where the content of B was reduced from 18.36 ppmw to 5.5 ppmw at the CaO/SiO2 = 1.2 for MG-Si slag refining and from 18.36 ppmw to 3.7 ppmw at CaO/SiO2 = 1.5 for 75 wt% Si–Sn alloy. Increasing the slag mass ratio by 2:1 mass ratio also increased B removal efficiency by approximately 15–20% more than an increase by 1:1.

Download Full-text