Silicon Powder Waste Research Articles

Promotion of silicon–oxygen control and green sustainable recovery from diamond wire saw silicon powder waste based on the viscous flow mechanism

Diamond wire saw silicon powder (DWSSP) waste is a highly promising secondary resource for recycling high-purity silicon, which is crucial for the sustainable development of the photovoltaic (PV) industry. However, because DWSSP is prone to oxidation, the purity and yield of the recovered silicon are generally low. In this study, the oxidation mechanism of DWSSP in water was systematically investigated, and kinetics analysis and microstructure analysis were conducted to determine the relationship between water diffusion and the growth of the oxide layer. The results indicated that oxidation was determined by the kinetic parameter b in the Reisman model. At T < 328 K and particle size > 1.56 μm, b was less than 1, indicating that the oxidation process was governed by the diffusion of H2O molecules. Through temperature regulation to achieve b < 1, the oxidation was inhibited, which could enhance recovery efficiency. Overall, this study demonstrated the feasibility of inhibiting oxidation by regulating the viscous flow of SiO2 molecules to promote the recycling of silicon resources and support sustainable development.

Investigation of the moisture classification and moisture removal behavior of diamond wire saw silicon powder waste cake

When processing silicon wafers for photovoltaic power generation, approximately 35 % of high-purity silicon is lost as a diamond wire saw silicon powder (DWSSP) waste cake with a high moisture content. The high moisture content of DWSSP results in the oxidation of high-purity silicon, which hinders the recovery and utilization of silicon resources. Disappointingly, a method for the removal of moisture from the DWSSP waste cake, which is crucial for silicon recovery, has not yet been revealed. In the present study, a novel investigation was conducted to determine the moisture classification of a DWSSP waste cake and to reveal the moisture removal behavior. The results indicate that the moisture content in the DWSSP waste cake can be divided into two distinct categories: surface adsorbed water and capillary water. Moreover, the kinetics analysis and simulation demonstrated that the elimination of moisture predominantly takes place during the constant-rate period and the falling-rate period. Increasing the drying temperature and reducing the equivalent diameter of the DWSSP waste cake will contribute to improving the efficiency of moisture removal. The application of the findings of this study can help to reduce the harmful environmental impacts of DWSSP and achieve the efficient recovery of silicon resources.

ZIF-67-derived porous nitrogen-doped carbon shell encapsulates photovoltaic silicon cutting waste as anode in high-performance lithium-ion batteries

The rapid development of the photovoltaic industry generates nearly 35 wt% micron-scale silicon powder waste in the form of a paste. This study reports the in-situ synthesis of ZIF-67 on the surface of low-cost silicon cutting waste. Submicron-scale porous cage-like silicon-based composites were obtained by carbonization. This hollow framework structure facilitated the large volume expansion/contraction of Si during charging/discharging. The porous nitrogen-doped carbon layer not only yielded rapid transport channels for Li+ and electrons but also improved the electrical conductivity of the material. In addition, the excellent pseudocapacitive performance of the Si@NC-ZIF composite also enhanced lithium storage. The composite exhibited excellent capacity retention of 1623.05 mAh/g after 100 cycles at 200 mA g−1, with the retention rate reaching 86.29 %. When the current was switched from 2000 to 100 mA g−1, the discharge capacity recovered to 1453.35 mAh/g, showing excellent rate performance. This study provides a new approach for the recycling and value-added utilization of photovoltaic silicon cutting waste in lithium-ion battery anodes.

Recovery of Ti-bearing blast furnace slag and diamond wire saw silicon powder waste by alloying and electromagnetic separation technique

Ti-bearing blast furnace slag (TBFS) and diamond wire saw silicon powder (DWSSP) waste are solid wastes that have been investigated by researchers. In this paper, the possibility of metal thermal reduction of TBFS is determined by calculating the component activities using the molecular interaction volume model (MIVM). The metal thermal reduction and electromagnetic separation technique was used to simultaneously recover titanium (Ti) and silicon (Si) from waste. DWSSP and Al were used as the reducing agents for the high-temperature reduction of TBFS in an induction furnace. The reduced Ti was alloyed with a small amount of Al and residual Si in DWSSP. The alloy and slag were separated by electromagnetic stirring because they were subjected to forces in opposite directions. The effects of CaF2 addition and holding time on the recovery rate of Ti were studied. It was found that the addition of CaF2 to the raw materials improved the separation of the alloy from the slag. Si and TiSi2 were the main phases in the recovered alloy. This simple process provides a new method to recover Ti and Si from TBFS and DWSSP.

Recovery and Purification of Silicon From Diamond Wire Saw Wasted Silicon Powder by a Technique of Induction Smelting Followed by Directional Solidification

A technique of induction smelting followed by directional solidification to recover and purify silicon from diamond wire saw waste silicon powder without the use of additives is presented herein. The silicon reaction and the effect of smelting time on the removal of impurities from silicon powder waste were investigated using a simple induction smelting and directional solidification method. Through the detection of byproducts and condensed volatiles, it is inferred that Si is volatilized and removed as silicon monoxide during smelting. Byproducts containing Si, SiC, or SiO2 phases can be generated by the reaction between silicon monoxide and graphite crucible after volatilization. Because the crucible is sealed with byproducts, the flow of volatile materials in the crucible disrupts the mass transfer balance in the silicon melt. The amount of residual impurities in silicon ingot trends downwards with the extension of smelting time. A 99 pct oxygen removal rate was obtained after the material was smelted three times. The silicon ingot achieved the lowest impurity content after smelting for 4 hours. The silicon powder waste can be potentially used as a metallurgical-grade silicon product after a simple one-step induction smelting process. Further purification of the silicon ingot by directional solidification can reduce residual impurities to 74 ppmw.

A new sustainable concept for silicon recovery from diamond wire saw silicon powder waste: Source control and comprehensive conservation

Metal impurities and SiO2 shell are two key components that must be eliminated for 6 N silicon remanufacturing from diamond wire saw silicon powder waste. Previous research on 6 N silicon recovery has focused more on metal impurity removal without paying sufficient attention to the relationship between metal impurities and the SiO2 shell, even though the surface oxidation of silicon particles is an important factor restricting metal removal. In this study, a novel investigation into the source of metal impurities and the SiO2 shell growth was conducted, combined with acid leaching and linear regression analysis to determine the relationship between the metal impurities and the SiO2 shell. The results indicated that both raw materials displayed strong negative correlations of -0.952 and -0.996 between the removal efficiency and the thickness of the SiO2 shell. And the Al, Fe, Ni, and Mg are more likely to be enriched in the SiO2 shell due to the improper management of metal contaminants and an increase in the O content in the waste stream. Furthermore, source control and comprehensive conservation are recommended for the efficient remanufacture of 6 N silicon. This study provides a new sustainable concept for silicon recovery from diamond wire saw silicon powder waste.

High-value recycling of photovoltaic silicon waste: Accelerated removal of impurity boron through Na3AlF6-enhanced slag refining

Recycling of environmentally hazardous silicon powder waste (SPW) is conducive to achieving “carbon neutrality”. However, the high-cost and low-efficiency impurity removal limit the industrial recovery of SPW. Herein, a combination strategy of vacuum sintering and Na3AlF6-enhanced slag refining is demonstrated to upgrade the traditional recycling process. The cost-effective vacuum sintering can remove 89.44% of oxygen in silicon waste, indicating that the oxide layer of SPW is removed effectively. In the Na3AlF6-enhanced CaO–SiO2 slag, the optimal Na3AlF6 content and CaO/SiO2 mass ratio are set to 20 wt% and 1.6 based on thermodynamic simulation. Na3AlF6 reduces the liquidus temperature and increases the interfacial tension of the slag system. Moreover, in Na3AlF6-containing slag, the diffusion pathway of BO33- is dredged. As a result, the silicon-slag interface is adjusted from a half-spherical to a cylindrical surface, and the interface area has increased by 14.69%. The boron removal rate by Na3AlF6-strengthened slag refining is 40.92% faster than that of traditional slag. This work improves the removal efficiency of key impurity boron, reducing the cost of SPW recovery. Based on economic evaluation, this strategy offers a commercially available way to achieve the high-value recycling of silicon waste.

Silicon recycling and iron, nickel removal from diamond wire saw silicon powder waste: Synergistic chlorination with CaO smelting treatment

During the processing of silicon wafers for photovoltaic power generation, nearly 30–40% of silicon ingot will be lost as diamond wire saw silicon powder (DWSSP) waste; this can result in reduced profits, potential danger, and environmental pollution. Driven by the rapid development of the photovoltaic industry, the demand for high-purity silicon and the production of silicon waste generated during silicon processing will continue to increase. Againstthistrend, the recycling of silicon from DWSSP waste is a desirable alternative to meet the growing demand for high-purity silicon. In this study, a novel process of chlorination with CaO smelting treatment is first proposed for the recycling of silicon and the removal of Fe and Ni from DWSSP waste. The results of this research indicate that the SiO2 shell can be absorbed by the added CaO, while eutectic NaCl-MgCl2 has a significant effect on the maximum recovery of silicon by reducing the viscosity of the molten slag and the removal of metals through the micro concentration cells. CaO and eutectic NaCl-MgCl2 play a synergistic role in the promotion of silicon separation and the removal of Fe and Ni. Silicon with a purity of 99.83% and a recovery rate of nearly 98.96% was obtained under the smelting conditions of DWSSP:CaO:NaCl:MgCl2 = 150.0:23.42:7.50:8.85 with a holding time of 2 h at 1823 K. This process overcomes the technical bottleneck of the removal of Fe and Ni via smelting treatment, which is favorable for the recycling of silicon from DWSSP waste at the industrial scale.

Al2O3 and CaO as sintering aids: A strategy to remove impurity boron and SiO2 surface-layer of diamond wire saw silicon waste

Removing the SiO2 surface-layer and impurity boron in diamond wire saw silicon powder waste (DWSSP) are two difficulties in the field of photovoltaic waste recycling. Aiming at the two difficulties, this paper proposes a method of mixing sintering aids to digest the SiO2 layer and remove impurity boron. Firstly, sintering aids Al2O3 and CaO were mixed into DWSSP, and DWSSP-ceramics were prepared by pressure-less sintering. The mixed sintering aids reacted with the SiO2 surface-layer of DWSSP, and the formed liquid slag phase plays a role in promoting the densification of DWSSP-ceramics (the relative density reached 85.97% when sintered at 1300 °C). Secondly, to obtain low-boron silicon, the slag phase was separated from DWSSP-ceramics by smelting treatment. The results showed that an optimal boron removal effect of 45.32% was reached after only 10.11 wt% sintering aids were mixed into DWSSP. The mechanism that the liquid slag phase gathered impurity boron during the sintering process, and then promoted boron to remove from silicon was reasonably deduced. The method of mixing sintering aids to remove the SiO2 surface-layer and impurity boron provides a novel insight into purification and recovery of DWSSP.

Ultrasound-Assisted Leaching of Iron from Silicon Diamond-Wire Saw Cutting Waste

Iron removal from silicon powder waste by ultrasound-assisted leaching has been investigated and the leaching conditions optimized to an ultrasonic frequency of 80 kHz, ultrasonic power of 270 W, temperature of 60°C, and sulfuric acid concentration of 12%, achieving an iron removal fraction of 95.24%. The maximum iron removal fraction was obtained after 80 min of leaching without ultrasound, whereas ultrasound-assisted leaching could achieve the same removal fraction after 50 min under the same conditions. The dissolution of iron is a two-step process and follows a homogeneous control model with a second-order rate-controlling step. With the aid of ultrasound, the reaction rate constants khs increased from 0.0677–0.0995 to 0.0792–0.1914 and from 0.0285–0.1086 to 0.0399–0.1422 in the first and second leaching stage, respectively. This increase of the khs values further supports the enhancement induced by the application of ultrasound.

Application of Pressure-less Sintering and Dynamic-Slag Treatment to Recover Diamond Wire Saw Silicon Powder

Recycling silicon from environmentally hazardous diamond wire saw silicon powder waste (DWSSP) and effectively removing boron is still an elusive aim. Here, pressure-less sintering and dynamic-slag...

Investigation of Na2CO3–CaO–NaCl (or Na3AlF6) additives for the remanufacturing of silicon from diamond wire saw silicon powder waste

The demand for high-quality silicon for solar cell preparation will continue to grow due to shortages of silicon feedstock driven by the photovoltaic industry. Consequently, the silicon lost in diamond wire saw silicon powder waste during silicon wafer production must be recovered for silicon production. Depending on the current yield of silicon and level of residual impurities, an optimization treatment for the increase of the recovery rate and purity of silicon collected from diamond wire saw silicon powder should be further developed. In this study, NaCl and Na3AlF6 are designed as additives to optimize Na2CO3–CaO to increase the silicon recovery rate and purity. The action mechanisms of NaCl and Na3AlF6 for silicon recovery and the removal of metal during the direct smelting process are investigated. It is found that NaCl and Na3AlF6 improve the silicon migration channels and stabilize the impurities in slag by reducing the slag viscosity and tuning the slag composition. After induction smelting at 1823 K for 2 h with the furnace feed mass ratios of Na2CO3:CaO:NaCl = 12.8:1.7:8.6 and Na2CO3:CaO:Na3AlF6 = 12.8:1.7:8.6, the obtained silicon recovery rates were respectively 76.39% and 79.25%, and the silicon purities were respectively 99.985% and 99.986%. Therefore, NaCl and Na3AlF6 could be used as potential additives to promote the efficient remanufacturing of silicon collected from diamond wire saw silicon powder waste, and are technically and economically feasible for large-scale application.

Silicon recovery from diamond wire saw silicon powder waste with hydrochloric acid pretreatment: An investigation of Al dissolution behavior

Silicon recovery from diamond wire saw silicon powder (DWSSP) waste is of great significance for increasing production profits and alleviating hazardous effects on the ecological environment. The purity of recovered silicon powder is determined by the purification efficiency during acid leaching pretreatment. Because the metallic impurities present in DWSSP are mostly physically mixed rather than chemically bound, the reaction rate is very fast in the initial stage of acid leaching, whereas it is difficult to dissolve the retained impurities in the later stage with the depletion of metal fragments adhered on the surface of the silicon matrix. Many prior studies have failed to consider the retained metallic impurities that reside in the inner silicon particle surfaces. Therefore, this study investigates the dissolution behavior of retained impurities via the dissolution of Al in HCl solution as an example. Thermodynamic results indicate that the Al dissolution process is dominated by entropic changes (ΔS0), rather than enthalpic changes (ΔH0). Furthermore, the dissolution behavior of Al is in accordance with the diffusion-controlled step in the Avrami mode, and the kinetic parameters were found to be A=5.85×107, Ea=49.27kJ·mol-1, and m<1. The determined dissolution behavior provides a clear understanding of the removal of retained metallic impurities from DWSSP via an acid leaching pretreatment. This study provides enlightenment for the further purification of silicon recovered from DWSSP waste.

Recycling high-purity silicon from diamond-wire saw kerf slurry waste by vacuum refining process

Approximately 35%–40% crystalline silicon becomes silicon powder waste (SPW) when producing silicon wafers. Substantial amount of SPW will be produced as the demand for wafers increases. Recycling Si from SPW for preparing silicon has been a significant issue. Considering the current recovery ratio of SPW is low, it is urgent to investigate an effective method to recycle SPW. In this paper, SPW was re-melted into high-purity silicon ingots by vacuum refining process and the recycling process involved two stages. In the first stage, SPW was pelletized by a double-roll type presser. In the second stage, the pellets were melted into high-purity silicon ingots by vacuum refining. The effects of the smelting time and atmosphere condition on the silicon recovery ratio, and the influence of the smelting time on impurities removal ratio were investigated. The maximum silicon recovery ratio could be increased from 56.5% by atmosphere smelting to 68.65% by vacuum smelting. Si ingots with a purity of 99.65%, B 0.21 ppmw and P 3.03 ppmw were prepared. The melting mechanism of the silicon powder and economical evaluation were also discussed in this paper. The recovery of SPW by vacuum refining can not only realize resource reutilization but also bring about economic benefits ($0.406/kg) at laboratory-scale.

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

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 occurren...

Novel Reaction Media of Na2CO3–CaO for Silicon Extraction and Aluminum Removal from Diamond Wire Saw Silicon Powder by Roasting–Smelting Process

Exploring a sustainable process to dispose diamond wire saw silicon powder (DWSSP) waste produced in the solar crystal silicon wafering process is a research field with significant theoretical rese...

Remanufacturing of silicon powder waste cut by a diamond-wire saw through high temperature non-transfer arc assisted vacuum smelting.

Non-transfer arc assisted vacuum smelting technology is presented for the first time to recycle harmful silicon powder waste derived from diamond-wire cutting. The final yield and filling rate of silicon could reach 93.9% and 73%, respectively. The oxidation characteristics of silicon powder waste, formation mechanism of a hollow silicon block and removal efficiency of impurities were analyzed in detail to offer profound insights into a non-transfer arc granulation method. The critical conditions for continuous and efficient preparation of a solid silicon block were further confirmed through orthogonal experiments with 7.5 kW welder output power, 3 mm vertical scanning height, and 5 mm/s scanning speed. The yield of the silicon block was more than 96%. Meanwhile, the granulating process demonstrated a favorable effect on removing most impurities, such as C, Al, and Na, without introducing any other impurities. The residual impurities could be further removed by vacuum directional smelting. Given the extremely low equipment cost and huge room for improvement, this work is crucial for large-scale recovery of silicon powder waste.

Study on the kinetics of iron removal from silicon diamond-wire saw cutting waste: Comparison between heterogeneous and homogeneous reaction methods

Silicon powder waste (SPW) from diamond-wire saw cutting process has a very low content of boron and phosphorus. Therefore, it is a promising and precious raw material for producing SoG-Si. The SPW also contains iron impurities which were from the worn of cutting wire during the silicon wafer producing process. Since the presence of iron will affect the quality of the silicon products, it is essential to remove the iron from SPW. In this paper, the removal of iron from SPW by acid leaching was researched and its kinetics were investigated by the heterogeneous and homogeneous reaction methods. Diluted sulfuric acid was selected as the leaching agent. The leaching parameters were optimized, i.e., temperature 60 °C, acid concentration 12%, liquid-solid ratio 10 mL/g and stirring speed 200 rpm. Under the optimized conditions, the removal rate of iron could reach 94.34%. It was found that the iron removing process can be divided into two stages. In both of the stages, the leaching process was controlled by second order rate of homogeneous reaction model, and the activation energy are 10.78 kJ/mol and 35.97 kJ/mol, respectively.

Recycling of silicon powder waste cut by a diamond-wire saw through laser-assisted vacuum smelting

This paper proposes laser granulating technology for recycling harmful silicon powder waste cut by a diamond-wire saw. The silicon block produced by laser was easily melted in a traditional vacuum smelting furnace to form a silicon ingot with a high yield and filling rate, which could reach up to 94.7% and 65.7%, respectively. The removal efficiency of the carbon contamination was 74.2% during laser melting process and reached 86% after 30 min of vacuum smelting. In addition, laser melting process promoted the removal of most metal impurities, such as Al, Na, Ca, Mg, and so on, in the silicon powder waste without introducing any other impurities. The residual impurities could be further removed by vacuum smelting. The experiment revealed that the out capacity of the silicon block melted by a single laser gun was 1.91 kg/h, the energy consumption of laser melting was 2.63 kWh/kg, and the yield of the silicon block exceeded 97% at a laser power of 2000 W, a laser scanning interval of 5 mm, and a scanning speed of 6 mm/s. Therefore, the proposed approach is one of the most simple and efficient silicon powder waste pretreatment methods.

An Economical Approach for the Recycling of High-Purity Silicon from Diamond-Wire Saw Kerf Slurry Waste

Large amounts of solar-grade silicon were wasted as silicon powder waste (SPW) during the diamond-wire saw slicing process. In this paper, the SPW was purified by acid leaching, and the purified SPW was pelletized. Then the pellets were melted in induction furnace in air atmosphere to produce high-purity silicon ingots. Firstly, the SPW as raw material was characterized. The results show that the particle size of the powder is mainly in the range of 0.14 $\sim $ 8.71 μm, the powder has a shape of thin flake, the contents of SPW are Si 83.99 wt%, silicon oxide 13.5 wt%, others 2.51 wt%, of which B (boron) 0.2 ppmw, P (phosphorus) 4.32 ppmw, and metallic impurities 16412 ppmw, respectively. Secondly, the SPW was purified by acid leaching and the leaching parameters were optimized, i.e. leaching time 80 min, temperature 60°, acid concentration 25%, liquid-solid ratio 10 mL/g and agitation speed 200 rpm. Thirdly, the purified SPW was pelletized and then melted in induction furnace in air atmosphere. High-purity silicon ingots with Si 99.99%, B 0.16 ppmw and P 1.1 ppmw were produced. The slag mainly consists of 48.63 wt% Si, 43.51 wt% SiO2 and 7.86 wt% SiC. The high-purity silicon ingots can be used to produce aluminum silicon alloy and silicon nitride. And it is prospective to use the high-purity silicon ingots as the feedstock to produce solar grade silicon (SoG-Si).