Silicon Kerf Research Articles

A novel strategy for recovery of heavy metals and synthesis of Co-rich alloy from the alkali-treated tungsten residue using photovoltaic silicon kerf waste

The treatment of spent cemented carbides using the conventional alkali-acid leaching process results in the generation of hazardous solid waste tungsten leaching residue. This study proposed an alternative process using the alkali-treated tungsten leaching residue (AW-residue) without the acid leaching step, preserving Co in the residue. By using photovoltaic silicon kerf waste (SKW) as a reducing agent, heavy metals (Co, Ni, W, Nb, and Ta) were efficiently extracted from AW-residue and a Co-rich alloy was obtained. The silicothermic reduction process facilitated the recovery of iron group metals (Co, Ni, and Fe) and effectively captured trace refractory metals (W, Ta, and Nb). Phase separation occurred through reduction reaction and viscosity-driven processes between the Co-rich alloy and the slag. Optimal conditions were identified as 20% SKW addition, MgO crucible, and a holding time of 120 min, achieving a total recovery yield of 95.5%, with specific yields for Co (97.7%), Ni (97.0%), W (82.5%), Nb (76.3%), and Ta (70.5%). A 20 kg pilot-scale experiment confirmed the feasibility of the process, yielding 47.0% Co-rich alloy from AW-residue compared to 48.3% in lab-scale experiment, and producing a harmless slag phase. This environmentally friendly approach promotes sustainable recycling of valuable metals in the tungsten industry.

Scalable Synthesis of a Si/C Composite Derived from Photovoltaic Silicon Kerf Waste toward Anodes for High-Performance Lithium-Ion Batteries

Scalable Synthesis of a Si/C Composite Derived from Photovoltaic Silicon Kerf Waste toward Anodes for High-Performance Lithium-Ion Batteries

Silicon kerf loss as a potential anode material for lithium-ion batteries

In this work, industrially processed silicon kerf loss (abbreviated to silicon kerf) from the photovoltaic industry is assessed as an anode material for the lithium-ion battery (LIB). The study includes both a characterization of processed silicon kerf from different sources and a comparison with commercially available nano-sized silicon (40 and 100 nm) in electrochemical testing. Such a direct comparison between these two silicon types in electrochemical testing provides a new insight into silicon kerf as an anode material. The silicon kerf particles are flake-like with varying lengths, with a mean particle size (d50) measured to ∼700 nm and a dimension of thickness of a few tens of nanometers. However, the specific surface area ranging from 20 to 26 m2/g is comparable to that of a silicon material of size ∼100 nm. The silicon oxide layer surrounding the particles was measured to 1–2 nm in thickness and, therefore, is in a suitable range for the LIB. In terms of electrochemical performance, the silicon kerf is on par with the commercial nano-sized silicon, further supporting the size evaluation based on the specific surface area considerations. Initial discharge capacities in the range 700–750 mAh/g (close to the theoretical value for the 12 wt% Si mixture with graphite) and first cycle efficiencies of 86%–92% are obtained. The cycling stability is comparable between the two materials, although the differential voltage analysis (DVA) of the galvanostatic data reveals that only the silicon kerf samples maintain silicon activity beyond 120 cycles. This study shows that industrially processed silicon kerf has characteristics similar to nano-sized silicon without reducing the size of the silicon kerf particles themselves. Considering its low carbon footprint and potentially lower cost, it can thus be an attractive alternative to nano-sized silicon as an anode material for the LIB industry.

Recycled solar-grade silicon kerf scraps and sandwiched by tunable porous carbon sheets as commercial anodes

To commercialize silicon/carbon (Si/C) anodes easy, the solar-grade silicon kerf scraps (SGSKS) abandoned from photovoltaic industry are purified and recycled as a cost-efficient silicon source for lithium storage. However, limited by commercial cathodes, pursuing good structural integrity and durable lifespans is more worthy of concern than super-high capacity for commercial Si/C anodes which is primarily impacted by silicon mass fraction and volume vibration tolerance. Hence, controlling silicon mass loading and providing sufficient void spaces for volume vibration are significant for the high-grade Si/C anodes. Herein, a highly-tunable and facile synthesis approach for Si/C composite sandwiched by porous carbon sheets (PCS/Si) is described using flake-like CaCO3 as template and SGSKS as raw materials. Through regulating the mass ratio of CaCO3 and silicon, it can effectively control silicon mass loading and void spaces in PCS/Si for strengthening structural integrity, prolonging lifespans, simultaneously achieving sufficient capacity to meet commercial demands. The experimental findings demonstrate that benefitting from this deliberate design, the optimized PCS/Si-2 composite with silicon mass loading of 30.62 wt% delivers a high-profile capacity retention of 853.4 mAhg−1 at 0.2 Ag−1 with a relatively good structural integrity. Moreover, full cells using PCS/Si-2 anodes matched with commercial LiCO2 cathodes exhibit a long-cycle steady capacity of 103.4 mAhg−1 at 0.2 C which also can light a row of LED bulbs for hours, facilitating a rosy potential for commercial application. Meanwhile, it offers an alternative and valuable viewpoint for high-value recycle and reutilization of photovoltaic waste, promoting resource conservation and environment protection.

Photovoltaic Wafering Silicon Kerf Loss as Raw Material: Example of Negative Electrode for Lithium‐Ion Battery**

AbstractSilicon powder kerf loss from diamond wire sawing in the photovoltaic wafering industry is a highly appealing source material for use in lithium‐ion battery negative electrodes. Here, it is demonstrated for the first time that the kerf particles from three independent sources contain ~50 % amorphous silicon. The crystalline phase is in the shape of nano‐scale crystalline inclusions in an amorphous matrix. From literature on wafering technology looking at wafer quality, the origin and mechanisms responsible for the amorphous content in the kerf loss powder are explained. In order to better understand for which applications the material could be a valuable raw material, the amorphicity and other relevant features are thoroughly investigated by a large amount of experimental methods. Furthermore, the kerf powder was crystallized and compared to the partly amorphous sample by operando X‐ray powder diffraction experiments during battery cycling, demonstrating that the powders are relevant for further investigation and development for battery applications.

Co-treatment of diamond-wire-saw silicon kerf and spent automotive catalysts for simultaneous recovery of PGMs, REEs, Zr, and high-purity Si

Spent automotive catalysts (SACs) and diamond-wire-saw silicon kerf (DWSSK) are classified as hazardous wastes. Currently, the two wastes are treated separately using unrelated approaches. More than two independent approaches are required to recover platinum group metals (PGMs), Zr and rare earth elements (REEs) from SACs, and recover Si from DWSSK, which is time-consuming and laborious. In this study, a new approach was proposed to co-treat the two wastes based on the concept of using waste treats waste: using DWSSK (∼89.85 wt% Si) as a new metal collector to extract PGMs, REEs, and Zr simultaneously from SACs to obtain a Si-VM alloy (VM: valuable metal); meanwhile, using the carrier of SACs to form molten slag to eliminate the main impurity, O, from DWSSK. The largest recovery ratios of Pd, Rh, Zr, Ce, La, and Nd from SACs were 99.50 ± 0.10%, 99.14 ± 0.14 %, 96.19 ± 0.76%, 67.18 ± 4.57%, 61.24 ± 4.93% and 47.65 ± 7.27%, respectively, and the largest removal ratio of O from DWSSK was 99.96%. After smelting, the Si-VM alloy was separated into high-purity Si and VM-containing acid solutions via acid leaching. The leaching ratios of Pd, Rh, Ce, La, Nd, and Zr were 99.78%, 98.15%, 99.93%, ∼100%, 99.76% and 99.98%, respectively. The purity of Si was upgraded from 89.85 wt% (in DWSSK) to 99.98 wt% after acid leaching. The new approach proposed in this study is considered more environmentally friendly and cost-effective than the regular approaches that treat the two wastes separately.

Synthesis of Si/C Composites by Silicon Waste Recycling and Carbon Coating for High-Capacity Lithium-Ion Storage.

It is of great significance to recycle the silicon (Si) kerf slurry waste from the photovoltaic (PV) industry. Si holds great promise as the anode material for Li-ion batteries (LIBs) due to its high theoretical capacity. However, the large volume expansion of Si during the electrochemical processes always leads to electrode collapse and a rapid decline in electrochemical performance. Herein, an effective carbon coating strategy is utilized to construct a precise Si@CPPy composite using cutting-waste silicon and polypyrrole (PPy). By optimizing the mass ratio of Si and carbon, the Si@CPPy composite can exhibit a high specific capacity and superior rate capability (1436 mAh g-1 at 0.1 A g-1 and 607 mAh g-1 at 1.0 A g-1). Moreover, the Si@CPPy composite also shows better cycling stability than the pristine prescreen silicon (PS-Si), as the carbon coating can effectively alleviate the volume expansion of Si during the lithiation/delithiation process. This work showcases a high-value utilization of PV silicon scraps, which helps to reduce resource waste and develop green energy storage.

Comprehensive recycling and utilization of photovoltaic waste: Use photovoltaic glass waste to refine silicon kerf waste

Large amounts of silicon kerf waste (SKW) and photovoltaic (PV) glass waste are being generated as the PV industry grows. At present, independent approaches have been adopted to recycle these waste materials. In this work, an original approach was first proposed for recycling silicon by using PV glass particles (PVGPs) that refine SKW. Compared with the experiment wherein no PVGPs were added, silicon yield increased from 51.44% to 87.66%. Furthermore, the transfer of the SiO2 surface-layer and the separation of silicon from slag were realized with different phase affinities. Moreover, network breakers, such as Ca2+ and F−, in PVGPs destroyed the network structure of SiO2 and provided a favorable microenvironment for silicon separation. This work innovatively used PV glass waste to refine SKW. It is expected to provide a green cleaning solution for the circular development of the PV industry.

Oxygen removal and silicon recovery from polycrystalline silicon kerf loss by combining vacuum magnesium thermal reduction and hydrochloric acid leaching

With the strengthened awareness of environmental protection and the growing interests of wastes recycling, silicon recovery from polycrystalline silicon kerf loss (PSKL) has drawn extensive attentions all over the world. In this paper, an efficient and environmental friendly approach for oxygen removal and silicon recovery from PSKL by combining vacuum magnesium thermal reduction (VMTR) and hydrochloric acid leaching was proposed. The effects of temperature, duration and particle size on the reduction of PSKL were investigated thoroughly. It is proved that the amorphous SiO2 in PSKL can be reduced by magnesium vapor at 923 K to generate MgO, and then the produced MgO can be dissolved by hydrochloric acid to eliminate the impurity oxygen. The oxygen removal fraction and the silicon recovery efficiency attained 98.43% and 94.46%, respectively, under the optimal conditions, indicating that a high efficiency recovery of silicon from PSKL was achieved. Compared to the existing PSKL deoxidation technologies, e.g., the high temperature process and the hydrofluoric acid leaching method, this method requires a relatively lower temperature and the waste acid can be easily recovered. Additionally, by taking into accounts the fact that the MgCl2 in leaching liquor can be recycled for cyclic utilization with a molten salt electrolysis method, it should be suggested that an efficient and environmental friendly process for PSKL recycling was obtained, which shows good prospects for commercial application.

Environmental assessment of silicon kerf recycling and its benefits for applications in solar cells and Li-ion batteries

Silicon and its usage in photovoltaics and advanced Li-ion traction batteries is a key material for the decarbonisation of the energy and mobility sector. To achieve sustainable silicon-based products, an efficient raw material processing is required. However, the production of silicon and its purification is energy- and resource intensive. Further, during the production of photovoltaic cells, about 40% of the silicon used is lost as sawdust, the so-called silicon kerf, which is often not recycled to a high quality. Compared to primary production, silicon recycling requires less electrical energy and no fossil reductants. However, an environmental assessment of the GHG reduction potential of silicon kerf recycling in comparison to primary production of silicon is limited in literature.In this paper, we will provide a comprehensive environmental assessment of silicon kerf recycling located in Sichuan and Xinjiang in China and Germany, since China is the biggest producer of silicon worldwide. For the assessment of the recycling, a detailed process-specific material and energy flow balance based on industry and literature data is used. The results are evaluated with relation to the primary production of metallurgical silicon and a sensitivity analysis of used electricity mix and transport distance is performed. Results show that recycled metallurgical silicon from silicon kerf creates up to 77% lower GHG emissions compared to conventional primary silicon. Further, environmental hotspots are identified and discussed. Based on the findings, recommendations for target-oriented process engineering are given to further reduce the material-related GHG impacts of silicon based products. Finally, the impact of the results is reflected on the market potential of innovative products like photovoltaics and Li-ion batteries.

Green synthesis of high-performance porous carbon coated silicon composite anode for lithium storage based on recycled silicon kerf waste

The effective management of silicon kerf waste produced from silicon wafer cutting processes of photovoltaic industry is of great significance for environmental protection and resources recycle. High-purity silicon kerf waste collected by acid-assisted separation and purification can be recycled as silicon source of silicon-based anode for lithium storage. Although volume volatility and low conductivity rooted in silicon anode are effectively handled by constructing carbon coated silicon composite with porous structure, it is always impeded by a HF-involved synthesis process for etching SiO2 as template. Here, a green systhesis approach for porous carbon encapsulated recycled silicon kerf waste ([email protected]) are reasonably designed that calcium carbonate (CaCO3) constructed as sacrificial layer is effortlessly removed away by HCl-assisted pickling, leaving porous structure. When evaluated in LIBs, the discharge capacity keeps at 712.6 mAhg−1 after 200th cycle at 0.5 Ag−1, whose initial capacity reaches to 2739.2 mAhg−1; Meanwhile, it demonstrates a significantly improved rate performance. In brief, this work provides a green and low-cost method to synthesize high-performance silicon/carbon composite with porous structure as anode for lithium storage based on recycled silicon kerf waste, meanwhile offers a new viewpoint for the effective management of silicon kerf waste from photovoltaic industry with high value.

Green Synthesis of High-Performance Porous Carbon Coated Silicon Composite Anode for Lithium Storage Based on Recycled Silicon Kerf Waste

Green Synthesis of High-Performance Porous Carbon Coated Silicon Composite Anode for Lithium Storage Based on Recycled Silicon Kerf Waste

Recycling silicon kerf waste: Use cryolite to digest the surface oxide layer and intensify the removal of impurity boron

The surface oxide layer (SiO2 layer) is still one of the main limitations of the recovery and purification of silicon kerf waste (SKW). Herein, to recycle SKW as the low-boron silicon ingot, an effective combination strategy that digests the surface oxide layer by pretreatment and then removes impurity boron by slag treatment is proposed. In the pretreatment part, the surface oxide layer of SKW was successfully digested into a liquid phase after mixing 10.5 wt% cryolite and sintering at 1400 °C, and the obtained SKW-ceramic has a dense structure. Moreover, when holding at 1400 °C for 2 h, the boron concentration in SKW-ceramic was decreased to 5.75 ppmw, and the removal rate reaches 14.18%. In the slag treatment part, CaO and SiO2 are selected as slag agents. The CaO/SiO2 mass ratio and reaction temperature were determined to be 2 and 1600 °C based on thermodynamic simulation. Besides, Na2O formed due to the dissociation of cryolite, which can enhance the oxygen ion activity and boron-absorbing capacity of the slag. The experimental result exhibited that the boron removal efficiency reached 86.56%. The simplicity and scalability of this strategy provide a better alternative for the recovery of SKW.

From magnesite directly to lightweight closed-pore MgO ceramics: The role of Si and Si/SiC

Partial/full replacement of traditional dense refractory aggregates (for furnace lining) with lightweight aggregates is considered to be an effective and promising strategy for energy saving and emission reduction. In this work, lightweight magnesia refractory ceramics with tailored closed porosity were prepared by one-step sintering at 1600 °C from high-purity magnesite added with silicon kerf waste in different ratios, with the emphasis on the evolution of their phase compositions, micromorphologies, and various properties. With the addition of additives, Mg2–xFexSiO4 solid solution was formed at the grain boundaries of the MgO matrix, and then the volumetric expansion effect (interfacial reaction) and activated sintering effect (vacancy defect) promote the decrease of apparent porosity and the increase of closed porosity, respectively. Consequently, MgO ceramics with apparent/closed porosity of 0.6%/6.5%, bulk density of 3.25 g cm−3, and lightweight index of 7.8% were successfully prepared, suitable for the working lining of metallurgical furnaces.

Green synthesis of porous SiC ceramics using silicon kerf waste in different sintering atmospheres and pore structure optimization

This work reported the feasibility of using silicon kerf waste as raw material for the preparation of porous SiC ceramics, as well as effects of sintering atmospheres and additives on the properties of as-prepared ceramics. Samples sintered in Ar, N2, and carbon embedded atmospheres exhibited entirely different properties because of the formed bonding phases of SiCw, Si3N4/Si2N2O, and Si2N2O. Moreover, the apparent porosity and closed porosity of the samples were increased with the additions of feldspar and starch. Preferably, a series of porous SiC ceramics with apparent/closed porosity of 24.15%–59.59%/5.83%–14.77%, bulk density of 1.13–1.91 g cm−3, cold compressive strength of 34.73–249.89 MPa, and thermal shock resistance of 110–118 cycles was synthesized at 1500 °C in carbon embedded atmosphere. Therefore, a low-cost and facile synthesis strategy for preparing high-quality porous SiC ceramics from solid waste is proposed in present study.

Facile synthesis of MgO–Mg2SiO4 composite ceramics with high strength and low thermal conductivity

The recycling of solid waste is a win-win solution for humans and nature. For this purpose, magnesite tailings and silicon kerf waste were employed to prepare MgO–Mg2SiO4 composite ceramics by solid-state reaction synthesis in the present work. Then, effects of sintering temperature and raw material ratio on as-prepared ceramics were systematically studied. As-prepared ceramics showed improvement in their relative density (from 47.55%–68.12% to 90.96%–95.25%) and cold compressive strength (from 7.34–118.66 MPa to 303.39–546.65 MPa) with the increase in sintering temperature from 1300 to 1600 °C. In addition, it was found that Si promoted synthesis process of Mg2SiO4 phase through transient liquid phase sintering and Fe2O3 accelerated sintering process through activation sintering. Consequently, the presence of Mg2SiO4 phase effectively improved the density and strength of MgO–Mg2SiO4 composite ceramic, while reducing its thermal conductivity. This work provides a potential reutilization strategy for magnesite tailings, and as-prepared products are expected to be applied in fields of construction, metallurgy, and chemical industry.

Carbon nanotubes-enhanced lithium storage capacity of recovered silicon/carbon anodes produced from solar-grade silicon kerf scrap

Recovered solar-grade silicon kerf scrap is touted as an ideal silicon source for Si-based anodes in advanced lithium-ion batteries (LIBs) whose development is always troubled by the volume expansion and low conductivity. Here, an effective approach for carbon nanotubes (CNTs) enhanced recovered silicon/carbon anodes encapsulated by polymethyl methacrylate (PMMA)-derived carbon coating (Si/CNTs@PMMA-C) is described. The Si/CNTs@PMMA-C anode presents an impressive Li ion storage capacity and long cycle lifespans, delivering a high initial discharge capacity of 3732.7 mAhg−1 and initial coulombic efficiency of 78.2% at 200 mAg−1 with a reversible capacity retention of 1024.8 mAhg−1 after 200th cycle. Moreover, full-cells composed of Si/CNTs@PMMA-C anodes and commercial LiCoO2 cathodes display a good electrochemical performance and high energy density. These excellent electrochemical properties boil down to the synergistic effect of PMMA-derived carbon shell and high-purity recovered silicon; meanwhile, CNTs can further support volume expansion tolerance and electrical conductivity. This effective method can provide a broader practical application prospect for the silicon/carbon composite anodes based on low-cost recovered solar-grade silicon kerf scrap with enhanced electrochemical performance in advanced LIBs.

An approach for simultaneous treatments of diamond wire saw silicon kerf and Ti-bearing blast furnace slag

Both diamond wire saw silicon kerf (DWSSK) and Ti-bearing blast furnace slag (TBBFS) are largely accumulated industrial wastes and important resources of Si and Ti. Currently, both are treated using independent approaches. In this study, a novel approach is proposed to simultaneously extract Ti from TBBFS to prepare TiO2 and recycle Si from DWSSK to prepare high-purity Si. Firstly, DWSSK (86.9 % Si) was employed as a reductant to extract Ti from TBBFS to prepare bulk Si-Ti alloys, and the largest extraction rate was 99.4 %. Secondly, Si and Ti in the bulk Si-Ti alloy were separated using a HF-containing acid solution. Ti in the Si-Ti alloy dissolved into the HF-containing acid solution, and high-purity Si was obtained after acid leaching. The purity of Si in DWSSK increased from 86.9% to 99.94%. Thereafter, a NaOH solution was used to precipitate Ti(OH)4 from the HF-containing acid solution, and TiO2 was prepared by roasting Ti(OH)4. Notably, the new approach had the advantage of concurrently eliminating impurities while recycling DWSSK. Finally, NaOH and HF solutions were used to prepare high-purity NaF (>98 %) to treat the waste solutions. The results of this study provides a new and sustainable technology for clean utilization of DWWSK and TBBFS.

Recovery of silicon kerf waste from diamond wire sawing by two-step sintering and acid leaching method

Silicon kerf waste from diamond-wire sawing of solar grade silicon is regarded as a promising resource for the clean production of high-purity silicon. In this study, silicon kerf waste is collected by a two-step sintering method (TSS) to obtain a ceramic product for the first time and its effect on the leaching behavior of silicon kerf was assessed. The results show that the relative density and grain size of silicon kerf ceramic could reach 91.72% and 0.75 μm under TSS3-10 h condition (1400 °C in the first stage and 1350 °C for 10 h in the second stage). The TSS process is confirmed to be beneficial for decomposing silicon oxide layer and promoting densification. Acid leaching experiment was conducted and the relationship between the relative density and impurity extraction was evaluated. It was found that the removal rate of impurities (except oxygen) from silicon kerf by direct acid leaching was higher than that through TSS3-10 h and acid leaching. However, the combined process can reduce 52.4% oxygen content and the yield of silicon was reached 96.03%. The present study aims to shed light on the feasible application of TSS on the hydrometallurgical recycling of silicon kerf.

Recycling of silicon kerf loss derived from diamond-wire saw cutting process to prepare silicon nitride

Abstract In this paper, silicon kerf loss derived from diamond-wire saw cutting process was recycled to synthesize Si3N4 powders and ceramics via the incorporation of carbothermal nitridation and direct nitridation. The effects of sintering temperatures and CaO additives on the nitridation behavior were studied in detail. The results showed that the main impurities were SiC and Si2N2O in Si3N4 powders products, and the content of impurities could be reduced with the increasing of sintering temperatures and CaO additives. In addition, the acceleration mechanisms of sintering temperatures and CaO additives on the nitridation were investigated and proposed by the thermodynamics calculation and density functional theory, respectively. Owing to the acceleration effect of CaO additives on the nitridation, the properties of the obtained Si3N4 ceramics were obviously improved. When the content of CaO additives was 5 wt%, the as-prepared Si3N4 ceramic had a bulk density of 2.31 g cm−3, apparent porosity of 25.42% and a compressive strength of 109 Mpa. In a word, this study presented a feasible approach for recycling silicon kerf loss to fabricate high-value Si3N4 materials, which could be applied to other harmful waste resources.