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6CCVD Research

Silicon Extraction from a Diamond Wire Saw Silicon Slurry with Flotation and the Flotation Interface Behavior

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2024-12-15
JournalMolecules
AuthorsLin Zhu, Dandan Wu, Shicong Yang, Keqiang Xie, Kuixian Wei
InstitutionsYunnan University, Kunming University of Science and Technology
Citations1
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This study proposes and validates an efficient flotation method for extracting high-purity silicon (Si) from Diamond Wire Saw Silicon Slurry (DWSSS), a critical waste stream from solar wafer production.

  • High Recovery Rate: A maximal silicon recovery of 98.2% was achieved, demonstrating the viability of flotation for this waste resource.
  • Optimal Conditions: The highest recovery was obtained using a Dodecylamine (DDA) collector dosage of 0.6 g·L-1 under natural slurry pH conditions (pH 4-5).
  • Rapid Kinetics: The flotation process conforms to a first-order rate model, with the majority of recovery occurring within the first 8 minutes, completing the process efficiently in 24 minutes.
  • Interface Mechanism: DDA spontaneously adsorbs onto the Si surface (confirmed by DFT calculations, ∆E = -3.28 eV), significantly increasing the silicon particle’s hydrophobicity (contact angle increased from 73.8° to >90°).
  • Surface Modification: Adsorption of DDA increased the surface roughness (Rq increased from 123 nm to 207 nm), enhancing floatability.
  • Process Advantage: The method offers a short processing cycle, easy operation, and minimizes the reintroduction of metal impurities, supporting sustainable 6N Si recycling.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Maximal Silicon Recovery98.2%Optimal DDA dosage (0.6 g·L-1)
Optimal DDA Dosage (Recovery)0.6g·L-1For 98.2% recovery
Optimal DDA Dosage (Kinetics)0.9g·L-1For maximal flotation rate constant (k)
Optimal Flotation pH Range4-5N/ANatural slurry pH
Total Flotation Time24minTotal duration for 98.2% recovery
Max Flotation Rate Constant (k)0.506min-1Achieved at pH 5, DDA 0.6 g·L-1
Initial DWSSS Solid Content2.11%Mass percentage of silicon in slurry
DWSSS Average Particle Size0.52”mBefore flotation
Silicon Purity (Source Material)6NN/AHigh-purity solar-grade silicon
Impeller Speed1920r·min-1Flotation cell operation speed
Air Pumping Rate200-300L/hFlotation air supply
Silicon Contact Angle (Before DDA)73.8°Surface wetting property
Silicon Contact Angle (After DDA)>90°Enhanced hydrophobicity
Surface Roughness (Rq, Before DDA)123nmSurface rms roughness
Surface Roughness (Rq, After DDA)207nmSurface rms roughness after DDA adsorption
Adsorption Energy (∆E)-3.28eVDFT calculation, confirming spontaneous adsorption
H-N Bond Length (DDA)1.96AShortest bond length after adsorption (strongest covalent bond)

Key Methodologies

Section titled “Key Methodologies”

The silicon extraction was performed using microflotation experiments combined with advanced surface characterization and Density Functional Theory (DFT) modeling.

  1. Slurry Preparation: 400 mL of DWSSS was placed in a 500 mL flotation cell and diluted with water to maintain a total slurry volume of 500 mL.
  2. Homogenization: The slurry was stirred at an impeller speed of 1920 r·min-1 for 2 minutes to ensure homogeneity.
  3. Collector Preparation: Dodecylamine (DDA) acetate was prepared by mixing DDA and glacial acetic acid (1:3 mass ratio). The mixed collector (DDA and kerosene, 2:3 ratio) was heated in a water bath at 50 °C for 10 minutes.
  4. Collector Addition: The optimal DDA dosage (0.6 g·L-1) was added to the slurry and stirred for 3 minutes.
  5. Flotation Process: Air was pumped into the cell at 200-300 L/h. The mineral-carrying froth was scraped every 5 seconds, collecting 12 concentrates over a total flotation time of 24 minutes.
  6. Recovery Calculation: Concentrates and tailings were filtered, dried at 80 °C to constant weight, and silicon recovery was calculated based on mass balance.
  7. Interface Characterization:
    • Zeta Potential: Measured using a Malvern ZEN-3700 analyzer to track surface charge changes with pH and DDA addition.
    • Hydrophobicity: Contact angle measured using a KrĂŒss K100 surface tension meter (dynamic capillary penetration).
    • Chemical Bonds: Analyzed via Fourier Transform Infrared Spectrometer (FTIR, Bruker ALPHA).
    • Morphology: Surface roughness (Rq, Ra) and three-dimensional height determined by Atomic Force Microscopy (AFM, Bruker Dimension Icon). Surface elemental composition analyzed by Scanning Electron Microscopy (SEM-EDS, ZEISS Gemini 300).
  8. DFT Modeling: Adsorption behavior was modeled using the Materials Studio (2023) Adsorption Locator module (COMPASS II force field) and CASTEP module (BFGS optimization, GGA, PBE functional, DFT-D3 dispersion correction) to calculate adsorption energy and charge density maps.

Commercial Applications

Section titled “Commercial Applications”

This research provides a validated, efficient, and environmentally sound pathway for recovering high-value silicon from industrial waste, directly impacting several key sectors:

  • Solar Photovoltaic (PV) Manufacturing: Enables the closed-loop recycling of 6N high-purity silicon kerf waste (DWSSS), significantly reducing raw material costs and environmental footprint in solar cell production.
  • High-Purity Material Supply Chain: The recovered silicon can serve as a secondary feedstock, potentially reducing reliance on primary metallurgical-grade silicon sources.
  • Waste Resource Management: Offers a scalable, short-cycle industrial process for treating micron-sized mineral slurries, applicable to other fine particle separation challenges.
  • Flotation Technology and Reagent Development: Validates the use of DDA/kerosene mixed collectors for non-sulfide, non-metallic mineral flotation, particularly for enhancing the hydrophobicity of silicon surfaces.
  • Sustainable Engineering: Supports the principles of circular economy by converting a major industrial waste product into a valuable resource, aligning with global sustainability goals for energy production.
View Original Abstract

Diamond wire saw silicon slurry (DWSSS) is a waste resource produced during the process of solar-grade silicon wafer preparation with diamond wire sawing. The DWSSS contains 6N grade high-purity silicon and offers a promising resource for high-purity silicon recycling. The current process for silicon extraction recovery from DWSSS presents the disadvantages of lower recovery and secondary pollution. This study focuses on the original DWSSS as the target and proposes flotation for efficiently extracting silicon. The experimental results indicate that the maximal recovery of silicon reached 98.2% under the condition of a dodecylamine (DDA) dosage of 0.6 g·L−1 and natural pH conditions within 24 min, and the flotation conforms to the first-order rate model. Moreover, the mechanism of the interface behavior between DWSSS and DDA revealed that DDA is adsorbed on the surface of silicon though adsorption, and the floatability of silicon is improved. The DFT calculation indicates that DDA can be spontaneously adsorbed with the silicon. The present study demonstrates that flotation is an efficient method for extracting silicon from DWSSS and provides an available option for silicon recovery.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2020 - Potential environmental risk of solar cells: Current knowledge and future challenges [Crossref]
  2. 2006 - Size distribution modeling for fluidized bed solar-grade silicon production [Crossref]
  3. 2023 - Phase transformation pre-treatment of diamond wire-sawn multi-crystalline silicon wafers for metal-assisted chemical etching of solar cells [Crossref]
  4. 2022 - A new strategy for de-oxidation of diamond-wire sawing silicon waste via the synergistic effect of magnesium thermal reduction and hydrochloric acid leaching [Crossref]
  5. 2022 - Review of resource and recycling of silicon powder from diamond-wire sawing silicon waste [Crossref]
  6. 2020 - Review of Silicon Recovery and Purification from Saw Silicon Powder [Crossref]
  7. 2016 - High-efficiency crystalline silicon solar cells: Status and perspectives [Crossref]
  8. 2012 - Boron removal from metallurgical-grade silicon using lithium containing slag [Crossref]
  9. 2020 - Occurrence State and Dissolution Mechanism of Metallic Impurities in Diamond Wire Saw Silicon Powder [Crossref]

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