Review of Silicon Recovery and Purification from Saw Silicon Powder

Abstract

The demand for crystalline silicon wafers is continuing to increase. It is inevitable that high-purity silicon will be lost as loose abrasive slurry silicon powder (LASSP) and diamond wire saw silicon powder (DWSSP) during the process of wafer preparation. For this reason, some advanced processes or methods require further development to solve the problems of the high production cost, silicon wafer shortage, and environmental pollution caused by these silicon resources. Some processes and technologies for silicon recovery and purification from LASSP and DWSSP are comprehensively reviewed in this paper. These investigations inform some anticipated technological trends and required improvements, and encourage the development of technological solutions. Furthermore, the authors propose that high-purity silicon for industrial implementations can be recycled from LASSP and DWSSP via a combined process of an acid leaching pretreatment and a high-temperature treatment. Additionally, some existing deficiencies and areas that require enhancement are also proposed for improved impurity removal and silicon recovery with a higher process efficiency.

Appendix

Abbreviation

LAS:

Loose abrasive slurry (–);

DWS:

Fixed abrasive diamond wire sawing (–);

LASSP:

Loose abrasive slurry silicon powder (–);

DWSSP:

Diamond wire sawn silicon powder (–);

Equations

$$ \frac{{{\text{d}}V(t)}}{{{\text{d}}t}} = \frac{\Delta P}{{\mu \left[ {R_{0} + R_{c} \rho \left\{ {V(t)} \right\}^{n + 1} } \right]}} $$

(1)

$$ u_{pm} = \frac{{(\rho_{p} - \rho )}}{18u}D_{P}^{2} g $$

(2)

$$ \frac{{\upsilon_{\text{SiC}} }}{{\upsilon_{\text{Si}} }} = \frac{{D_{\text{SiC}}^{2} (\rho_{\text{SiC}} - \rho )}}{{D_{\text{Si}}^{2} (\rho_{\text{Si}} - \rho )}} $$

(3)

$$ x = \left( {\frac{RTt}{{3\pi \mu D_{P} N_{A} }}} \right)^{0.5} $$

(4)

$$ t = \frac{d}{{V_{t} (\text{Sin} \theta + \text{Cos} \theta \cdot \tan \alpha )}} $$

(5)

$$ {\text{SiO}}_{2} + 6{\text{HF}} \to {\text{H}}_{2} ({\text{SiF}}_{6} ) + 2{\text{H}}_{2} {\text{O}} $$

(6)

$$ \left\{ O \right\}{\text{wt}} .\% = 4.0 \times 10^{ - 3} (1 + 9{\text{Si wt}} .\% ) $$

(7)

$$ {\text{Si}} + 2{\text{NaOH}} + {\text{H}}_{2} {\text{O}} \to {\text{Na}}_{2} {\text{SiO}}_{3} + 2{\text{H}}_{2} $$

(8)

$$ 4{\text{Al}} + 3{\text{SiC}} \to {\text{Al}}_{4} {\text{C}}_{3} + 3{\text{Si}} $$

(9)

$$ 2{\text{SiC}}({\text{s}}) + {\text{SiO}}_{2} ({\text{l}}) = 3{\text{Si}}({\text{l}}) + 2{\text{CO}}({\text{g}}) $$

(10)

$$ {\text{Si}}({\text{s}}) + {\text{SiO}}_{2} ({\text{s}}) = 2{\text{SiO}}({\text{g}}) $$

(11)

$$ {\text{SiO}}_{2} ({\text{s}}) + 2{\text{C}}({\text{s}}) \to {\text{Si}}({\text{s}}) + 2{\text{CO}}({\text{g}}) $$

(12)

$$ \frac{{(1 - x)^{ - 2} - 1}}{2} = \left( {1.11 \times 10^{14} C_{\text{HCl}}^{2.81} \exp \left( { - \frac{97300}{RT}} \right)} \right)t $$

(13)

$$ {\text{Si}}({\text{s}}) + 2{\text{H}}_{2} {\text{O}}({\text{l}}) = {\text{SiO}}_{2} ({\text{s}}) + 2{\text{H}}_{2} ({\text{g}}) $$

(14)

Notation

• 1. $V(t)$—filtration volume [m³];

• 2. $\Delta P$—pressure [Pa];

• 3. $R_{0}$—filtration resistance [m⁻³];

• 4. $R_{c}$—cake resistance [m⁻³ kg⁻¹];

• 5. $n$—compression coefficient;

• 6. $\rho$—concentration of solid materials in waste coolant [kg m³];

• 7. $\rho_{P}$—density of the particle;

• 8. $\rho$—density of the solution;

• 9. $u$ –viscosity of the solution

• 10. $\upsilon_{SiC}$ and $\upsilon_{Si}$—the sedimentation velocities of the SiC and Si particles, respectively;

• 11. $D_{SiC}$ and $D_{Si}$ –particle diameters of the SiC and Si particles (μm), respectively

• 12. $x$—mean square diffusion displacement;

• 13. $R$—gas constant (8.314 [J (mol K)⁻¹]);

• 14. $T$—temperature (K);

• 15. $t$—time;

• 16. $\mu$—viscosity of solution;

• 17. $D_{P}$—particle diameters (μm);

• 18. $N_{A}$—Avogadro constant;

• 19. $d$—fixed depth in settling tank;

• 20. $V_{t}$—terminal velocities for Si and SiC;

• 21. $\theta$—angles for particles move along inclined paths;

• 22. $\alpha$—ramp angle;

• 23. $x$—removal efficiency (%);

• 24. $C$—HCl concentration (M);

• 25. $T$—reaction temperature (K);

• 26. $t$—leaching duration (min);

• 27. $R$—ideal gas constant (8.314 [J (mol K)⁻¹]);