WO2016120663A1

WO2016120663A1 - Non-chemical method and system for recovering silicon carbide particles and glycol from a slurry

Info

Publication number: WO2016120663A1
Application number: PCT/IB2015/050612
Authority: WO
Inventors: Wee Meng CHUA; Audley Weng Hin THAM; Ryan Morris Lim LABBAO
Original assignee: METALLKRAFT AS
Current assignee: METALLKRAFT AS
Priority date: 2015-01-27
Filing date: 2015-01-27
Publication date: 2016-08-04
Anticipated expiration: 2017-07-27
Also published as: TWI562816B; SG11201706012RA; TW201627049A; EP3250507A1

Abstract

The invention relates to a non-chemical method and a system for recovering silicon carbide (SiC) particles and glycol, and in particular, to a non-chemical method and a system for recovering SiC particles and glycol that have been used in suspension in a cutting medium for the cutting or sawing of silicon wafers for solar cells and electronic objects often called slurry.

Description

NON-CHEMICAL METHOD AND SYSTEM FOR RECOVERING SILICON CARBIDE PARTICLES AND GLYCOL FROM A SLURRY

{00011 The invention^' relates to a non-chemicai method and a system for recovering silicon carbide (SiC particles and glycol, and- in- particular, to a non-chemicai method and a system for recovering SiC particles and glycol that have been used in suspension in a cutting medium for the cutting or sawing, of silicon wafers for solar cells and electronic objects often called slurry.

Background

[0002] When sawing thin silicon discs, commonly referred to as "wafers", particles of silicon carbide (SiC) of specific grit sizes, such as FEPA classes F500, P60O, and F800, are dispersed in an organic liquid, thus forming a suspension, which is used as a cutting medium, or slum'. Common dispersing agents -are -organic giycolic liquids such as polyethylene glycol (PEG), dipropylene glycol (DPG), diethylene glycol (D-EG-), and propylene glycol (PG). Sometimes surfactants that reduce surface tensions are added to the slurry_*.

[0003| The sawing is usually conducted by a wire saw, wherein the abrasive slurry is earned by a thin, hardened iron wire with brass on the surface, towards the "sawing z mT where it performs its "cut grinding^''' process and cuts the silicon (Si) block into a series of thin wafers. During the sawin process, the slurr ^'becomes contaminated with Si from the Si block, iron (Fe) ^' from the cutting wire, and SiC lines (i.e. fine particles) -from the breaking down of abrasive grains. This contamination, coupled, with the increase in water content (due to hygroscopic nature of glycol), also changes the properties of the glycol significantly* such as density, p¾ conductivity, viscosity, and colour. 0OO4 Typically, the Si wafers are used for the manufacture of electronic or microelectronic devices, or for the .manufacture of solar cell panels for the production of electr ic power. The cleanliness requirement of these Si wafers is typically so high that, 5» practice, only Si free and Fe free slurry have been used for the cutting. Furthermore, the requirement for particle size distribution is precisely specified in. order to obtain smooth surfaces on the Si wafers. SiC particles for sawing lies within a narrow grain size range, i.e. that there is little or minimal difference between the size of the largest and the smallest grains . At the same time, the properties of the glycol are also precisely specified in order to ensure a consistent sawing performance from the start to the end of the sawing process..

(0OOSj After having beers used for some time, the slurry becomes so contaminated with SiC fines. Si and Fe particles that it has to be replaced by a new suspension. In addition, particle size distribution of SiC. particles, as well as the properties of the glycol, have also shifted out of the desired narrow range, ^'There are existing technologies to recover the shirty to a re-usable level, but ail of which involves the usage of chemicals, either directly or indirectly. For example, acid and/or caustic soda are used directly to treat the contarnmated SiG particles to rid it of the. Si and Fe particles. Hydrogen peroxide and other minerals are used directly to remove colour in the glycol Acid and caustic sod are used, indirectly to regenerate the deioniser columns- which remove dissolved ions in the glycol. Consequently, a. huge amount: of ehemical waste is generated, which presents another environmental problem.

[W66f From a resource, cost, safety and environmental point of view, it is thus desirable to develop non-ehemical processes by which slurry may be recycled, that is, SiC fines, Si and Fe particles may be removed and recovered, nd. (he properties of the glycol may be reinstated to its desired levels. 0007} An economically and. feasible process implies that it should give .high -yields, of the^' recovered components for reuse, and that the waste contaminated with Fe, Si and SiC fines should be reused as valuable resources e.g. for use in the production of iron and steel, ferro-alloys or refractory materials. By adopting a nors-ehemical process, cost can be reduced significantly,, due to the avoidance or omission of the following costs - purchase of chemicals and treatment disposal of chemical waste. By the same argument, safety is further enhanced in a non-chemical process, and the lack of chemical waste and high recycling rates means less strain, to the environment.

[0008] FEPA FS00, F600 and F800 microgrits are commonly used in. the sawing of Si. wafers and it is important that the grains of SiC conform to the standards of harrow particle size distribution, and low impurity levels- to obtain a good result. The conventional practice is to dilute the slurry with large quantity of water and separate the solid and liquid fractions by physical means.

Subsequently, the solid fraction, consisting of SiC particles, SiC fines, Si and Fe particles* is first cleansed by centrifugal separation process, which makes use of the fact that the SiC particles have larger diameters than the contaminants of SiC fines, Fe and Si. This step is capable of achieving the narrow particle size distribution requirement, hut is usually unable to meet the low impurity levels. This is especially prevalent with smaller SiC grit sizes such as F800, where the SiC particles are much closer in diameter to the contaminants, hence making it more difficult to separate, Therefore, ■a chemical treatment step is required, in which caustic soda and acid -are used to chemically reduce Si and Fe respectively to the required levels. The liquid fraction, consisting of glycol, water, fine particles and dissolved ions, is recovered through a series of processes— filtration, colour removal (using chemicals directly), deionizaiion (using_, chemicals indirectly), and evaporation.. The use of chemicals in the recycling process not just adds to the cost, but also presents an environmental problem in terms of disposal.

[1)009] Therefore, there remains a need to provide for alternative methods and systems for recovering the reusable SiC. particles and glycol from slurry using^■■non-chemical means.

Su mary fftjffiej in a first aspect of the disclosure, there is provided a method for recovering silicon carbide (SiC) particles and glycol from a slurry, wherein the slutty comprises a mixture of SiC, Si, and Fe particles suspended in glycol, by physically removing fine grain, particles.

[0911 The method may include: separating in a slurry filter press the .slurry into a first, solid phase stream and a first liquid phase stream, wherein the first solid phase stream comprises essentially the SiC, Si, and Fe particles and wherein the first liquid phase stream comprises essentially glycol, water, suspended fine particles, and dissolved ions;

treating the first solid phase stream to a solid purification stage,, wherein the solid purification stage comprises;

adding water, to the first solid phase stream to obtain a suspension of SiC, Si, and Fe particles in water:

feeding the suspension of SiC, Si, and Fe particles to a hydrocyclone system to obtain a .underflow -stream comprising recovered SiC particles in water and an overflo stream comprising essentially fine particles of SiC, Si and Fe suspended In water, wherein the hydrocyclone system comprise one or more hydrocyclones feeding the underflow stream to a product filter press to obtain the recovered SiC and to remove water;

treating the first liquid phase stream to a liquid purification stage, wherein the liquid purification stage comprises:

feeding the first liquid phase stream to a water distillation column to obtain a first residue a d a first distillate comprising water;

feeding the first residue to a glycol distillation column to. obtain a second distillate comprising glycol.

[0012] In a second aspect of the disclosure_* there is disclosed a system for recovering silicon carbide (SiC) particles and glycol from a starry, wherein the slurry comprises a mixture of SiC, Si, and Fe particles suspended in glycol.

[0013] The system may include: a slurry filter press for separating the slurry into a first solid phase stream and a first liquid phase stream, wherein the first solid phase stream comprises essentially the SiC, Si, and F particles and wherein the first liquid phase stream comprises essentially glycol, water, suspended fine particles, and dissolved ions;

a solid purification stage, wherein the solid purification stage comprises:

a hydrocyelone system to obtain an underflow stream comprising recovered SiC particles in water and an overflow stream comprising essentially fine particles of SiC, Si and Fe suspended .in water, wherein the hydrocyelone system comprises one or more hydroeyciones;

a product filter press to obtain the. recovered SiC and to remove water;

a liquid purification stage, wherein the liquid purification stage comprises:

a water distillation column t obtain, a first residue and a first distillate comprising water; and a glycol distillation, column to obtain a second distillate comprising glycol.

Brief Description of the Drawings

[06141 in the drawings, like reference characters- generally refer to the same parts throughout the different views.. The drawings are not necessarily drawn to scale, emphasis instead generally being placed upon illustrating the principles of various embodiments. In the follo wing description, various embodiments- of the invention are described with, reference to the following drawings.

{00X51 Figure i shows a process flow of present method and system_*

[0016] Figure 2 A shows a SEM (2000x magnification) of the recycled F50O grit size SiC particles recovered from present method according- t the operating conditions given in Table 1. la this ease. Si content is about 0, 13 wt% and e content is -about 0,05 wt%.

[^'00171 Figure 2B shows a SEM (2000x magnification) of the recycled JIS2000 grit size SiC particles recovered from present method according to. the operating conditions given in Table 1, In this case, Si content is about 0.43 wt% and Fe content is about 0.63 wt%.

[1)0181 Figure 2C shows a SEM (2000x magnification) of the recycled F80G grit size: SiC particle recovered from presen method according to the operating conditions given- in Table 1. In this case. Si content is about 0.14 wt -and Fe content is about 0,65 wt%. f 0019| Figure 3 shows a photograph of the product glycol, specifically, PEG,. DPG, DEG, and PG, .recovered by the present liquid purification stage.

Deseripiio

|O02 The following deiaiied description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may- be practised. These embodiments are- described in sufficient detail to enable those skilled in the art to practise the_. invention, Other .embodiments- .may be utilized and_.simctural, logical, and eiectricai changes may be made without departing from, the scope of the invention. The various embodiments are not necessarily mistuaily exclusi ve, as some embodiments can be combined with one or more other embodiments to form- new embodiments.

(00211 .method and a system for recovering silicon carbide (SiC) particles and glycol that have been used in suspension in a cutting medium, such -as glycol, for the cirting or sawing of silicon wafers for solar cells and electronic objects often called slurry are disclosed herein,

Advantageously; the_: method allows recovery of SiC of a narrow grain size range by physically removing (i.e. without involving use of chemicals) from the SiC particles smaller particles such as, but not limited to, iron (Fe), silicon (Si) and SiC fines. The method also allows recovery of glycol properties to its desired levels by means of distillation (i.e. again without involving the use of chemicals). The method and system can. be applied cost-effectively on an industrial scale and at the same time have minimal negative impacts on the environment. f 00221 In- resent context, recycled particles of SiC within the FEPA (Federation of European Producers of Abrasives) standards of microgrits are obtainable. FEPA is the- international standard to which these kinds of materials- have to comply. The relevant, standard - is FEPA standard 42-6B 1 84, R 1 93. (The same definition is incidentally defined fay ISO 6344-3 1 68, part 3;.

"Determination of grain size distribution of microgrits F230 to F.12-09" j. Alternatively, the Japanese industrial Standards (JiS) may also be applicable here and recycled particles of SiC within the JIS of microgrits are also obtainable. 0023] By ordinar classification, the smallest particles will be present as individual grains that may be separated from the larger particles by a convenient choice of process parameters. With respect to these SiC particles, however, subsequent to the removal, and recovery of glycol from the used slurry, the small particles will adhere to the larger, say F500, F600 or F800 SiC grains that are: typically applied for sawing silicon wafers.

[00241 Thus, in a first aspect of the disclosure, there is provided a method for recovering silicon carbide (SiC) particles and glycol from a slurry, wherein the slarry comprises a mixture of StC, Si, and Fe particles suspended in glycol.

[0025] The method comprises die following steps: separating in a slurry filter press the slurry into a first solid phase stream and a first liquid phase stream, wherein the first solid phase stream comprises essentially the SiC, Si, and Fe particles and wherein the first liquid phase stream comprises essentially glycol, water, suspended fine particles, and dissolved ions;

treating the first solid phase stream to a solid purification stage, wherein the solid purification stage comprises:

adding water to the first solid, phase -stream to. obtain a suspension, of SiC, Si, and Fe particles hi water;

feeding the suspension of SiC, Si, and Fe particles to a hydrocyc!one system to obtain an underflow stream comprising recovered SiC particles in water an an overflow stream comprising essentially fine particles of SiC, Si,, and Fe suspended in water, wherein the hydroeycione system comprises one or more hydfocyclones;

feeding the underflow stream to a product filter press to obtain the recovered SiC and to remove water;

treating the first liquid phase stream, to a liquid purification stage, wherein the liquid purification stage comprises: feeding the firSi liquid phase stream to a water distillation column to obtain a. first residue and a first distillate comprising water;

feeding die first residue to a glycol distillation column to obtain a second distillate comprising glycol.

0026] An outline process flow of the method and accordingly a system implementing the method is illustrated in Figure 1.

(0027] Used slurry, which is essentially made up of the solid particles suspended in glycol, is fil tered to separate the solid stream from the liquid stream. Water may be added to the used slurry for dilution before tire separation.

[0028] hi various embodiments, diluted used slurry is separated into solid and liquid i a slurry filter press. Pressure filtration, improved cake washing and air blowing help to enhance tlie solid- liquid separation, achieving low water content -and trace glycol (as the organic liquid medium) levels in the solid content. Optimum reflux, time prior to filtration and quality of filter cloth, also pla a vital role in filtration efficiency.

{0029] The solid phase, stream may include essentially the SiC. Si, and Fe particles.

[0030] The. liquid phase stream may include essentially glycol, water, suspended fine particles and dissolved ions. This liquid stream is further purified in a separate sequence of liquid purification steps to be. described later,

[003.1 J Water may be added to the solid phase stream obtained from the slurry filter press to obtain a suspension of SiC, Si, and Fe particles of a predetermined solid-liquid ratio.

[0.032] Referring to Figure i , the suspension of SiC* Si, and Fe particles is then fed to a hydrocyclone system to obtain an underflow stream and. an. overflow stream. Hydrocyclone is a form of wet centrifugal separation ©f the particles into coarse and fine .fractions. The feed enters the h drocyciofle &nge¾tiafly_s after which the heavy or coarse particles start to spiral down the conical bottom section and leaves as an "underflow". On the other hand, the fine fraction leaves via the to section of the hydrocycione as an. "overflow",

|0033j The hydrocycione system may include one or more hydrocyelones. In various

embodiments, the hydrocycione system may include 4 to 8. hydrocyciones. The hydrocyciones may be connected in series. Other forms of connecti on of the hydioeyclones. may also be possible.

[00341 fit various embodiments, one or more of the hydrocyciones, such as 4 to 8. hydrocyciones including 4, 6, or 8 hydrocyciones, May be connected in series and operate in a counter-current arrangement, in suc arrangement* each hydrocycione may produce an overflow stream and an underflo stream. Bach underflow stream of an upstream hydrocycione: m y be fed to

downstream hydrocycione. Each overflow stream of a downstream hydrocycione may be fed to an upstream, hydrocycione.

[0035] .It has been found by the inventors that a series of 4 to 8. hydrocyciones operating in a counter- current arrangement is able to achieve optimal separstioii of fines with high yields of recycled SIC.

[00361 The inventors have surprisingly found that in the operation of the present hydrocycione system, a combination of feed pressure, solid content in the feed to the hydrocycione system, temperature, and use of ultrasonic may be useful in aiding the separation and SiC recovery process. 0037] hi various embodiments, the temperature may be set in the range of 45 °C .to 60 °C.

[0038{ In various embodiments, the ultrasonic frequency may be set at more than 24 kf x.

[00391 In various embodiments, the feed ressure may be set at 3.5 ± 0.5 bar. {0040] In various embodiments, the solid ..concentration in the feed may be set at between 11 wt% and 15 wt¾. f 0041 In one example, by treating a -slurry with JIS20Q0 grit size using a temperature range of 45 °C- to 60 "C and ultrasonic frequency at more than 24 kHz, the Si impurities can be further reduced by at least 60% while the Fe impurities can be further reduced by at least 20%, as disclosed in copending international Application No. PCT/IB2013/O5 60i filed on October 24, 2013, the contents of which are- incorporated herein in its entirety.

{0042.) in addition to the use of the temperature range and ultrasonic frequency mentioned above, by_. selecting the following feed pressure and solid concentration in the feed for the respective SiC grit size, the corresponding impurities level can be achieved (Table I):

Table ¾ . Performance of hydro cyclone system using various feed pressure and solid concentration in combination with a temperature range of 45 °C to 60 °C and ultrasonic frequency at more than 24 kFlz. Recovery Yield; Estimated to be > 8S¾,

10043] Figure. 2 A shows a SEM (20Q0x. magnification) of the recycled F5Q0 grit size SiC particles recovered from present ^'method according to the operating conditions given in Table 1. in this case, Si content i about 0.13 wt% and Fe content is about 0.05 wt%. [0044] Figure 2B shows a SEM (2Q00x magnification) of the -recycled J.IS2OG0 grit size S iC particles recovered from present method according to the operating conditions given in Table I . in this case, Si content is about 0.43 wt% and Fe contest is about 0,63

I004SJ Figure 2C: shows a SEM (2000x magnification) of the recycled FS00 grit size SiC particles, recovered from present method according to the- operating conditions given in Table 1 , this- case, Si content: is about 0.14 wt% and Fe content is about 0.65 wt%._:

(0Θ46] in- arious embodiments, after the hydrocye!one system treatment, the underflow from the last hydrocyclone is separated into solid and liquid via a product .filter press. Pressure filtration, cake wasliing and air blowing ensure the solid-liquid separation, achieving low water content in the solid. Optimum reflux time prior to filtration and quality of filter cloth also play vital roles in filtration -.efficiency. The solid is then transferred for drying and the filtrate is recycled within the process.

[0047] In various embodiments, ki the next step continuous drying of the solid from product filter press takes place in a product dryer under atmospheric pressure, using either heat or microwave. As the solid is conveyed along the dryer continuously, heat or microwave is applied to achieve .uniform drying. This allows the powder to be dried in a continuous and even manner, without over- dryin -Of "baking". The condensate is exhausted out of the -dryer through a bag filter. Dried powder is discharged and conveyed pneumatically to the next step.

|0O48| In various embodiments, the solid from product filter press are dried in the product dryer at a drying. temperature of 150 °C to 200 °C. In one example, the water content in the solid from the product filter press is < 20 wt%. With the right range of temperauue, final moisture, content of <0.30-wt% can be achieved. The same effect can be achieved by using I fcW of microwave for ever 1 kg water/hour to be dried. 10049 After the drying step, the dried powder may -be fed to a product sieve. The purpose of ultrasonic .. sieving is to separate any agglomerates or large particles (overs) in the dried SiC. The overs retained on the 42μηι mesh screen are being collected and returned to the process as rework material 005O] in various embodiments, after the hydrocyclone system treatment, (lie overflow from the first !iydroeyefone is separated into solid and liquid in HC fines filter press. Pressure filtration and air blowing ensure the solid-liquid separation, achieving low water content in the solid. Optimum re-flux time prior to filtration and quality of filter cloth also playvital role in filtration efficiency. The solid is transferred for drying and the filtrate is recycled within the process.

(0051] Continuous drying of the solid from HC fines filter press takes place in a HC fines dryer under atmospheric pressure, using either heat or microwave, The condensate is exhausted out of the dryer through a bag filter. Dried powder is discharged and collected as SiSiCar®,

[00521 various embodiments, the solid from HC fines filter press are dried in the HC fines dryer at a drying temperature of 120 *C to 160 °C . In one example, the water content in the solid from the product filter press is < 30 wt%. With the right range of temperature, a final moisture content of < 5 wt%_: can be achieved. The same effect can be achieved by using 1 kW of microwave for every 1 kg water/hour to be dried.

10053] Turning now to the liquid purification stage, removal, of water from the first liquid phase stream takes place in a water^■.distillation column. By using distillation technology, it enables precise separation as only the pure component gets evaporated, making it possible to evaporate, condense and collect the distillate water for reuse in other process. By distilling only water from the liquid stream, a residue comprising of only glycol wife trace amount of water, suspended, fine particles, and dissolved ions is obtained. This residue is then transferred to the next step for glycol recovery,

{0054] in various embodiments, the water distillation column is operated at between 110 °C and 120 °C and at a vacuum, pressure of 70 ± 10 mbar. The feed composition may-include water content: 52 wt% - 60 wt%, and glycol content : 40 wt% - 48 wt%; With the righ t range of operating : temperature and vacuum pressure, a final moisture content of < 0.50 wt% can.be achieved.

|0055] Glycol recovery is done by processing the water distillation column residue through a glycol distillation column. Under vacuum condition, it decreases the boiling point of glycol resulting in a significant reduction of utility required and prevents any risk of glycol cracking. In this step, glycol will be evaporated, condensed and collected as a distillate while the residue, which is made up of minimal amount of glycol, fine particles, and dissolved ions, will be disposed as waste.

[005.6] The Operation conditions for the various types of glycol distillation are summarized in Table 2 below:

O erate Ccfidsttcn

Tgmperaiufe (¾} V-acaufR Presses {ai ar}-

Poiyethylsne G iycci

iSO ^'C a¾- 0,t m 3i

^:Die¾yienefilycoh

15Q - Ι?ΰ¾

|D£Gi

?repySei«6iycel (PG} Ϊ15 -Wit 7Gil0ru¾≤r

Dipr pyiene <5; co!

w-m ^■TBtlOmbar

{0057; [0858] Table 2, Summary of opening coilditions for yarioxiS- glycol distillations with a feed composition of glycol content; > 99 5 wt% and water content: < 0.5 wl- o.

(00591 With the right rauge-of operating; temperature and vacuura pressure, the following imparities level and product glycol properties can be achieved (Table 3):

[06601

100611 Table 3· Product glycol pro&eru s .based on opiating conditions given in Tabled

Recovery yteRof ?5-99% canb obtained.

[0062] Table 4 below gives the specific operaiiug conditions for various glycols, and the product glycol quality,

Table 4. Results of the piO c jiycoLquaiit ^' 0r various glycols for the specified operating conditions.

[0064] Figure 3 shows photograph of the product glycol, specifically, PEG, DPG, DEC, and PG, recovered by the present liquid purification stage, corresponding to Table 4,

|0065] In a second aspect of the disclosure, there is disclosed a system for recovering silicon carbide (SiC) particles and glycol from a slurry, wherein the slurry comprises a mixture of SiC, Si, and Fe particles suspended in glycol.

[0066] The system may include:

a s irty filter press for separating the slurry into a first solid phase stream and a first liquid phase stream, wherein the first solid phase stream comprises essentially the SiC, Si, and Fe particles and wherein the first liquid phase stream com rises: essentiall glycol, water, suspended fine particles, and dissolved ions; a solid purification stage, wherein the solid purification stage comprises: a hydrocyclone system to obtain an underflow. Stream comprising recovered SiC particles in water and an overflow stream comprising essentially fine particles of SiC, Si and Fe suspended in water, wherein the hydrocyclone system comprises one or more hydrocyck es.;. a product filter press to obtain the recovered SiC and to remove water; a liquid purification stage, wherein the liquid purification stage comprises- a water distillation column to obtain a first, residue and a first distillate comprising water; and a glycol distillation column to obtain a second distillate comprising .glycol. 8067j In various embodiments,, the hydrocyelone system, comprises more than one hydroeycione. For example, the hydro^'cyclone system comprises 4 to 8 hydrocyclones.

|^'0O68] hi various embodiments, the hydrocycloues are connected ½ series. For example, the hydrocyclones cormected in -series operate in a counter-current asxangerrseni, whexemeach hydrocyelone produces an overflow stream and an underflow stream, wherein, each: underflow Stream of an upstream .hydrocyelone is fed to a downstream hydro eye lone, and wherein each overflow stream of a downstream hydrocyclone is fed to an upstream hydroeyelone.

[0069] in various, embodiments, the system comprises a product dryer downstream of the product filler press for drying the recovered SiC particles and may further comprise a product sieve downstream of the product dryer for sieving the dried S C particles to separate any agglomerates or large particles (overs). ¾Μ>70] In various embodiments, the system ma further comprise ^'fines filter press configurable, to receive the overflow from the hydrocyclone system.

[0071] In additional embodiments, the system may further comprise a fines dryer downstream, of the fines, filter press for drying the fines products from the fines filter press.

10672| By "comprising" it is meant, including, but not limited to, whatever follows the word "comprising". Thus, use of the term "comprising" indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present

[0073} By "consisting of" is .meant including, an limited to, whatever follows the phrase

"consisting of. Thus, the phrase "consisting o ' indicates thai the listed elements: are required or mandatory, and that no other elements may be present. {0074} The inventions illustratively deseribed herein may suitably be practiced in the absence of any element or elements, limitation or Hmitations, not. specifically disclosed herein. Thus, for example, the terms '^•'comprising",, "including'⁵, "containing", etc. shall be read, expansively and without Mini tatiort. Additionally, the terms and expressions employed herein have been used as ienns of deacripiion and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and deseribed or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification, and variation of the inventions embodied. therein. herein disclosed may be resorted to by those skilled in {h art, and that such modifications and variations are considered to be within the scope of this invention.

{00751 The invention has been described broadly and. genetically herein. Each, of the narrower^' species and sub-generic groupings falling within the generic disclosure also form part of the invention. This includes the generic, description of the invention with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein,. 0076{ Other embodiments, are within the following claims and non-limiting examples.

I S

Claims

A method for recovering silicon carbide (SiC) partieies and giyeoi from, a siurry, wherein the slurry comprises a mixture of SiC, Si, and Fe particles suspended in giyeoi. the. method, comprising: separating in a slurry filter press th slurr into a first solid: phase stream, and a first liquid phase stre m whereisi the first solid phase stream eomprises essentially the SiC, Si, and Fe particles and wherein the first liquid phase stream comprises essentially glycol, water, suspended fine particles, and dissolved, ions;

treating the first solid phase stream to & solid purification stage, wherein the solid purification stage comprises:

adding water to the first solid phase stream to obtain a suspension of SiC, Si, and Fe particles in water;

feeding the suspension of SiC, Si, and Fe particles to a hydrocycione system to obtain an underflow stream comprising recovered SiC particles in water and an overflow stream comprising essentially fine particles of SiC, Si and Fe suspended in water, wherein: the hydrocycione system comprises one: or more hydrocyclones; feeding the underflow stream to a product filter press to obtain the recovered SiC and to remove water; treating the first liquid phase stream to a liquid, purification stage, wherein the liquid purification stage comprises:

feeding the. first .liquid phase stream to. a water distillation column to obtain a. first residue and a first distillate comprising water; feedin the first -residue to a glycol distillation column to obtain a second distillate comprising glycol.

The method of claim 1 , wherein the water distillation, column is operated at between 1 10 °C and 120 °€ and at a vacuum pressure of 70 ± 10 mbar,

The method of claim I or 2, wherein the glycol is polyethyiene. glycol 200 (PEG), the distillation -column is operated at .180 °C and at a vacuum pressure of 0. 1 to 0.1 mbar.

The method of claim 1 or 2, wherein the glycol is diethylene glycol (PEG), me distillation column is operated at between 150 °C and 170 °C and at a. vaeuum. -pressure of 70 ± 10 mbar.

The method of claim 1 or 2,. wherein the glycol is propylene glycol (PG), the: distillation column is operated at between 115 °C and 140 ^CC and at a vaeuum pressure of 70 ± 10 mbar.

The method of claim 1 or 2,. wherein the glycol is dipropylene glycol (DPG), the .distillation eo!utnn is operated at between. 130 °C and ISO °C and at a vacuum pressure .of 70.* 10 mbar.

The method of any one of claims 1-6, wherein fee suspension fed to the hydrocyeloae system is heated at a range of 45 °C to 60 °C and is treated with ultrasonic frequency of at least 24 kHz, further wherein the suspension is fed at a feed pressure of 3,5^■± 0.5 bar and the solid concentration of SiC, Si, and Fe particles in the suspension is set at between 11 wt% and 15 wt .

The method of any one of claims 1-7, wherein the hydroeyelone system, comprises more than one hydroeyelone.

The method of claim 8, whereiu the hydroeyelone system comprises 4 to 8 hydroeyclones. The method of claim 9, wherein-.-the hydrocyclones are connected in series. The method of claim 10, wherein the hydrocye-lones connected in. series operate in a counter- eurreat arrangement, wherein each hydrocycione produces an overflow stream md &n underflow stream, wherein each underflow stream of an upstream hvdrocvcloae is- ed to a downstream hydroeyckrae, wherein each underflow stream is heated at. a range of 45 °C to 60 "C and each underflow stream is treated with ultrasonic frequency of at least 24 kHz, and wherein each overflow stream of a downstream hydrocyclone- is fed to an upstream hydroeyelorie.

The method of any one of claims 7-11, wherein the feed pressure is set at 3.5 bar.

The method of any one of claims 7- 12, wherein the solid concentration -of SiC. Si, and Fe particles in the suspension is set at 12 wt%, 12,5 wt%, or 13 wt%.

Hie method of any one of claims 1-13, further comprising feeding the recovered S C particles to a product dryer, either at a drying temperature of 150 °C to 200 °C or 1 kW of microwave for every 1 kg water/hour to be dried.

The method of claim 1 , further comprising sieving the dried SiC particles to separate any agglomerates o iarge particf.es (overs).

The method of any one of claim ΙΛ 5, further comprising feeding the overflow stream from the hydrocyclone system to a. fines filter press to remove water, thereby recovering fine particles of SiC, Si and Fe.

The method of claim 16, further comprising feeding the recovered fine particles of SiC, Si and Fe to a fines dryer, either at a drying temperature of 120 °C to 160 °C, or 1 kW of microwave for every I kg water/hour- to be dried. A system for recovering silicon, carbide (SiC) particles and glycol torn a slurry, wherei the slurry comprises a mixture of SiC, Si, and Fe particles suspended in glycol, the system, comprising:

^•a slurry filter press for separating the slurry into a first solid phase stream and a first liquid phase stream, wherein the first solid phase stream comprises essentially the SiC, Si, and Fe particles and wherein the first liquid phase stream comprises essentiall glycol, water, suspended Sue particles, and. dissolved ions

a solid purification stage, wherein the solid purification stage comprises:

a hydrocyclorie system to obtain an underflow stream comprising recovered SiC partieles in water and an overilow stream comprising essentially fine particles of SiC, Si and Fe suspended in water, wherein the hydroeycione system comprises one or more hydrocyclones; a product filter press to obtain the recovered SiC and to remove water; a liquid purification stage, wherein, the liquid pmification stage comprises:

a water distillation column to obtain a first residue and a first distillate comprisin water; and

a glycol distillation column to obtai a second distillate comprising glycol.

The system of claim IS, wherein the hydroeycione system comprises more than one hydroeycione.

The system of claim 1 , wherein the hydrocyeloae system comprises 4 to 8 hydrocyclones. The system of claim 19 or 20, wherein the hydrocyclones are connected in series.

22. The system of claim 21, wherein the ydrocyc!ones connected in series operate in a.eounter- curreni arrangemeiit, wherein each hydrocyctone produces an overflow stream and an underflow stream, wherein eaeh ^'underflow stream of an upstream hydrocyclone is fed to a downstream hydrocyclone, and wherein each overflow stream of a downstream hydrocyclone is fed to an ups tream: hydrocyclone.

23. The system of any one of claims 18-22, further comprising s product dryer downstream of the product filter press for drying the recovered SiC particles.

24. The system of claim 23, further comprising; a product sieve downstream of the product dryer for sieving the dried SiC particles to separate any agglomerates or large particles (overs).

25. The system of any one of claims- 18-24, further comprising a fines filter press configurable to receive the overflow from the hydrocyclone system,

26. The system of claim 25, further comprising a fines dryer downstream of the- fines filter press for drying the fines products from the fines filter press.