WO2007116326A2

WO2007116326A2 - Production of solar and electronic grade silicon from aluminosilicate containing material

Info

Publication number: WO2007116326A2
Application number: PCT/IB2007/050535
Authority: WO
Inventors: Tsvi Kaufman; Evgeny Meyerovich
Original assignee: Hyattville Company Ltd.
Priority date: 2006-02-20
Filing date: 2007-02-20
Publication date: 2007-10-18
Also published as: EP1991500A2; WO2007116326A3

Abstract

The present invention relates to the recovery of silica from aluminosilicate-containing material and the production of solar and/or electronic grade silicon there from. In particular, a process for manufacturing silicon comprises subjecting highly pure and particulate silica in amorphous form to an in-flight plasma carbothermic reduction in a plasma reactor comprising a plasma torch and a vessel suitable for plasma-associated chemical reaction of silica and collection of liquid silicon. The highly pure and particulate silica is preferably produced using a process for manufacturing silica and/or alumina from an aluminosilicate-containing material comprising mixing the material with a metal chloride, preferably calcium chloride, being in the form of a solution or slurry, subjecting the wet mixture to a granulation step, burning the granules at a temperature of 900-1300°C, leaching the obtained heated mixture with hydrochloric acid to obtain a salt solution and insoluble silica, separating insoluble silica from the salt solution, and recovering dry silica. Alumina may be produced by crystallizing AlCl3 from the salt solution and heating the AlCl3*6H2O crystals to produce alumina.

Description

Production of solar and electronic grade silicon from aluminosilicate containing material

The present invention relates to the recovery of silica from aluminosilicate-containing material and the production of solar grade silicon there from. The present invention also relates to a device suitable for silicon production.

The majority of today' s solar cells are based on silicon. The life cycle of a multicrystalline silicon solar cell module starts with the mining and refining of silica (quartz). Silica is reduced with carbon and the reduction step is followed by a lengthy purification process. The resulting highly pure silicon is melted and cast into blocks of multicrystalline silicon. The blocks are portioned into ingots, which are subsequently sliced into wafers. The wafers are processed into solar cells by etching, texturing, formation of the emitter layer, application of back surface layer and contacts and passivation and antireflective coating. The solar cells are tested, interconnected and subsequently encapsulated and framed into modules.

There are several methods for the production of solar grade silicon. Whether a chemical process purification methods or a metallurgical process, all these methods follow the carbothermic reduction of silica and subsequently a lengthy purification of silicon to upgrade it from a purity level of about 98.5% to >99.999%, which is necessary for solar cell application .

There is a strong need in the art for simpler and more cost-effective method for production of solar grade silicon from silica. It was surprisingly found by the present invention that the provision of highly pure silica in a certain particulate form from aluminosilicate-containing material allowed its subsequent conversion to solar grade silicon through in-flight plasma carbothermic reduction.

EP 0 866 769 discloses a process for the recovery of alumina and silica from aluminosilicate-containing material, comprising the steps of mixing the aluminosilicate-containing material with calcium chloride, heating the mixture at a temperature of 900-1300⁰C, leaching the obtained heated mixture with mineral acid to obtain a solution of aluminium and calcium salts and insoluble silica, separating insoluble silica from the solution, and further processing the salt solution. The silica coming out of this process is not suitable for use in the preparation of solar grade silicon by in-flight plasma carbothermic reduction.

The present invention discloses that provision of the mixture of a metal chloride and the aluminosilicate-containing material in the form of granules combined with subsequent burning of the granules advantageously provides silica with characteristics suitable for use in the production of solar grade silicon by in-flight plasma carbothermic reduction.

Thus, in a first aspect, the present invention provides a process for manufacturing of silica from an aluminosilicate- containing material comprising: mixing the material with a metal chloride being in the form of a solution or slurry, subjecting the wet mixture to a granulation step, burning the obtained granules at a temperature of 900-

1300⁰C, leaching the obtained heated mixture with a mineral acid to obtain a salt solution and insoluble silica, separating insoluble silica from the salt solution, and recovering the silica.

The aluminosilicate-containing material may be any material suitable for the recovery of silica, for instance may contain industrial residues like coal ash or fly ash.

In a preferred embodiment, the aluminosilicate- containing material is substantially free from boron. More preferably, the boron level of the aluminosilicate-containing material is maximally 5 ppmw, most preferably maximally 1 ppmw. The aluminosilicate-containing material may be composed of several different aluminosilicate raw materials, for example coal ash, fly ash and/or dross tailings (metal oxide values extracted from the salt cake residue produced during the melting of aluminum scrap in a secondary aluminum recycling process) that are appropriately mixed to obtain a suitable aluminosilicate-containing starting material, for instance fulfilling the requirements for boron level.

The aluminosilicate-containing material is mixed with a metal chloride. The metal chloride preferably is calcium chloride, sodium chloride, potassium chloride and/or ammonium chloride, more preferably is calcium chloride. The mixing with the metal chloride, e.g. calcium chloride, may occur simultaneously with mixing of the different raw materials as described above. Preferably, the metal, e.g. calcium, chloride is added to the aluminosilicate-containing material at a weight ratio of 0.5-3:1 depending on the phase composition of the material and its relative alumina and silica content. More preferably, the weight ratio is in the range of 0.5-2:1, most preferably is 1.5:1. Also preferably, metal, e.g. calcium, chloride is added to the aluminosilicate-containing material in the form of a solution or slurry. When dry metal chloride is used, sufficient water may be added to the mixture to enable granulation .

Mixing may preferably be done by proceeding the aluminosilicate-containing material (or the different raw materials making up the aluminosilicate-containing material), preferably in the form of a slurry, into a wet ball mill together with a metal chloride solution or slurry. The aluminosilicate material as well as the metal chloride preferably have a concentration in the slurry or solution of about 30-50% (w/w) , preferably of about 40% (w/w) .

Sedimentation in the resulting slurry is avoided, preferably by constant stirring at room temperature.

The slurry of aluminosilicate-containing material and metal chloride is subsequently transferred to a granulation unit, preferably by spraying the slurry into the granulation unit. More preferably, the slurry is sprayed into the granulator at the bottom of the granulator.

Prior to spraying the slurry into the granulator, the slurry may be filtered over a membrane with a pore size < 500 μm to avoid clogging of the spraying nozzle (s). The nozzle may be a one- or a two- or more-component nozzle.

Preferably, granulation is performed by fluidized bed granulation. A fluidized bed for production of about 1.7 ton/hour has a distribution plate with an area of 1.5-2.5 m², preferably 1.8-2.3 m². A temperature is applied of 550-650 ⁰C under the distribution plate and 130-180 ⁰C in the bed. Dust from the drying bed is preferably recycled into the wet ball mill. Granulation conveniently is accompanied by drying.

The bulk weight of the dry granules is about 0.8-1 kg/m³ with a water content of about 1%. The average granule size is 2-10 mm, preferably 3-8 mm.

The dry granules are transferred to a heating unit, for instance a rotary kiln, or any other appropriate industrial furnace. Heating (typically called burning) occurs at a temperature just below the melting temperature of the granulate. Preferably, burning occurs at a temperature of 900-1300 ⁰C, preferably 1150-1250 ⁰C, more preferably 1150-1200 ⁰C, for a time period of at least 2 hours. During burning, HCL is sublimated.

The components of the aluminosilicate-containing material as well as the calcium chloride react in the burning step. This reaction implies breaking down the acid-resistant Mullite (Al₂O₃^SiO₂) phase and forming a calcium aluminium silicate phase, preferable Gehlenite (2CaO*Al₂O₃*SiO₂) .

The material from the heating unit (the burnt material or clinker) may then be cooled in an air cooling unit. The burnt material is pneumatically pushed by the cooling air into a cyclone for separation of the solids that go to the leaching reactor from gases and dust. The hot air (at a temperature of about 600⁰C) may be recycled by returning it into the heating kiln.

The hot gases (at about 700 ⁰C) from the heating unit, including dust and HCl gas, are transferred into a unit, called the dust cell, to precipitate most of the dust and exchange heat with a steam heater. The temperature is reduced to about 300⁰C and the cooled gases enter the quencher (preliminary scrubber) to separate the remaining dust. The gases then flow to a scrubber to absorb HCl for the production of concentrated hydrochloric acid. Conveniently, a fan is used to blow the clean gases into the ecological scrubber. The clinker is fed into a leaching reactor, along with a mineral acid, preferably HCl, H₂SO₄ and/or HNO₃, more preferably concentrated HCl. Leaching typically occurs at 95-100 °C for a period of about 1 hour and results in a salt solution and insoluble silica.

The resulting salt solution may contain a number of salts in addition to AICI3 and CaCl2, such as FeCl₃, MgCl₂ and heavy metal salts. The solid silica residue may be separated from the salt solution by known methods such as filtration and/or decantation.

Preferably, the slurry of the insoluble material in the acidic salt solution is delivered to a filtration unit. Silica recovery comprises washing the silica cake on the filter and drying the silica. The recovered silica may be subjected to quality control prior to its transfer to a storage unit. Optionally, the silica may be subjected to a fine milling process .

The process of the invention provides amorphous silica with a combination of characteristics hitherto unknown in the art. These characteristics advantageously allow the silica to be used in an in-flight plasma carbothermic reduction process for the preparation of solar-grade silicon.

The amorphous silica obtainable by the process of the first aspect forms a second aspect of this invention and preferably has the following characteristics. It has a purity (silica content) of at least 99.7%, preferably at least 99.9%; a boron content of at the most 1 ppm; a phosphorous content of at the most 5 ppm, preferably at the most 1 ppm; a surface area (BET) of 150-350 m²/g, preferably 175-325 m²/g, more preferably 200-300 m²/g; an average particle size of 5-80 μm, preferably 5- 20 μm, more preferable 5-10 μm; a LOI (1050⁰C) of 6-8%, preferably of 7-7.5% ; a tapped density of 200-500 g/1, preferably of 250-300 g/1; a pH of at least 4.

The amorphous silica preferably has a particle size distribution as follows: D(90): 10-80 μm, D(50): 5-40 μm, D(25): 1-25 μm, D(IO): <10 μm, preferably as follows: D(90): 12-50 μm, D(50): 6-15 μm, D(25): 2-5 μm, D(IO): <1 μm, more preferably as follows: D(90): 13-20 μm, D(50): 6-9 μm, D(25): 3-5 m, D(IO): <1 μm; Especially preferred silica' s have specifications as follows :

SiO₂ ≥ 99.7%

Boron max. lppmw

Phosphorous max. 5ppmw

Surface area (BET) 150-350 m²/g Particle size distribution :

D(90) : 12-50 μm

D(50) : 6-15 μm

D(25) : 2-5 μm

D(IO) : <1 μm

LOI (1050° C) 6-8% pH >4

Density (tapped) 200-500 g/1

And preferably:

SiO₂ > 99.9%

Boron max . lppmw

Phosphorous max. lppmw

Surface area (BET) 200-300 m²/g

Particle size distribution :

D(90) : 13-20 μm

D (50) : 6-9 μm

D(25) : 3-5 μm

D(IO) : <1 μm

LOI (1050° C) 7-7.5% pH >4

Density (tapped) 250-300 g/1

And more preferably:

SiO₂ > 99.9%

Boron max . lppmw

Phosphorous max . lppmw

Surface area (BET) 200-300 mVg

Particle size distribution :

D(90) : 15 μm

D (50) : 8 μm

D (25) : 3 μm

D(IO) : <1 μm LOI ( 1050 ° C ) 7 - 7 . 5 % pH >4

Density (tapped) 250-300 g/1

The above features are measured using techniques commonly known in the art. The surface area is measured by nitrogen absorption (BET) , the particle size distribution by laser diffraction. The pH of Silica is measured using a suspension of 10 gr of dry silica in 100 ml of water at 25°C. The impurity content is analyzed with atomic-absorption spectroscopy and the silica content is calculated as a residual value .

In a third aspect, the present invention provides a process for manufacturing silicon from silica comprising subjecting highly pure and particulate silica in amorphous form to an in-flight plasma carbothermic reduction using a plasma reactor comprising a plasma torch and a vessel for chemical reaction and collection of liquid silicon.

The process of the third aspect advantageously provides silicon with a purity of > 99.99%, preferably > 99.999%, more preferably > 99.9999%.

For the in-flight plasma carbothermic reduction process, highly pure and particulate silica in amorphous form is preferably used. In the context of this invention, "highly pure and particulate silica" means that the silica has a purity of at least 99%, preferably at least 99,5%, more preferably at least 99,7%, most preferably at least 99.9% and consists of particles with a average particle size of:

D(90) 10-80 μm D(50) 5-40 μm D(25) 1-25 μm D(IO) <10 μm, preferably of D(90) 12-50 μm D(50) 6-15 μm D(25) 2-5 μm D(IO) <1 μm, and more preferably of D (90) : 13-20 μm

D(50) : 6-9 μm D(25) : 3-5 μm D(IO) : <1 μm, and with an average surface area (BET) of 150-350 m²/g, preferable of 175-325 m²/g and more preferable of 200-300 m²/g.

In a preferred embodiment, silica is used that is obtainable by the process of the first aspect of this invention. This silica conveniently is stored in silos having a capacity of a one month production, protected from dust and dirt.

In Figure 1, a plasma reactor is depicted suitable for use in the carbothermic reduction of silica according to the invention .

The plasma reactor 1 contains one or more plasma torches 2, also called plasmatron, suitable for an in-flight process, and a vessel 3 suitable for plasma-associated chemical reaction and collection of liquid silicon, and containing an outlet 4 for further processing of liquid silicon.

The plasma flame for the in-flight carbothermic reduction process may be generated by all available plasma torch systems, for example a DC arc plasma torch or an RF electromagnetic field torch or others. Preferably, the plasma torch is a DC arc plasma torch charged with an electric capacity suitable to perform the thermodynamic reactions with consideration of energy losses (about 50%), and more preferably is an 8-10 MWh DC arc plasma torch. The system is suitable for production of about 260-320 kg silicon/hour.

In the preferred DC plasma torch the electric arc originates at the cathode tip and attaches at the start of the anode (length = 0.1-0.25 m) . The flow in the nozzle and in the jet is axial (no swirl component), steady state, and rotationally symmetric. Pressure is constant and equal to atmospheric pressure around the plasma plume. The electric discharge is stationary. Since the anode is water cooled, the torch wall temperature is about 700⁰C for the entire column.

The vessel 3 of the plasma reactor is a vessel suitable for plasma-associated chemical reactions and liquid silicon collection and contains an outlet 4 for further processing of liquid silicon. Further processing may include gas blowing refining, electromagnetic casting, directional solidification and/or subjecting silicon to a Czochralski process.

The plasma torch 2 is positioned in such a way that the hot plasma stream that is generated in the plasma torch is directed into vessel 3. The highly pure and particulate silica is fed into the plasma stream, preferably in the area where the temperature is highest, i.e. immediately downstream of the plasma torch. Feeding may be done by, for instance, use of a screw-feeder for feeding through a pneumatic transporter, with the aid of a transport gas. The transport gas comprises nitrogen and/or a burning gas that helps to control the reducing medium. The high temperature of the plasma sublimates the silica into gaseous form, together with small quantities of volatile impurities. The impurities may be selectively reduced and separated by controlling the equilibrium phase. At the same time, reaction gas is sparged into the centre of the plasma stream, as close as possible to the silica evaporation point. Preferably, the reaction gas enters the reaction vessel via the plasma torch. The reaction gas comprises air and a burning gas like methane or a propane/butane mixture.

In the plasma, the hot, ionized reaction gas reacts to form carbon monoxide that reduces the silica in gaseous form within less then 10 μs. The resulting silicon is then cooled into liquid form on the walls of the reaction/collection vessel and collected into the collection area of the vessel.

The production of pure polycrystalline silicon is achieved by reduction and purification of amorphous silica.

The reduction process is based on the reaction:

SiO₂ + 2C → Si + 2CO (1)

To obtain a reducing medium, burning gas (e.g. CH₄) and air are supplied in a proportion that provides for the reactions :

CH₄ —→ C + 2H₂ (2) at a temperature > 2000⁰C

2CH₄ + O₂ → 2CO + 4H₂ (3) in the presence of oxygen

Reaction (1) occurs at the lower part of the plasma at a temperature of about 3000 °-5000⁰C . To secure a complete reduction, burning gas is supplied in excess as compared to the stoichiometric amount of reaction (1) . Reaction (2) and (3) occur in the upper plasma area, where the burning gas and air are supplied to produce the reducing CO stream that flows to the lower part of the plasma area, to react with the silica.

In a preferred embodiment, a plasma reactor is used as is provided by a further aspect of this invention.

To avoid contamination, the walls of the reaction/collection vessel are made of an inert material, such as stainless steel, and are cooled, for instance water-cooled. At the start of operation, the silicon will deposit on the walls as a solid thin layer until reliable heat-isolation of the walls is achieved that would allow maintaining 1700 - 2000⁰C inside the vessel. At that temperature the silicon in liquid form will flow down the walls to a collection area and accumulate there.

At the high temperature-liquid melt state of silicon (1700 °C-2000⁰C) , the impurities, like metals, will transfer into the gas phase. This allows their discharge, along with other off-gases, to a water-cooled cyclone 5, where the impurities are collected in the form of solid particles. At the cyclone outlet, gases will pass through a flame igniter for securing burning of highly flammable off-gases.

In a first embodiment, the collected liquid silicon may reach at this stage the high purity level, e.g. ≥ 99.999% or the preferred purity level > 99.9999%.

However, due to practical production reasons and/or specific purity requirements, e.g. ≥ 99.999999% (>8N) , and to insure constant production of very high purity levels, still further purification steps may be necessary.

Thus, in a second embodiment, the obtained silicon may be further purified by subjecting the silicon in liquid form online to a multistage gas blowing refining process that performs additional chemical reactions and allows evaporation of impurities to form volatile molecular species to be separated from the liquid silicon.

In the multistage gas blowing refining process, the gas is delivered through a water cooled tube connected vertically and submerged in the melt. The gas may be any gas that will cause an exothermic reaction with the molten silicon, which provides heat to keep the silicon in the molten stage and evaporates the metal impurities. The used gas may be oxygen, HCl, chlorine, steam; preferably oxygen. This process may be performed together with liquid stirring by gas or with electromagnetic stirring, allowing further refining.

The refining process is preferably performed in a device comprising multiple water cooled metallurgical vessels (two or more but maximally five) connected online and equipped with gas blowing pipes to obtain continuous exothermic reactions .

The process may take an hour to achieve super pure silicon >99.999999 (8N) preferable >99.9999999 (9N).

Further purification may include directional solidification and/or ingot casting and/or electromagnetic casting.

In a third embodiment, liquid silicon may be subjected to an electromagnetic casting process (EMC) . During the casting process liquid silicon is added on a vertical moveable substrate base shaped in the required ingot form and protected from dropping by an electromagnetic field. A flow of inert gas cools the substrate and the ingot surface starting ingot solidification. Down movement of the solid (cooled) ingot with a controlled speed creates multicrystalline solidification. In the ingot top an area of transformation from liquid to solid is created (floating zone) . Growth of the floating zone is accompanied by a purification process (zone refining) as for most impurities the segregation coefficient is smaller than 1, i.e. the equilibrium concentration is smaller in the solid then in the melt: k = C solid / C liquid < 1. Due to that fact the metallic impurities will concentrate in the liquid (top) and will be reduced significantly in the solid ingot.

In a fourth embodiment, monocrystalline silicon may be produced by subjecting the silicon melt to a Czochralski process .

Especially a combination of one or two or three embodiments will provide silicon with a purity level of ≥ 99.9999%, preferably > 99.999999% and most preferable > 99.9999999%.

In a fourth aspect, the present invention provides a device comprising a plasma reactor suitable for in-flight plasma carbothermic reduction and, optionally, a secondary vessel for further purification.

The plasma reactor 1 contains one or more plasma torches 2, also called plasmatron, suitable for an in-flight process, and a vessel 3 suitable for plasma-associated chemical reaction and collection of liquid silicon.

Preferably, the plasma torch is a DC arc plasma torch. The requirement that the vessel is suitable for plasma- associated chemical reactions and liquid silicon collection implicates that the vessel should be capable to withstand the high temperature of the plasma reactions and the liquid silicon. Preferably, the walls of the reaction/collection vessel are made of an inert material, such as stainless steel.

The vessel should contain an outlet 4 for further processing of liquid silicon. The outlet is positioned in the bottom part of the vessel, where liquid silicon is collected. The outlet preferably comprised a siphon configuration.

A secondary vessel for additional silicon purification may comprise a water cooled vessel suitable for a multistage gas blowing refining process and/or a water cooled ladle suitable for pouring liquid silicon to an electromagnetic casting process for directional solidification equipped with a melt discharge system and/or a melt discharge for ingot casting suitable for further processing, for example a Czochralski process.

In a further aspect, the present invention provides a process for manufacturing alumina from an aluminosilicate- containing material comprising: mixing the material with metal chloride, preferably calcium chloride, being in the form of a solution or slurry, subjecting the wet mixture to a granulation step, burning the granules at a temperature of 900-1300⁰C, leaching the obtained heated mixture with a mineral acid, preferably hydrochloric acid, to obtain a salt solution and insoluble silica, separating insoluble silica from the solution, crystallizing aluminium chloride hexahydrate from the solution, heating the aluminium chloride hexahydrate crystals to produce alumina . The alumina preferably is recovered from the process of the first aspect for silica production. The salt solution obtained according to the process of the first aspect after separation of solid silica is subjected to aluminium chloride hexahydrate (A1C1₃*6H₂O) crystallization.

Crystallization of aluminium chloride hexahydrate is carried out in a strongly acidic environment (HCl) . Due to differences in solubility in the presence of a high chloride ion concentration, the aluminium chloride hexahydrate crystallizes from solution selectively. Preferably, the crystallization is carried out in a sparging HCl gas crystallization unit, more preferably at a temperature of 45⁰C. HCl gas is sparged through an injector.

The aluminium chloride hexahydrate crystals then are separated from the acidic solution, preferably by filtration. The slurry of aluminium chloride crystals in concentrated HCl is transferred to a filtration unit. The crystals on the filter are washed with concentrated HCl and the pure crystals proceed to the alumina conversion stage.

The filtrate is heated in a heat exchanger and enters into the stripping and distillation stage. At this stage, the distilled HCl gas is recycled into the crystallizer, the surplus water from the vaporization is used as process water and the calcium chloride solution is recycled back into the raw material mixing stage.

Conversion of aluminium chloride hexahydrate to alumina is performed by heating at 400-600⁰C (thermal decomposition) and heating at 1000-1200°C (calcination), for instance in a rotary kiln, such that calcined alumina is produced.

Some secondary materials may be recovered as follows. The solids from the rotary kiln dust chamber are subjected to a recovery step during the heating of the granular aluminosilicate material. The solids are washed with water to separate the soluble salts from the insoluble ones. The solids are returned to the mixing and granulation stage while the solution containing mainly KCl (-24%) and NaCl (-6.5%) and a small amount of MgCl₂, is processed to extract and dry the KCl for selling as potash. During the stripping stage in the alumina process Ti- phosphate salt is crystallized. This salt is used in the paint industry without requiring additional processing.

The CaCl₂ solution resulting after the crystallization of the AICI₃ is forwarded to a metal precipitation stage where Al(OH)₃ and Fe(OH)₃ are precipitated with limestone and separated from the solution by a thickener. The solution is then treated with Ca(OH)₂ to precipitate Mg(OH)₂. The CaCl₂ solution is recycled to the mixing and drying stage where overcapacities are heated to increase the CaCl₂ concentration (about 77%) and sold as CaCl₂*2H₂O flakes.

Claims

1. A process for manufacturing silicon from an aluminosilicate-containing material comprising mixing the material with a metal chloride being in the form of a solution or slurry, subjecting the wet mixture to a granulation step, burning the obtained granules at a temperature of 900-1300⁰C, leaching the obtained heated mixture with a mineral acid to obtain a salt solution and insoluble silica, separating the insoluble silica from the salt solution, recovering dry silica, and subjecting the silica to an in-flight plasma carbothermic reduction process in a plasma reactor comprising a plasma torch and a vessel suitable for plasma-associated chemical reaction and collection of liquid silicon.

2. The process according to claim 1, wherein the in-flight plasma carbothermic reduction process comprises generating a plasma stream in the plasma torch, feeding silica into the plasma stream with the aid of a transport gas to allow sublimation of the silica into gaseous form, sparging reaction gas into the plasma stream center to allow reduction of silica in the plasma stream, collecting the resulting silicon in liquid form, optionally subjecting the silicon in liquid form to further purification, and allowing the silicon to solidify.

3. The process according to claim 1 or 2, further comprising subjecting silicon in liquid form to a gas blowing refining process.

4. The process according to any one of the claims 1-3, further comprising subjecting silicon in liquid form to directional solidification and/or ingot casting and/or electromagnetic casting.

5. A process for manufacturing silica and/or alumina from an aluminosilicate-containing material comprising mixing the material with a metal chloride being in the form of a solution or slurry, subjecting the wet mixture to a granulation step, burning the obtained granules at a temperature of 900-1300⁰C, leaching the obtained heated mixture with a mineral acid to obtain a salt solution and insoluble silica, separating the insoluble silica from the salt solution, and recovering dry silica and/or crystallizing aluminium chloride hexahydrate from the salt solution, and heating the aluminium chloride hexahydrate crystals to produce alumina.

6. The process according to any one of the preceding claims wherein an aluminosilicate-containing material with a desired composition is obtained by appropriately mixing different raw materials.

7. The process according to any one of the preceding claims wherein the aluminosilicate-containing material is substantially free from boron.

8. The process according to any one of the preceding claims, wherein the metal chloride and the aluminosilicate- containing material are mixed in a weight ratio of 0.5-3:1, preferably in a weight ratio of 0.5-2:1, more preferably in a weight ratio of 1.5:1.

9. The process according to any one of the preceding claims, wherein the aluminosilicate-containing material and/or the metal chloride are in the form of a slurry and/or solution of 30-50% (w/w) , preferably of 40% (w/w) .

10. The process according to any one of the preceding claims wherein the metal chloride is calcium chloride, sodium chloride, potassium chloride and/or ammonium chloride, preferably is calcium chloride.

11. The process according to any one of the preceding claims wherein the granulation is performed by fluid bed granulation .

12. The process according to any one of the preceding claims wherein the mineral acid is HCl, H₂SO₄ and/or HNO₃.

13. Amorphous silica having a SiO₂ content at least 99.7%, preferably at least 99.9%; a boron content of at the most 1 ppm; a phosphorous content of at the most 5 ppm, preferably at the most 1 ppm; a surface area (BET) of 150-350 m²/g, preferably 175- 325 m²/g, more preferably 200-300 m²/g; an average particle size of 5-80 μm, preferably 5-20 μm, more preferable 5-10 μm; a LOI (1050⁰C) of 6-8%, preferably of 7-7.5%; a tapped density of 200- 500 g/1, preferably of 250-300 g/1; a pH of at least 4.

14. The silica of claim 11 having a particle size distribution as follows: D(90): 10-80 μm, D(50): 5-40 μm, D(25): 1-25 μm, D(IO): 1-10 μm, preferably as follows: D(90): 12-50 μm, D(50): 6-15 μm, D(25): 2-5 μm, D(IO): <1 μm, more preferably as follows: D(90): 13-20 μm, D(50): 6-9 μm, D(25): 3-5 m, D(IO): ≤l μm;

15. A process for manufacturing silicon comprising subjecting highly pure and particulate silica in amorphous form, preferably silica according to claim 13 or 14, to an in-flight plasma carbothermic reduction process in a plasma reactor comprising a plasma torch and a vessel suitable for plasma- associated chemical reaction and collection of liquid silicon.

16. The process according to claim 15, wherein the inflight plasma carbothermic reduction process comprises generating a plasma stream in the plasma torch, feeding silica into the plasma stream with the aid of a transport gas to allow sublimation of the silica into gaseous form, sparging reaction gas into the plasma stream center to allow reduction of silica in the plasma stream, collecting the resulting silicon in liquid form, optionally subjecting the silicon in liquid form to further purification, and allowing the silicon to solidify.

17. The process according to claim 15 or 16, further comprising subjecting silicon in liquid form to a gas blowing refining process.

18. The process according to any one of the claims 15-17, further comprising subjecting silicon in liquid form to directional solidification and/or ingot casting and/or electromagnetic casting.

19. Use of silicon obtainable from the process according to any one of the claims 1-4 or 15-18 for the manufacturing of a solar cell and/or a semiconductor wafer.

20. A device comprising a plasma reactor for in-flight plasma carbothermic reduction of silica to silicon, the reactor comprising a plasma torch and a reaction vessel suitable for plasma-associated chemical reaction and liquid silicon collection.