Abstract: A system and method for nitridizing a glass article includes supplying a source of a nitridizing gas including gaseous NH3 to a glass article supported within a furnace assembly and heating the glass article. In some embodiments, the system includes a handle assembly configured to support the glass article within the furnace assembly and a gas supply conduit carried by the handle and configured to supply the nitridizing gas to the glass article. In some embodiments, a method of nitridizing a glass article includes supplying the nitridizing gas such that a residence time of the nitridizing gas at temperatures greater than 500° C. corresponds to a predetermined time period. In some embodiments, a method of nitridizing a glass article includes supplying the nitridizing gas such that the glass articles is exposed to the nitridizing gas within a contact time tc.

Abstract: Described is a process for the refinement of a quartz powder, comprising the step of separating microparticles of refractory minerals, in particular minerals containing rare earth metal compounds, from the quartz powder by an elutriation step.

Abstract: Methods and systems for treating mined sand to remove an impurity in accordance with the disclosure. An example method mined sand provides mined sand containing the impurity, contacting the mined sand with an aqueous treatment fluid comprising an ethoxylated alcohol and a sulfonic acid derivative, and drying the mined sand; wherein at least a portion of the impurity is removed from the dried mined sand after contact of the mined sand with the aqueous treatment fluid.

Abstract: Shippable modular units configured for use in sequestering CO2 are provided. Aspects of the units include a support having one or more of: a CO2 gas/liquid contactor subunit, a carbonate production subunit and an alkali enrichment subunit; associated therewith. Also provided are systems made up of one or more such modular units, and methods for using the units/systems in CO2 sequestration protocols.

Abstract: Methods and systems for cost effectively transforming lower quality sands into higher quality sands for use as proppants in fracking operations. One or more of an attrition process, a microwaving process and a tumbling process, and systems therefor, are disclosed and shown to be applied to sands having inferior physical properties in order to increase the performance of those sands as proppants in hydrocarbon formation fracturing.

Abstract: The present invention relates to a method for producing high purity silicon comprising providing molten silicon containing 1-10% by weight of calcium, casting the molten silicon, crushing the silicon and subjecting the crushed silicon to a first leaching step in an aqueous solution of HCl and/or HCl+FeCl3 and to a second leaching step in an aqueous solution of HF and HNO3. The leached silicon particles is thereafter subjected to heat treatment at a temperature of between 1250° C. and 1420° C. for a period of at least 20 minutes and the heat treated silicon is subjected to a third leaching step in an aqueous solution of HF and HNO3.

Abstract: Methods, systems, and apparatus are disclosed herein for recovery of high-purity silicon, silicon carbide and PEG from a slurry produced during a wafer cutting process. A silicon-containing material can be processed for production of a silicon-rich composition. Silicon carbide and PEG recovered from the silicon-containing material can be used to form a wafer-saw cutting fluid. The silicon-rich composition can be reacted with iodine containing compounds that can be purified and/or used to form deposited silicon of high purity. The produced silicon can be used in the photovoltaic industry or semiconductor industry.

Abstract: It is an object of the invention to provide a synthetic silica glass for a cladding of a core from a fiber laser. The refractive index should be low and there should be no foaming foreign substances. This object is achieved by a synthetic silica glass for an optical element, which contains paramagnetic E? defect centers in an amount that is sufficient to set the absorption coefficient at 215 nm is in the range between 0.001 cm?1 and 2 cm?1; it contains paramagnetic oxygen defect centers in an amount that is sufficient to set the absorption coefficient at 250 nm is in the range between 0.001 cm?1 and 2 cm?1; the OH group concentration is 5 wtppm or less; the viscosity at 1100° C. is in the range between 1×1013.5 poise and 1×1015.5; the total content of metallic elements of Group 3 and Group 13 of the periodic table is 50.000 wtppm or less; and the relative refractive index difference of said synthetic silica glass is in the range between +0.

Abstract: Process for the production of precipitated silica from olivine including the following steps: providing olivine particles with a particle size preferably below 1 mm in diameter, preferably mixing olivine and water to form an olivine/water slurry, mixing the olivine/water slurry with hydrochloric acid (HCl), preferably at a Concentration at 18 wt % or above, and at a temperature preferably between 50 -130° C., and reacting for a period of time, preferably between 20-360 minutes, removal of coarse mineral impurities (sand product), separation of precipitated silica from mother solution, mechanical treatment of the separated precipitated silica and optionally some water to obtain a slurry, preparation of a low viscosity slurry by adding sodium aluminate or another suitable aluminate, preferably to 100-6000 p.p.m., and adjusting the pH, preferably to values between 4-9 ageing at a temperature between 50-150° C.

Abstract: A process for producing from olivine precipitated silica with controlled specific surface area and high degree of purity. The process comprises adding olivine in a controlled manner to a heated mineral acid solution; after separating undissolved olivine and filtering the silica is slurried in aqueous solution to obtain a low viscosity high solid content silica slurry that can be efficiently degritted and dried with a relatively low energy consumption. The obtained silica can be in powder, bead or granule form and preferably has a specific surface area of at least about 100 m2/g.

Abstract: A method of producing a range of diatomaceous earth filter aids having selectable permeabilities and less than about 1 percent by weight total crystalline silica. The method includes milling diatomaceous earth ore to a size range of between about 100 micrometers and about 1400 micrometers; calcining the milled diatomaceous earth in a calciner; and milling the calcined diatomaceous earth in an adjustable milling and classification system to produce diatomaceous earth filter aids. Systems to implement such methods and compositions produced by such methods are also described.

Abstract: A method is provided for producing a silica container arranged with a substrate, having a rotational symmetry, comprised of mainly a silica, and containing gaseous bubbles at least in its peripheral part, and an inner layer, formed on an inner surface of the substrate and comprised of a transparent silica glass; wherein a powdered silica, having particle diameter of 10 to 1000 ?m, containing Ca, Sr, and Ba with the total concentration of 50 to 5000 ppm by weight, and releasing hydrogen molecules with the amount of 3×1016 to 3×1019 molecules/g upon heating at 1000° C. under vacuum, is prepared at least as a powdered raw material for forming the inner layer, and then the inner layer is formed from the powdered silica as the powdered raw material for forming the inner layer.

Abstract: Precipitated silica is produced by a process that includes a step for filtering and washing an aqueous suspension (S), comprising the following steps: (a) filtering a first portion (S1) of a precipitated silica suspension (S), whereby a cake (G1) is formed and said cake (G1) is then washed and a suspension (S?1) is formed by suspending the thereby obtained washed cake (G1), notably by dilution with water; (b) filtering a second portion (S2) of the suspension (S), whereby a cake (G2) is obtained; and (c) filtering said suspension (S?1) emanating from step (a) through the cake (G2) obtained at the end of step (b), employed as a filtration precoating layer.

Abstract: To provide a treatment method having excellent purification effect, in which impurities having high ionicity in a silica powder can be removed in a short time, a apparatus thereof, and a purified silica powder. A purification method of a silica powder comprises: making a silica powder into a fluid state; contacting a purified gas to the silica powder in the fluid state at high temperature; and thereby removing impurity components of the silica powder. In the method, the silica powder in the fluid state is positioned in a magnetic field region. Further, the silica powder is contacted with the purified gas, while applying voltage to the silica powder by an electric field generated by moving of the silica powder. Preferably, the silica powder in a fluid state is positioned in the magnetic region of 10 gausses or more, and contacted with the purification gas at a temperature of 1000° C. or more.

Abstract: A continuous process and related system for producing high purity silica are disclosed. The process and system utilize a unique high temperature rotary reactor which excludes oxygen. The use of one or more anoxic gases is described, that upon administration into the system promote the exclusion of oxygen.

Abstract: A continuous process and related system for producing high purity silica are disclosed. The process and system utilize a unique high temperature rotary reactor which excludes oxygen. The use of one or more anoxic gases is described, that upon administration into the system promote the exclusion of oxygen.

Abstract: Disclosed herein are a method of reductively bleaching a mineral slurry comprising adding in the mineral slurry an effective amount of a formamidine sulfinic acid (FAS) and an effective amount of a borohydride to reductively bleach the mineral slurry, compositions comprising a mineral slurry, a FAS, and a borohydride, and final products comprising a mineral obtained by the method disclosed herein.

Abstract: A production process for producing high-purity silica from a crude silica source by means of fluosilic acid, including the steps of: (a) subjecting the crude silica souce and the fluosilicic acid to a reaction in a reaction stage, so as to produce silicon tetrafluoride and water; (b) selectively evaporating the silicon tetrafluoride with respect to at least a portion of at least one impurity derived from the crude silica source, and (c) reacting the silicon tetrafluoride with water to produce the high-purity silica, wherein the reaction stage (a) is performed at a temperature above 75° C.

Abstract: A process for removing iron impurities from sand by treatment of an aqueous slurry of the sand with a chelating agent for iron cations.

Abstract: In a known method for the cleaning of SiO2 grain, a fill of particles in a reactor having a vertically oriented center axis will be heated and simultaneously exposed to a treatment gas which is passed at a specified flow velocity from the bottom to the top through the reactor and the fill. To provide on this basis an improved cleaning method and a suitable simple device for it, it is proposed according to the invention and with regard to the cleaning method that a chloric treatment gas will be used which is set to a treatment temperature of at least 1,000° C. in the area of the fill, and that the flow velocity is set to at least 10 cm/s. With regard to the device according to the invention for the implementation of the method according to the invention, a gas shower is provided for the gas inlet, the gas shower comprising below the fill a multitude of nozzle openings distributed laterally to the center axis, for introduction of the treatment gas into the fill.

Abstract: A process for the treatment of geothermal residue includes contacting the pigmented amorphous silica-containing component with a depigmenting reagent one or more times to depigment the silica and produce a mixture containing depigmented amorphous silica and depigmenting reagent containing pigment material; separating the depigmented amorphous silica and from the depigmenting reagent to yield depigmented amorphous silica. Before or after the depigmenting contacting, the geothermal residue or depigmented silica can be treated with a metal solubilizing agent to produce another mixture containing pigmented or unpigmented amorphous silica-containing component and a solubilized metal-containing component; separating these components from each other to produce an amorphous silica product substantially devoid of metals and at least partially devoid of pigment. The amorphous silica product can be neutralized and thereafter dried at a temperature from about 25° C. to 300° C.

Abstract: A process for removing impurities contained in the crystal lattice of minerals, comprising the steps of forming a mixture of a mineral capable of structurally reorganizing its crystal lattice which contains an impurity in its crystal lattice and a halogen anion, and water; heating the mixture to the mineral's structural reorganization transition temperature; holding the mixture at the structural reorganization transition temperature for a sufficient period of time to allow the impurity to freely migrate from the lattice to combine with the halogen anion; and separating the combined impurity and anion from the mixture to render the mineral essentially free of the impurity. The process is applicable to numerous minerals and impurities, but is especially useful to remove arsenic from fluorspar. Numerous halogen anions can be employed, such as chlorides, fluorides, bromides and iodides, but the preferred halogen anion is a metal chloride such as calcium chloride.

Abstract: The present invention relates to a method for producing microsilica having a reflectivity between 65 and 90% in a smelting furnace for production of ferrosilicon or silicon by using a charge comprising an SiO2 source and a solid carbonaceous reduction agent, where microsilica is recovered from the off-gases from the smelting furnace, wherein the solid reduction agent supplied to the furnace contains an amount of volatile matters of less than 1.25 kg per kg produced microsilica and that the temperature in the gas atmosphere in the furnace above the charge is kept above 500° C.

Abstract: A process of purifying crystalline quartz to remove impurities within the lattice structure comprising the steps of heating the quartz to the tridymite polymorphic form and evaporatively reacting the heated quartz with an aqueous acid solution reactive with the impurities in the quartz to form water soluble metal salts. The residue of the evaporative reaction is washed with water to dissolve the metal salts leaving purified crystalline quartz. The disclosure also includes the product of the process.

Abstract: A process for the purification of SiO2 granulate is provided, where the SiO2 granulate is supplied into a reaction zone, heated therein and exposed to a treatment gas which comprises a halogen-containing component. The treatment gas comprises a fuel gas with hydrogen-containing component, which component is combusted in the reaction zone, forming a fuel gas flame to which the SiO2 granulate is exposed. The treatment gas reacts with contaminants in the SiO2 granulate to create volatile reaction products which are removed from the reaction zone. The process produce SiO2 granulates of high purity in a reproducible manner, while incurring relatively low expenditures in time, material and money. The apparatus for implementation of the process comprises a burner supplied with a fuel gas for generating a fuel gas flame and a with halogen-containing component, a supply device which feeds the SiO2 granulate to the fuel gas flame, and a separating device for separating the SiO2 granulate from a waste gas.

Abstract: A process for removing impurities contained in the crystal lattice of minerals, comprising the steps of forming a mixture of a mineral capable of structurally reorganizing its crystal lattice which contains an impurity in its crystal lattice and a halogen anion, and water; heating the mixture to the mineral's structural reorganization transition temperature; holding the mixture at the structural reorganization transition temperature for a sufficient period of time to allow the impurity to freely migrate from the lattice to combine with the halogen anion; and separating the combined impurity and anion from the mixture to render the mineral essentially free of the impurity. The process is applicable to numerous minerals and impurities, but is especially useful to remove arsenic from fluorspar. Numerous halogen anions can be employed, such as chlorides, fluorides, bromides and iodides, but the preferred halogen anion is a metal chloride such as calcium chloride.

Abstract: High purity silica is obtained by the reaction of impure by-product waste silica with hydrogen fluoride preferably in the presence of water or sulfuric acid, producing silicon tetrafluoride gas and a mother liquor. The silicon tetrafluoride is separated from the mother liquor, which retains the impurities originally contained within the impure silica. The silicon tetrafluoride gas is contacted with high-purity water, in a clean environment, to form a slurry of high purity silica and high-purity hydrofluosilicic acid (FSA). A portion of the silica is filtered from the slurry and washed producing a high purity silica product. The rest of the silica-FSA slurry is preferably reacted with ammonia to form a slurry of ammonium fluoride and silica. The silica is separated from the ammonium fluoride and preferably washed and calcined to remove any remaining ammonium fluoride, leaving additional high purity silica product.

Abstract: In a method for manufacturing silica a leaching of natural silicates is performed with hydrochloric acid or other mineral acids, draining, drying and possibly a grinding up of the residue of the product obtained. In order to obtain a spherical silica with a controlled particle size and surface characteristics a mineral olivine with the highest possible degree of purity is employed as the basic material. This raw material is reduced to a grain size between 0.05 and 5 mm. The particles are pretreated and washed for the removal of dust on the grain surfaces and heavy materials such as spinel and at least a part of the foliar and stem-like minerals such as serpentine, talc and pyroxene are removed. The olivine particles are then leached in a controlled leaching process where the acid concentration, leaching temperature and leaching time are controlled in order to achieve the desired primary particle size, specific surface and pore volume measured according to the BET method on the extracted silica.

Abstract: A rotating cylindrical quartz glass tube is partitioned into at least 3 chambers comprising a pre-heating chamber, a reaction chamber, and a gas desorption chamber. The process comprises pre-heating the starting quartz powder by continuously supplying it into the pre-heating chamber, refining the powder by transferring it into the reaction chamber in which the powder is brought into contact with a chlorine-containing gas atmosphere, and transferring the powder into the gas desorption chamber; the chambers may be partitioned using a sectioning plate having an opening. Alkali metal elements such as sodium and potassium, as well as transition metal elements such as iron, copper, chromium, and nickel are removed from a powder of naturally occurring quartz. The process also removes alkaline earth metal elements such as magnesium and calcium. Furthermore, it is of high productivity because it can be operated continuously to yield high purity quartz powder at a low cost.

Abstract: A process for the manufacture of pure amorphous silica from rocks containing non-crystalline silica is described. The process comprises the steps of: (a) dissolution of said rock in an alkaline solution comprising sodium hydroxide and sodium carbonate, obtaining a solution of sodium silicate; (b) precipitation of pure amorphous silica by adding sodium bicarbonate into said sodium silicate and co-producing sodium carbonate, the weight ratio between SiO.sub.2 and Na.sub.2 O in said dissolution step is in the range of between 0.5 to 3.0; and (c) the sodium carbonate solution is transformed into crystalline sodium bicarbonate, by a salting out reaction with sodium chloride, being recycled to the process. According to a preferred embodiment, the alkaline solution is obtained by the caustification of sodium carbonate with calcium hydroxide. The preferred concentration of sodium hydroxide in said dissolution step is in the range of 4% to 14% by weight.

Abstract: A process for aqueous biphasic extraction of metallic oxides and the like from substances containing silica. Control of media pH enables efficient and effective partition of mixture components. The inventive method may be employed to remove excess silica from kaolin clay.

Abstract: A process for the elimination of iron from silica sand, comprising: abrasive-attritioning sand particles by subjecting the sand particles, in a single step and under dry conditions, to centrifugal rotation and simultaneously imparting an agitation with a translative eccentric movement and downstream and upstream movements causing that substantially all the sand particles be abrasive attritioned to each other wearing their surfaces to remove impurities covering said sand particles; and separating said iron impurities from said sand particles by magnetic separation, flotation or other known methods, thus simplifying the conventional processes just to one attrition step and suppressing the chemical treatment with acids or alkalis which was necessary in conventional processes.

Abstract: The invention provides a process for the production of a high grade amorphous silica having a purity of at least 90% active silica of the formula SiO.sub.2.nH.sub.2 O, comprising the steps of:a. comminuting and wet classification of porcellanite rock to form granules having an average diameter of 200 microns to 8 mm;b. combining the resulting granules with NaOH at a temperature of up to 100.degree. C. to form a product containing sodium silicates;c. separating a liquid containing the sodium silicates from solid waste;d. adding CO.sub.2 to the liquid product to form SiO.sub.2.nH.sub.2 O and Na.sub.2 CO.sub.3 ;e. washing the resulting product to effect a separation of the precipitated SiO.sub.2.nH.sub.2 O from the soluble Na.sub.2 CO.sub.3 ; andf. recovering SiO.sub.2.nH.sub.2 O of a purity of at least 90%.

Abstract: A process for preparing silica having a low silanol content which comprises heating amorphous silica in an atmosphere of a low partial pressure of water vapor to maintain the amorphous silica at a temperature in a range of from 600.degree. to 1000.degree. C. at a first heating step and then maintain at a temperature of 1200.degree. C. or more at a second heating step. The silica having a low silanol content obtained according to the present invention is advantageously used as a raw material for quartz glass, particularly as a raw material for preparing crucibles used to pull up silicon single crystals.

Abstract: The present invention provides high grade opaliform porcellanite having a purity of at least 80% active silica. The invention also provides a process for the production of a high grade opaliform porcellanite having a purity of at least 80% active silica comprising grinding and screening porcellanite rock to form granules having an average diameter of between about 0.6 and 18 mm and then subjecting said granules to wet disintegration to remove soft clays and limestone and gravitic separation to separate the lower density opaliform active silica from higher density impurities intermixed therewith.

Abstract: A system for cleaning solids contaminated with solvent-soluble contaminants. The system, which includes both process and apparatus, comprises the use of at least two successive cleaning zones, each of which includes a slurrying stage and a centrifuge separation stage, wherein the solids to be cleaned and the solvent used for cleaning flow in countercurrent relationship to each other between the successive zones.

Abstract: Quartz is purified by removing mineral impurities, particularly alkali metal impurities, from within the quartz crystal lattice structure. According to the disclosed process, quartz crystals are subjected to a pretreatment that removes surface bound impurities and then contacted with gaseous HCl at a temperature of from 800.degree. C. to 1600.degree. C. for a period of time of from a few minutes to several hours, thereby diffusing the mineral impurities to the quartz crystal surface where they form salts with chloride ion, removing the salts, and recovering the purified quartz crystals.

Abstract: A method and apparatus for the elimination of unwanted impurities and inclusions from a variety of non-conductive base materials by the application of high power, variable frequency RF energies in selective of rarefied atmospheres. Refined natural quartz is a product acquired by the method using the apparatus herein described.

Abstract: Quartz is purified by removing mineral impurities, particularly alkali metal impurities, from within the quartz crystal lattice structure. According to the disclosed process, quartz crystals are subjected to a pretreatment that removes surface bound impurities and then contacted with gaseous HCl at a temperature of from 800.degree. C. to 1600.degree. C. for a period of time of from a few minutes to several hours, thereby diffusing the mineral impurities to the quartz crystal surface where they form salts with chloride ion, removing the salts, and recovering the purified quartz crystals.

Abstract: Granular silicon dioxide is placed in a treatment chamber which is heated to a temperature ranging from 700.degree. to 1300.degree. C. The chamber is then rotated for a prescribed period of time to mix the grains while a gaseous atmosphere of chlorine and/or hydrogen chloride is passed through the treatment chamber. The mixing period is followed by a resting period which is at least ten times longer than the mixing time. During the resting period the grains are exposed to a constant electric field having a strength of 600 to 1350 V/cm applied across the chamber. The foregoing cycle is repeated several times. For working the process a device is used which includes a quartz glass rotary tube into which hollow silicon carbide electrodes extend.

Abstract: Green sand having a residuum of retained clay is reconditioned by screening and predrying it to about zero moisture; calcining the sand to burn off organic matter; cooling the sand; mechanically scrubbing the cooled sand to free mechanically bonded clay and a portion of the clay magnetically adhered to the sand; mixing an acid/water solution with the sand to react with the remaining magnetically adhered clay to permit such clay to break free from the sand; drying the sand to release the freed clay; and extracting the thus-released clay from the sand.

Abstract: The disclosed process separates impurities, including admixed minerals other than quartz and quartz particles having relatively high levels of lattice impurities, from a quartz containing particulate material to recover a high purity quartz product. The process involves treatment with a solvent to reduce the size of the impurities relative to the quartz product and the thus treated material is then classified by size to recover the purified product. If impurities less soluble than the quartz product are also present, a second solvent treatment is conducted to reduce the size of the quartz particles relative to the less soluble impurity and a second classification by size is conducted. In a preferred embodiment, the quartz is subjected to a heat/quench cycle to fracture quartz particles thereby exposing occluded and interstitial impurities to the solvent leach. The intermediate product exiting the final solvent treatment and classification steps is dried, blended and roasted in a vacuum to remove gases.

Abstract: Starting from pegmatitic sand, the invention provides a method of purifying quartz sand, in which the amount of iron is reduced to less than 0.3 ppm, the amount of zircon to less than 1 ppm, and the amount of phosphor to less than 0.2 ppm. Gas nuclei are also removed. The method is carried out by washing with solution which contains at least 15% by weight of HF in water until at least 40% by weight of the quartz sand is dissolved, and washing with a solution which contains at least 20% by weight of HCl in water at a temperature from 5.degree. to 95.degree. C. for at least 30 minutes. In this method, the grains of the sand are freely suspended in an upward stream of the acid. Such quartz sand can suitably be used for the manufacture of very pure quartz glass for use in mercury discharge lamps, in glass fibers for telecommunication purposes (cladding glass), or in semiconductor arrangements.

Abstract: A starting material composed of calcium carbonate is dissolved in a nitrate aqueous solution containing alkali nitrate under application of heat and pressure. The starting material is hydrothermally synthesized within the nitrate aqueous solution to effect the rapid growth of calcium carbonate single crystal.

Abstract: A process is provided for reducing the total concentration of heavy metals, notably lead, copper and zinc, naturally occurring in silica-rich sludge precipitated from geothermal brine in a brine handling system such as a geothermal brine electric generating plant. The process includes washing the sludge with hot water to displace any brine entrapped in the sludge, dewatering the washed sludge and leaching the silicious solids residue with hydrochloric acid having a concentration of between about 2 and about 9 weight percent and an acid-to-sludge weight ratio between about 0.10 and about 0.33. The acid-sludge mixture is heated to a temperature of at least about 50.degree. and the leaching time is at least about one hour. The leaching solution is separated from the leached sludge and the solids residue are washed with water. Preferably the water used in both washing steps is condensate of steam derived from the geothermal brine. Effluent from the process is preferably combined with the brine for reinjection.

Abstract: This invention deals with a process for manufacturing high purity silica which comprises making an aqueous alkali silicate solution into fine fibrous gel in a coagulant, treating the fibrous gel obtained with an acid-containing solution, and then with water to extract and remove impurities; and optionallly heating a resulting silica at a temperature of 1,000.degree. C. or higher. Thus obtained silica is preferably used as a filler, especially, the one for resin compositions for encapsulating electronic parts; etc.

Abstract: This invention concerns a process for purifying silica produced from an alkali silicate aqueous solution, which usually contains more than 200 ppm of impurities, to silica containing less than 30 ppm of impurities. Concretely, the purification process of silica comprises: dispersing silica gel, containing a lot of impurities, in water and filtering the solution; dispersing the filtered out silica gel again in an aqueous solution of pH 2 or less and filtering the aqueous solution; putting the silica gel to heat-treatment and acid-treatment with continuous stirring in order to break the inside siloxane link and dissolve out impurities therefrom and filtering the acid solution; rinsing a produced cake with pure water to wash away the inside residual solution and drying the cake.

Abstract: The present invention relates to a method for purifying silica waste obtained in the manufacture of aluminium fluoride from hexafluosilicic acid and aluminium hydroxide, whereby the silica, is subjected to an acidic leaching at a pH below 3 to leach out part of the fluorine and substantially all the aluminium present in said waste, and is thereafter subjected to an alkaline leaching at pH 8.5-11.5 to leach out remaining fluorine present in said waste. The leachings are preferably carried out at elevated temperatures, normally 60.degree.-90.degree. C., and for a time sufficient to considerably reduce the contents of aluminium and fluorine, normally 1-3 hrs.The silica obtained is highly reactive and can be used as such or transformed into sodium silicate by a reaction with sodium hydroxide. The contents of fluorine and aluminium can be transferred to a process for the production of cryolite or similar compounds.

Abstract: A process for treating sand which includes one or more stages in which sand is mixed with a dilute aqueous solution of hydrofluoric or sulphuric acid together with zinc or sodium hydrosulphite and the resulting slurry is agitated at ambient temperature in an atmospheric oxygen-free environment.

Abstract: A process of removing iron impurities from ores, particularly useful for removing stains of iron impurities adhered to silica sand particles, comprises grinding the ore, washing and desliming the ground ore to remove the major part of the clay-type binder, attrition-scrubbing the deslimed particles to release further amounts of binder therefrom, washing and desliming to remove said binder, drying and heating the ore particles, treating the hot particles with a chemical agent suitable to conver the iron impurities into water soluble iron compounds, attrition-scrubbing the hot suspension of chemically treated particles to release the stains of iron impurities, and washing with cold water and desliming to recover the purified ore particles.