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.
A process for the purification of SiO.sub.2 granulate is provided, where the SiO.sub.2 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 SiO.sub.2 granulate is exposed. The treatment gas reacts with contaminants in the SiO.sub.2 granulate to create volatile reaction products which are removed from the reaction zone. The process produce SiO.sub.2 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 SiO.sub.2 granulate to the fuel gas flame, and a separating device for separating the SiO.sub.2 granulate from a waste gas.
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 ; and f. recovering SiO.sub.2.nH.sub.2 O of a purity of at least 90%.
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.
A separation process is provided for treating a feed material comprising silica, feldspar, and metal impurities, including at least one of mica, iron impurities, or refractory heavy minerals, to form one or more products for use in making glass. In the process, the feed material is floated in the presence of a depressant to inhibit the flotation of feldspar and thereby form a concentrate containing at least most of the silica and a tailings fraction containing at least most of the feldspar. The concentrate and tailings fractions can be converted into the products by magnetically removing the metal impurities therefrom.
