CA1184740A - Process for obtaining high purity silica - Google Patents
Process for obtaining high purity silicaInfo
- Publication number
- CA1184740A CA1184740A CA000401560A CA401560A CA1184740A CA 1184740 A CA1184740 A CA 1184740A CA 000401560 A CA000401560 A CA 000401560A CA 401560 A CA401560 A CA 401560A CA 1184740 A CA1184740 A CA 1184740A
- Authority
- CA
- Canada
- Prior art keywords
- silica
- high purity
- ppm
- less
- purity silica
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
ABSTRACT OF THE DISCLOSURE
A method of producing high purity silica containing less than 2 ppm iron oxides and less than 50 ppm alumina from particulate silica or quartz concentrates containing both sur-face and occluded mineral impurities wherein the concentrate is agitated with an aqueous solution containing 3-20% by weight hydrofluoric acid at a temperature between 50°C and the boiling point of the solution. The impurities dissolve at a greater rate than the silica and can be washed away or separated as a slime.
A method of producing high purity silica containing less than 2 ppm iron oxides and less than 50 ppm alumina from particulate silica or quartz concentrates containing both sur-face and occluded mineral impurities wherein the concentrate is agitated with an aqueous solution containing 3-20% by weight hydrofluoric acid at a temperature between 50°C and the boiling point of the solution. The impurities dissolve at a greater rate than the silica and can be washed away or separated as a slime.
Description
B~CKGROUND OF THE INVENTION
This invention relates to a method ~or obtaining high purity silica from sand and sllica concentrates.
High purity silica with relatively low impurity levels, typically containing less than 1 ppm of iron, is one of the most important raw materials used by the semiconductor and by the optical fibre industries. Such high purity silica or quartz usually has, heretofore, been obtained by expensive and high energy-consuming melting and vapour phase processes.
PRIOR ART
The removal of iron contamination from sand by leach-ing in mineral acids, such as hydrochloric or sulphuric acids, is described in the prior art. U.S. Patent No~ 1,983,270, for example, teaches the leaching of sand by dilute hydrochloric or sulphuric acid, then heating and evaporating the slurry to increase the acid concentration~ The process of U.S. Patent No. 1,983,27~ applies mechanical rubbing or attrition to the sand particles prior to acid leaching, in order to increase the surface of the sand accessible to leaching. U.S. Patent No.
4,042,671 describes a container, a method of layering of sand and pebbles, and ways of recycling the leaching acid in a process for the removal of iron compounds from sand.
There are known methods of silica purification wherein silica is first completely digested and subsequently precipitated in a purified form. One such methGd is described for example in U.S. Patent No. 3,808,309 in which amorphous silica is dissolved in aqueous alkaline solution and an acid is added to form silicic acid which is then extracted with an organic hydrogen bonding agent and then polymerized in the presence of a fluoride catalyst.
4q~
It is also well known, and i~ used in various glass technology processes, that hydrogen fluoride, in substantial concentration, completely dissolves silica or silica-bearing compounds to form fluosilicic acid.
U.S. Patent No. 3,968,197 describes a process in which sodium silicofluoride, obtained by prior reaction with hydrogen fluoride, is reacted wi-th ammonia to precipitate very pure silica gel and sodium fluoride.
Removal of impurities, specifically of iron oxides, from the surface of sand by leaching in a solution containing sulphuric acid and sodium chloride in approximately equal quanti-ties, is described in U.S. Patent No. 2,306,021. In a preferred embodiment of this process about one percent hydrofluoric acid is added to the above leaching solu-tion, for what is described as soft~ning of the silica pore walls, and enhancing the leach-ing action of the above reagents.
In a process for the purification of sand, U.S. Patent No. 2,381,843 teaches the soaking of silica-bearing minerals in a solution containing titanous sulphate and about 2 lbs of hydrogen fluoride per ton of sand, then washing. In a similar process for the removal of ferruginous coating, U.S. Patent No. 2,583,280 teaches the treatment of sand in a solution containing less than 0.1% hydrofluoric acid together with sulphurous acid and/or sodium hydrosulphite. In anoth~er process described in U.S. Patent 2,769,540, sulphuric acid leaching is followed by several flotation steps utilizing h~drofluoric acid and organic amine conditioners for cleaning, and separating ~and from feldspar. In all the above described sand cleaning processes, hydrofluoric acid is used only in small quantities ~L8~7~6~
and in conjunction ~ith a principal leaching reagent to enhance the purifying action of the latter.
U.S. Patent NoO 2,952,516 teaches the purification of sand by the leaching action of hot hydrochloric and fluo-silicic acids, either added together, or applied in separate but subsequent leaching steps. The fluosilicic acid utilized in this process is prepared by acidifying alkali metal fluoride solution or by hydrolysing silicon tetrafluoride with hydro-chloric acid.
lQ In most of the above processes, the purified sand product still contained several hundred parts per million iron oxide. This level of impurity, however, is too high for the current industrial processes utilizing high purity silica, which for the purposes of the present specification, is considered as such, when the main impurities present are only iron oxide and alumina in quantities less than 2 ppm and 50 ppm, respectively.
OBJECT OF THE INVE2iITION
.. .. _ Thus, it is an object of the pxesent invention to provide a process for the production of high puri-ty silica, as herein defined, by relatively inexpensive chemical means.
SUMMARY OF TElE INVENTION
.. ... _ A relatively inexpensive method has now been found whereby iron and other impurities such as feldspar, and other alumina and calcia-bearing compounds, can be removed from silica and quartz concentrates, not only from the-surface of the particles as taught by the prior art, but also impurities that are occluded, trapped or are strongly adherent to silica are made accessible to separation.
By one aspect of this invention there is provided `:, 1847~
a process Eor producing high purity silica containing less -than
This invention relates to a method ~or obtaining high purity silica from sand and sllica concentrates.
High purity silica with relatively low impurity levels, typically containing less than 1 ppm of iron, is one of the most important raw materials used by the semiconductor and by the optical fibre industries. Such high purity silica or quartz usually has, heretofore, been obtained by expensive and high energy-consuming melting and vapour phase processes.
PRIOR ART
The removal of iron contamination from sand by leach-ing in mineral acids, such as hydrochloric or sulphuric acids, is described in the prior art. U.S. Patent No~ 1,983,270, for example, teaches the leaching of sand by dilute hydrochloric or sulphuric acid, then heating and evaporating the slurry to increase the acid concentration~ The process of U.S. Patent No. 1,983,27~ applies mechanical rubbing or attrition to the sand particles prior to acid leaching, in order to increase the surface of the sand accessible to leaching. U.S. Patent No.
4,042,671 describes a container, a method of layering of sand and pebbles, and ways of recycling the leaching acid in a process for the removal of iron compounds from sand.
There are known methods of silica purification wherein silica is first completely digested and subsequently precipitated in a purified form. One such methGd is described for example in U.S. Patent No. 3,808,309 in which amorphous silica is dissolved in aqueous alkaline solution and an acid is added to form silicic acid which is then extracted with an organic hydrogen bonding agent and then polymerized in the presence of a fluoride catalyst.
4q~
It is also well known, and i~ used in various glass technology processes, that hydrogen fluoride, in substantial concentration, completely dissolves silica or silica-bearing compounds to form fluosilicic acid.
U.S. Patent No. 3,968,197 describes a process in which sodium silicofluoride, obtained by prior reaction with hydrogen fluoride, is reacted wi-th ammonia to precipitate very pure silica gel and sodium fluoride.
Removal of impurities, specifically of iron oxides, from the surface of sand by leaching in a solution containing sulphuric acid and sodium chloride in approximately equal quanti-ties, is described in U.S. Patent No. 2,306,021. In a preferred embodiment of this process about one percent hydrofluoric acid is added to the above leaching solu-tion, for what is described as soft~ning of the silica pore walls, and enhancing the leach-ing action of the above reagents.
In a process for the purification of sand, U.S. Patent No. 2,381,843 teaches the soaking of silica-bearing minerals in a solution containing titanous sulphate and about 2 lbs of hydrogen fluoride per ton of sand, then washing. In a similar process for the removal of ferruginous coating, U.S. Patent No. 2,583,280 teaches the treatment of sand in a solution containing less than 0.1% hydrofluoric acid together with sulphurous acid and/or sodium hydrosulphite. In anoth~er process described in U.S. Patent 2,769,540, sulphuric acid leaching is followed by several flotation steps utilizing h~drofluoric acid and organic amine conditioners for cleaning, and separating ~and from feldspar. In all the above described sand cleaning processes, hydrofluoric acid is used only in small quantities ~L8~7~6~
and in conjunction ~ith a principal leaching reagent to enhance the purifying action of the latter.
U.S. Patent NoO 2,952,516 teaches the purification of sand by the leaching action of hot hydrochloric and fluo-silicic acids, either added together, or applied in separate but subsequent leaching steps. The fluosilicic acid utilized in this process is prepared by acidifying alkali metal fluoride solution or by hydrolysing silicon tetrafluoride with hydro-chloric acid.
lQ In most of the above processes, the purified sand product still contained several hundred parts per million iron oxide. This level of impurity, however, is too high for the current industrial processes utilizing high purity silica, which for the purposes of the present specification, is considered as such, when the main impurities present are only iron oxide and alumina in quantities less than 2 ppm and 50 ppm, respectively.
OBJECT OF THE INVE2iITION
.. .. _ Thus, it is an object of the pxesent invention to provide a process for the production of high puri-ty silica, as herein defined, by relatively inexpensive chemical means.
SUMMARY OF TElE INVENTION
.. ... _ A relatively inexpensive method has now been found whereby iron and other impurities such as feldspar, and other alumina and calcia-bearing compounds, can be removed from silica and quartz concentrates, not only from the-surface of the particles as taught by the prior art, but also impurities that are occluded, trapped or are strongly adherent to silica are made accessible to separation.
By one aspect of this invention there is provided `:, 1847~
a process Eor producing high purity silica containing less -than
2 ppm iron oxide and 50 ppm alumina, from par-ticulate siliceous materials containing adhering and occluded mineral impurities, comprising:
treating said particulate material with an aqueous solution containing between about 3% and about 20~ by weiyht hydrofluoric acid at a temperature above about 50C.
DESCRIPTION OF DRAWINGS
Figure 1 is a schematic flowsheet of the process of the present invention.
DETAILED DESCRIPTION_OF PREFERRED EMBODIMENTS
The sand, quartz, or other siliceous minerals to be purified, according to the present invention, have generally already been subjected to beneficiation, and are found as tailings from some other ore separation proces.s. Prior treat-ment may include size separation, wet or dry screening, magnetic separation, flotation, or a combination of any of these separa-tion proeess steps. It is usually advantageous to have the sand or silica concentrate in a -50 Tyler mesh size, but the particle size is in no way critical to the present process. It is how-ever, important for achieving bes-t results, to restrict the ferric oxide content of the siliceous material to less than 150 ppm and the alumina content to below 1% on a dry weight pereent basis. The sand, quartz or silica concentrate is -then subjeeted to dilute hydrofluoric acid treatment with agitation, at a temperature above 50C and below the boiling point of the solution, for a period of several hours. The strength of the acid can vary between 3 and 20 percent. Hydrofluoric acid concentrations below 3 percent would be very slow acting, ' ,;
~3 i 347~Q
resulting in a commercially impracticable process. The use of an acid concentration above 20 percent would, on the other hand, lead to a considerable loss of high purity silica by dissolution also to increased corrosion of e~uipment, and to health hazards to operating personnel. The duration of the treatment, the acid concentration and temperature are adjusted between the specified limits, according to the mineral nature and size of the sand or the silica concentrate. I:E metallic containers and stirrers are used it is advantageous that they be lined or coated with some dilute acid resistant polymer, rubber or plastic material.
It is well known, as mentioned hereinabove, that hydrofluoric acid attacks sand, feldspar and other alumina and calcia-bearing siliceous materials. It has been found, surpris-ingly, that in the hydrofluoric acid concentration and tempera-ture ranges described by the present process, the dissolution rate of silica by the acid is considerably slower than the rate of dissolution of the impurities. As a result, the feldspar, alumina and calcia-bearing siliceous materials and iron will go into solution, or appear as slime. Another effect is that -the iron oxide impurity can be leached not only from the surface of the particles but also in an occluded state. The various alumina and calcia-bearing materials that are strongly adherent to the sand particles are thus separated by the preEerential action o~ the acid on these impurities and are rendered access-ible to the acid before the silica is substantially dissolved.
After the dilute hydrofluoric acid treatment has been completed the solid impurities are separated by desliming, flotation or similar physical separation methods, and the, dissolved impurities are washed off with water. The high purity 4~
silica obtained by the present process usually contains less than 1 ppm iron oxide.
The following examples show the improvement resul-ting from the application oP the process described hereinabove.
E mple 1 40 lbs. of silica, obtained as tailings from a previous flotation separation and then subjected to magnetic separation, was treated by 58 lbs. of 14.5%HF solu-tion in a polyethylene lined vessel, with continuous stirring. The temperature of the solution was controlled at 63C.
The impurities present in the silica tailings are listed below:
Fe23 41 ppm A123 0.23% by wt.
Na2O 0.101% by wt.
K2O 0.061% by wt.
CaO 0.025% by wt.
After 4 hours treatment the iron oxide content of the silica was reduced to less than 1 ppm and the alumina content to less than 30 ppm. The treatment was continued for another 18 hours, without substantial further reductions in the impurity levels. At the end of the total 22 hours' period of hydroPluoric acid treatment, 30 lbs. of high purity silica was obtained with iron and alumina contents below 1 ppm and 28 ppm respectively. The -200 Tyler mesh slimes separated, contained 6 ppm iron oxide and over 42 ppm alumina.
Example 2 40 lbs. of silica tailings, with a composition described in Example 1, was agitated in a 9.1 wt. % hydrofluoric :~L8~
acid solution with the t~mperature maintained at 62C. After 7 hours treatment 36.5 ]b. of high purity silica was obtained with Eerric oxide and alumina conten-ts at 1 ppm and 37 ppm respectively. The -200 Tyler mesh slimes were found to contain 102 ppm ferric oxide and 0.067% alumina.
treating said particulate material with an aqueous solution containing between about 3% and about 20~ by weiyht hydrofluoric acid at a temperature above about 50C.
DESCRIPTION OF DRAWINGS
Figure 1 is a schematic flowsheet of the process of the present invention.
DETAILED DESCRIPTION_OF PREFERRED EMBODIMENTS
The sand, quartz, or other siliceous minerals to be purified, according to the present invention, have generally already been subjected to beneficiation, and are found as tailings from some other ore separation proces.s. Prior treat-ment may include size separation, wet or dry screening, magnetic separation, flotation, or a combination of any of these separa-tion proeess steps. It is usually advantageous to have the sand or silica concentrate in a -50 Tyler mesh size, but the particle size is in no way critical to the present process. It is how-ever, important for achieving bes-t results, to restrict the ferric oxide content of the siliceous material to less than 150 ppm and the alumina content to below 1% on a dry weight pereent basis. The sand, quartz or silica concentrate is -then subjeeted to dilute hydrofluoric acid treatment with agitation, at a temperature above 50C and below the boiling point of the solution, for a period of several hours. The strength of the acid can vary between 3 and 20 percent. Hydrofluoric acid concentrations below 3 percent would be very slow acting, ' ,;
~3 i 347~Q
resulting in a commercially impracticable process. The use of an acid concentration above 20 percent would, on the other hand, lead to a considerable loss of high purity silica by dissolution also to increased corrosion of e~uipment, and to health hazards to operating personnel. The duration of the treatment, the acid concentration and temperature are adjusted between the specified limits, according to the mineral nature and size of the sand or the silica concentrate. I:E metallic containers and stirrers are used it is advantageous that they be lined or coated with some dilute acid resistant polymer, rubber or plastic material.
It is well known, as mentioned hereinabove, that hydrofluoric acid attacks sand, feldspar and other alumina and calcia-bearing siliceous materials. It has been found, surpris-ingly, that in the hydrofluoric acid concentration and tempera-ture ranges described by the present process, the dissolution rate of silica by the acid is considerably slower than the rate of dissolution of the impurities. As a result, the feldspar, alumina and calcia-bearing siliceous materials and iron will go into solution, or appear as slime. Another effect is that -the iron oxide impurity can be leached not only from the surface of the particles but also in an occluded state. The various alumina and calcia-bearing materials that are strongly adherent to the sand particles are thus separated by the preEerential action o~ the acid on these impurities and are rendered access-ible to the acid before the silica is substantially dissolved.
After the dilute hydrofluoric acid treatment has been completed the solid impurities are separated by desliming, flotation or similar physical separation methods, and the, dissolved impurities are washed off with water. The high purity 4~
silica obtained by the present process usually contains less than 1 ppm iron oxide.
The following examples show the improvement resul-ting from the application oP the process described hereinabove.
E mple 1 40 lbs. of silica, obtained as tailings from a previous flotation separation and then subjected to magnetic separation, was treated by 58 lbs. of 14.5%HF solu-tion in a polyethylene lined vessel, with continuous stirring. The temperature of the solution was controlled at 63C.
The impurities present in the silica tailings are listed below:
Fe23 41 ppm A123 0.23% by wt.
Na2O 0.101% by wt.
K2O 0.061% by wt.
CaO 0.025% by wt.
After 4 hours treatment the iron oxide content of the silica was reduced to less than 1 ppm and the alumina content to less than 30 ppm. The treatment was continued for another 18 hours, without substantial further reductions in the impurity levels. At the end of the total 22 hours' period of hydroPluoric acid treatment, 30 lbs. of high purity silica was obtained with iron and alumina contents below 1 ppm and 28 ppm respectively. The -200 Tyler mesh slimes separated, contained 6 ppm iron oxide and over 42 ppm alumina.
Example 2 40 lbs. of silica tailings, with a composition described in Example 1, was agitated in a 9.1 wt. % hydrofluoric :~L8~
acid solution with the t~mperature maintained at 62C. After 7 hours treatment 36.5 ]b. of high purity silica was obtained with Eerric oxide and alumina conten-ts at 1 ppm and 37 ppm respectively. The -200 Tyler mesh slimes were found to contain 102 ppm ferric oxide and 0.067% alumina.
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for producing high purity silica containing less than 2 ppm iron oxide and 50 ppm alumina, from beneficiated particulate siliceous materials containing adhering and occluded mineral impurities, comprising:
(a) treating said particulate material with an aqueous solution containing between about 3% and about 20% by weight hydrofluoric acid at a temperature above about 50°C and below the boiling point of the solution, for a period of at least several hours;
(b) separating said mineral impurities from said high purity silica after said treatment step; and (c) separating the high purity silica from said aqueous solution.
(a) treating said particulate material with an aqueous solution containing between about 3% and about 20% by weight hydrofluoric acid at a temperature above about 50°C and below the boiling point of the solution, for a period of at least several hours;
(b) separating said mineral impurities from said high purity silica after said treatment step; and (c) separating the high purity silica from said aqueous solution.
2. A process as claimed in claim 1 wherein said mineral impurity separating step is a desliming step.
3. A process as claimed in claim 1 or 2 wherein said particulate siliceous material contains less than 150 ppm ferric oxide and less than 1% by weight alumina.
4. A process as claimed in claim 1 or 2 wherein said particulate material is agitated with said aqueous hydrofluoric acid solution for a period of time between about 4 and 22 hours.
5. A process as claimed in claim 1 or 2 wherein said particulate material is less than 50 Tyler mesh.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US26758281A | 1981-05-27 | 1981-05-27 | |
| US267,582 | 1981-05-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1184740A true CA1184740A (en) | 1985-04-02 |
Family
ID=23019394
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000401560A Expired CA1184740A (en) | 1981-05-27 | 1982-04-23 | Process for obtaining high purity silica |
Country Status (2)
| Country | Link |
|---|---|
| AU (1) | AU551045B2 (en) |
| CA (1) | CA1184740A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20180111835A1 (en) * | 2015-05-06 | 2018-04-26 | Alliance Magnésium | Method for the production of amorphous silica with controlled specific surface area from magnesium silicate ore |
| EP3763683A1 (en) | 2019-07-12 | 2021-01-13 | Heraeus Quarzglas GmbH & Co. KG | Purification of quartz powders by removal of microparticles of refractory materials |
| WO2024036664A1 (en) * | 2022-08-17 | 2024-02-22 | 鞍钢集团矿业有限公司 | Method for low-carbon efficient extraction of high-purity sio2 from high-silicon hematite tailings |
-
1982
- 1982-04-23 CA CA000401560A patent/CA1184740A/en not_active Expired
- 1982-05-10 AU AU83558/82A patent/AU551045B2/en not_active Ceased
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20180111835A1 (en) * | 2015-05-06 | 2018-04-26 | Alliance Magnésium | Method for the production of amorphous silica with controlled specific surface area from magnesium silicate ore |
| US10752508B2 (en) * | 2015-05-06 | 2020-08-25 | Alliance Magnésium Inc. | Method for the production of amorphous silica with controlled specific surface area from magnesium silicate ore |
| EP3763683A1 (en) | 2019-07-12 | 2021-01-13 | Heraeus Quarzglas GmbH & Co. KG | Purification of quartz powders by removal of microparticles of refractory materials |
| EP3763682A1 (en) * | 2019-07-12 | 2021-01-13 | Heraeus Quarzglas GmbH & Co. KG | Purification of quartz powders by removal of microparticles of refractory materials |
| US20210009461A1 (en) * | 2019-07-12 | 2021-01-14 | Heraeus Quarzglas Gmbh & Co. Kg | Purification of quartz powders by removal of microparticles of refractory materials |
| TWI757789B (en) * | 2019-07-12 | 2022-03-11 | 德商賀利氏石英玻璃有限兩合公司 | Purification of quartz powders by removal of microparticles of refractory materials |
| US11878937B2 (en) * | 2019-07-12 | 2024-01-23 | Heraeus Quarzglas Gmbh & Co. Kg | Purification of quartz powders by removal of microparticles of refractory materials |
| WO2024036664A1 (en) * | 2022-08-17 | 2024-02-22 | 鞍钢集团矿业有限公司 | Method for low-carbon efficient extraction of high-purity sio2 from high-silicon hematite tailings |
Also Published As
| Publication number | Publication date |
|---|---|
| AU8355882A (en) | 1982-12-02 |
| AU551045B2 (en) | 1986-04-17 |
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