High purity quartz

Quartz raw material is often thought of as an "excessive" commodity that easily may be exploited. This may be correct for low purity quartz commodities with more than 300 parts per million (0.03 wt.%) impurities, but intermediary (50 to 300 ppm) to high purity qualities (<50 ppm) are much more challenging to find in nature.

Impurities in quartz

Fluid inclusions and rutile inclusions in quartzFluid inclusions (left) and rutile inclusions (right) in quartzImpurities in quartz are caused by either fluid inclusions (i.e. milk quartz or snow quartz), inclusions of other minerals (i.e. rutile) or foreign ions (trace elements) incorporated within the quartz lattice.

Every refinement process step towards a higher and less contaminated quality will cause equally higher costs. The production costs of high quality products are much lower if the mined quartz has a low trace element content.

Quartz crystal lattice with structural bound trace elements (impurities). Redrawn from Bragg, W.L. 1937: Atomic structure of minerals. Cornell University Press Quartz crystal lattice with structural bound trace elements (impurities). Redrawn from Bragg, W.L. 1937: Atomic structure of minerals. Cornell University Press These facts are reflected in the great price margin between low quality quartz, which costs 15 to 20 U$ per ton, and high purity quartz, which costs 2000 U$ per ton or even more. The main supplier of high purity quartz concentrates is the Unimin Cooperation, USA that mines pegmatite deposits at Spruce Pine, North Carolina. The quartz concentrate produced by the company is divided into several grades that have become world standards of high quality (Table 1). The size of the worldwide market is estimated at about 30,000 tons per year for the 99.99% purity and above material.

Trace element concentrations of high purity quartz products sold on the world market and of potential high purity quartz deposits in Norway
Product Al B Fe K Li Na P Ti
Drag NC1CG* 25,0 - 0,8 1,6 4 3,8 - 3,0
Drag NC2A* 8,0 - 0,2 0,3 0,8 1,0 - 7,0
Drag NC3X* 9,4 - 0,2 0,3 0,8 0,03 - 0,6
Drag NC4A* 14,0 - 0,3 0,5 0,6 0,9 - 1,2
Drag NC4X* 14,0 - 0,06 0,1 0,5 0,05 - 1,2
Iota 6** 8,0 0,04 0,15 0,07 0,15 0,08 0,05 1,4
Iota 4** 8,0 0,04 0,30 0,35 0,15 0,9 0,05 1,4
Iota 4** 16,2 0,08 0,28 0,60 0,90 0,9 0,10 1,3
Svanvik,
Finnmark ***
15,0 <1,0 1,0 1,0 15,0 0,1 1,0
Jouvvacorrú,
Nordland ***
6,2 <6 <1 <2 2,9
* Data from Norwegian Crystallites 23. nov. 2009
** Iota high purity quartz, Unimin
*** in situ laser ablation ICP-MS analyses of potential high purity quartz deposits done at NGU

Impurities of trace elements in quartz:

Imi impurity figure 1
Processes controlling the concentration, distribution and speciation of trace element impurities in quartz are poorly defined. Al, Ti, Li, H, Na, K, Ca, Fe, P, Ge, Ga, B (in order of average frequency) are the most common trace elements in natural quartz. The trace element content in quartz depends mainly on the pressure and temperature conditions and the chemistry of the fluid or melt from which the quartz crystallised. But subsequent metamorphic overprint and alteration may cause the internal redistribution, uptake and/or expulsion of trace elements and lattice defects (silicon and oxygen vacancies, broken bonds). Imi impurity figure 2
Recent studies of quartz relating formation conditions and trace element signature have been revealed some affiliations. Hydrothermal quartz has generally low Ti concentration (<20 ppm) but it can contain up to several thousands ppm of Al. Quartz which were formed at temperature above 500ºC contains commonly >50 ppm Ti. Al and its interstitial charge compensators Li+, K+, Na+ and H+ can be removed from the quartz lattice during metamorphism >350ºC and >1.5 kbar whereas structural Ti in quartz is mostly kept in the lattice at these conditions.

Use of high purity quartz

High purity quartz has become one of today's key strategic raw materials for the high-tech industry. Silica glass melted out of high purity quartz offers a wide range of exceptional optical, mechanical and thermal properties, which are essential for manufacturing many high-tech products in areas such as semi-conductor technologies, high temperature lamp tubing, telecommunications and optics. Applications for the high purity quartz are high quality optical devise, optical fibres, quartz glass, synthetic quartz wafers, crucibles for the production of solar grade silicon, quartz wool and fillers for electronics. Read more about high purity quartz in electronics

High purity quartz glass is used in production of lenses for telescopes and laboratory optical devices, communication devices, diffraction lenses, projection displays, optics for scanning devices and printers, lasers, as well as photo cameras, ultra-flat TV screens, flame control devices, etc. Crucibles from melted quartz glass are used to produce metallic silicon and polysilicon. In order to produce metallic silicon suitable for production of high-quality semiconductor plates, polysilicon is placed into a quartz crucible heated to a high temperature, and a silicon monocrystal is drawn out of the melt. Fused quartz is one of the few materials that combine high purity and heat resistance required for the process.

Quartz wool: Quartzel® Wool, a Saint-Gobain Quartz ProductQuartz wool: Quartzel® Wool, a Saint-Gobain Quartz ProductFiber optics is one of the youngest and most progressive branches of silica-based industry. Supporting tubes for light guides are made of natural as well as of synthetic quartz. The latter has better properties but is much more expensive. That is why most plants successfully develop and use their own technologies for production of light guide supporting tubes from natural quartz. Quartz wool is used for high temperature insulation (cables for refractory insulation), filtration of high temperature corrosive gases and liquids and as barrier plug for combustion tubes. Quartz tissues, woven and non-woven, are used as the basis for lamination of high-quality printed circuits and radar shields. Non-woven materials from quartz glass are used in removable cones for space shuttles.

High purity quartz in electronics

Imi Idea Figure
The main products from ultra pure quartz glass in lighting industry are quartz tubes. The tubes are used for high-temperature mercury, halogen and UV lamps, thermocouples, semiconductor products, wave-guide auxiliaries and other high-temperature devices. Tubes from synthetic high purity quartz with low content of water in the crystal lattice, used in casing and bandages for UV and ozone lamps, medical and chemical equipment and in latest models of semiconductor devices. Tubes from melted quartz of high chemical purity and high heat resistance are perfect furnaces for production of silicon wafers for semiconductor industry. The tubes have a diameter of up to 550 mm with an overall content of impurities less than 25 ppm.

Occurences of high purity quartz

Quartz of every quartz deposit being sand, sandstone, quartzite, hydrothermal vein or pegmatite, has its own specific properties and only a few deposits have high purity quality. There are no rules or general consensuses how high purity quartz is formed and how and where it preferentially occurs. The currently mined high purity quartz deposits are pegmatites (Drag, Norway; Spruce Pine, USA) or hydrothermal veins (Saranpaul, Russia). Undeveloped deposits of high purity quartz in Norway are hydrothermal veins (Svanvik) and kyanite quartzites.

High purity quartz deposits are mined in open pits or in shallow underground mines if is a sufficient tonnage of quartz economically recoverable and if the quality of the raw material and its suitability for high-value applications tested. The laboratory investigations include the determination of chemical, mineralogical and physical impurities of the deposit material. Based on these results it will be tested what degree of purity can be obtained at reasonable costs and which applications can be considered. The perfect combination of processing techniques has to be find for each deposit.

Refinement


Which processes make the quartz clean?Which processes make the quartz clean?The first steps of processing (physical) include crushing, contamination-free grinding, flotation and magnetic and electrostatic separation techniques. Chemical refining by leaching of quartz with medium to strong mineral acids at elevated temperatures dissolves feldspar intergrowths, mica admixtures, mineral coatings and contaminated microfissures. Chlorination is the best way to achieve ultra- pure specification, by removing a great part of the contaminating elements. Quartz is heated at temperatures of 1,000 to 1,200ºC in a chlorine or hydrogen chloride gas which removes alkalis and transition metals. Subsequent specific heat treatment and suitable calcinations processes remove fluid and gaseous inclusions.

Chemical analysis of quartz is carried out after each stage of quartz refining, in order to determine the success of the refining step.

High purity quartz in Norway

Norway has a few of quartz deposits which can be considered as future deposits of high purity quartz.

The most famous high purity quartz deposit is mined by Norwegian Crystallites, which is one of the few and most important producers of high purity quartz in the world. It produces successfully high purity quartz from zoned pegmatite deposits since 1996 at Drag in the Tysfjord area of Nordland. The pure quartz is mined underground 70 m below surface from the core of the pegmatite. The quartz raw material is crushed and milled into required grain sizes and is cleaned in a series of wet and dry processes to remove impurities. The company produces 5 grades of quartz concentrate in fractions of 0-150 micron and 100-300 micron.

Another high purity quartz deposits in Norway is the undeveloped deposits of Svanvik at Pasvik, Finnmark. The Svanvik deposit, discovered in 1985, is a more than 500 m long and 20 m wide, mostly hidden hydrothermal quartz vein with more than 1,000,000 tons resources. The vein strikes WSW-ENE and dips 75º towards NNW. In 1986/87 six drill holes up to 50 m long, three seismic profiles and five trenches were performed by NGU to justify the quartz resources. The quartz commonly contains calcite which requires raw material refinement by flotation and acid leaching.

Quartz kyanite, detail from hand specimenQuartz kyanite, detail from hand specimen. The fine-grained kyanite quartzite from the Gullsteinberget in Solør contains about 80 weight % high purity quartz and 20 weight % kyanite which gives the rock the dim turquoise colour. The dark dots are tiny pyrite crystals. Photo: A. Müller.
In addition to traditional quartz deposits, a new possible source of high purity quartz have recently been discovered as low trace element concentrations of quartz in kyanite quartzites from Solør, Surnadal, Nasafjell and Jouvvacorrú (Skjomen). Kyanite quartzites are rare, fine-grained quartzites with 70 to 85 vol.% quartz and >15 vol.% kyanite (Al2SiO5) which occur in Proterozoic supracrustal units. Kyanite quartzites form stratiform lens-shaped bodies, which can extend several kilometers. Kyanite quartzites are assumed to be metamorphosed hydrothermal altered mafic or felsic volcanic rocks.

The disadvantage from the economic point of view is the small crystal size of quartz (0.1 to 0.5 mm) in the kyanite quartzites.

High purity quartz research at NGU

Because the demands of quality and supply of the high quality quartz raw material are increasing, the industrial mineral group of NGU is doing systematic evaluation of potential quartz deposits in Norway that have been conducted over the last decade.

Concentrations of structural bounded Li, Be, B, Na, Mg, Al, P, K, Ca, Ti, Mn, Fe and Ge in quartz are determined in situ with laser ablation inductively coupled mass spectrometry at NGU for rapid screening of possible high purity quartz resources (Flem et al. 2002). The method eliminates the need to remove solid and liquid inclusions by expensive dressing techniques prior to chemical analysis of structural impurities. Information on the petrogenetic history of the quartz is obtained by scanning electron microscope cathodoluminescence (SEM-CL). SEM-CL is used to reveal growth zoning and alteration structures in quartz crystals and to identify quartz from different generations of crystallisation that cannot be distinguished easily by optical microscopy (e.g., Müller et al. 2002).

Central people working with quartz and quartzites in this group are Axel Müller, Peter Ihlen and Jan Egil Wanvik.

Litterature

  • Flem, B., Larsen R.B., Grimstvedt, A., Mansfeld, J. 2002. In situ analysis of trace elements in quartz by using laser ablation inductively coupled mass spectrometry. Chemical Geology 182: 237-247
  • Haus, R. 2005. High demands on high purity. Industrial Minerals, October 2005: 62-67.
  • Jakobsen, B.M., Nielsen, E. 1977. Kyanite kvartsit projektet 1976-1977. Laboratorienrapport. Endogen Laboratorium. Geol Institut Århus Universitet. p.19.
  • Moore, P. 2005. High purity quartz. Industrial Minerals, August 2005: 53-57.
  • Müller A., Kronz A., Breiter K. 2002. Trace elements and growth patterns in quartz: a fingerprint of the evolution of the subvolcanic Podlesí Granite System (Kru¿ne Hory, Czech Republic). Bulletin of the Czech Geological Survey, 77/2: 135-145
  • Müller, A, Ihlen, P. M., Wanvik, J. E. 2007; Norwegian kyanite quartzites - High purity quartz and aluminum deposits. NGU Focus no 5 2007 (pdf).
  • Müller, A., Wanvik, J.E. 2005. Norwegian kyanite quartzites - potential resources of high purity quartz. Norwegian Geological Survey, Report 2005.039.
  • Wanvik, J.E. 1989. Statusrapport 1989 for undersøkelse av Svanvik kvartsforekomst. Norwegian Geological Survey, Report 89.078.
  • Wanvik, J.E. 1989. Sluttrapport for undersøkelse av Svanvik kvartsforekomst. Norwegian Geological Survey, Report 89.165.