Grinding Sand to Determine its Mineral Composition

Sand is a very common unconsolidated sedimentary rock, with its particle size varying between 0.063 and 2.0 mm. It also has an extremely variable mineral composition.

Many types contain quartz or silicon dioxide (SiO₂). Sand is primarily used in the glass and construction industry because of its chemical and physical characteristics.

The comminution of quartz sand is a prerequisite for the analytical evaluation of its chemical composition and to establish how appropriate it is for intended uses. FRITSCH offers a broad range of suitable mills for the comminution.

To characterize particle size distribution, FRITSCH provides sieve shakers and instruments for particle sizing through static laser scattering, as well as instruments for the dynamic image analysis. The tracking and optimization of the comminution processes can be accomplished with these technologies.

Composition of Silicon Dioxide

20 g sand as base material for a test milling

SiO₂ is the main element of quartz sand. The oxygen atoms combine with the silicon atom in the center to form a tetrahedral structure. Every oxygen atom is simultaneously connected with two silicon atoms.

In this arrangement, the tetrahedral structures have a cross-linked high-molecular weight, and SiO₂ gets its special hardness of 7 on the Mohs scale (diamond’s hardness value is 10) together with an extremely high melting point of 1713 °C. These features allow its use in the construction or semiconductor industry. ^{[1] [2]}

Utilization of Quartz Sand

20 g Sand ground with the PULVERISETTE 2 after 30 minutes, agate grinding set

Quartz sand is a naturally occurring commodity, found everywhere, and has always been used for the production of glass and as a construction material. Documents on glass, dating to approximately 1600 BC, come from Ugarit. Through various developmental stages, it has become possible to produce glass in a cost-efficient manner, making it suitable for daily use.

Glass in many variations is used in almost every industry. Additional characteristics of quartz sand have been discovered through physical or chemical treatments.

As early as 1899, the chemist Robert Küch was able to produce pure quartz glass, after he conducted the first melting tests with pure SiO₂. Chemically pure crystalline SiO₂ exhibits a heavy piezoelectric effect, which makes it ideal for use in computer chip production and semiconductor technology.

Another proven use is as vibratory quartz in quartz clocks. However, the most important application is the use of silica sand to produce concrete.

Other areas of utilization of quartz sand are:

• Filter sand in waste water treatment plants ^[1]
• Abrasive products in metal processing ^[2]
• Artificial bone substance (medical technology) ^[3]

Comminution of Quartz Sand

100 g sand ground in 5 minutes in the PULVERISETTE 6, 250 ml agate grinding bowls, 20 mm grinding balls

The comminution of sand is unproblematic because it is brittle. However, due to its composition, sand may have varying degrees of abrasiveness. Typically, a mill with impact forces is chosen to minimize this influence. For effective and fast processing, the FRITSCH Planetary Mills are well-suited.

In order to optimize the grinding even further, in regards to sample amount, instrument choice, addition of liquids, and many other parameters, the application consultants performed a series of internal inter-laboratory comparisons.

These comparisons prove that the FRITSCH Planetary Ball Mills perform better than the FRITSCH Mortar Grinder for the preparation of sand in terms of grinding duration and effectiveness. This is due to the transmission of energy and power.

In order to obtain maximum energy impact, the Planetary Ball Mills are optimized. A distinct feature is provided in the FRITSCH Planetary Ball Mill premium line: by increasing the rotational speed, wet grinding is enabled for the particle size in the range of a few nanometers.

The Task

In the case of concrete, very pure quartz sand was required to be ground to a particle size of less than 100 µm. Prepared this way, water glass can be melted from the ground material. The iron content is then photometrically determined without any difficulty.

Minute traces of iron significantly discolor glass, and the glass produced would be rendered unusable. For example, if window glass or a drinking glass displayed an uncontrolled brown discoloration. It is of vital importance to the glass industry that the iron content in quartz sand be effectively and accurately monitored.

Initially, a Mortar Grinder was employed for this task. 20 g quartz sand was ground to a specific amount of fineness using the Mortar Grinder PULVERISETTE 2 with agate bowl for 30 minutes. However, it took only 5 minutes to grind 100 g of quartz sand to a comparable analytical fineness employing the Planetary Mono Mill PULVERISETTE 6 classic line, with a 250 ml agate grinding bowl and 15 agate balls with 20 mm diameter.

The Measurements

The particle size distributions were measured using the Laser Particle Sizer ANALYSETTE 22 NanoTec plus. Particle size distributions in the range between 10 nm and 2 mm can be determined in a quick and effective manner using static light scattering.

As a large volume corresponds better to a representative sample, a sample of 100 g was chosen. Using a Mortar Grinder, this amount cannot be ground to a comparable final fineness even in an hour’s time.

The following can be derived from the tests:

• Planetary Ball Mills are recommended for fast comminution of hard and brittle materials
• Based on representative sampling, the grinding bowl with 250 ml volume of the Planetary Ball Mill is recommended
• Although grinding sets made of various materials are available, in order to avoid the disruptive elements that can occur during grinding, agate is recommended for the concrete case

Sources and continuative Literature:

[1] Werkstoffkunde 17. Aufl., W. Weißbach, Vieweg Verlag
[2] Praxiswissen der chemischen Verfahrenstechnik: Handbuch für Chemiker und Verfahrensingenieure 2. Aufl., Springer Verlag
[3] Chemie 10. Aufl., C. Mortimer und U Müller, Thieme Verlag

This information has been sourced, reviewed and adapted from materials provided by FRITSCH GmbH - Milling and Sizing.

For more information on this source, please visit FRITSCH GmbH - Milling and Sizing.