How silica sand is dug

Glass sand may carry no more than 0.03% iron oxide, so plants clean it by rubbing the grains against each other.

stations: 5
things downstream: 146

The short version

Glass-grade sand gets rubbed clean against itself. Miners quarry sandstone, truck dry sand from pits, or pump wet deposits with a dredge, then screen the grains and churn them in a dense slurry that scours off iron stain. Slimes wash away, flotation can lift out mica and heavy minerals, and the sand is dewatered and dried for glassmakers, potters or oil wells.

Quarry or pump the deposit

Sandstone is quarried like hard rock, crushed, and rod-milled back to its natural grain size. Dry pits simply load the loose grains into trucks. Deposits below the water table are mined hydraulically with dredge pumps.
Screen off the oversize

Water carries the feed across a vibrating screen, and anything coarser than 20 mesh goes to waste or back to the mill. Cyclones or rake classifiers then pull out excess water.

20 mesh
Scour the grains clean

Thick wet feed enters an attrition scrubber, where propellers keep the whole mass in violent motion. Grains grind against one another, which strips off iron stain and stubborn clay. A second set of cyclones carries away the loosened slime.

70 to 75% solids
Float out the impurities

Harder deposits go to flotation in an acid pulp. Mica, feldspar and iron-bearing heavy minerals ride the froth to waste, while clean silica leaves the far end of the machine. Some feed meets its specification after scrubbing and skips this step.
Dewater and dry

Dewatering screens or classifiers drain the product to about 15% moisture, since every bit of water left costs fuel at the dryer. Rotary dryers fired by oil or gas finish the job where a dry product is wanted, and frac grades then cross a final sizing screen.

End of the lineSilica sand Next it goes into toothpaste, silicone, fiberglass and 18 more.

Worth repeating

Quartz is the most common constituent of sand inland and in non-tropical coastal settings, because it is chemically inert and hard enough to resist weathering.
Wind blows desert sand grains round, and round grains will not bind into solid concrete.
Frac sand has to be round and crush-resistant, because its grains prop open fissures in rock so oil and gas can flow out.