Some of the efficient methods reported so far are thermal annealing & acid leaching, by organic acid leaching, by gravity and magnetic separation, resin coating, scrubbing etc..

The chemical analysis of silica sand indicates 90 to 92% silica with 3-3.5% Fe and 2-2.5% alumina. The attached slime coating can be removed by scrubbing. After scrubbing ,the sand is processed through magnetic separation and floatation to achieve a product containing more than 95% pure silica containing less alumina and iron.

I found a recent article on removal of impurites from tailing (quartz). It said: The aim of this study was the removal of impurities from tailing (quartz) obtained from Bitlis kyanite ore by flotation. In this regard, three group experiments were made. The first group experiments results showed that a quartz product containing 98.8% SiO2 and 0.05% Fe2O3 with 68.35% recovery was obtained by the flotation of impurities in acidic medium. The second group experiments results showed that a quartz product containing 99.3% SiO2 and 0.01% Fe2O3 with 84.75% recovery was obtained by the magnetic separation and flotation of impurities in acidic medium. The third group experiments results showed that a quartz product containing 86.61% SiO2 and 0.01% Fe2O3 with 62.21% recovery was obtained by the magnetic separation and flotation of impurities in neutral medium. The quartz product obtained from the second group experiments was met the suitable properties, used in glass industry.

More can be found at: http://www.ijastnet.com/journals/Vol.1_No.1;_March_2011/11.pdf

There are the followin methods

1. High magnetic field strength separation

2. Flotation

3. Heavy liquid separation with bromoform (as it is also used for coal)

H.G.Dill