Sand is needed as a building material and raw material for glass and provides the silicon for the semiconductors used in the computer industry and photovoltaics. Sand washed up in the oceans and along bodies of water is suitable for use. However, demand for this kind of sand is growing exponentially worldwide and sand is becoming scarce. The overexploitation of shore sand is already causing environmental problems and land subsidence in many parts of the world.
Artem Golev, The University of Queensland, Australia, and colleagues have found that overburden from ore mines could be suitable as a sand substitute. The metal raw materials make up only a small percentage of the ore rock; most of the rock extracted from underground remains as crushed overburden. The team used samples from ore mines owned by the Vale Group in Brazil to determine whether the rock residue left over after the ore is extracted has the mechanical, chemical, and other characteristics that a sand replacement requires.
The ore-bearing rock is first crushed and ground. Then the iron-containing portion is separated, among other things by magnets, flotation, and separation according to the density of the material. After drying in addition to the iron ore a rock dust reminds—a material named ore sand by the researchers.
Tests of the ore sand showed that chemically the material is very similar to natural sand: it contained about 90 % silicate and 9 % iron oxides, plus small amounts of other metal oxides. It has a nearly neutral pH, very low electrical conductivity, and contains extremely low levels of soluble sulfates and chlorides. It is inert and non-toxic.
But to use sand in concrete production, for example, the granules must be as round and stable as possible and not too finely powdery. The ore sands could compete with natural sand in terms of strength and shape. At 21 to 22 % by weight, however, the material has a higher fineness than is recommended for processed sands.
According to the scientists, the ore sand could nevertheless replace at least some of the natural sand in concrete production and other building materials. Filtering could also reduce the amount of fine dust. According to the researchers, the ore sands could also be suitable as a raw material for glass production. If an additional processing step is added to further reduce the metal oxide content, the ore tailings could be brought up to a silicate content of 99.5 to 99.7 %.
- Ore-sand: A potential new solution to the mine tailings and global sand sustainability crises: Final report,
Artem Golev, Louise Gallagher, Arnaud Vander Velpen, Josefine R. Lynggaard, Damien Friot, Martin Stringer, Stephanie Chuah, Diana Arbelaez-Ruiz, Douglas Mazzinghy, Luanna Moura, Pascal Peduzzi,
UQ eSpace 2022.