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While crystalline silicas have some associated health issues, the synthetic amorphous forms are nontoxic products. The assessment studies focus on respiratory exposure, and all studies conclude that at the current exposure limit of solids in air, there is no risk associated to long-term exposure. In common with all dusty materials, they can cause skin and eye irritation. They are also approved for food applications and used as food additives.
Silica makers are syndicated in the ASASP association. Amorphous silicas have been registered in REACH in 2010 (http://www.reach-sas.org/index.htm).
Precipitated silicas are made from sand, soda ash (sodium carbonate), and sulfuric or hydrochloric acid. Life cycle analyses show that the environmental impact of their manufacture and use in tires is lower than for any other component (source: Goodyear) and also that it is dwarfed by the savings during use (OECD 2014). Some producers are starting to use waste amorphous silicas (such as rice hull ash) instead of conventional crystalline silicas like quartz, as the raw material. This reduces energy consumption, both by eliminating mining and by lowering the temperature needed for solubilization. An interesting new sustainable sourcing opportunity is arising from plans to recover useable silica from geothermal power plant operations (see www.environmetals.co.nz).
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