|MadSci Network: Environment & Ecology|
Hi Ed. Silica refers to naturally occurring minerals composed principally of silicon dioxide (SiO2). Silicon dioxide exists in both crystalline and amorphous forms. Quartz, cristobalite and tridymite are the three most common crystalline forms. These forms are interrelated and can change their form under different conditions of temperature and pressure. There are two different forms of quartz that are designated by the prefixes alpha and beta. The most common form is alpha-quartz which is a major component of igneous rocks, such as granite and pegmatite, but is also found in sandstone and sedimentary rock such as slate and shale. Beta- quartz is less common. Many synthetic forms of quartz also exist. Crystaline silica or essentially sand can be removed mechanically with as turbo separaterwhich essentially has a container that the sand settles do to the swirling motion of the water and then physically removed. Silica is found in makeup water from regions of high volcanic activity. Parts of California, New Mexico, Mexico, and other regions contain silica concentrations in excess of 30 mg/L in the makeup water. Silica scale can take many forms. Amorphous silica scale or water glass will form in the coolest and lowest pH portions of a system. This is opposite of calcium carbonate that will deposit in the hottest and highest pH portion of a system. Silica will react with divalent metal cations such as iron and magnesium. The resultant scale will be very hard and difficult to remove. Mineral acids such as hydrochloric, sulfamic, citric, and sulfuric have no effect on dissolving silica. Toxic acids such as Hydrofluoric (HF) or other fluoride compounds such as Ammonium Bifluoride (ABF) must be used to remove silica scale. Without special treatment schemes, maximum acceptable silica concentrations in cooling towers is 150 to Silica chemistry is very site specific because silica can react with a wide variety of ions. Silicon does not occur as a free element in nature, but it occurs as silicates and silicon dioxide as above so what you are telling me about silicon cannot be possible unless it is being place within the water source artificially. You didn't say water your water source is (city, well, pond, etc) but as I say the silicon would have to be added to the supply to exist there and I would be more concerned about that if it is indeed happening.. I hope this imformation helps….Mark
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