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Lime Softening

Lime Softening. EWB-UCB lime softening research group. Basic process of lime softening. 1. Rapid Mixing of Lime. 2. Flocculation of Solids. Solid colloids agglomerate into larger particles. 3. Sedimentation. Solids settle out. Basic Chemistry.

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Lime Softening

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  1. Lime Softening EWB-UCB lime softening research group

  2. Basic process of lime softening • 1. Rapid Mixing of Lime. • 2. Flocculation of Solids. • Solid colloids agglomerate into larger particles. • 3. Sedimentation. • Solids settle out.

  3. Basic Chemistry • Lime provides OH-which increases the pH of water. • Dissolved CO2 is changed to Bicarbonate (HCO-1) then to carbonate (CO3-2) as pH increases. • CaCO3 first precipitates. • Then at higher pH, Mg(OH)2 precipitates.

  4. Arsenic removal is dependent on pH • Coprecipitates with magnesium hydroxide • Less than 10% precipitates at pH 9.6 • Removal of As(V) approaches 100% and As(III) 75% at pH 10.5

  5. Choice of Lime: Lime or Lime-Soda? • Lime: Only Carbonate hardness • Lime and Lime-Soda: A lot of non-carbonate hardness. • Other variations?

  6. Obstacles to arsenic removal • Trace amounts of orthophosphate and Carbonate reduces coprecipitation with magnesium hydroxide • Other problems?

  7. Future Steps • Look into quality of hardness • Is it carbonate or noncarbonate? • What are the variations of lime based on the quality of the hardness • Lime, soda, other additives and grades of Lime • What are possible obstacles to precipitation • How to deal with pH>11 • Leave it as is, stabilize it, reduce it? • What is to be done with the sludge • Use in gardens as fertilizer? Other outcomes? • Anything Else?

  8. Sorry I Can’t Be here, I am teaching People how to sail.

  9. References • EPA Wastewater Technology Fact Sheet Chemical Precipitation • Fields, K. A., Chen, A. S. C., Wang, L., Supply, N. R. M. R. L. (US) W., & Division, W. R. (2000). Arsenic removal from drinking water by coagulation/filtration and lime softening plants. Contract. National Risk Management Research Laboratory, Office of Research and Development, US Environmental Protection Agency. Retrieved from http://www.epa.gov/nrmrl/pubs/600r00063/600r00063.pdf • Wikipedia • http://dx.doi.org/10.1515/REVEH.2006.21.1.25

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