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Scale Control-Lime Softening Tech Manual Excerpt Water Chemistry and Pretreatment Scale Control Lime Softening Lime softening can be used to remove carbonate hardness by adding hydrated lime: → Ca(HCO3)2 + Ca(OH)2 2 CaCO3 + 2 H2O → Mg(HCO3)2 + 2 Ca(OH)2 Mg(OH)2 + 2 CaCO3 + 2H2O The noncarbonate calcium hardness can be further reduced by adding sodium carbonate (soda ash): → CaCl2 + Na2CO3 2 NaCl + CaCO3 The lime-soda ash process can also be used to reduce the silica concentration. When sodium aluminate and ferric chloride are added, the precipitate will include calcium carbonate and a complex with silicic acid, aluminum oxide, and iron. With the hot lime silicic acid removal process at 60 – 70°C, silica can be reduced to 1 mg/L by adding a mixture of lime and porous magnesium oxide. With lime softening, barium, strontium, and organic substances are also reduced significantly. The process requires a reactor with a high concentration of precipitated particles serving as crystallization nuclei. This is usually achieved by upflow solids- contact clarifiers. The effluent from this process requires media filtration and pH adjustment prior to the RO elements. Iron coagulants with or without polymeric flocculants (anionic and nonionic) may be used to improve the solid-liquid separation. Lime softening should be considered for brackish water plants larger than 200 m3/h (880 gpm). More details are described in water treatment textbooks. /3, 4, 5/ Page 1 of 2 Form No. 45-D01549-en, Rev. 4 April 2020 Excerpt from FilmTec™ Reverse Osmosis Membranes Technical Manual (Form No. 45-D01504-en), Chapter 2, "Water Chemistry and Pretreatment." Have a question? Contact us at: All information set forth herein is for informational purposes only. This information is general information and may differ from that based on actual conditions. Customer is responsible for determining whether products and the information in this document are www.dupont.com/water/contact-us appropriate for Customer's use and for ensuring that Customer's workplace and disposal practices are in compliance with applicable laws and other government enactments. The product shown in this literature may not be available for sale and/or available in all geographies where DuPont is represented. The claims made may not have been approved for use in all countries. Please note that physical properties may vary depending on certain conditions and while operating conditions stated in this document are intended to lengthen product lifespan and/or improve product performance, it will ultimately depend on actual circumstances and is in no event a guarantee of achieving any specific results. DuPont assumes no obligation or liability for the information in this document. References to “DuPont” or the “Company” mean the DuPont legal entity selling the products to Customer unless otherwise expressly noted. NO WARRANTIES ARE GIVEN; ALL IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE ARE EXPRESSLY EXCLUDED. No freedom from infringement of any patent or trademark owned by DuPont or others is to be inferred. DuPont™, the DuPont Oval Logo, and all trademarks and service marks denoted with ™, ℠ or ® are owned by affiliates of DuPont de Nemours Inc. unless otherwise noted. © 2020 DuPont. Page 2 of 2 Form No. 45-D01549-en, Rev. 4 April 2020.
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