Simultaneous Removal of Hardness and Silica

Taxonomy

• Desalination
• Sustainable Desalination
• Desalination Pre-treatment
• Desalination
• Water Hardness
• Silica Removal

11 Answers

1. Several softening  methods Lime soda process is better.Bicarbonate hardness removed by lime and chloride,MG removed by soda ash.Other methods ION XCHANGE and Zeolilite process followed with Ultrafiltation is better for silica as well as hardness removal.

2. My first instinct is chemical precipitation. I agree with other answers that the final quality and maybe use of the treated water should be defined. Also need TDS, alkalinity, pH, TSS of feed to answer the question well. With no feed quality, the most flexible choice is chemical precipitation using MgO and/or aluminate for silica, and depending on pH, add caustic or lime or acid to get pH to about 10. Then clarify and/or filter as finely as needed, adjust pH as needed. Good luck.

3. Definitely softener for hardness removal, of course depending on quantity of consumption. If quantities are big maybe antiskalant can be a solution. For silica it still depends on type of silica. Sand filtration can be the first one. If sand filtration doesn't work than Reverse osmosis is required. 

4. In the Heavy Oil industry (Alberta) this is commonly done with (Hot or Warm) Lime softening, with and Magox to reduce content of Silica.

   At effluent: Hardness is 30 and Silica about 40-50; to prepare BFW the softened Produced water then passes to WAC beds.

   2 Comments

   1. Co-precipitation of Silica is achieved with simultaneous addition of Lime (to rise the pH) and Mg(OH)2 known as Magox... If you want , provide me an email I have a paper  -40 pages- and will send it to you.

      1 Comment reply

      1. Thank you my email is qasempur@gmail.com

   2. Thank you for your reply ,can explain more about Magox solution.

5. I forgot to mention that this process also provides pre-heated make-up water for the boiler system- reducing overall "raw" thermal input and related environmental impact.

6. A very effective process is to boil the solution and condense to create essentially pure distilled water. Waste heat (including heat from boiler exhaust or condensing excess steam) can be an effective thermal source.

7. To best answer your question,  more information is need. 

   What else is in the water.  What is the water to be used for.  What are the constraints on the product and waste water streams.  What is the desired product flow rate and water quality. Are there other constraints. Such as discharge limits,  supply/access issues for the site (availability/reliability of power supply,  access to site).

   Depending on the scale of your problem  and the existing/ available infrastructure,  then ion exchange (chemical, electrochemical), cold Lime softening, warm lime softening, EDR or other process could be your best available solution.

    

    

8. These answers are correct below.  I am agreeing that what you have is best solved via 2 steps: Utilizing Ionic Cationed/Anion Softeners, and then by RO's into Mixed Bed vessels.  I would like to know if 1: Your Hardness of 1500 is true, and exactly what the end result would be - what are the tolerance levels? Many other questions remain, as to best answer you.  What is the water to be used for (Boilers, potable)? What will the flow rates be? Is this a pre-job or existing plant? Especially, what will the budget be like?  Obviously, if money were no option, we could say that 3PPB impurities are easily achievable... I would think to better answer your question Sir, we need a bit more information to do so.  The more information you can provide, the better we may answer your question, tailored to your exact needs.

   1 Comment

   1. Thanks for your reply , 1500 Hardness is true and end result of that  will be use in feed of RO . The flow rate is 250 m3/hr .

9. 100 ppm is extremely high for natural sources of water. Before removing silica, we need to know the nature of silica. Is silica present in colloidal form or in dissolved form. It is best to remove colloidal silica by precipitation using combinations of polyelectrolytes as coagulant and flocculants. The poly and its dose is best selected by way of Jar Test in laboratory. Hardness can be removed using Ion Exchange method.  Treatment also depends upon the treated water quality desired by you. For more informaiton, please provide the data as mentioned above. 

   1 Comment

   1. Thanks for you reply , the silica is in dissolve form and r silica and hardness removal is pretreatment of  RO

10. the silica can be precipitated out through addition of sodium aluminate and then filtered out. The ex-filter water can then be passed through a suitably sized softener (tailored for 2000 ppm total hardness with regeneration warning for product quality control), after which a reverse osmosis system may be used for a more refined output depending on how stringent the product quality stipulations are.

11. I thing, that it is no simple in one simultaneous process. Theoreticly the hardness and silica can be removed by jonic exchange proces (kationic and anionic). But it can be expensive, becaus the hardness is high. May be a good solution will be two stages process: first - removal hardness by chemical precipitation and second: removal of residual hardness and silica by jonic exchange ( a strong cation exchanger and strong anion exchanger).