Aluminum Sulfate or Ferric Chloride?

Hello everyone,

In your experience, what factors should I consider to decide between these two coagulants: aluminum sulfate vs ferric chloride? May I used either with the same sort of water? Can you say that one is better?

Very grateful in advance.

Taxonomy

• Treatment
• Purification
• Chlorination
• Water Supply
• Inorganic Chemicals
• Sulfates
• Utility Chemicals

9 Answers

1. It really depends on the water you are screening, the downstream processing units, and ability of you to dispose of sludge.

   Ferric will usually create a greater volume and mass of sludge to be disposed of compared to alum, but can do a better job of removing TOC components in the raw water.

   Both chemicals consume alkalinity in their coagulation activity so expect significant pH depression and need for post clarification pH adjustment. If you are looking at demineralizing/ion exchange after the clarification, both will add significant ionic loading (especially considering the pH adjustment needed) and shorten your run times.

   There are coagulants that do not produce the amount of sludge these metal salts do and clarify equally as well. They also make coagulant blends containing ferric or some aluminum salt paired with an organic coagulant that will help reduce sludge production while still maintaining the clarification and TOC reduction desired by the metal coagulants alone.

   Bottom line, jar test and see what works best.

2. Hi Joel.
   It depends on the type of water you need to treat and the use of this. I always use aluminum sulphate for Italian swimming pools.

3. Joel:

   If water is for human consumption at some stage then use ALUM.

   Many people in Australia draw water from rivers or canals that is used for irrigation purposes and drink that water.

   EVERYONE uses ALUM as the flocculent to clean their drinking water of suspended solids/colloids.

   Some use additional cleaning/filtering, some do not.

    

   SEE ATTACHED

   Stay safe,

   Hugh.

4. I have used FeCl3 in some of my projects successfully. It's cheaper than Al sulfate and it covers a broader range of pH in comparison to Al sulfate but before you select the coagulant please conduct Jar Test to be sure 

5. If you are using UV the ferric will stain the sleeves and everything else it comes in contact with. With an orangish yellow color which will cause the UV to be inefficient . Aluminum is usually more expensive than Ferric though.

6. Hey JOEL BAUTISTA ,we have a good article with the pros and cons of both. (Full article here: Pros and cons of alum and ferric

7. Up to your jar test, AlSO4normally world wild using for supply water but FeCl3 if you load over dose the clear water become to be slightly yellow color treated ww

8. The resultant pH after addition of the coagulant is the main criteria.

   With aluminum sulfate, optimum coagulation efficiency and minimum floc solubility normally occur at pH 6.0 to 7.0. Iron coagulants can be used successfully over the much broader pH range of 5.0 to 11.0.

   Jar test shall be used for selection and optimization of coagulant/poly-electrolyte.

9. If the application is seawater RO desalination, Ferric Chloride.

    

   Aluminium sulphate is commonly used in river/lake water coagulation but never used with seawater. The residual aluminium ions left can be a major issue for fouling membranes.