Softeners and Iron

Published on by in Academic

Softeners and Iron
How does both soluble and insoluble iron impact an ion-exchange-based water softener?

Media

Taxonomy

5 Answers

  1. Hello,The ion xnge is good for removal of dissolved inorganics impurities.  iron removal better to use either oxydation/aeration( if PH is greater than 8.5) adding oxydation agent such as CL or KMNO4

    In ion xnge the cation and anion xnge takes place with NACL solution(H as cation and OH as anion).

  2. Here is the short answer. suspended iron is a physical foulant. Dissolved iron (ferrous primarily) gets removed by exchange. The Ferrous then is oxidized to ferric while associated to the resin. It essentially plugs up the resin pores. To remove it, it needs to be reduced to ferrous. Enter sodium hydrosulfite. The worse the pore pluggage, the greater the damage to the resin. adding 1lb of citirc acid to every 100lbs of salt every 4th regeneration will help keep the resin cleaner and decrease iron fouling/damage.

  3. Soluble and insoluble iron in my humble opinion are to be considered foulants for ion exchange resin.  The resin is that binding to the resin may be more or less non-reversible by typical regeneration procedures.  Resin cleaner products are nominally effective, but require system down-time.  It is best to make sure there is no ferrous (Fe2+) iron in solution, and if it is, then it must be oxidized (permanganate/zeolite treatment works best).  Filter media should be watched more carefully and back-washed on Delta Pressure, or a timer.

    If the water softeners are pretreatment for an RO system, then extra caution is required to ensure that no particulate (and no soluble iron) makes it through the softeners, as once iron deposits on membranes, any chlorine punch-through will result in blistering of the membrane at the location of iron particles.

  4. If

    If the source water contains oxygen and the pH of the water is more than 6.8, thesoluble iron will oxidize on the resin and reduce the ion exchange capacity of the resin. Oxidation of 1 mg of iron requires only 0.143 mg of oxygen. If the amount of iron in the source water is more than 0.5 mg/l, it is better to install a system of pre-removal of iron. In theory, if the water is acidified before softening to obtain a pH water of less than 6.8, i.e. having only the soluble iron in the water, it can be removed on the ion exchange resin without loss of exchange capacity. I think it might work for artesian water.

     

     

  5. James,

    Insoluble Fe that has already precipitated will act like TSS.  It will be largely filtered by the resin.  It will increase TSS to the extent of it's concentration and be removed during a proper backwash.

    Soluble Fe that has not been oxidized will exchange on the resin, just like Ca or Mg.  In fact, due to it's greater valance, it will exchange before Ca or Mg.  So, it needs to be considered when sizing a softener as it takes up exchange capacity.  Also, Fe is not as easily removed during regeneration.  Depending on how much Fe, it may be wise to investigate a resin cleaner to use during backwash/regen.

    1 Comment