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How Does Resin Work?

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Resin that is used in water softeners are an ion exchange resin that acts as a medium for the ion exchange. The ion exchange according to Wikipedia’s website is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. It is a support structure normally in the form of a small microbead. These beads are typically empty, which traps some ions and releases other ions, which is why this is called the ion exchange. These beads are used for separation, purification, and the decontamination process of water.

Over its lifetime, resin will oxidize, lose capacity and simply backwash down the drain. When the life span of the resin is coming to an end, the external forces of work on the resin beads will affect the functional groups that attract hardness ions, creating reduced capacity. 

How it Works

90% of the ion exchange happens in the interior of the bead. Once in the resin bead, free ions diffuse onto fixed immobile negative exchange sites as they pass through the beads. Mineral salts disassociate into ions in water and are free to exchange with ions of similar charge, these ions are mobile and free to move around. The surface of the polystyrene strands have negatively charged functional groups that attract free positively charged ions.

Hardness ions, such as calcium and magnesium, enter the softener and flows through the resin beads, attaching to groups and dislodging sodium/potassium ions. Water softeners work because this process is reversible, which is called regeneration.

How does regeneration work?

Think of regeneration as an exchange. When exhausted, softening resin beads hold hardness ions, they need to regenerate. To clear resin of hardness ions, the regeneration cycle flushes the resin beads using a solution. A 10% sodium chloride solution will regenerate the beads to their sodium state, this is called brine cycling. This occurs when a mass of salt brine enters the softener, building in strength until a wave of 10% brine pushes through the resin and removes the same amount of hardness ions. Once the exchange is complete, the resin bead will contain a volume of unused sodium chloride brine that rinses to drain.

What is the lifespan of resin?

Resin beads fight with strong oxidants, such as chlorine and chloramines. The presence of these oxidizers will shorten the working life of resin.

Chlorine and chloramines kill softening resin as it ages by oxidation and destroying the DVB crosslinking. As oxidants attack the beads, they swell and take on moisture, which makes them mushy. When a resin bead swells, pores and channels through the beads close. The divinylbenzene (DVB) is the crosslinking agent that gives the beads their physical strength. If the DVB is destroyed, the walls of the resin bead will come apart. A quick sign that resin is in the advanced stages of chlorine degradation/oxidation damage is the ability to crush the beads with your hand. Another sign of resin breakdown is pressure loss. As the beads mush, they cause bead compaction and will increase pressure drop during service flow.

Resin beads will swell and contract as they exhaust and regenerate. Their design allows them to resist damage from this action, but external conditions weaken the beads making them susceptible to this stress. Osmotic shock is the swelling and contracting of the bead. Beads will crack in osmotic shock, as they crack, they break apart and lose mass. Partial beads lift higher in the backwash process and can exit out the drain. Hydraulic shock is the physical destruction of the bead by external water force over time.

Under conditions of high concentrations of brine, water is drawn out of the bead due to osmosis and the bead shrinks. Water that enters the bead in large amounts will cause it to swell, crack and possibly burst. This is the reasoning behind the “slow rinse “cycle. Rinsing the resin bed slowly help to prevent this condition.

Why is iron a problem?

Iron is a major contributor to ending the lifespan of resin. Iron runs through resin just like hard water would. Iron oxidizes to a ferric state and attaches to the surface of the interior bead. A simple salt regeneration will not remove iron oxide from a bead. When iron is present in a water supply resin cleaner will help regenerate to prevent the iron from harming the resin beads. If the resin bead is beyond the point of cleaning, then it will be time to replace the resin.

Resin goes through a lot so you can have clean water. The great thing about 602abcWater is that we have a system that can meet every water filtration need you have. Call us for information of systems that can eliminate iron.

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