Ion exchange calculator

Enter each ion concentration with its correct unit. You can convert concentrations without entering sizing data. For resin sizing, enter the exchange capacity, service flow, cycle duration and settled bed depth. Resin bulk density is optional and is used only to estimate resin mass.

Table 1: Input table for anion concentrations

Anions	MW g/mol	Concentration	unit	converted concentration	unit
NO3-	62.00		eq/L meq/L g/L mg/L mol/L mmol/L		eq/L meq/L g/L mg/L mol/L mmol/L
NO2-	46.01		eq/L meq/L g/L mg/L mol/L mmol/L		eq/L meq/L g/L mg/L mol/L mmol/L
Cl-	35.45		eq/L meq/L g/L mg/L mol/L mmol/L		eq/L meq/L g/L mg/L mol/L mmol/L
SO42-	96.06		eq/L meq/L g/L mg/L mol/L mmol/L		eq/L meq/L g/L mg/L mol/L mmol/L
HCO3-	61.02		eq/L meq/L g/L mg/L mol/L mmol/L		eq/L meq/L g/L mg/L mol/L mmol/L
F-	19.00		eq/L meq/L g/L mg/L mol/L mmol/L		eq/L meq/L g/L mg/L mol/L mmol/L
TOTAL			eq/L

Table 2: Input table for cation concentrations

Cations	MW g/mol	Concentration	unit	converted concentration	unit
Na+	22.99		eq/L meq/L g/L mg/L mol/L mmol/L		eq/L meq/L g/L mg/L mol/L mmol/L
K+	39.10		eq/L meq/L g/L mg/L mol/L mmol/L		eq/L meq/L g/L mg/L mol/L mmol/L
Ca2+	40.08		eq/L meq/L g/L mg/L mol/L mmol/L		eq/L meq/L g/L mg/L mol/L mmol/L
Mg2+	24.31		eq/L meq/L g/L mg/L mol/L mmol/L		eq/L meq/L g/L mg/L mol/L mmol/L
NH4+	18.04		eq/L meq/L g/L mg/L mol/L mmol/L		eq/L meq/L g/L mg/L mol/L mmol/L
Mn2+	54.94		eq/L meq/L g/L mg/L mol/L mmol/L		eq/L meq/L g/L mg/L mol/L mmol/L
TOTAL			eq/L

Table 3: Table for some sizing parameters for an ion exchange installation

	Anion removal	Cation removal
Assumed resin exchange capacity			eq/L meq/L
Settled resin bulk density			kg/L kg/m3
service flow			m3/h l/h m3/day l/day
time between 2 regenerations (1 cycle)			hour(s) day(s)
Ions in water (1 cycle)			eq/cycle
Estimated resin volume for one cycle			L
Estimated resin mass			kg
Settled resin bed depth			m
Estimated bed cross-sectional area			m2
Estimated single-column diameter			m

Table 4: Illustrative equilibrium loading and distribution of resin sites

Anions Equilibrium loading qi (eq/L) Occupied sites (%) Equilibrium ratio qi/ci Lwater/Lresin NO3- NO2- Cl- SO42- HCO3- F- total

Cations Equilibrium loading qi (eq/L) Occupied sites (%) Equilibrium ratio qi/ci Lwater/Lresin Na+ K+ Ca2+ Mg2+ NH4+ Mn2+ total

Ask about resin selection

How to interpret the results

Ion exchange resins exchange dissolved ions with counterions held on the resin. Cation resins exchange positively charged ions; anion resins exchange negatively charged ions. The equivalents unit accounts for electrical charge: 1 mmol of a monovalent ion is 1 meq, while 1 mmol of a divalent ion is 2 meq. For example, 61.02 mg/L bicarbonate is approximately 1 meq/L, and 48.03 mg/L sulfate is approximately 1 meq/L.

Resin volume and column geometry

The calculation uses load per cycle = total ion concentration (eq/L) × flow (L/h) × cycle duration (h), and resin volume (L) = load (eq) / assumed capacity (eq/L resin). Resin mass equals resin volume multiplied by the supplied bulk density. For each resin bed, cross-sectional area (m²) = resin volume (L) / [1000 × settled bed depth (m)], and diameter (m) = √(4 × area / π). The diameter represents one cylindrical bed and excludes freeboard, backwash expansion and hydraulic design checks.

The capacity entered is a model assumption. Total exchange capacity and operating capacity are different: practical sizing requires an operating capacity appropriate to the selected resin, regeneration conditions and water composition. The default bed depth of 1 m is an editable calculation assumption, not a resin recommendation. A complete water analysis should have similar anion and cation totals when expressed in equivalents; this calculator includes only the listed species.

Illustrative equilibrium model

The built-in separation factors are fixed examples, not resin-specific design data. For each anion or cation group, the model uses q_i = Q × f_ic_i / Σ(f_jc_j), where Q is the entered capacity, c is concentration in eq/L, and f is the built-in separation factor. The occupied-site percentage is 100q_i/Q. The ratio q_i/c_i has units of litres of water per litre of resin. It is an equilibrium treatment ratio and does not predict an actual service volume or breakthrough time.

Actual breakthrough depends on the selected resin, competing ions, flow, bed depth and the permitted effluent concentration. Confirm the resin parameters and performance under the intended service conditions before using the estimates for equipment selection.

Worked example using the calculator's factors

This example considers only the anion mixture shown below; it is not a complete, electrically balanced water analysis. The assumed anion exchange capacity is 1.4 eq/L resin. Concentrations are converted to eq/L before applying the factors.

The weighted concentration sum is 0.02496 eq/L. For chloride, q = 1.4 × 0.001 / 0.02496 = 0.05609 eq/L resin, and q/c = 56.09 L water/L resin. The loadings sum to the entered capacity and the occupied-site percentages sum to 100% before rounding.

For every different application of water conditioning specific ion exchange resins (Rohm & Haas / Purolite) are available. Lenntech can advise you which is most appropriate.

Other calculators

Warning: Lenntech BV cannot be held responsible for errors in the calculation, the program itself or the explanation. For questions or remarks please contact us.