Bentonite Activation & Drying: Ion Exchange & Moisture Kinetics (2D)

Activation

Soda ash dose (Na₂CO₃) 4.0%

Activation temperature 25 °C

Drying

Dryer air temperature 110 °C

Initial moisture content 28%

Live Readout

Na⁺-exchange

Swell index

8.0 ml/2g

Moisture

28.0%

Batch time

0.0 min

How it works

Raw calcium bentonite is a poor swelling clay. Soda ash (Na₂CO₃) drives a cation exchange that replaces exchangeable Ca²⁺ on the montmorillonite platelets with Na⁺, which is what actually gives "sodium-activated" bentonite its large swelling volume. The exchanged fraction follows pseudo-first-order kinetics toward a dose-limited equilibrium:

f_eq  = min(1, dose / dose_full)      dose_full ≈ 5% w/w
k1    = k1_0 · exp[(T_act − 25) / 30]  (Arrhenius-style rate)
f(t)  = f_eq · (1 − e^(−k1·t))

swell(f) = swell_Ca + (swell_Na − swell_Ca) · f   [Foster test, ml/2g]

Once exchange is essentially complete the batch moves to the rotary dryer. Moisture content follows the classic falling-rate exponential drying-curve model used for thin-layer drying, with the equilibrium moisture and the rate constant both set by dryer air temperature:

Me   = max(4, 13 − 0.045·(T_dry − 60))
k2   = k2_0 · exp[(T_dry − 80) / 50]
M(t) = Me + (M0 − Me) · e^(−k2·(t − t_dry_start))

Platelet grid — clay tiles shift from grey (Ca²⁺) toward amber (Na⁺) as exchange proceeds, then dim and shrink as moisture leaves during drying.
Swell curve — live plot of swelling index (Foster method, ml per 2 g) rising toward the sodium-activated plateau.
Moisture curve — live plot of moisture content decaying toward the dryer's equilibrium value once drying begins.

Idle

Swell index (ml/2g) Moisture (%) Ca²⁺-platelet → Na⁺-platelet