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Producing protein intercalated bentonite — Equilibrium, kinetics and physical properties of gelatin–bentonite system

Shamsuddin, Rashid M. / Verbeek, Casparus J.R. / Lay, Mark C.

Abstract Protein intercalated bentonite was produced using gelatin with calcium (CaBt), sodium (NaBt) and octadecylamine-modified bentonite (amine Bt). Adsorption isotherms and rates were investigated from pH3 to pH9 and 4 to 20mg/ml initial gelatin concentrations using 3g of adsorbent loading per 100ml solution. At 20mg/ml gelatin solution, the highest gelatin adsorption obtained for CaBt was 372mg/g or 58.9% gelatin recovery between pH3 to pH5.23 while NaBt showed the best adsorption between pH7 to pH9 with 405mg/g or 60.4% gelatin recovery. Amine Bt showed consistently poor adsorption with the highest gelatin adsorption of 222mg/g or 33.5% recovery at pH3. Basal spacing (d-value) for CaBt increased from 16.3 to 20Å while NaBt increased from 12.4 to 20–23Å, indicating that intercalation had occurred. Adsorption equilibriums were modelled using the Langmuir, Freundlich, Langmuir–Freundlich and Temkin isotherms. The best regression coefficients were given by the Langmuir–Freundlich isotherm for CaBt and NaBt, and by the Freundlich isotherm for amine Bt. Adsorption was rapid with gelatin–bentonite solutions reaching equilibrium within 10–20min. Adsorption rates decreased with increasing initial gelatin concentration suggesting that protein diffusion decreased due to increased solution viscosity.

Highlights • Calcium adsorbs best at pH7 and 9; sodium at pH3 and 5.23; amine adsorbs poorly. • Solution pH has greater influence on adsorption than other factors. • Langmuir–Freundlich isotherm models the adsorption data best. • Bentonite has good potential for cleaning stickwater and to be used in nanocomposites.