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

• Calcium adsorbs best at pH 7 and 9; sodium at pH 3 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.

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 pH 3 to pH 9 and 4 to 20 mg/ml initial gelatin concentrations using 3 g of adsorbent loading per 100 ml solution. At 20 mg/ml gelatin solution, the highest gelatin adsorption obtained for CaBt was 372 mg/g or 58.9% gelatin recovery between pH 3 to pH 5.23 while NaBt showed the best adsorption between pH 7 to pH 9 with 405 mg/g or 60.4% gelatin recovery. Amine Bt showed consistently poor adsorption with the highest gelatin adsorption of 222 mg/g or 33.5% recovery at pH 3. Basal spacing (d-value) for CaBt increased from 16.3 to 20 Å while NaBt increased from 12.4 to 20–23 Å, 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 10–20 min. Adsorption rates decreased with increasing initial gelatin concentration suggesting that protein diffusion decreased due to increased solution viscosity.