Studies on the performance of bentonite and its composite as phosphate adsorbent and phosphate supplementation for plant

Organo-bentonite (OrB) was prepared by modifying bentonite with chitosan, and natural surfactant extracted from Sapindus rarak fruit. The physical alteration post-modification, performance of phosphates (Pi) adsorption, and possibility as a Pi-supplementation for plants of OrB were assessed and compared to acid-activated bentonite (AAB). The physical alteration due to modification of bentonite was characterized. SEM images were not indicating significant morphology differences between OrB and AAB. Existence of chitosan layers in OrB causes a decrease in basal spacing as characterized using XRD. The BET surface area of OrB was decreased compared to AAB due to pore coverage by chitosan. Adsorption studies reveal that OrB has a higher adsorption capacity towards Pi than AAB, which is 97.608 and 131.685 mg/g at 323 K for AAB and OrB, respectively. The H-shape isotherm curve indicates that chemisorption is dominantly controlling the adsorption. The isotherm and kinetics adsorption were well fitted to Langmuir and Pseudo-second order models, respectively. Performance of AAB and OrB as Pi-supplementation was assessed based on growth phenotypes of Arabidopsis thaliana; seedlings show that supplementation of Pi@AAB and Pi@OrB (at half doses) can promote primary root extension. These results also demonstrate the safety of direct disposal of the materials into the soil.

Keywords: Adsorption; Organo bentonite; Phosphate; Rarasaponin; Root elongation.