Chromium (VI) removal efficacy from aqueous solution by modified tea wastes-polyvinyl alcohol (TW-PVA) composite adsorbent

Abstract

Hexavalent chromium [Cr (VI)] from anthropogenic sources leads to toxicity in aquatic system and hence require efforts to remove it from the aqueous phase. Among many techniques, adsorption is used for Cr (VI) removal from aqueous phase. In the present investigation, tea waste-polyvinyl alcohol (TW-PVA) composite was synthesized to eliminate Cr (VI) from aqueous solution. Batch experiments showed operating conditions (dose, initial concentration, duration, pH and tempera-ture) play significant role in Cr (VI) removal efficiency. However, TW-PVA composite (removal 94.22%) was found better in Cr (VI) removal efficiency compared with raw tea wastes (removal 81.99%). The maximum Cr (VI) removal (96%) was attained at 0.25 g TW-PVA composite dose and adsorption capacity decreased with the increase of dosages. Moreover, removal of Cr (VI) by TW-PVA composite decreased by elevated pH and the maximum removal efficiency of chromium (VI) was 94.91% at pH 2. Furthermore, the removal efficiency dropped as initial Cr concentration was increased. The highest Cr (VI) sorption was found to be 4.711 mg/g at 20°C and the adsorption capacity decreased with increasing temperature at a constant pH. The adsorption process reached at equilibrium within the first 50 min. It also well fitted with both Freundlich and Langmuir isotherm models and the overall kinetic data can be satisfactorily explained by pseudo-second-order rate expression which together attributes the chemisorption mechanism. The FTIR analysis revealed that carboxylate anion, sulfonyl chloride, and sulfonate groups were mainly involved in binding process of Cr (VI) onto the TW-PVA composite.