Physical appearance and arsenate removal efficiency of Fe(III)-modified clinoptilolite beads affected by alginate-wet-granulation process parameters

Abstract

Fe(III)-modified clinoptilolite (Fe-Clin) was encapsulated into beads using sodium alginate (NaAlg) and Ca2+ and/or Fe3+ ions by a simple wet-gelation method to obtain Fe-Clin beads. The impacts of various parameters including mixture pH, type of cross-linker, concentration of cross-linking solution and initial mass ratio of NaAlg to Fe-Clin were investigated on the appearance of beads and also their performance in As(V) removal. To increase the net negative surface charge of alginate, pH value of the mixture was essentially adjusted to the level 12–13. This strong alkaline condition increased the ability of alginate mixture to form stable and well-shaped beads. Ca2+ acting as a cross-linker showed a less impact on the beads shape than Fe3+ due to the strong tendency of Fe3+ ions to react with oxygen atoms in carboxylate groups of alginate. A loosely cross-linked Ca2+-alginate network formed during preparation of Fe-Clin beads was considered as the main reason for their lower arsenate removal efficiency of 29.4% rather than 60.5% for those cross-linked in FeCl3. In addition, there were found optimal values of FeCl3 cross-linking solution concentration and initial mass ratio of NaAlg: Fe-Clin as 2% (w/v) and 1:4, respectively to achieve the maximum As(V) removal efficiency of 82%.