Dual ionic cross-linked alginate/clinoptilolite composite microbeads with improved stability and enhanced sorption properties for methylene blue

Environmentally friendly and low-cost composites based on sodium alginate and clinoptilolite (Alg/CPL) were prepared as microbeads and were used as sorbents for removal of methylene blue (MB) from simulated wastewaters. A combination of various characterization techniques pointed out that CPL could also act as ionic cross-linker for Alg chains through the Ca2 + ions adsorbed on its surface, and consequently, leading to dual ionic cross-linked Alg/CPL composites with improved chemical stability. The composite microbeads containing a 1:5 weight ratio between Alg and CPL (Alg1CPL5) showed an enhanced sorption capacity for MB (qm: 452.25 mg g− 1) compared to Alg microbeads (qm: 151.73 mg g− 1) and CPL (qm: 48.12 mg g− 1). Chemisorption was considered the main mechanism governing the MB sorption process as indicated by the better fitting of pseudo-second order equation on the kinetic data. The desorption studies confirmed further the mechanism of dye sorption and showed the possible recovery of MB as well as the reusability of Alg/CPL composites in three consecutive sorption/desorption cycles. The comparison with other Alg-based sorbents highlighted the enhanced sorption capacities, the improved stability during regeneration and high reusability of dual cross-linked Alg/CPL composites, suggesting the promising potential of these materials as efficient sorbents in dye wastewater treatment.