Abstract
Efficient capture of barium (Ba) from solution is a serious task in environmental protection and remediation. Herein, the capacity and the mechanism of Ba adsorption by natural and iron(III) oxide (FeO) modified allophane (ALO), beidellite (BEI) and zeolite (ZEO) were investigated by considering the effects of contact time, temperature, pH, Ba2+ concentration, adsorbent dosage, the presence of competitive ions and adsorption–desorption cycles (regenerability). Physicochemical and mineralogical properties of the adsorbents were characterized by XRD, FTIR, SEM with EDX and N2 physisorption techniques. The Ba2+ adsorption fitted to a pseudo-first-order reaction kinetics, where equilibrium conditions were reached within <30 min. BEI, ALO and ZEO with(out) FeO-modification yielded removal efficiencies for Ba2+ of up to 99.9%, 97% and 22% at optimum pH (pH 7.5–8.0). Adsorption isotherms fitted to the Langmuir model, which revealed the highest adsorption capacities for BEI and FeO-BEI (44.8 mg/g and 38.6 mg/g at 313 K). Preferential ion uptake followed in the order: Ba2+ > K+ > Ca2+ >> Mg2+ for all adsorbents; however, BEI and FeO-BEI showed the highest selectivity for Ba2+ among all materials tested. Barium removal from solution was governed by physical adsorption besides ion exchange, intercalation, surface complexation and precipitation, depending mainly on the absorbent type and operational conditions. BEI and FeO-BEI showed a high regenerability (>70–80% desorption efficiency after 5 cycles) and could be considered as efficient sorbent materials for wastewater clean-up.
Highlights
The accumulation and overconcentration of hazardous metal ions in the aquatic and terrestrial environments of the Earth is a major threat for the ecological system and for human health, as most metal ions are non-biodegradable and tend to cumulate in living organisms, causing diseases and disorders [1,2,3,4]
Barium removal from solution was governed by physical adsorption besides ion exchange, intercalation, surface complexation and precipitation, depending mainly on the absorbent type and operational conditions
The results obtained from the kinetic studies indicate that the adsorption of Ba2+ was completed within
Summary
The accumulation and overconcentration of hazardous metal ions in the aquatic and terrestrial environments of the Earth is a major threat for the ecological system and for human health, as most metal ions are non-biodegradable and tend to cumulate in living organisms, causing diseases and disorders [1,2,3,4]. Available wastewater treatment technologies include, for example, chemical precipitation, flocculation, coagulation, electrochemical methods, reverse osmosis, membrane separation and adsorption [7,8]. These methods greatly vary in effectiveness and operational costs; there is still a high demand for the development of new, Materials 2020, 13, 2582; doi:10.3390/ma13112582 www.mdpi.com/journal/materials. Materials 2020, 13, 2582 efficient, green and low cost adsorbent materials [9,10,11] Silicate based adsorbents, such as clay minerals and zeolites, can be advantageous over non-siliceous materials or composite materials, because they provide a plenty of adsorption sites due to the very small particle size, high surface area, porous structure and presence of surface functional groups and exchangeable sites, rendering these components ideal for wastewater treatment [12,13,14,15]. The short-range-order aluminosilicate phase allophane exhibits good sorption capacities for certain metal ions, such as Cs+ , Ba2+ , Co2+ , Cu2+ , Sr2+ and Zn2+ , owning to its unique physicochemical and surface (charge) properties, amphoteric ligand capacity and hollow “nanoball”
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
