Removal of Barium, Cobalt, Strontium, and Zinc from Solution by Natural and Synthetic Allophane Adsorbents

Abstract

Abstract:The capacity and mechanism of the adsorption of aqueous barium (Ba), cobalt (Co), strontium (Sr), and zinc (Zn) by Ecuadorian (NatAllo) and synthetic (SynAllo-1 and SynAllo-2) allophanes were studied as a function of contact time, pH, and metal ion concentration using kinetic and equilibrium experiments. The mineralogy, nano-structure, and chemical composition of the allophanes were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and specific surface area analyses. The evolution of adsorption fitted to a pseudo-first-order reaction kinetics, where equilibrium between aqueous metal ions and allophane was reached within <10 min. The metal ion removal efficiencies varied from 0.7 to 99.7% at pH 4.0 to 8.5. At equilibrium, the adsorption behavior is better described by the Langmuir model than by the Dubinin-Radushkevich model, yielding sorption capacities of 10.6, 17.2, and 38.6 mg/g for Ba 2+ , 12.4, 19.3, and 29.0 mg/g for HCoO − 2 ; 7.2, 15.9, and 34.4 mg/g for Sr 2+ ; and 20.9, 26.9, and 36.9 mg/g for Zn 2+ , by NatAllo, SynAllo-2, and SynAllo-1, respectively. The uptake mechanism is based on a physical adsorption process rather than chemical ion exchange. Allophane holds great potential to effectively remove aqueous metal ions over a wide pH range and could be used instead of other commercially available sorbent materials such as zeolites, montmorillonite, carbonates, and phosphates for special wastewater treatment applications.

Аdsorption of Co2+ and radioactive 60Со by mesoporous TiO2

“…These patterns of dependence of adsorption Co 2+ on pH are in good agreement with those shown in literature [27,29].…”

“…60 Co emits two -lines with energy 1.17 and 1.33 MeV [19]. The activity of aqueous radioactive solutions of 60 Co was determined by a gamma-counter using a NaI-(TI) scintillation spectrometer [1,19,[27][28][29]. Arithmetic mean and deviation of arithmetic mean were calculated using source [30].…”

Removal of Barium from Solution by Natural and Iron(III) Oxide-Modified Allophane, Beidellite and Zeolite Adsorbents

“…Detections limits are always below 1 µg/L for the elements of interest. NIST 1640a, in-house and SPS-SW2 Batch 130 standards were measured at the beginning, at the end and in between individual sample sequences [ 13 ]. The analytical error is ±2% for Mg and Na and ±3% for Al, Ba, Ca, Fe, K and Si analyses, respectively (2 SD, 3 replicates for each sample).…”

“…However, these methods greatly vary in effectiveness and operational costs; thus there is still a high demand for the development of new, 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 ].…”

“…and for radioactive waste treatment due to their worldwide abundance, high thermal and radiation stability and uniform three-dimensional pore structure [ 5 ]. The short-range-order aluminosilicate phase allophane also exhibits good sorption capacities for certain metal ions, such as Cs + , Ba 2+ , Co 2+ , Cu 2+ , Sr 2+ and Zn 2+ , owning to its unique physicochemical and surface (charge) properties, amphoteric ligand capacity and hollow “nanoball” structure [ 13 , 16 , 17 , 18 ]. Smectite group minerals, such as beidellite and montmorillonite, are also in use as adsorbents, ion exchangers and catalysts due to their low cost, high reactivity and worldwide distribution [ 15 , 19 , 20 ].…”