Abstract
A new type of absorbent with high efficiency was synthesized by KOH-activated slag-based geopolymer microspheres (K-SGM), which exhibited higher adsorption capacities for recycling Co(II) (Qe,K-SGM = 192.31 mg/g, Qe,Na-SGM = 91.21 mg/g) than NaOH-activated ones (Na-SGM). During the Co(II) adsorption process, these two kinds of geopolymeric adsorbents could be combined with heavy metal ions to optimize each other and form heavy metal-grown aid adsorbents. The morphology of Na-SGM and K-SGM was different which varied from coarse pores to nanonetwork or nanosheets after Co(II) adsorption, and the Brunauer–Emmett–Teller (BET) surface areas of Na-SGM (10.46 m2/g) and K-SGM (22.96 m2/g) increased to 117.38 and 228.73 m2/g after Co(II) adsorption, respectively. The BET surface area of K-SGM is twice that of Na-SGM whether before or after Co(II) ion adsorption. The hydrated ionic radius of K and Na, the alkalinity degree of K+ and Na+, the electronegativity of Na-SGM and K-SGM surface, the BET surface area and Fourier transform infrared changes of CO32– and OH before and after Co(II) adsorption, and X-ray photoelectron spectroscopy analysis like the relative content of geopolymer gel and bridging oxygen bonds in the Na-SGM and K-SGM are the fundamental reasons for the obvious differences in Co(II) adsorption between Na-SGM and K-SGM.
Highlights
Cobalt, a heavy metal, is a trace element strongly affecting human health.[1]
It is significant that a kind of adsorbent is easy to recycle and continue adsorbing because their BET surface areas are increasing during heavy metal adsorption
The morphology of M-SGM and M-SGM-Co after Co(II) adsorption was observed by field emission scanning electron microscopy (FESEM, Hitachi SU8220), and their chemical components were determined by energy dispersive X-ray spectroscopy (EDX, Bruker)
Summary
A heavy metal, is a trace element strongly affecting human health.[1]. excess amounts of the metal can cause various pathological effects, such as gastrointestinal dysfunction, pneumonia, myocarditis, and goiter.[2]. It is significant that a kind of adsorbent is easy to recycle and continue adsorbing because their BET surface areas are increasing during heavy metal adsorption. Its microspheres are commonly used to be the heavy-metal adsorbents[13] because of low cost, high efficiency, simple post treatment,13b and easy recycling. Alkaline activator solutions with different pH values will cause differences of the aluminum salt monomer and the silicon salt monomer after dissolution. There are significant differences on Co(II) adsorption capacity between KOHactivated and NaOH-activated slag-based geopolymers. Because of this difference, it brought a significant change in morphology, BET surface area, average pore diameter, and pore volume after Co(II) adsorption. The derived findings in this study could provide significant information for the evaluation of adsorption behaviors between K-SGM and Na-SGS geopolymer microspheres
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