Preliminary study on removing Cs⁺/Sr²⁺ by activated porous calcium silicate—A by-product from high-alumina fly ash recycling industry

Abstract

-containing radioactive wastewater is one of the most important problems that the world has been facing with. A by-product, activated porous calcium silicate, is generated at high levels by the pre-desiliconizing and soda-lime-sintering processes for producing Al 2 O 3 from high-alumina fly ash. In order to examine if this by-product could be used as an absorbent for removal of Sr2+ from radioactive wastewater, various parameters, such as pH, adsorbent dose, contact time, and initial concentration, were discussed. Results indicated that the equilibrium reached in about 2 hr. Activated porous calcium silicate was highly pH sensitive and able to remove Cs + /Sr 2+ in a near-neutral environment. The adsorption equilibrium was best described by Freundlich isotherm equations, and the adsorption of Cs + /Sr 2+ was a physical process. The adsorption kinetic data could be better fitted by the pseudo-second-order model, and the adsorption was controlled by multidiffusion. Current study showed that activated porous calcium silicate has a good adsorption of Cs + /Sr 2+ for their removal. However, other characteristics, such as selectivity because of coexisting cations, elution and regeneration, thermal stability, and acid resistance, should be discussed carefully before using it in an actual field. Implications:Removing 137 Cs + / 90 Sr 2+ from radioactive wastewater is one of the tough issues that has been attracting more and more attention world widely, which is the same as fly ash. For recycling high-alumina fly ash, in which Al is extracted to produce Al 2 O 3 , a huge amount of activated porous calcium silicate is generated year by year. In this paper, this by-product was successfully used as an absorbent to remove 137 Cs + / 90 Sr 2+ from radioactive wastewater for the first time. Factors that affect the absorbability and the mechanisms were discussed in details, providing a possible choice for disposal of 137 Cs + / 90 Sr 2+ -containing radioactive wastewater.

Superadsorbents for Strontium and Cesium Removal Enriched in Amidoxime by a Homo-IPN Strategy Connected with Porous Silica Texture

“…As Figure shows, the sorption of Sr 2+ was faster than that of Cs + , irrespective of the composite sorbent, and always faster in the case of composite PSi1/AOX3 than PSi2/AOX4 and PSi2/AOX5. The same difference between Cs + and Sr 2+ concerning the order of sorption kinetics has been reported for other sorbents . Fast kinetics have been also reported for the adsorption of other metal ions onto amidoxime groups containing sorbents , and even faster for the sorption of Sc 3+ onto macroporous silica polymer and for Pb 2+ onto a microporous silica-supported cation exchanger …”

“…As can be seen, the maximum sorption capacity of PSi1/AOX3 for both metal ions is comparable with the performances of the best composite sorbents, such as zeolite Y modified with a surfactant and aspartic acid, 2 Algal/PEI beads functionalized with amidoxime, 7 magnetic Prussian blue graphene oxide, 50 chalcogenide open framework (KTS-3), 61 and zeolitic chalcogenide (K-RWY). 62 The sorption capacity is even higher than those reported for the sorption of Cs + onto magnetic bentonite/chitosan composite beads 5 and activated porous calcium silicate 51 and of Sr 2+ onto hydroxyapatite. 17 Therefore, the fast kinetics of sorption and the high levels of sorption capacity for Cs + and Sr 2+ cations recommend these composite sorbents as very attractive alternatives for the removal of radionuclides such as 137 Cs and 90 Sr.…”

“…The same difference between Cs + and Sr 2+ concerning the order of sorption kinetics has been reported for other sorbents. 51 Fast kinetics have been also reported for the adsorption of other metal ions onto amidoxime groups containing sorbents 31,32 and even faster for the sorption of Sc 3+ onto macroporous silica polymer 26 and for Pb 2+ onto a microporous silica-supported cation exchanger. 27 Tables S4 and S5 present the kinetic parameters obtained by fitting three kinetic models (equations for PFO, PSO, and Elovich models are presented in Table S1) with the experimental data obtained for the sorption of Cs + and Sr 2+ , respectively, onto four composite sorbents (Figures 6 and S3).…”