Synthesis of nonthermal plasma-irradiated polyvalent manganese (hydro)oxide functionalized nanosilica for intensifying geopolymerized solidification/stabilization of thallium-contaminated soil and mechanism exploration

Abstract

Thallium (Tl) enrichment in soils can cause an immeasurable ecological disaster, disturbing ecological balance and threatening human health. In this study, nonthermal plasma (NTP) irradiation was employed to synthesize polyvalent Mn-based (hydro)oxide-functionalized nanosilica (NTP-P-Mn-nSi). Mixtures of alkali-activated geopolymers and NTP-P-Mn-nSi were subsequently prepared for the efficient solidification and stabilization (S/S) of Tl-containing soils. The synthesis of NTP-P-Mn-nSi and the geopolymerization of soils were both optimized to obtain maximum adsorption capacities and achieve excellent immobilization of the matrix. The influence of the initial pH and concentration of Tl+ on NTP-P-Mn-nSi was investigated. The leaching concentration of Tl and the compressive strengths from the soil matrix were monitored. Comprehensive strategies were adopted for soils and solidified samples to investigate the vital role played by NTP-P-Mn-nSi in the geopolymers of soils. The pseudofirst-order, intraparticle, and Elovich models were suitable for evaluating the uptake dynamics of Tl+ to NTP-P-Mn-nSi. Langmuir, Freundlich, and Tempkin were all appropriate in analysing the isotherms of heterogeneous adsorption. Four maximum monolayer adsorption capacities of NTP-P-Mn-nSi responding to Tl+ ions reached 93.90, 123.00, 355.87, and 323.62 mg/g at initial pH values of 7, 9, 11, and 13, respectively. NTP-P-Mn-nSi in the geopolymer explicitly inhibited leaching and intensified the immobilization of Tl ions in the matrix with the lowest leaching concentration of 0.16 µg/L Tl from the matrix being achieved. The increase in NTP-P-Mn-nSi dosage accelerated the growth rates of nucleation, enhanced the formation of alkali-activated gelation, induced the formation of flocculent surfaces and three-dimensional structures, and intensified the elemental overlap between Mn and Tl in the geopolymerized matrix.