Microwave irradiation assisted sodium hexametaphosphate modification on the alkali-activated blast furnace slag for enhancing immobilization of strontium

Fly ash treatment via conventional and microwave-assisted organic acid leaching: kinetics and life cycle assessment

Heedless disposal of oil-based fly ash contributes to the contamination of the air, water, and soil. Acid leaching of industrial solid wastes is recognized as a versatile, cost-effective, and environmentally friendly solid waste treatment approach. The present study investigated the viability of conventional leaching (CL) and microwave-assisted leaching (MAL) of predominant heavy metals from Mazut-burnt fly ash. For this purpose, the practicality of four organic acids with various specifications (ascorbic, gluconic, citric, and oxalic acids) on the dissolution efficiency of fly ash components was examined. Utilization of oxalic acid led to achieving full V recovery, complete Fe removal, and Ni enrichment in the residue in both CL and MAL setups. The Ni content of the sample was enriched from 6% in the calcinated sample to 23.7% in the oxalic acid leaching residue. Using citric acid resulted in the co-extraction of V, Ni, and Fe with nearly 70% V, 50% Ni, and 89% Fe dissolved in CL. The dissolution efficiencies were slightly lower in MAL. Oxalic acid was selected as the most promising organic acid reagent for fly ash treatment, so its CL kinetics was studied and defined by the shrinking particle model. The model showed that the controlling steps in the leaching of V differ over time, changing from a chemical reaction before 60 min to fluid film diffusion or mixing afterward. The kinetic study proved MAL as an effective technique in overcoming the leaching kinetic barriers. A life cycle assessment study was conducted to determine the environmental impacts of the proposed process. Accordingly, the MAL using oxalic acid was the most environmentally friendly process among the studied ones, and the utilization of microwaves leads to the reduction of the leaching processes' environmental impacts by decreasing the processing time.

Evidence for chromium crosses blood brain barrier from the hypothalamus in chromium mice model

It has been shown that exposure to hexavalent Chromium, Cr (Ⅵ), via nasal cavity can have neurotoxicological effects and induces behavioral impairment due to the fact that blood brain barrier (BBB) does not cover olfactory bulb. But whether Cr (Ⅵ) can cross the BBB and have a toxicological effects in central nervous system (CNS) remains unclear. Therefore, we investigated the effects of Cr (Ⅵ) on mice treated with different concentrations and exposure time (14 days and 28 days) of Cr (Ⅵ) via intraperitoneal injection. Results revealed that Cr accumulated in hypothalamus (HY) in a timely dependent manner. Much more severer neuropathologies was observed in the group of mice exposed to Cr (Ⅵ) for 28 days than that for 14 days. Gliosis, neuronal morphological abnormalities, synaptic degeneration, BBB disruption and neuronal number loss were observed in HY. In terms of mechanism, the Nrf2 related antioxidant stress signaling dysfunction and activated NF-κB related inflammatory pathway were observed in HY of Cr (Ⅵ) intoxication mice. And these neuropathologies and signaling defects appeared in a timely dependent manner. Taking together, we proved that Cr (Ⅵ) can enter HY due to weaker BBB in HY and HY is the most vulnerable CNS region to Cr (Ⅵ) exposure. The concentration of Cr in HY increased along with time. The accumulated Cr in HY can cause BBB disruption, neuronal morphological abnormalities, synaptic degeneration and gliosis through Nrf2 and NF-κB signaling pathway. This finding improves our understanding of the neurological dysfunctions observed in individuals who have occupational exposure to Cr (Ⅵ), and provided potential therapeutic targets to treat neurotoxicological pathologies induced by Cr (Ⅵ).

Investigating the synergistic effects of magnesia-coal slag based solid waste cementitious materials and its basic characteristics as a backfill material

Applying solid waste resources as backfill material can reduce both the cost of backfill and the environmental problems caused by solid waste landfills. In this paper, the synergistic reaction effects of solid waste modified magnesia slag (MMS), coal gasification slag (CGS), and desulfurized gypsum (DG) as magnesium-coal slag based cementitious materials (MCC) and their preliminary feasibility as mining cementitious materials in synergy with coal gangue for the preparation of backfill materials are investigated. The results show that the order of the compressive strength of the cementitious systems is ternary system > binary system > monolithic system, which proves the existence of synergistic effect among MMS, CGS, and DG and determines the optimal dosing of each raw material in the ternary system. At early ages, the physical effect of CGS and the chemical effect of DG in the ternary system can promote the hydration reaction of MMS, but the synergistic effect between the three is weak; At later ages, a synergistic effect occurred among silica-aluminate depolymerization in CGS, dissolved sulfate from DG and hydration products from MMS, which promoted the production of more hydration products calcium-silicate(aluminum)-hydrate (C-S(A)-H) and AFt, and improved the compressive strength. In addition, the strength, fluidity and leaching of the backfill material prepared by MCC in collaboration with coal gangue can meet the preliminary feasibility for mine backfill. In the present work, the full solid waste MCC is developed to completely replace cement and use it to prepare backfill materials, which is of great importance to the comprehensive utilization of bulk solid waste, the reduction of backfill costs, and the enhancement of the economic and ecological interests of mines.

Conventional and microwave-assisted acid pretreatment of tea waste powder: analysis of functional groups using FTIR

Tea waste powder (TWP) is one of the potential biomass waste to recover valuable chemicals and materials. The prime objective of this work is to investigate the role of acid pretreatment on TWP. Diluted acids (HCl, H₃PO₄, CH₃COOH, and H₂SO₄) were used to soak the TWP to understand the role of acids on bond cleavage and chemicals formation. One gram of TWP was soaked in 100 mL of diluted acids for 24 h. The soaked samples were further subjected to a hot air oven (temperature: 80 °C, duration: 6 h), orbital shaking (shaking speed: 80-100 rpm, duration: 6 h), and microwave irradiation (microwave power: 100 W, duration: 10 min) to understand the synergistic effects of acids and mode of exposure. The pretreated solid samples and liquid samples were analyzed using FTIR to understand the presence of functional groups. The mass loss of TWP after treatment significantly varied with the type of acid and exposure mode used. In the orbital shaker, the mass loss was varied in the following order: H₂SO₄ (36%) > CH₃COOH (32%) > H₃PO₄ (22%) > HCl (15%). In hot air oven, high mass loss was observed compared to orbital shaking [HCl (48%) > CH₃COOH (37%) > H₂SO₄ (35%) > H₃PO₄ (33%)]. The mass loss in microwave irradiation is lower (19 to 25%) with all acids compared to orbital shaking. In the solid samples, O-H stretching, C-H stretching, C=O stretching, C=C stretching, -C-O-, and -C-OH- functional groups were noticed. Similarly, C=O and C=C peaks and C-O and -C-OH peaks were noticed in liquid samples. Interestingly, microwave irradiation showed promising results in 10 min of pretreatment, whereas orbital shaking and hot air oven pretreatments require 6 h to achieve the same result.

Thermomechanical properties of environmentally friendly slag-based geopolymer foam composites in different curing conditions

This study investigates the effect of curing temperature and foam/slag ratio on Na₂SiO₃- and NaOH-activated slag-based geopolymer foam composites (GFC) having thermal insulation properties. In this regard, samples used in the study were produced by adding foam at three different ratios (12.5, 15, and 17.5% by weight of slag) to the slag-based GFC having solutions with two different activator concentrations (7 M NaOH and 3 M Na₂SiO₃). Then, these samples were exposed to three different curing temperatures (40, 60, and 22 °C). The compressive strength, dry density, unit weight, water absorption, capillarity, apparent porosity, ultrasonic pulse velocity, and thermal conductivity tests were performed on the GFC samples for 1, 3, 7, and 28 days. Scanning electron microscopy (SEM) analyses were also conducted to characterize the pore structure and crack development of the GFCs. In addition, XRD analyses were performed on selected series to determine the formed reaction products of GFCs. As a result, it was observed that high curing temperature both improved mechanical strength and physical properties in GFC samples. The highest mechanical strength was obtained in the GFC with a 12.5% foam ratio and curing at 60 °C, while the lowest thermal conductivity coefficient was achieved in GFC with a 17.5% foam ratio and cured at 60 °C. In general, with the increase of foam ratio in slag-based GFC samples, unit weight, compressive strength, and ultrasonic pulse velocity results decreased, while capillarity, water absorption, and apparent porosity results increased. According to the results, it was seen that slag-based GFCs could be used in the construction of load-bearing and non-load-bearing walls.

Enhancement of Uranium Recycling from Tailings Caused by the Microwave Irradiation-Induced Composite Oxidation of the Fe-Mn Binary System

The extraction of uranium (U)-related minerals from raw ore sands via a leaching procedure would produce enormous amounts of tailings, not only causing radioactivity contamination to surroundings but also wasting the potential U utilization. Effective recycling of U from U tailings is propitious to the current issues in U mining industries. In this study, the influence of the composite oxidation of Fe(III) and Mn(VII) intensified by microwave (MW) irradiation on the acid leaching of U from tailings was comprehensively explored in sequential and coupling systems. The U leaching activities from the tailing specimens were explicitly enhanced by MW irradiation. The composite oxidation caused by Fe(III) and Mn(VII) further facilitated the leaching of U ions from the tailing under MW irradiation in two systems. Maximum leaching efficiencies of 84.61, 80.56, and 92.95% for U ions were achieved in the Fe(III)-, Mn(VII)-, and Fe(III)-Mn(VII)-participated coupling systems, respectively. The inappropriateness of the shrinking core model (SCM) demonstrated by the linear fittings and analysis of variance (ANOVA) for the two systems explained a reverse increase of solid cores in the later stage of leaching experiments. The internal migration of oxidant ions into the particle cores enhanced by MW accelerated the dissolution of Al, Fe, and Mn constituents under acidic conditions, which further strengthened U extraction from tailing specimens.

Non-thermal plasma irradiated polyaluminum chloride for the heterogeneous adsorption enhancement of Cs+ and Sr2+ in a binary system

The natural ecosystem will continually deteriorate for decades by the leakage of Cs and Sr isotopes. The exploration of the new materials or techniques for the efficient treatment of radioactive wastewater is critically important. In this study, a dielectric barrier discharge (DBD) configuration was constructed to operate the non-thermal plasma (NTP). The NTP was incorporated into the synthesis of polyaluminum chloride (PAC) in two different procedures to intensify the synthesis of PAC (NTP-PAC) and enhance the further removal of Cs and Sr from wastewater. The employment of NTP in two procedures both had significantly changed the physicochemical characteristics of PAC materials, which facilitated the further adsorption application of NTP-PAC on the treatment of Cs⁺ and Sr²⁺. Different molecular, morphological, and adsorption characteristics were confirmed to the NTP-PAC materials. The heterogeneous adsorption of the NTP-PAC can be appropriately fitted by both the pseudo-first-order kinetic model and the Elovich model. Both physisorption and chemisorption reaction mechanisms were ensured for the heterogeneous adsorption of the NTP-PAC material towards Cs⁺ and Sr²⁺, which guaranteed the excellent adsorption performance of NTP-PAC materials compared to PAC. The electron collisions caused by NTP with alum pulp created highly reactive growth precursors and intensified the nucleation and hydrolysis polymerization of PAC. The employment of NTP explicitly broadens the reaction pathways between PAC and cationic contaminants in the aqueous environment, which expands the application area of PAC materials in environmental sustainability.

A microwave irradiation-persulfate-formate system for achieving the detoxification and alkali-activated composite geopolymerization of the chromate-contaminated soil

A microwave (MA) irradiation-persulfate-formate system was constructed to detoxify Cr contamination and solidify the geopolymerization of the alkali-activated composite material. Three series of experiments were correspondingly conducted to evaluate the treatment for the chromate-contaminated soil. The changes in the molar ratios of formate to persulfate and the mass rates of fortifier to soil led to a significantly greater reduction of Cr^VI in the detoxification experiments. The increase of blast furnace slag from 50% to 80% in the composite cementitious materials (CCM) intensified the immobilization efficiencies of chromate and the compressive strengths of geopolymer blocks. MA irradiation potentially enhanced the binding of Ca cations to the aluminosilicate compounds. The degree of reaction in the phenomenological kinetics model mathematically verified the geopolymerization process. Ettringite was formed within the structure of the geopolymer in the coupling system. Sulfate radicals released from persulfate not only contributed to the detoxification process but also strengthened the immobilization process.

Microwave irradiation coupled with zero-valent iron that enhances the composite geopolymerization of chromite ore processing residue and its mechanisms

In this work, microwave (MW) irradiation was employed to enhance the zero-valent iron (ZVI)-dominated de-contamination of chromite ore processing residue (COPR). A coupling system and the traditional two-step procedure were both conducted to evaluate the effects of MW irradiation on the reduction and the incorporation of COPR into the composite materials-based geopolymers. The factors including the ratios of liquid to solid, the mass ratios of ZVI to COPR, and the acid dosage had some obvious influence on the reduction of COPR in the MW system. The compressive strengths of 31.54 and 41.56 MPa were determined from the two-step procedure and the coupling system at the COPR dosage of 10% (mass ratio), respectively. The employment of MW irradiation not only strengthened the formation of the geopolymer matrices but also improved the chemical stabilization of Cr species in the solidified blocks. The coupled process was more conducive to incorporating the treated COPR into the geopolymer-based crystalline microstructures compared with the subsequent usage of ZVI reduction and MW irradiation.

Hydroxyapatite nanoparticle functionalized activated carbon particle electrode that removes strontium from spiked soils in a unipolar three-dimensional electrokinetic system

Biohazard performance of Sr radionuclide can be significantly magnified by its release from the contaminated sedimentation. In this study, hydroxyapatite nanoparticle-functionalized activated carbon electrode (AC-HAP) was synthesized and stacked to the cathode compartment of the electrokinetic (EK) system to develop a unipolar three-dimensional (3D) electrochemical process for Sr²⁺ removal from spiked soils. Sr²⁺ adsorption by AC-HAP can be fitted by the pseudo-first-order and pseudo-second-order kinetic models and the Langmuir, Freundlich, and Temkin isotherm models. The largest monolayer adsorption capacity of AC-HAP of 69.49 mg g^-1 was evaluated in the pH range of 10-12 and at 40 °C. 3D EK further intensified the adsorption process of AC-HAP and the corresponding Sr²⁺ removal from aqueous environments. Voltage gradients and proposing time had a significant effect on the migration and transmission of Sr²⁺ in the electrolyzer. The influence of competitive ions on Sr²⁺ removal in the stock solutions followed Al³⁺ < Mg²⁺ < K⁺ < Na⁺ < Ca²⁺ while followed Al³⁺ < Na⁺ < K⁺ < Mg²⁺ < Ca²⁺ in 3D EK. The first three cycles for AC-HAP had taken roughly 50% of the reusability percentage. Sr²⁺ removal from spiked samples in 3D EK was achieved by acid dissolution, electromigration, and selective uptake on particle electrode.

Green rust functionalized geopolymer of composite cementitious materials and its application on treating chromate in a holistic system

Green rust functionalized geopolymer of composite cementitious materials (GR-CCM) was synthesized to improve the adsorption and subsequent stabilization/solidification of chromate in a holistic operating system. The initial pH in solution exhibited the most significant effect on the chromate removal by GR-CCM among three adsorption factors. The maximum monolayer adsorption capacity and theoretical saturation capacity of GR-CCM for Cr(VI) in the acidic condition were 55.01 mg/g and 41.70 mg/g, respectively. Amorphousness brought by loading GR weakened the crystallinity of composite cementitious materials (CCM), which enhanced the adsorption capacity of CCM and boosted the solidification process. The mixed-valent iron species in the GR-CCM not only directly engaged in the adsorption and reduction of chromate also positively strengthened the solidification of Cr species during the whole treatment. This study facilitates the application of GRs on the geopolymer materials and demonstrates the combination of adsorption and immobilization for the treatment of other potential heavy metal contamination.