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Fly ash (FA) is characterized by its porous structure and richness in silicon and aluminum oxides; thus, it can be used as an adsorbent for heavy metals. In order to enhance the absorption efficiency and stabilization effect, we prepared a new fly ash (FAKCa) using calcium hydroxide (Ca(OH)2) and phosphate (KH2PO4) through a simple one-step low-temperature alkali dissolution method and investigated its adsorption performance for lead and cadmium in water solutions and the stabilization effects of lead and cadmium in soils under flooding condition. Results showed that the Langmuir model best fit the adsorption behavior of lead and cadmium, and the maximal adsorption capabilities of lead (128 mg/g) and cadmium (39.1 mg/g) for FAKCa were increased by 236% and 14.5% compared with the unmodified FA, respectively. The adsorption of lead and cadmium by FAKCa was better fitted to the second-order kinetic model. The enhancement of adsorption capacities for lead and cadmium may be partly due to the specific surface area of FAKCa, which was increased by 94.0% compared to unmodified FA. FTIR, XRD, and XPS analysis showed that the Si-O and Al-O functional groups, carbonate, and hydroxide precipitation were facilitated by the adsorption of lead and cadmium. Thus, ion exchange, surface complexation, and formation of metal hydroxide and carbonate precipitation were the main adsorption mechanisms for lead and cadmium by FAKCa. In addition, the application of 0.1–0.6% FAKCa increased soil pH by 0.19–0.67 units and decreased the CaCl2-extractable lead by 12.3–86.5% compared to FA. Meanwhile, FAKCa was more effective in transforming lead and cadmium from exchangeable to stable fractions. This study shows that calcium hydroxide–phosphate-modified fly ash could effectively increase the adsorption and stabilization of lead and cadmium and, thus, has great potential for large-scale applications in contaminated soil. [ABSTRACT FROM AUTHOR]

Permanent magnet coupling (PMC) generates a large amount of thermal energy due to the eddy current induced in the metal isolation cylinder, resulting in performance degradation. The magnetic-thermal-mechanical coupling analysis has an important impact on the design and operation of PMC devices. In this paper, the Maxwell equations are solved based on the separated variable method; the 3D eddy current loss and magnetic torque equations are proposed; and the electrical conductivity, the convective heat transfer coefficient, and the magnetic-thermal-mechanical properties of PMC are presented. The 3D analytical coupling model calculates the temperature field and presents an uneven distribution of temperature along the coolant flow direction, and it then obtains a more precise magnetic field and torque under various temperatures. Furthermore, the working conditions such as rotor speed, coolant flow rate, and applied load are taken into consideration in the 3D analytical model. The results show that the eddy current loss is proportional to the square of the speed. With an increase in the load, the eddy current decreases. However, with an increase in the coolant flow, more eddy current loss would be produced, but the generated heat would be taken away by the increased coolant flow, resulting in a decrease in the temperature. The 3D analytical coupling model results are in good agreement with the experimental data, which is helpful to the design and optimization of the PMC system. [ABSTRACT FROM AUTHOR]

Phytoextraction is a promising technology for remediating heavy metal-contaminated soil. Continuously screening potential plants is important for enhancing the efficiency of remediation. In this study, fourteen local native plant species and four cultivated plant species, along with their paired soils, were collected from around a copper smelter. The characteristics of soil pollution were evaluated using contaminant factors (CF) and a geoaccumulation index (Igeo). The phytoextraction potential of plants was investigated using the translocation factor (TF) and bioconcentration factor (BCF). The soils around the smelter were very acidic, with a mean pH of 5.01. The CF for copper and cadmium were 8.67–32.3 and 5.45–44.2, and the Igeo values for copper and cadmium were 2.43–4.43 and −0.12–2.29, respectively, indicating that the level of soil contamination was moderate to severe. The copper concentrations in the root (357 mg/kg), shoot (219 mg/kg), and leaf (269 mg/kg) of Elsholtzia splendens Nakai were higher than that in the other species. The cadmium in the shoot (32.2 mg/kg) and leaf (18.5 mg/kg) of Sedum plumbizincicola was the highest, and Phytolacca acinosa Roxb. had the highest cadmium level (20 mg/kg) in the root. Soil total and CaCl2-extractable copper and cadmium were positively correlated with copper and cadmium in the plant roots, respectively. The results of TF and BCF for copper and cadmium suggested that the accumulation and translocation capacities for cadmium were higher than those of copper in the eighteen plant species. Although not all plants met the criteria of being hyperaccumulators, Sedum plumbizincicola, Mosla chinensis Maxim, and Elsholtzia splendens Nakai showed the most potential as candidates for the phytoextraction of copper and cadmium contaminated soils, as indicated by their TF and BCF values. [ABSTRACT FROM AUTHOR]

Fly ash (FA) is promising for environmental remediation, but how to modify the FA with high remediation efficiency through an environmentally friendly and low-cost modification method is scare. A modified FA (MFA) was prepared through a one-step hydrothermal modification with Ca(OH)2 and KH2PO4. Results indicated that irregular agglomerates occurred on the surface of the MFA and that the specific surface area increased by 1.94 times compared to that of FA. Compared to FA, glassy compositions in MFA were destroyed and amorphous Si/Al and alkaline aluminosilicate gels were formed. The soil application of 0.2–0.6% MFA significantly increased soil pH by 0.23–0.86 units compared to FA and decreased available lead (Pb) and copper (Cu) by 25–97.1% and 13.5–75%, respectively. MFA significantly decreased exchangeable Pb and Cu by 12.5–32% and 11.4–35.2%, respectively, compared to FA. This may be due to the high pH and specific surface area of MFA, which promoted to the formation of amorphous Si/Al, metal–phosphate precipitation, and complexation with functional groups. In addition, MFA slightly increased the biomass of shoots and roots and decreased the uptake of Pb and Cu by ryegrass. This study provides a new modification method for the utilization of FA in the heavy metal-contaminated soils. [ABSTRACT FROM AUTHOR]

Phosphorus (P)-laden biochar has been widely used for environmental lead (Pb) remediation, but the P release risk and their adsorption and immobilization effect on soil potentially toxic elements (PTEs) between inherent P-laden biochar and exogenous P-laden biochar are rarely investigated. In this study, two biochars loaded with low and moderate inherent P (LPIB and MPIB) and two biochars loaded with moderate and high exogenous P (MPEB and HPEB) were produced by wheat straws with total P concentrations of 2.53, 4.71, 5.24, and 10.8 mg g−1, respectively. Water-extractable P was dominated in LPIB (49.5%), MPIB (35.9%), and MPEB (42.1%), while residual P was predominant in HPEB (43.5%). Meanwhile, labile P in MPEB (3002 mg kg−1) was 1.32 times higher than that in MPIB (2272 mg kg−1). Maximum P release capacity followed the order: LPIB (1.53 mg g−1) < MPIB (2.13 mg g−1) < MPEB (2.65 mg g−1) < HPEB (4.37 mg g−1), which was more suitable for the pseudo-second-order model. Lower pH, common anions (Cl−, NO 3 −, SO 4 2−, HCO 3 −) and cations (Na+, K+) significantly promoted P release from biochar, but Ca2+ and Mg2+ inhibited P release. Langmuir sorption isotherms were better fitted the sorption of Pb2+ by the four biochars and the maximum adsorption capacities followed the order of HPEB (116 mg g−1) > LPIB (105 mg g−1) ≈ MPEB (104 mg g−1) ≈ MPIB (103 mg g−1). Four biochars applications significantly increased soil pH by 0.66–0.68 and decreased CaCl 2 -extractable Pb and exchangeable Pb by 72.1–92.7% and 27.3–33.0%, promoting Pb bounding to carbonate and organic matter by 57.2–60.9% and 367–467%, respectively. HPEB application increased labile P by 25.6% and 37.2% compared to MPIB and MPEB applications. This study implies that biochar loaded with exogenous P has higher P release risk than that loaded with inherent P when they have similar Pb adsorption and immobilization effects. [Display omitted] • Four inherent and exogenous P-laden biochars with various P were prepared. • P release risk was increased with increasing the contents of total P in biochars. • Exogenous P-laden biochar had higher labile P than inherent P-laden biochar. • Exogenous P-laden biochar had higher P release risk than inherent P-laden biochar. • Four biochars had similar Pb adsorption and immobilization effects. [ABSTRACT FROM AUTHOR]

The remediation of cadmium-contaminated farmland was linked to major strategic needs involving national ecological security, and food safety. The benefits of phytoextraction included in-situ remediation, thoroughness, green practices, low cost, and minimal environmental disturbance while the remediation efficiency was limited. It was believed that the key was to develop enhanced phytoextraction technologies. Starting with how to improve the efficiency of phytoextraction, the screening of hyperaccumulators and high-biomass tolerant plants, and the auxiliary remediation potential of chemical, microbial, agronomic regulation as well as combined enhanced measures were systematically expounded. Finally, a prospect is put forward for the future research direction of enhanced phytoextraction of cadmium-contaminated farmland, containing expanding the screening of high-biomass economic crops suitable for remediation of moderately and mildly cadmium-contaminated farmland, developing more environmentally friendly, efficient and low-cost assisted materials, strengthening the exploration of different soil-plant-enhanced systems, as well as paying more attention to revealing the synergistic mechanisms of enhanced phytoextraction. [ABSTRACT FROM AUTHOR]

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