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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]

To study the remediation effect of hydroxyapatite with different particle sizes, a field in situ experiment was carried out by adding conventional hydroxyapatite (0.25 mm) and microhydroxyapatite (3 μm) and nanohydroxyapatite (40 nm) to the contaminated soil and planting Elsholtzia splendens. The distribution and migration of copper (Cu) and cadmium (Cd) in soil were investigated after 4 years. The results show that the application of three different particle sizes of hydroxyapatite significantly raise the soil pH, total phosphorus, and soil organic carbon. Moreover, the addition of hydroxyapatite can reduce the EXC fraction of Cu and Cd by 73.7%–80.1% and 20.8%–35.2%, respectively. In addition, the concentrations of Cu and Cd in >2 mm, 0.25–2 mm, 0.053–0.25 mm, and <0.053 mm aggregate are significantly increased. This improvement indicates that there are risks which may cause the increasing of total Cu and Cd in the soil where the pollution sources still exist. Furthermore, the content of soil colloid is significantly increased, and the colloidal Cu and Cd distribution percentage have been significantly increased by 49.9%–120% and 30.3%–181%. This result illustrates that the application of hydroxyapatite may greatly increase the possibility of colloid and dust migration of Cu and Cd. [ABSTRACT FROM AUTHOR]

In order to evaluate the ecological risk reductions of copper (Cu) and cadmium (Cd) and the change of nutrient contents and stoichiometry in a smelter-impacted farmland in Guixi, Jiangxi Province, China, with ∼ 800 mg Cu kg−1 soil and 0.8 mg Cd kg−1 soil, an three years in situ experiment was conducted. The field trial consisted of 4 × 5 m plots in a completely randomised block design. Hydroxyapatite was added at 10 g kg−1 soil and Sedum plumbizincicola, Elsholtzia splendens, and Pennisetum sp. were planted. Post-treatment soil and plant samples were collected annually and analysed for Cu and Cd bioaccessibility, soil carbon: nitrogen: phosphorus (C:N:P), and the stoichiometries of soil β-glucosidase (BG), N-acetylglucosaminidase (NAG), and acid phosphatase (AP) activity levels. The results indicated that the hydroxyapatite treatments significantly reduced Cu and Cd bioaccessibility as well as the ratio of C:P and N:P. Moreover, BG, NAG, and AP activity levels all increased relative to those in untreated soil. Plants may also influence soil BG, NAG, and AP activity. This study demonstrated that in situ Cu and Cd stabilisation by hydroxyapatite and phytoextraction is ecologically safe and can alter soil mineral nutrient ecological stoichiometry and enzyme activity. [ABSTRACT FROM AUTHOR]

It is well known that alkaline amendments could effectively decrease the bioavailability of heavy metals in soils. However, the vertical distribution of heavy metals and the nutrients enriching in amendments are little concerned during long-term field remediation. Thus, the objective of the present study was to investigate the vertical distribution and availability of Cu, Cd, Ca, and P after a 7-year field experiment. In this study, a single application of lime and apatite was conducted with the rates of 1.71-6.84 and 6.84-19.8 tons/ha, respectively. Soil pH and immobilization efficiency of Cu and Cd were both increased with increasing dosages of lime and apatite (0-50 cm). Applications of lime and apatite decreased the mobility of Cu and Cd although soil Cu and Cd in the surface soil were increased due to the input by atmospheric dry and wet deposition. Moreover, concentrations of Cu and Cd in lime- and apatite-amended soils (0-13 cm) were higher than those in the control group. However, applications of lime and apatite decreased the downward eluviations of heavy metals in soils (13-50 cm). For soil nutrients, the Ca concentrations at 0-13 and 13-30 cm were both enhanced with increasing amendment dosages, while only soil P concentration at 0-13 cm was increased in apatite-treated soils and majority of them presented in stable-P. In addition, resin-P was increased with increasing dosages of the apatite, which suggested that high eutrophication risk was induced by excessive P loss. Thus, more attention should be paid to the nutrients (phosphorus) and pollutants enriching in the amendments during in-situ remediation of heavy metal-contaminated soils. [ABSTRACT FROM AUTHOR]