[Application of Fe3[KG-*2/5]O4/Mulberry Stem Biochar Effects on Soil Arsenic Species and Rice Arsenic Content].

The passivation effect of Fe3O4/mulberry pole biochar (Fe-MBC) prepared at different carbonization temperatures on soil available arsenic content was studied through soil culture experiments, and Fe-MBC-800 (prepared by carbonization at 800℃) with good passivation effect was selected and characterized. The effects of 1%-7% (mass fraction of biochar to soil) Fe-MBC-800, MBC-800, and Fe3O4 on soil pH value, soil electrical conductivity, soil arsenic form, rice biomass, and total arsenic (As) content in rice were studied using a pot experiment. The results showed that:①Fe-MBC-800 successfully loaded Fe3O4, and its main functional groups were C=O double bond, O-H bond, C-O bond, and Fe-O bond. The specific surface areas of Fe-MBC-800, MBC-800, and Fe3O4 were 209.659 m2·g-1, 517.714 m2·g-1, and 68.025 m2·g-1, respectively. ②The addition of Fe-MBC-800 could increase the soil pH value, decrease the soil EC value, increase the content of residual arsenic in soil, and reduce the content of water-soluble arsenic and available arsenic in the soil. Under the treatment using 7% Fe-MBC-800 (ω) amendments, the content of water-soluble arsenic and available arsenic in the soil decreased by 81.6% and 56.33%, respectively. ③When the addition ratio of Fe-MBC-800 in the soil was 5%-7%, it could promote the growth of rice plants, increase rice biomass, and reduce the bioaccumulation of arsenic by between 62.5% and 68.75%.

[Preparation of Magnetic Iron Oxide/Mulberry Stem Biochar and Its Effects on Dissolved Organic Carbon and Arsenic Speciation in Arsenic-Contaminated Soils].

In this study, original mulberry-biochar (M-BC) and magnetic iron oxide/mulberry stem biochar (Fe-BC) materials were prepared and characterized using mulberry stems as the raw material. The effects of carbonized temperature of Fe-BC and M-BC on dissolved organic carbon (DOC) and arsenic(As) speciation in soil leaching solutions were studied using soil incubation experiments. The results showed that:① Fe-BC was mainly composed of Fe3O4 and was magnetic, and the main functional groups were a C＝O double bond, O-H bond, C-O bond, and Fe-O bond. The point of zero charge values (pHzpc) of Fe-BC-400, Fe-BC-500, and Fe-BC-600 were 8.92, 8.74, and 9.19, respectively, and the specific surface areas of Fe-BC-400, Fe-BC-500, and Fe-BC-600 were 447.412, 482.697, and 525.708 m2·g-1, respectively. ② With the increase in the carbonization temperature of M-BC and Fe-BC, the ρ(DOC) of soil leaching solution decreased 11.6-315.6 mg·L-1 and 78-365.6 mg·L-1, respectively. The DOC concentration of soil leaching solution was negatively correlated with soil EC. On day 35 of the incubation experiments, compared with that in soil after incubation without biochar (control), the As concentration of the soil leaching solution with Fe-BC-600 decreased by 55.96%, and there was no significant correlation between the As concentration of the soil leaching solution and the DOC concentration of the soil. ③ The available As concentration on day 35 in soil after incubation with Fe-BC was lower than that of the control group; the available As concentration on day 35 in soil incubated with Fe-BC-600 was reduced by 39.21%. ④ The residue As concentration on day 35 in soil incubated with M-BC decreased by 17.76%-49.11%. The residue As content on day 35 in soil incubated with Fe-BC-600 increased by 80%. Fe-BC-600 was most beneficial to reduce the DOC concentration and the available As content in soil leaching solution and increased the residue As content, thus reducing the bioavailability of soil arsenic. Therefore, this study can provide a theoretical basis for magnetic iron oxide/biochar remediation in arsenic-contaminated soil.

[Remediation Performance via the Passivation of a Porous Biomorph Genetic Composite of α-Fe2O3/Fe3O4/C Using a Bamboo Template on As(â ¤) Contaminated Soils].

Red soil from Guangxi, China was selected as the background soil, and a porous biomorphic genetic composite of α-Fe2O3/Fe3O4/C comprising a bamboo template (PBGC-Fe/C) was used as a passivator to remediate As(Ⅴ) contaminated soils. The performance of PBGC-Fe/C was characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR). The results showed that PBGC-Fe/C could improve the passivation effect of As(Ⅴ) from the contaminated soils compared with a single passivation material. Under the conditions of a 5% dose addition, 25% water content, and particle size of 100 mesh, the stability rates of PBGC-Fe/C on As(Ⅴ) contaminated soils with different concentrations of 500 mg·kg-1 and 1000 mg·kg-1 could reach 80.95% and 73.49%, respectively. The porous biomorphic genetic composite of bamboo charcoal provided a large number of adsorption sites for As(Ⅴ), and the acidity of the soil was favorable for the remediation of As(Ⅴ) via passivation. Moreover, PBGC-Fe/C could not only adsorb and fix As(Ⅴ), but also promoted the stabilization of As species. Chemical complexation and ion exchange played major roles in this passivation process.

[Passivation and Remediation Effects and Mechanisms of Plant Residual Modified Materials on Lead-Contaminated Soils].

The specific characteristics and mechanism of passivation of Pb in soil were studied using HAP/C composite (PBGC-HAP/C) as passivation, and using proportion of PBGC-HAP/C, particle size and type of passivator, soil moisture content, soil pH value of Pb, and particle size of the material as influencing factors. The results showed that with an increase in dosage of the passivator and passivation time, the passivation effect increases gradually. Reducing the particle size of the passivator is beneficial to improving the passivation effect. pH has a greater impact on passivation, with the passivation effect obviously rising with increased pH, and the passivation rate in an alkaline environment can reach above 99%. An increase in water content is beneficial to the improvement of the passivation effect, but the contribution is not significant. Through comparative analysis of the XPS, XRD, and FT-IR of materials before and after passivation, the results indicated that the passivation of PBGC-HAP/C to Pb is mainly through direct and indirect effects. Direct effects include physical adsorption, chemical complexation, electrostatic interaction, ion exchange, and precipitation; the indirect effect is mainly enhanced by increasing the pH value of the organic matter.

[Removal of Pb2+ from Aqueous Solution by Magnesium-Calcium Hydroxyapatite Adsorbent].

A novel magnesium-calcium hydroxyapatite adsorbent was prepared by the Sol-gel method with different proportions of Mg/(Ca+Mg) using Mg2+ as doped ions, and the removal characteristics and process mechanism of Pb2+ on the magnesium-calcium hydroxyapatite in an aqueous solutions were studied. The results show that the surface of the adsorbent is composed mainly of a hydroxyphosphonite compound[Pb10(PO4)6(OH)2], The morphological characteristics of the magnesium-calcium hydroxyapatite adsorbent surface was investigated as crystal structure changes from short rods to needle structures according to scanning electron microscopy (SEM). Testing at a temperature of 25℃ and pH of 5 showed that the adsorption of Pb2+ by magnesium-calcium hydroxyapatite reached equilibrium within 720 min. The adsorption capacity was determined to be 813.17 mg·g-1 at a dosage of 0.6 g·L-1. The thermodynamic test results of ΔGθ<0, ΔSθ>0, and ΔHθ>0 indicated that the adsorption process of Pb2+ by magnesium-calcium hydroxyapatite is a spontaneous process with endothermic reaction and entropy increments, and higher temperatures were considered be favorable for adsorption at a range of 25-45℃. The adsorption could be effectively described by a pseudo-second-order kinetic equation. The equilibrium data were found to follow the Langmuir adsorption model. Material characterization and adsorption tests showed that surface complexation and dissolution-precipitation were the main mechanisms for the removal of Pb2+ by magnesium-calcium hydroxyapatite in an aqueous solution.

[Adsorption Characteristics of Copper in Water by the Porous Biomorph-Genetic Composite of HAP/C with Eucalyptus Wood Template].

The specific characteristics and mechanism of adsorption of Cu(Ⅱ) were studied by using HAP/C composite (PBGC-HAP/C) as adsorbent, and using pH value of the solution system, initial concentration of Cu(Ⅱ) and particle size of the material as influential factors. The results showed that when the solution was weak acid (pH=5), the adsorption effect was the best; the increase of the initial concentration of the reaction system was not conducive to the enhancement of the adsorption effect; and the decrease of the particle size of the adsorbent facilitated the adsorption process. The pseudo-second-order kinetic model could accurately describe the adsorption process, and the calculated adsorption capacity(0.99, 1.93, 4.03 mg·g-1)was close to the experimental measured values(0.99, 1.93, 4.05mg·g-1); Langmuir model could fit the adsorption process very well, which indicated that adsorption was monolayer adsorption and the increase of temperature was conducive to adsorption. The thermodynamics test results of ΔGθ<0, ΔSθ>0 and ΔHθ>0 showed that the adsorption process was endothermic and spontaneous. Through comparative analysis of the SEM, EDS, XRD and FTIR of materials before and after adsorption, the results indicated that the chemical complexation reaction of Cu(Ⅱ) with the oxygen functional groups on the surface of PBGC-HAP/C was the main purification mechanism, which was accompanied with physical adsorption, electrostatic adsorption and ion exchange.

Feasibility of constructed wetland planted with Leersia hexandra Swartz for removing Cr, Cu and Ni from electroplating wastewater.

As a low-cost treatment technology for effluent, the constructed wetlands can be applied to remove the heavy metals from wastewater. Leersia hexandra Swartz is a metal-accumulating hygrophyte with great potential to remove heavy metal from water. In this study, two pilot-scale constructed wetlands planted with L. hexandra (CWL) were set up in greenhouse to treat electroplating wastewater containing Cr, Cu and Ni. The treatment performance of CWL under different hydraulic loading rates (HLR) and initial metal concentrations were also evaluated. The results showed that CWL significantly reduced the concentrations of Cr, Cu and Ni in wastewater by 84.4%, 97.1% and 94.3%, respectively. High HLR decreased the removal efficiencies of Cr, Cu and Ni; however, the heavy metal concentrations in effluent met Emission Standard of Pollutants for Electroplating in China (ESPE) at HLR less than 0.3 m3/m2 d. For the influent of 5 mg/L Cr, 10 mg/L Cu and 8 mg/L Ni, effluent concentrations were below maximum allowable concentrations in ESPE, indicating that the removal of Cr, Cu and Ni by CWL was feasible at considerably high influent metal concentrations. Mass balance showed that the primary sink for the retention of contaminants within the constructed wetland system was the sediment, which accounted for 59.5%, 83.5%, and 73.9% of the Cr, Cu and Ni, respectively. The data from the pilot wetlands support the view that CWL could be used to successfully remove Cr, Cu and Ni from electroplating wastewater.

Combined toxicity of the mixtures of phenol and aniline derivatives to Vibrio qinghaiensis sp.-Q67.

To test whether the dose addition and independent action models can predict the combined toxicity of the mixtures of phenol and aniline derivatives, six phenolic and two aniline derivatives were selected as the test components. The inhibition toxicity of the derivatives and their mixtures to Vibrio qinghaiensis sp.-Q67 indicated that all dose-response relationships could be effectively described by the Weibull function with correlation coefficients greater than 0.99. The combined toxicity of two equivalent-effect concentration ratio mixtures and eight uniform design concentration ratio mixtures could be predicted successfully by the dose addition model within 95% confidence intervals. However, it was also well predicted by the independent action model, especially at lower concentrations.

Heavy metal contamination and risk assessment in water, paddy soil, and rice around an electroplating plant.

PURPOSE: The objective of this paper is to assess the impact of long-term electroplating industrial activities on heavy metal contamination in agricultural soils and potential health risks for local residents. METHODS: Water, soil, and rice samples were collected from sites upstream (control) and downstream of the electroplating wastewater outlet. The concentrations of heavy metals were determined by an atomic absorption spectrophotometer. Fractionation and risk assessment code (RAC) were used to evaluate the environmental risks of heavy metals in soils. The health risk index (HRI) and hazard index (HI) were calculated to assess potential health risks to local populations through rice consumption. RESULTS: Hazardous levels of Cu, Cr, and Ni were observed in water and paddy soils at sites near the plant. According to the RAC analysis, the soils showed a high risk for Ni and a medium risk for Cu and Cr at certain sites. The rice samples were primarily contaminated with Ni, followed by Cr and Cu. HRI values >1 were not found for any heavy metal. However, HI values for adults and children were 2.075 and 1.808, respectively. CONCLUSION: Water, paddy soil, and rice from the studied area have been contaminated by Cu, Cr, and Ni. The contamination of these elements is related to the electroplating wastewater. Although no single metal poses health risks for local residents through rice consumption, the combination of several metals may threaten the health of local residents. Cu and Ni are the key components contributing to the potential health risks.

Solubility and stability of lead arsenates at 25 degrees C.

Lead arsenates were the most extensively used arsenical insecticides in the past. Their residues, especially the water-soluble fractions in environment may pose a potential human health risk. The solubility products (K(sp)) and free energies of formation (Delta G(f) degrees) of PbHAsO(4).2H(2)O(c), Pb(5)(AsO(4))(3)OH.H(2)O(c), Pb(3)(AsO(4))(2)(c) and Pb(8)As(2)O(13)(8PbO.As(2)O(5))(c) at 25 degrees C were determined by precipitation and dissolution experiments. The composition of precipitates depended on the Pb/As molar ratios and pH values. The solid precipitates were lamellar PbHAsO(4).2H(2)O(c) at pH = 3-5 and Pb/As = 1.0, columnar Pb(5)(AsO(4))(3)OH.H(2)O(c) at pH = 12-13 and Pb/As = 1.5, Pb(5)(AsO(4))(3)OH.H(2)O(c) with little amounts of Pb(8)As(2)O(13)(c) at pH = 12-13, Pb/As = 1.67 and 2.0. The mixture of PbHAsO(4).2H(2)O(c) and Pb(3)(AsO(4))(2)(c) formed at pH = 6.51 and Pb/As = 1.5. Based on the analytical results, the solubility products (K(sp)) of PbHAsO(4).2H(2)O(c), Pb(5)(AsO(4))(3)OH.H(2)O(c), Pb(3)(AsO(4))(2)(c) and Pb(8)As(2)O(13)(c) were calculated by the computer program PHREEQC as 10(-10.70)(10(-7.81)-10(-14.32)), 10(-81.75)(10(-74.37)-10(-84.83)), 10(-33.83)(10(-32.05)-10(-34.49)) and 10(-174.24)(10(-156.64)-10(-178.35)), respectively. Correspondingly, the free energies of formation (Delta G(f) degrees) of these lead arsenates were calculated to be -1274.36 kJ/mol, -2928.33 kJ/mol, -1563.12 kJ/mol and -3909.69 kJ/mol.

Chromium accumulation by the hyperaccumulator plant Leersia hexandra Swartz.

Leersia hexandra Swartz (Gramineae), which occurs in Southern China, has been found to be a new chromium hyperaccumulator by means of field survey and pot-culture experiment. The field survey showed that this species had an extraordinary accumulation capacity for chromium. The maximum Cr concentration in the dry leaf matter was 2978 mg kg(-1) on the side of a pond near an electroplating factory. The average concentration of chromium in the leaves was 18.86 times as that in the pond sediment, and 297.41 times as that in the pond water. Under conditions of the nutrient solution culture, it was found that L. hexandra had a high tolerance and accumulation capacity to Cr(III) and Cr(VI). Under 60 mg l(-1) Cr(III) and 10 mg l(-1) Cr(VI) treatment, there was no significant decrease of biomass in the leaves of L. hexandra (p>0.05). The highest bioaccumulation coefficients of the leaves for Cr(III) and Cr(VI) were 486.8 and 72.1, respectively. However, L. hexandra had a higher accumulation capacity for Cr(III) than for Cr(VI). At the Cr(III) concentration of 10 mg l(-1) in the culture solution, the concentration of chromium in leaves was 4868 mg kg(-1), while at the same Cr(VI) concentration, the concentration of chromium in leaves was only 597 mg kg(-1). These results confirmed that L. hexandra is a chromium hyperaccumulator which grows rapidly with a great tolerance to Cr and broad ecological amplitude. This species could provide a new plant resource that explores the mechanism of Cr hyperaccumulation, and has potential for usage in the phytoremediation of Cr-contaminated soil and water.