Hongqing Hu

Immobilization of lead in anthropogenic contaminated soils using phosphates with/without oxalic acid.

Understanding the effects of oxalic acid (OA) on the immobilization of Pb(II) in contaminated soils by phosphate materials, has considerable benefits for risk assessment and remediation strategies for the soil. A series of phosphate amendments with/without oxalic acid were applied to two anthropogenic contaminated soils. We investigated the immobilization of Pb(II) by KH2PO4, phosphate rock (PR), activated phosphate rock (APR) and synthetic hydroxyapatite (HAP) at different phosphate:Pb (P:Pb) molar ratios (0, 0.6, 2.0 and 4.0) in the presence/absence of 50 mmol oxalic acid/kg soil, respectively. The effects of treatments were evaluated using single extraction with deionized water or CaCl2, Community Bureau of Reference (BCR) sequential extraction and toxicity characteristic leaching procedure (TCLP) methods. Our results showed that the concentration of water extractable, exchangeable and TCLP-Pb all decreased with incubation time. The concentration of water-extractable Pb after 120 days was reduced by 100% when soils were amended with APR, HAP and HAP+OA, and the TCLP-Pb was <5 mg/L for the red soil at P:Pb molar ratio 4.0. Water-soluble Pb could not be detected and the TCLP-Pb was <5 mg/L at all treatments applied to the yellow-brown soil. BCR results indicated that APR was most effective, although a slight enhancement of water-soluble phosphate was detected at the P:Pb molar ratio 4.0 at the beginning of incubation. Oxalic acid activated phosphates, and so mixing insoluble phosphates with oxalic acid may be a useful strategy to improve their effectiveness in reducing Pb bioavailability.

Influence of pyrolytic and non-pyrolytic rice and castor straws on the immobilization of Pb and Cu in contaminated soil

ABSTRACT Soil contamination with heavy metals has become a global environmental health concern. In the present study, European Community Bureau of Reference (BCR) sequential extraction and toxicity characteristic leaching procedure (TCLP) techniques were used to evaluate the Pb and Cu subsequent transformations, immobilizing impact of pyrolytic and non-pyrolytic rice and castor straws and their efficiency to reduce the metals mobility and leachability in the polluted soil. Obtained results highlight the potential of biochar over non-pyrolytic residues to enhance the immobilization of Pb and Cu in the soil. Castor leaves-derived biochar (CLB), castor stem-derived biochar (CSB), and rice straw-derived biochar (RSB) prominently decreased the mobility (acid-soluble fraction) of Pb 49.8%, 31.1%, and 31.9%, respectively, while Cu decreased 15.8%, 11.5%, and 12%, respectively, as compare to control. Sequential extraction showed that biochar treatments prominently modified the proportioning of Pb and Cu from acid soluble to a less bioavailable fraction and increased the geochemical stability in the polluted soil as compared to relative feedstocks as well as the controlled soil. Additionally, the soil pH increased markedly after the addition of biochar. Compared with control, the TCLP-extractable Pb and Cu were reduced to 29.2–41.4% and 5.7–22.8% from the soil respectively by the application of CLB. The immobilization and reduction in leachability of Pb and Cu were correlated with the soil pH. The biochar effect on the Pb immobilization was much better as compared to Cu in co-contaminated soil. Overall addition of CLB offered the best results and could be effective in both Pb and Cu immobilization thereby reducing their mobility and bioavailability in the co-contaminated soil.

Transformation and Bioavailability of Selenate and Selenite Added to a Nicotiana tabacum L. Planting Soil

Selenium (Se) is an essential nutrient for humans and is beneficial for plant growth. To investigate the transformation and bioavailability of Se in tobacco planting soil, selenite and selenate were applied. A pot experiment and sequential extraction scheme were used to investigate the Se contents in different forms in soils treated with Se. A series of equations were applied to model the transformation behavior of Se in this study. The results showed that the forms of selenium were increased significantly by applying the different valence state of water-soluble selenium. The carbonate-bound and iron-manganese (Fe-Mn) oxide–bound species were improved in selenite-added soil, whereas the soluble and exchangeable forms were increased in selenate-added soil. Michaelis-Menten equation fitting results indicated that estimated maximal selenium contents of leaves, stems, and roots in selenate-added soils were 1.83, 15.81, and 20.98 times larger than in selenite-added soils. The utilization levels of selenate were 4.3 to 7.9 times larger than selenite for Nicotiana tabacum L. In conclusion, the bioavailability and mobility of selenate were greater than selenite in Nicotiana tabacum L. planting soil.

Immobilization and phytotoxicity of Pb in contaminated soil amended with γ-polyglutamic acid, phosphate rock, and γ-polyglutamic acid-activated phosphate rock

Pot experiments were conducted to investigate the effects of γ-polyglutamic acid (γ-PGA), phosphate rock (PR), and γ-PGA-activated PR (γ-PGA-PR) on the immobilization and phytotoxicity of Pb in a contaminated soil. The proportion of residual Pb (Re-Pb) in soil was reduced by the addition of γ-PGA but was increased by the application of PR and γ-PGA-PR. The addition of γ-PGA in soil improved the accumulation of Pb in pak choi and decreased the growth of pak choi, suggesting the intensification of Pb phytotoxicity to pak choi. However, opposite effects of PR and γ-PGA-PR on the phytotoxicity of Pb to pak choi in soil were observed. Moreover, in the examined range, γ-PGA-PR activated by a higher amount of γ-PGA resulted in a greater proportion of Re-Pb in soil and weaker phytotoxicity of Pb to pak choi. The predominance of γ-PGA-PR in relieving the phytotoxicity of Pb was ascribed mainly to the increase of soil pH and available phosphate after the amendment, which could facilitate the precipitation of Pb in soil and provide pak choi with more phosphorus nutrient.

The effect of pH on the bonding of Cu2+ and chitosan-montmorillonite composite

Based on the contradict statements on the mechanisms of the bonding between metal ions and chitosan based adsorbent, this paper present studies on the Cu2+ adsorption by the chitosan-montmorillonite composite. The in situ attenuated total reflectance Fourier transform infrared spectroscopy and two dimensional correlation analysis were used to record the spectra during the adsorption and the pH perturbation, and analyze the interaction sequence of the groups related to the adsorption, respectively. The results showed that the bonding with -NH3+ might attribute the adsorption capacity greater than that with hydroxyl. The hydroxyl of chitosan (or composite) take part in the Cu2+ adsorption at pH 3.0-5.0 and were more active at lower pH. The amino replaced hydroxyl as the bonding sites with the change of -NH3+ to -NH2 by proton exchange when pH was near 5.0.

Characteristics of iron-manganese cutans and matrices in Alfisols and Ultisols of subtropical China.

Abstract Iron (Fe)-manganese (Mn) cutans and their matrix soils in Fragiudalf, Ferrudalf (FER), and Hapludult (HAP) soils of subtropical China were compared for their specific surface area (SSA), point-of-zero charge (PZC), adsorption, and oxidation characteristics on heavy-metal elements. They were studied by chemical analysis and equilibrium adsorption/redox. In the cutans, SSA were greater and PZC were less in their corresponding matrices, which was affected by the high clay organic matter and Fe-Mn oxide contents in the cutans. The SSA of the cutans treated with hydroxylamine hydrochloride (HAHC) was markedly less than the corresponding matrix soils. The PZC were 3.13, 3.65, and 3.90 for matrix soils of Fragiudalf, FER, and HAP, and the PZC were 3.26 and 3.42 for the cutans of FER and HAP, respectively. The cutans adsorbed more Pb2+, Cu2+, Cd2+, and Zn2+ than the corresponding matrix soils. The maximums amounts of heavy-metal elements (Pb2+, Cu2+, Cd2+, Zn2+) adsorbed by cutans treated with HAHC decreased in a range from 53% to 100% compared with those adsorbed by Fe-Mn cutans in the three soils. The maximum of Cr3+ oxidized by cutans treated with HAHC decreased by about 87% to 100% compared with the original cutans of these soils. These results indicate that Mn oxides in the tested Fe-Mn cutans are the main sorbents for heavy-metal ions and the main oxidants of Cr3+.

Effects of sulfur on toxicity and bioavailability of Cu for castor (Ricinus communis L.) in Cu-contaminated soil

The biogeochemical cycling of sulfur (S) in soil has an important impact on the bioavailability of heavy metals and affects the utilization of soil polluted by heavy metals. In addition, S-containing compounds are involved in heavy metal detoxification. This study investigated the effects of S on the toxicity and bioavailability of copper (Cu) in castor (Ricinus communis L.) grown in Cu-contaminated mine tailings. The results showed that the application of S reduced the accumulation of Cu in castor and promoted its growth. With the addition of S, the malondialdehyde (MDA) content of castor leaves decreased significantly compared with control plants, indicating the alleviation of oxidative stress. Superoxide dismutase (SOD) and catalase (CAT) activities and glutathione (GSH) content decreased significantly with the alleviation of oxidative stress. The sequential extraction of Cu fractions showed that the application of S significantly reduced the reducible Cu fraction, and increased the oxidizable Cu fraction. It also increased the residual Cu fraction in the soil. The transformation of chemical speciation reduced the bioavailability of Cu in soil, which then reduced the accumulation of Cu in castor. Our results demonstrated that S application was effective at promoting castor growth by reducing the bioavailability and uptake of Cu in Cu-contaminated mine tailings.

Adsorption of phosphate on pure and humic acid-coated ferrihydrite

PurposeHumic acid and mineral oxides are simultaneously present in soils and can form organomineral complexes. These complexes can influence the transport and fate of phosphate in the environment. The objective of this study was to investigate the adsorption of phosphate on these complexes by comparing them with phosphate adsorption on only the mineral.Materials and methodsPhosphate adsorption on ferrihydrite (FH) and the humic acid (HA)-coated ferrihydrite (FH–cHA) complex, as a function of pH and ionic strength, was investigated through adsorption measurements of zeta potential and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy.Results and discussionThe FH–cHA complex had a lower isoelectric point and less specific surface area than FH. A greater amount of phosphate was adsorbed on FH than on the FH–cHA complex, and phosphate adsorption increased with increasing ionic strength. The adsorption process was controlled by chemisorption. The zeta potential strongly decreased with an increase of phosphate adsorption at low pH, while it less obviously decreased at higher phosphate adsorption at high pH. The ATR-FTIR showed that the phosphate species on the FH–cHA complex was dominated by bidentate inner-sphere complexes. The addition of HA did not change the formation of the inner-sphere phosphate complexes, but it diminished the non-protonated bidentate complexes at lower pH. Also, the HA inhibited the non-protonated bidentate complexes at lower pH and generated P = O···H or P–O···H bonds by its acid groups.ConclusionsResults suggested that the affinity of phosphate for the FH–cHA complex was lower than for FH, and HA also influenced the formation of the phosphate species.

Effects of exogenous sulfur on growth and Cd uptake in Chinese cabbage ( Brassica campestris spp. pekinensis ) in Cd-contaminated soil

Soil pollution with heavy metals has many adverse effects on ecosystem health as well as food security. A pot experiment was performed to investigate the effects of different valence states of exogenous sulfur (S) on the uptake of cadmium (Cd) in Chinese cabbage in Cd-contaminated soil. The results showed that S significantly promoted plant growth in Chinese cabbage, with the following order of magnitude for the different S treatments: sodium sulfite (Na2SO3) > sodium sulfate (Na2SO4) > powdered sulfur (S0). Additionally, enzyme activity and the content of reductive substances in the leaves markedly increased, while malondialdehyde content significantly decreased; hence, S observably enhanced the ability of Chinese cabbage to tolerate Cd stress. S0 significantly reduced soil pH, thus increasing the mobility and bioavailability of Cd in the soil, while Na2SO3 increased soil pH, and Na2SO4 had no effect on soil pH. The acid-soluble and oxidizable fractions of Cd in soil increased with the S0 treatment. The applied Na2SO3 and Na2SO4 both increased the residual fraction of Cd in the soil, but they reduced the amount of the acid-extractable, reducible, and oxidizable Cd. The results showed that compared with S0, the Na2SO3 and Na2SO4 treatments decreased the acid-extractable Cd concentrations by 6.3 and 4%, respectively, in the most contaminated soil. In conclusion, the influence of S on the bioavailability and speciation of Cd varied not only with the soil Cd content but also with the application rate and S valence state.

Effects of organic ligands on adsorption of phosphate on a noncrystalline Al hydroxide.

The effects of oxalate (OX), tartrate (TR), and citrate (CT) on the adsorption of phosphate (P) on a synthetic noncrystalline Al-hydroxide [Al(OH)x] were studied at different initial phosphate/ligand molar ratios and different reaction conditions. The quantities of P adsorbed by the Al(OH)x varied with the ligand concentrations and the reaction conditions. When OX was introduced to the reaction system before P (OX before P), the effect of OX in decreasing P adsorption was greater than that when OX was added as a mixture with P (OX+P) or when P was introduced before OX (P before OX). When P was added after OX adsorption and removal of residual OX solution (OX(-) before P), the effect of OX in preventing P adsorption was lower than that in the system of OX before P. When P was added to the Al(OH)x as a mixture with two or three organic ligands, the reduction of P adsorption was related to the nature and concentration of the organic ligands. The combined effect of organic acids on P adsorption was not equal to the sum of the individual effect of each organic ligand. P adsorption increased with the equilibrium time from 1 to 7 days more in the presence of OX than CT. These findings have important implications for P availability in acidic soils.