Qingling Fu

Mechanism of lead immobilization by oxalic acid-activated phosphate rocks

Lead (Pb) chemical fixation is an important environmental aspect for human health. Phosphate rocks (PRs) were utilized as an adsorbent to remove Pb from aqueous solution. Raw PRs and oxalic acid-activated PRs (APRs) were used to investigate the effect of chemical modification on the Pb-binding capacity in the pH range 2.0-5.0. The Pb adsorption rate of all treatments above pH 3.0 reached 90%. The Pb binding on PRs and APRs was pH-independent, except at pH 2.0 in activated treatments. The X-ray diffraction analysis confirmed that the raw PRs formed cerussite after reacting with the Pb solution, whereas the APRs formed pyromorphite. The Fourier Transform Infrared spectroscopy analysis indicated that carbonate (CO3(2-)) in raw PRs and phosphate (PO4(3)) groups in APRs played an important role in the Pb-binding process. After adsorption, anomalous block-shaped particles were observed by scanning electron microscopy with energy dispersive spectroscopy. The X-ray photoelectron spectroscopy data further indicated that both chemical and physical reactions occurred during the adsorption process according to the binding energy. Because of lower solubility of pyromorphite compared to cerussite, the APRs are more effective in immobilizing Pb than that of PRs.

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.

Cadmium mobility, uptake and anti-oxidative response of water spinach (Ipomoea aquatic) under rice straw biochar, zeolite and rock phosphate as amendments

Agricultural soils contamination with cadmium (Cd) has become a serious concern through anthropogenic activities. The possible environmental friendly solutions for Cd are required to address its mobility through various cost effective amendments. This study aims to evaluate the impact of rice straw biochar (BC), zeolite (ZE) and rock phosphate (RP) stabilizers to minimize the potential risk of Cd mobility and its uptake by water spinach in acidic soil through pot experiment. Concentration of Cd in TCLP and CaCl2 extract gradually decreased with the increase of amendments (BC, ZE and RP) rates. The increase in BC addition from 1.5% to 3% significantly decreased CaCl2-extractable Cd by 65.78%-72.89% and TCLP extractable Cd by 31.16%-37.66% respectively, over control. Whereas, RP addition decreases 53.4%-65.18% and 11.68%-19.48% in CaCl2 and TCLP extractable Cd respectively, as compared to control soil. The addition of BC, ZE and RP decreased Cd uptake by 22.91%-61.82% with 1.5% and 3% application rate, respectively. Moreover, the antioxidant enzymes activity i.e., superoxide dismutase (SOD) and peroxidase (POD) decreased with the addition of BC, ZE and RP under Cd stress. In conclusion, rice straw biochar could be highly recommended as a safe stabilizer to immobilize Cd in polluted agricultural soils.

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.

Immobilization of Pb and Cu in polluted soil by superphosphate, multi-walled carbon nanotube, rice straw and its derived biochar.

Lead (Pb) and copper (Cu) contamination in croplands pose severe health hazards and environmental concerns throughout soil-food chain transfer. In the present study, BCR, TCLP, CaCl2, and SBET techniques were employed to evaluate the simultaneous effectiveness of rice straw (RS) and its derived biochar (BC), multiwall carbon nanotube (MWCNT), and single superphosphate (SSP) to immobilize the Pb and Cu in co-contaminated soil. The BCR sequential extraction results suggested that with increasing BC and SSP amount, the acid-soluble fractions decreased while oxidizable and residual proportions of Pb and Cu were increased significantly. Compared to SSP, the application of BC amendment substantially modified partitioning of Cu from easily exchangeable phase to less bioavailable residual bound fraction. The immobilized Pb and Cu were mainly transformed to reducible forms. The TCLP and CaCl2-extracted Pb and Cu were reduced significantly by the addition of BC compared to RS and MWCNT, whereas the bio-accessibility of Pb significantly reduced with RS addition. SSP showed better results for Pb immobilization while marginal for Cu in co-contaminated soil. Overall, the addition of BC 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.

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.

Efficiency of C3 and C4 Plant Derived-Biochar for Cd Mobility, Nutrient Cycling and Microbial Biomass in Contaminated Soil

Biochar is considered a novel soil amendment to reduce metal mobility, but its influence on soil chemical and biochemical properties is not fully understood. In the present study, biochar derived from rice straw (RSB), rice hull (RHB), and maize stover (MSB) was used to evaluate comparative efficiency on Cd mobility and soil biochemical properties. Ammonium nitrate extractable Cd significantly decreased among all the applied biochar types and application rates. The European Community Bureau of Reference (BCR) technique showed significant decrease in acid-soluble Cd by 24%–32%, 19%–23%, and 22%–27% for RSB, RHB, and MSB, respectively at the 1.5% and 3% rate. However, the concentration of Cd in the residual increased by 38%, 35% and 36% for RSB, RHB and MSB, respectively at a 3% application rate. Soil microbial biomass (C and N) and inorganic nitrogen forms (NH4 and NO3) significantly increased among all biochar applications. Overall, RSB demonstrated positive results as soil amendments for Cd immobilization, increasing soil nutrient availability, and enhancing soil microbial biomass.