Fasheng Li

Screening and assessment of solidification/stabilization amendments suitable for soils of lead-acid battery contaminated site.

Lead exposure via ingestion of soil and dust generally occurs at lead-acid battery manufacturing and recycling sites. Screening solidification/stabilization (S/S) amendments suitable for lead contaminated soil in an abandoned lead-acid battery factory site was conducted based on its chemical forms and environmental risks. Twelve amendments were used to immobilize the Pb in soil and assess the solidification/stabilization efficiency by toxicity leaching tests. The results indicated that three amendments, KH₂PO₄ (KP), KH₂PO₄:oyster shell power=1:1 (by mass ratio; SPP), and KH₂PO₄:sintered magnesia=1:1 (by mass ratio; KPM) had higher remediation efficiencies that led to a 92% reduction in leachable Pb with the addition of 5% amendments, while the acid soluble fraction of Pb (AS-Pb) decreased by 41-46% and the residual fraction (RS-Pb) increased by 16-25%. The S/S costs of the three selected amendments KP, SPP, and KPM could be controlled to

Distribution and integrated assessment of lead in an abandoned lead-acid battery site in Southwest China before redevelopment

22.3 per ton of soil when the Pb concentration in soil ranged from 2000 to 3000 mg/kg. The results of this study demonstrated that KP, SPP, and KPM can effectively decrease bioavailability of Pb. These findings could provide basis for decision-making of S/S remediation of lead-acid battery contaminated sites.

Correlation between DNAPL distribution area and dissolved concentration in surfactant enhanced aquifer remediation effluent: A two-dimensional flow cell study.

Lead-acid battery sites have contributed enormous amounts of lead to the environment, significantly affecting its global biogeochemical cycle and leaving the potential risks to human health. An abandoned lead-acid battery site prepared for redevelopment was selected in order to study the distribution of lead in soils, plants, rhizosphere soils and soil solutions. In total, 197 samples from 77 boreholes were collected and analyzed. Single extractions by acetic acid (HOAc) were conducted to assess the bioavailability and speciation of lead in soils for comparison with the parts of the plants that are aboveground. Health risks for future residential development were evaluated by the integrated exposure uptake biokinetic (IEUBK) model. The results indicated that lead concentrations in 83% of the soil samples exceeded the Chinese Environmental Quality Standard for soil (350 mg/kg for Pb) and mainly occurred at depths between 0 and 1.5 m while accumulating at the surface of demolished construction waste and miscellaneous fill. Lead concentrations in soil solutions and HOAc extraction leachates were linked closely to the contents of aboveground Broussonetia papyrifera and Artemisia annua, two main types of local plants that were found at the site. The probability density of lead in blood (PbB) in excess of 10 µg/dL could overtake the 99% mark in the residential scenario. The findings provided a relatively integrated method to illustrate the onsite investigations and assessment for similar sites before remediation and future development from more comprehensive aspects.

Competitive immobilization of Pb in an aqueous ternary-metals system by soluble phosphates with varying pH

During the process of surfactant enhanced aquifer remediation (SEAR), free phase dense non-aqueous phase liquid (DNAPL) may be mobilized and spread. The understanding of the impact of DNAPL spreading on the SEAR remediation is not sufficient with its positive effect infrequently mentioned. To evaluate the correlation between DNAPL spreading and remediation efficiency, a two-dimensional sandbox apparatus was used to simulate the migration and dissolution process of 1,2-DCA (1,2-dichloroethane) DNAPL in SEAR. Distribution area of DNAPL in the sandbox was determined by digital image analysis and correlated with effluent DNAPL concentration. The results showed that the effluent DNAPL concentration has significant positive linear correlation with the DNAPL distribution area, indicating the mobilization of DNAPL could improve remediation efficiency by enlarging total NAPL-water interfacial area for mass transfer. Meanwhile, the vertical migration of 1,2-DCA was limited within the boundary of aquifer in all experiments, implying that by manipulating injection parameters in SEAR, optimal remediation efficiency can be reached while the risk of DNAPL vertical migration is minimized. This study provides a convenient visible and quantitative method for the optimization of parameters for SEAR project, and an approach of rapid predicting the extent of DNAPL contaminant distribution based on the dissolved DNAPL concentration in the extraction well.

Health and ecological risk-based characterization of soil and sediment contamination in shipyard with long-term use of DDT-containing antifouling paint

Chemical immobilization by phosphates has been widely and successfully applied to treat Pb in wastewater and contaminated soils. Pb in wastewaters and soils, however, always coexists with other heavy metals and their competitive reactions with phosphates have not been quantitatively and systematically studied. In this approach, immobilization of Pb, Zn, and Cd by mono-, di-, and tripotassium phosphate (KH2PO4, K2HPO4, and K3PO4) was observed in the single- and ternary-metals solutions. The immobilization rates of the three metals were determined by the residual concentration. The mineral composition and structure of the precipitates were characterized by powder X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). The results indicated that competitive reaction occurred in Pb-Zn-Cd ternary system, with immobilization rates decrease of <3.6%, <78%, and <89% for Pb, Zn and Cd (molar ratios of P: metal <1), respectively, compared to single metal system. The reaction of Pb with three phosphates exhibited intense competitiveness and the phosphates had a stronger affinity for Pb when Cl(-) was added. Pb-phosphate minerals formed by KH2PO4 with the better crystalline characteristics and largest size were very stable with a low dissolution rate (<0.02%) in the solution of pH 2.88, compared to K2HPO4 and K3PO4. This study demonstrated that Pb could be firstly and effectively immobilized by phosphates in multi-metal solutions containing Pb, Zn and Cd. Moreover, the research provided the insight of the importance of phosphate with low pH (e.g. KH2PO4) and the presence of Cl(-) for more efficient immobilization of Pb in the multi-metals pollution system.

Spatial distribution of heavy metals, salinity and alkalinity in soils around bauxite residue disposal area

Dichlorodiphenyltrichloroethane (DDT) was a frequently occurring type of persistent organic environmental pollutant in China and DDT-containing antifouling paint could be the main contributor of DDT to shipyards and fishing harbors. A field survey was conducted in a shipyard in southern China to investigate the content and distribution of DDT in soil and sediments. Human health and screening-level ecological risk assessments were conducted for DDT contamination in soil and sediments and the results indicated that total DDT in all samples tested exceeded present advisory safe limits. Analysis of the composition and distribution implicated DDT-containing antifouling paint used for ship maintenance as an important source of DDT. Individual and cumulative health risks for residents exceeded the extra lifetime cancer risks of 10(-6) and 10(-5), mainly from exposure to soil, ingestion and dermal contact. DDT in sediments is associated with a high level of toxicity for the benthic community when >99% of samples exceed the threshold concentration likely to be responsible for effects and severe effects. Further risk control for DDT is required to ensure safety for human health, the benthic community and the environment.

Microscopic evidence for humic acid induced changes in lead immobilization by phosphate in a counterdiffusion system

The existence of bauxite residue disposal area (BRDA) is a serious problem in China owing to the huge quantity as well as toxicity and high alkalinity of bauxite residue. To assess the impact of uncontrolled release of bauxite residue on soil, 80 surface soil samples from areas nearby the BRDA in China, were tested to obtain the levels of heavy metals, as well as exchangeable sodium percentage, pH, electrical conductivity (EC), and total alkalinity (TA). High levels of total concentrations of Cd, V, Pb, and Mo were detected in the study area, along with high pH and exchangeable Na, K, Ca, and Mg. Spatial distribution generated by Kriging interpolation of data on surface soils indicated variabilities in the concentrations of heavy metals, alkalinity, and salinity. Factor analyses confirmed the spatial distribution variance and the influence of prevailing winds. The enrichment factors of soil showed extreme enrichment of Mo, moderate enrichment of Cd and V; and high synthesis scores for soil salinization degree were noted from the eastern to southeastern region of the BRDA. This study provides a range of strategies with significant effort in planning, implementation, and monitoring activities to ensure effective dust control in BRDA management.

Phosphate-induced differences in stabilization efficiency for soils contaminated with lead, zinc, and cadmium

Abatement of lead (Pb) contamination in soil via chemical immobilization can reduce potential risks but is influenced by soil organic matter. The aim of this study was to observe and understand the influence of organic matter on Pb immobilization by phosphate. For this purpose, humic acid (HA) was introduced into a counterdiffusion system to mimic ionic reactions of the mineralization processes between the pollutant (Pb) and amendment agent (phosphate) in soil system, and were characterized jointly by in situ optical microscopy and ex situ XRD, SEM, TEM, and LSCM. The results indicate that lead immobilization in the counterdiffusion system involves a time-dependent crystallization process and that supersaturation occurs at nearly central region of the reaction zone. Entrapped HA had influence on crystal growth and size, causing more fragmented crystal morphology with increasing HA content, which can be explained by HA wrapping of the nucleation products and subsequent inhibition of reactions and crystal growth, as indicated by TEM and LSCM images. Mineral conversion from secondary lead orthophosphates to pyromorphite implies the promotion of more stable minerals. This approach provides evidence for a more intuitive understanding of the effects of HA on the immobilization of lead by phosphates.

Potential sources of and ecological risks from heavy metals in agricultural soils, Daye City, China

AbstractPhosphates can cost-effectively decrease the mobility of Pb in contaminated soils. However, Pb always coexists with other metals in soil, their competitive reactions with phosphates have not been tested. In this study, the abilities of KH2PO4, K2HPO4, and K3PO4 to stabilize Pb, Zn, and Cd in soils contaminated with a single metal or a ternary metal for different phosphorus/metal molar ratios were investigated. Results indicated that the stabilization efficiency of KH2PO4, K2HPO4, and K3PO4 for Pb, Zn, and Cd in single metal contaminated soil (P/M ratio 0.6) was 96.00%–98.74%, 33.76%–47.81%, and 9.50%–55.79%, respectively. Competitive stabilization occurred in the ternary system, Pb exhibited a strong competition, the stabilization efficiency of Zn and Cd reduced by 23.50%–31.64%, and 7.10%–39.26%, respectively. Pyromorphite and amorphous lead phosphate formed with excess KH2PO4 or K2HPO4 addition, while K3PO4 resulted in the formation of a hydroxypyromorphite precipitate. Amorphous Zn and Cd phosphates and hydroxides were the primary products. The immobilization rate of Zn and Cd depends on pH, and increased significantly in response to the excess phosphate application. This approach provides insight into phosphate-induced differences in stabilization efficiency in soils contaminated with multiple metals, which is of theoretical and engineering significance.