Removal Rate Of Pb Research Articles

Heavy metal distribution in particle size fractions of floodplain soils from Dongchuan, Yunnan Province, Southwest China.

The heavy metal pollution level in soils is heavily affected by the soil particle size distribution. However, the heavy metal loss during particle size extraction and the effect of calcite on the heavy metals removal in terms of the particle size are unclear. In this study, the distribution of heavy metals (Cu, Cd, Cr, Co, Ni, Zn, Pb, U, and V) was determined in five particle fractions (> 2, 2-0.25, 0.25-0.02, 0.02-0.002, and < 0.002 mm) of two soil and one sediment samples collected from the floodplain of Dongchuan, Yunnan Province, Southwest China. The sampled floodplain soils were mainly composed of gravel and sand fractions (> 97%). The concentrations of all nine heavy metals in the sampled soils and sediment increase significantly with decreasing particle sizes. The maximal loss rate of Cd and Cu reaches 54% and 8.6%, respectively, which should be considered in the process of particle size fraction extraction in soils. The removal amount and removal rate of heavy metals in solution by pure calcite ranks in the order of Pb2+ > Cu2+ > Cr6+, while the removal rate of Pb (93.13%) is much higher than that of Cu (24.56%) and Cr (10.71%), which increase with the calcite particle size decreasing. The stabilization of carbonate minerals in soils is crucial for heavy metal pollution control in floodplain soils with high carbonate concentrations in Dongchuan, China.

Organotemplate-free synthesis of MOR zeolite from coal fly ash through simultaneously effective extraction of Si and Al

In this study, high-purity mordenite (MOR) zeolite was successfully synthesized from coal fly ash (CFA) using a simple and green method without organotemplate. The Al and Si used for MOR synthesis were simultaneously extracted from CFA, which were transformed to aluminosilicate gel by co-precipitation and then coupled with MOR seed for MOR synthesis instead of using organotemplate in common method. The results showed that the Al and Si extraction efficiencies were high, reaching up to 82.18% and 93.15%, respectively. The synthesized CFA-based MOR zeolite had a low Si/Al ratio of 3.92, and micropores is the dominating pore structure in the synthesized zeolite, accounts for up to 63.16% of its total pore volume. The possible mechanisms of MOR zeolite from CFA by gel coupling seed assisted synthesis were discussed. Furthermore, the CFA-based MOR was applied in CO 2 adsorption, heavy metal ions adsorption in aqueous solution and catalyst carrier for NH 3 -SCR reaction. The results presented that the CO 2 adsorption capacity of the CFA-based MOR was 1.92 mmol/g with high cycle stability. The removal rate of Pb 2+ was above 99.99% with Pb 2+ initial concentration of 51.30 mg/L. Mn-MOR catalyst was obtained through loading 3.36 wt% Mn by ion-exchange, which had a NO conversion rate of 93.58% at 200 °C. This study demonstrates that the gel coupling seed assisted method without organotemplate is a potential way to synthesize zeolite materials using the Si and Al simultaneously extracted from CFA. • CFA-based MOR zeolite was synthesized by an organotemplate-free method. • Al and Si were extracted from CFA with efficiencies of 82.18% and 93.15%, respectively. • Aluminosilicate gel coupling seed assisted method was used to synthesize MOR. • CFA-based MOR showed good performance in CO 2 capture, metal adsorption and NH 3 -SCR.

High efficiency removal of Pb(ii) in aqueous solution by a biochar-supported nanoscale ferrous sulfide composite.

A biochar-supported nanoscale ferrous sulfide composite was prepared and applied for the treatment of Pb(ii) ions in aqueous solution. The experimental results of SEM, EDS, XRD, and FT-IR spectroscopy clearly implied that the biochar was successfully modified with nanoscale ferrous sulfide composite. The maximum adsorption capacity of Pb(ii) ions by FeS@biochar reached 88.06 mg g−1. Compared with other reported adsorbents, the removal rate of Pb(ii) ions by FeS@biochar was higher. The pseudo-second-order kinetic model and Langmuir isotherm model could better fit the experimental adsorption results. The removal rate of Pb(ii) ions by FeS@biochar was controlled by the chemical reaction and monolayer adsorption on the surface of FeS@biochar. The mechanisms of Pb(ii) removal from aqueous solutions by biochar involved electrostatic attraction, hydrogen bonding, physical adsorption, ion exchange, and chemical precipitation. Additionally, the chemical stability and reusability of FeS@biochar were good. It is also an environment-friendly material for low-cost wastewater treatment.

Optimization of low-cost biosurfactant produced by Bacillus subtilis SASCBT01 and their environmental remediation potential.

The present research aims to enhance the biosurfactant (BS) production using agricultural by-products as a low-cost substrate with the statistical approach. BS production from Bacillus subtilis SASCBT01 was carried out with four different variables such as pH, incubation time, cassava peel waste (CPW) and palmira sprout (PS). The model expected the highest emulsification activity of 65±1·2% after 96-h incubation with 3·0gl-1 of CPW and PS at pH 7·0. The SASCBT01 strain-based BS was successful at retrieving up to 18% and the highest Pb removal rates were found at 65%. These BS have considered high quality in bioremediation applications.

A green method for extraction of Bi and Pb from bismuth-rich melt by super-gravity

The traditional method of separating bismuth-rich melt produced from the fire smelting of bismuth slags has some imperfections of the complicated operation, low recovery rate of metals and harmful to the environment and human health. As a result of these concerns, a green method for extraction of Bi and Pb from the bismuth-rich melt by super-gravity has been proposed in this study. The extraction mechanism of Bi and Pb was discussed in detail. And influences of the super-gravity field on the separation of bismuth-rich melt were investigated. It can be noted that the Bi solid was difficult to be separated from the liquid phase under a normal-gravity field. In contrast, after centrifugal filtration with optimum conditions of G=600, T=130°C and t=90s, the mass-specific gravity for Bi residual of Bi-5wt%Pb and Bi-15wt%Pb melts achieved 87.92% and 63.28%, and the purity of Bi residual could be up to 99.49% and 99.28%. Meanwhile, the removal rate of Pb reached 89.80% and 95.20%, respectively. Therefore, it is a promising technology for green extraction of Bi and Pb from the bismuth-rich melt in terms of the remarkable advantages of high separation efficiency, continuous operation and environmentally friendly.

Removal of toxic hexavalent chromium (Cr(VI)) and divalent lead (Pb(II)) ions from aqueous solution by modified rhizomes of Acorus calamus

This work reports on readily available and low cost acorus calamus rhizome (PCR) treated by hydrochloric acid (HCl) and sodium hydroxide (NaOH) solutions to develop new materials labelled acid treated calamus rhizome (ACR) and base treated calamus rhizome (BCR) respectively. The materials were used as adsorbents for the removal of Cr(VI) and Pb(II) ions. The characterization revealed that surface area for PCR at 5.78 cm2/g was low. However, ACR and BCR surface area increased to 9.98 and 11.65 cm2/g respectively. The maximum uptake for Cr(VI) ions was 14.64, 21.93, 24.48 mg/g at pH = 1 and Pb(II) ions 74.32, 76.12, 88.08 mg/g at pH = 8.5 onto PCR, ACR and BCR respectively. Isotherm data showed that Langmuir better fitted the adsorption processes. It was observed that the removal rate of Pb(II) was more rapid than for Cr(VI) ions. The adsorption processes for Cr(VI) ions was better described by pseudo-second order while Pb(II) was described by pseudo-first order. The uptake of both metal ions increased when temperature of the solution was increased indicating that the nature of the adsorption was endothermic. Reusability studies revealed that the adsorbents may be regenerated and reused several times and this shows the economic benefits of the materials.

Lettuce-derived rhizosphere polyamine-producing bacteria and their potential to reduce Cd and Pb accumulation in lettuce (Lactuca sativa L.)

Microbial immobilization is a novel and environmentally friendly technique in which microbes are used to immobilize heavy metals in the soil. Polyamine-production screening media and high-pressure liquid chromatography were used to isolate polyamine-producing bacteria from Cd- and Pb-polluted rhizosphere soil of lettuce. Enhancement of lettuce growth and reduced accumulation of Cd and Pb in lettuce by the polyamine-producing strains were investigated. Two polyamine-producing bacteria Bacillus megaterium N3 and Enterobacter bugandensis XY7 were obtained by screening. The Cd and Pb removal rates of strains N3 and XY7 ranged from 73.5 %–87.6 % in solution containing 1 mg L−1 Cd2+ and 5 mg L−1 Pb2+. Strains N3 and XY7 increased the dry weight (22.2 %–66.7 %), improved the polyamines contents and reduced the Cd (57.3 %–74.2 %) and Pb (44.1 %–62.9 %) contents of lettuce. Moreover, the strains decreased the bioavailable Cd (27.1 %–62.1 %) and Pb (35.4 %–73.7 %) contents but increased polyamines contents and the relative abundance of aguA gene in lettuce rhizosphere soil. The results suggested that strains N3 and XY7 decreased the uptake of Cd and Pb and their translocation into lettuce shoots by i) bacterial cell adsorption, ii) chelation of polyamines to Cd and Pb, iii) decreasing available Cd and Pb in the rhizosphere soil and Cd and Pb translocation from the roots to the shoots, and iv) increasing the polyamine contents and the relative abundance of aguA gene in lettuce rhizosphere soil. Our findings may provide technical support for the remediation of heavy metal contaminated farmlands by bacteria and for safe growth of vegetables crop species.

Renewable P-type zeolite for superior absorption of heavy metals: Isotherms, kinetics, and mechanism

Zeolite is a characteristic material for removing heavy metals exhibiting by low tolerance quantities. It is particularly desirable although challenging to cultivate an unmodified and reusable zeolite for eradicating heavy metals with great capacity. Herein, we sought out and firstly synthesized the uniform octahedral zeolite Na6Al6Si10O32·12H2O for heavy metal ions trap, proven extraordinarily effective decontamination of M2+ (Pb2+, Cd2+, Cu2+, and Zn2+). The maximum capacities of Pb2+, Cd2+, Cu2+, and Zn2+ were 649, 210, 90 and 88 mg/g, and the distribution coefficients (Kd) was ~108 mL/g for Pb2+ which emphasized the superior effectiveness of Na6Al6Si10O32·12H2O contrasted with other zeolites. Rapid adsorption was observed that Pb2+ concentration (7.5 ppm) was reduced to 0.6 ppb in 2 min. The removal mechanism was ascribed to the ion exchange and hydroxyl groups thereby affording high adsorption capacity. We also investigated the heavy metal removal of zeolite 13X and 4A for comparison and concluded the determining factor affecting absorption capacity. The removal rate of Pb remained at 97% even after five regeneration recycles. The zeolite was therefore promising for practical water purification and industrialization.

Alkyl Thiourea Functionalised Silica for the Effective Removal of Heavy Metals from Acanthopanax senticosus Extract.

Acanthopanax senticosus extract with excessive standard of Pb, Cd, Hg, and Cu was used as the research object, and the alkyl thiourea functionalised silica was used as a new heavy metal removal scavenger. The heavy metal removal process was optimised by orthogonal experiment with dynamic and static adsorption modes. Meanwhile, the content of Acanthopanax B and Acanthopanax E, the solid content, and the HPLC fingerprint similarity were used as quality monitoring indicators of Acanthopanax senticosus heavy metal removal before and after. Then, the technical adaptability of heavy metal removal by alkyl thiourea functionalised silica was evaluated. Under the optimal dynamic adsorption conditions, the average removal rates of Pb, Cd, Hg, and Cu were 91.64%, 93.04%, 81.77%, and 83.11%, respectively. Under the optimal static adsorption conditions, the average removal rates of Pb, Cd, Hg, and Cu were 82.22%, 89.95%, 81.26%, and 82.97%, respectively. During Acanthopanax senticosus extract heavy metal removal before and after, the change percentage of Acanthopanax B and Acanthopanax E was less than 2.00%, the solid content loss rate was only 0.18%, and the fingerprint similarity was over 99.9%. The method can be used to satisfy the high efficiency of selective removal of harmful elements in Acanthopanax senticosus extract and the effective composition of almost no effect; the method is simple and easy, so it can be recommended for pretreatment of heavy metals in Traditional Chinese Medicine extracts, and this way provides a new thought and research technique to decrease the contents of heavy metals.

Experimental study on electrokinetic remediation of Pb-contaminated kaolinite

The treatment of heavy metal pollution by electrokinetic remediation has the characteristics of low cost, easy operation and less secondary pollution and has broad application prospects. Electrokinetic remediation tests, and some combined with a permeable absorbing layer were conducted to analyze the distribution patterns of conductivity, Pb(II), pH and moisture content in lead (Pb)-contaminated kaolinite. The influences of factors such as remediation time, type of fillers and location of a permeable adsorbing layer on the remediation effects of Pb-contaminated kaolinite were explored. The results reveal that the soil water content decreases with increasing energization time and that the water content near an anode chamber was highest, whereas that near a cathode chamber was lowest. When the test was conducted for 7 days, the conductivity near the cathode side was relatively high, whereas the Pb near the anode side was largely removed. Prolonged energization time was conducive to the removal of Pb. In an electrokinetic test, no alkaline region was detected in kaolinite. When a permeable adsorbing layer was placed in the middle of a soil sample, the removal effect was the best. Compared with bone char, a permeable adsorbing layer of calcareous sand significantly improved the Pb removal rate and effectively reduced energy consumption.

Low-cost bio-based sustainable removal of lead and cadmium using a polyphenolic bioactive Indian curry leaf (Murraya koengii) powder.

There is an increasing trend of developing various low-cost biogenic sorbents for the efficient and economical removal of noxious metals . Curry leaf powder (CLP), a promising non-toxic biosorbent containing several bioactive compounds was prepared by the pulverization of the dried leaves for the effective removal of Lead (Pb) and Cadmium (Cd). Various batch sorption experiments were carried out under constant temperature (25°C), different pH (4.5-10.5), initial concentrations (50-200mgL-1), adsorbent dosages (0.10-0.40g) and contact times (0-60min) to understand the optimum experimental conditions and simultaneously evaluate the adsorption isotherms and removal kinetics of CLP. Adsorption equilibrium was established in less than an hour interval (50min). The pseudo-equilibrium process was best described by the pseudo-second-order kinetic (R2≥0.99), Freundlich and Langmuir isotherm model (R2≥0.94). The removal rate of Pb and Cd gradually increased (15.7 and 12.7mgg-1 for Pb and Cd) at 100mgL-1 of initial concentration till 60min of contact period in a single contaminant system, the effect was non-significant for multiple adsorbent dosage systems (p>0.05; t-test) though. The regeneration potential of the exhausted biosorbent was excellent upto 5 cycles with the better efficiency observed for Pb. The obtained results explicitly validated the probable utilization of CLP as a promising green adsorbent for metal removal . Future study may highlight the decontamination aspects of emerging contaminants with such green bio sorbents in large scale as well as mimicing the stomach conditions.

Effects and Mechanisms of Calcium Ion Addition on Lead Removal from Water by Eichhornia crassipes.

Karst water is rich in calcium ions (Ca2+) and exhibits poor metal availability and low biodegradation efficiency. This study sought to analyze the effects and mechanisms of Ca2+ on lead (Pb) removal and absorption by Eichhornia crassipes (a floating plant common in karst areas). Moreover, the morphology and functional groups of E. crassipes in water were characterized via SEM, and FTIR. The results demonstrated that the removal rate of Pb in karst water (85.31%) was higher than that in non-karst water (77.04%); however, the Pb bioconcentration amount (BCA) in E. crassipes roots in karst water (1763 mg/kg) was lower than that in non-karst water (2143 mg/kg). With increased Ca2+ concentrations (60, 80, and 100 mg/L) in karst water, the Pb removal rate increased (85.31%, 88.87%, and 92.44%), the Pb BCA decreased (1763, 1317, and 1095 mg/kg), and the Ca BCA increased (6801, 6955, and 9368 mg/kg), which was attributed to PbCO3 and PbSO4 precipitation and competitive Ca and Pb absorption. High Ca2+ concentrations increased the strength of cation exchange, alleviated the fracture degree of fibrous roots, reduced the atrophy of vascular bundles, protected the cell wall, promoted C–O combined with Pb, enhanced the strength of O‒H, SO42−, C=O, and reduced the oxidization of alkynyl acetylene bonds.

+Efficient dewatering and heavy-metal removal in municipal sewage using oxidants

Municipal sewage sludge (MSS) is widely used in agriculture. In this study, three oxidants (Fenton’s reagent, K2S2O8, and CaO2) were used to simultaneously dehydrate MSS and remove heavy metals, and the heavy metals in the supernatant were separated via the addition of CaO. The respective removal rates of Pb, Zn, Cu, and Cd were 56.8%, 84.9%, 88.3%, and 92.3% using Fenton’s reagent; 66.9%, 86.1%, 88.9%, and 82.8% using K2S2O8; and 53.0%, 58.3%, 64.8% and 2.1% using CaO2. Thus, Fenton’s reagent and K2S2O8 were preferable for heavy metal removal, especially for Cd. The treated sludge was safe for agricultural use based on the standards for pollutants in sludge for agricultural use (GB4284-84). The oxidants also exhibited good dewatering performance for MSS and caused the extracellular polymeric substance (EPS) of MSS to decompose quickly. The water content of the sludge was reduced from 99.08% to 76.1% (Fenton’s reagent), 74.7% (K2S2O8), and 66.5% (CaO2). Hence, the treated sludge was easy to transport and could be safely used in agricultural production. After oxidant treatment, CaO was added to the supernatant, allowing the metals in the supernatant to be separated. This method can reduce Wc and heavy metal content of sludge at low cost.

Highest and Fastest Removal Rate of PbII Ions through Rational Functionalized Decoration of a Metal-Organic Framework Cavity.

To overcome the challenge of developing a multipurpose adsorbent for effective removal of toxic and carcinogenic PbII ions from aqueous solutions, a made-for-purpose functional group (N1 ,N2 -di(pyridine-4-yl)oxalamide) was rationally designed and incorporated into the cavities of a Zn metal-organic framework (MOF), namely, TMU-56. Large enough pore size along with high densities of strong metal chelating sites lead not only to the highest uptake capacity for PbII ions, but also the fastest removal rate that has ever been reported for functionalized MOFs, occurring in just 20 s. Moreover, high concentrations of lead ions favor the ion exchange reaction, resulting in a high degree of metal exchange. In addition, TMU-56 can be a practical adsorbent because of its notable performance in the simultaneous removal of several toxic and carcinogenic heavy metals from wastewater, which has rare precedence.

Removal of Pb(II) from Aqueous Solutions by Periclase/Calcite Nanocomposites

Periclase/calcite nanocomposites (PCN) were synthesized via calcination and carbonation treatment of dolomite. The surface and structural properties of PCN were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption-desorption isotherm, thermogravimetry (TG), and transmission electron microscopy (TEM). The potential of PCN to remove Pb(II) from aqueous solutions was examined by batch experiments. The effects of solid-liquid ratio (0.1–1 g L−1), initial solution pH (2–7), reaction time (0–60 min), temperature (303–323 K), and initial Pb(II) concentration (100–500 mg·L−1) on lead removal were investigated. The results showed that the removal rate of Pb(II) firstly increased and then kept stable with the increasing initial pH from 2 to 7, and the optimal solid-liquid ratio was determined as 0.2 g L−1. The adsorption kinetics of Pb(II) on PCN was well fitted to pseudo-second-order model. The adsorption equilibrium isotherm of Pb(II) over PCN could be well fitted by Langmuir model, and the maximum removal capacity was 1150.06 mg g−1 at 323 K. The thermodynamic parameters indicated that the adsorption of Pb(II) was an endothermic and spontaneous process. According to the mechanism study, the gradual release of OH− and CO32− from the dissociation of periclase and calcite can react with Pb(II) to form hydrocerussite (Pb3(CO3)2(OH)2) on PCN surface.

Reduction of excessive heavy metals accumulation in drinking water with natural zeolites

This paper reports on the study of heavy metal removal from groundwater intended for human consumption using natural aluminosilicates of the zeolite group. The natural zeolite material has been extracted from the Sokirnica deposit located in the Zakarpattia Region in Ukraine. The central focus of this study was the course of the heavy metal adsorption process itself, in which natural zeolites were applied for the removal of Cr, Cd, Ni and Pb ions from aqueous solutions in the presence of large amounts of Ca and Mg ions, competing for ion exchange sites. The capacity of zeolite as an adsorbent was assessed with the use of adsorption isotherms prepared for the heavy metals under tests, whereas the mathematical description of the process was provided by Freundlich and Langmuir isotherm equations. The results from the analysis confirm the high efficiency, and thus the applicability, of zeolite deposits in water filtration. The effective Cr, Cd, Ni and Pb removal rate from groundwater intended for human consumption was confirmed even when the content of these metals in water was exceeded by a factor of 10, compared to the permissible limits provided in legal regulations.

Community Structure of Heavy Metal Immobilized Bacteria in the Lettuce (Lactuca sativa L.) Rhizosphere in Soil Polluted by Heavy Metals and Its Effects on Reducing Heavy Metal Accumulation in Lettuce

To investigate the diversity of culturable bacteria and heavy metal-immobilizing bacteria in vegetable rhizosphere soil with high concentrations of heavy metals and explore these microbial resources, two samples of Italian lettuce rhizosphere soil with high heavy metal concentration (HY) and low heavy metal concentration (DK) were collected from Xinxiang, Henan Province. The diversity of culturable bacteria and heavy metal-immobilizing bacteria in the rhizosphere soil of lettuce was compared by culturable separation technology and a solution adsorption experiment. The enhancement of Cd and Pb immobilization and lettuce growth by the strains was also investigated in a hydroponic experiment. The results showed that 400 strains belonging to 3 phyla and 14 genera were isolated from the HY sample, with β-Proteobacteria being the dominant phylum. Meanwhile, 400 strains belonging to 4 phyla and 30 genera were isolated from the DK sample, with Firmicutes being the dominant phylum. A total of 146 strains had a strong ability to immobilize heavy metal and the Cd and Pb removal rates were greater than 80% in the HY sample; Brevundimonas, Serratia, Arthrobacter, and Pseudarthrobacter were the main genera. However, 44 strains had a strong ability to immobilize heavy metal and the Cd and Pb removal rates were greater than 80% in the DK sample, with Bacillus being the main genus. Compared with the control, inoculation with Serratia liquefaciens HY-22, Bacillus thuringiensis HY-53, and Acinetobacter lwoffii HY-157 significantly increased the dry weight of roots (7.5%-77.6%) and shoots (15.4%-67.2%) of the Italian lettuce and cauliflower lettuce and reduced the contents of Cd (38.7%-66.6%) and Pb (34.7%-62.5%) in roots and shoots of Italian lettuce. In addition, the contents of Cd and Pb in the fresh shoots of Italian lettuce and cauliflower lettuce in the presence of Bacillus thuringiensis HY-53 were lower than the Cd and Pb limits set by national food safety standards. Thus, the results provided strain resources and a theoretical basis for the remediation of Cd-and Pb-contaminated farmlands for the safe production of crops.

Feasibility of using Fe0 to remediate groundwater lead pollution in an abandoned tailings dam

In order to provide technical support for the remediation of heavy metal of Dajiaoling tailings dam, experiments concerning the Pb(II) removal efficiency and its influencing factors in groundwater by iron (Fe0) were conducted on the basis of analysis of the heavy metal content and distribution. The results show that the lead pollution in groundwater can be efficiently removed by Fe0 by redox reaction and floc adsorption. The optimal parameters were obtained by experimentation: the particle size of iron powder is 400 mesh, the original concentration of Pb(II) is 10 mg/L and the reaction time is 90 min. With increases in the iron powder dosage, the removal rate of Pb(II) increases. When the iron powder dosage increases by some degree, the removal rate of Pb(II) will not increase obviously. The removal rate of Pb(II) is significantly increased by an acid pretreatment and a binary metal addition. Simultaneous use of Fe0 and sawdust achieves better and more stable removal efficiency because of the combination effects with chemical reactions and microorganisms. The best reaction rate and removal efficiency are shown after activated carbon is added, arising from a combined effect by chemical, biological and physical actions.

Electrokinetic remediation of Pb near the e-waste dismantle site with Fe(NO3)3 as cathode electrolyte

ABSTRACT In this study, Pb-contaminated soil in the e-waste dismantle site was remediated by activated carbon fiber (ACF) enhanced electrokinetic remediation. Experiments were conducted using Fe(NO3)3 as catholyte and citric acid-sodium citrate as anolyte with different conditions: pH value of anolyte, voltage and the electrode gap. At the same time, we set up a group of contrast test without ACF to investigate the adsorption performance of ACF for Pb. Results showed that the highest removal rate of Pb after the remediation was 80.53% at 4 cm from the anode when the electrode gap was 31 cm, pH value was 3 and the voltage was 28 V, and the total removal rate increased significantly with the decrease of the pH value of anolyte and the increase of voltage. Characterization of ACF after reaction showed that ACF effectively adsorbed heavy metal Pb, and the adsorption amount was 1.42 mg/g. Sequential extraction analysis revealed that Pb mainly existed in the forms of organic matter bound and residual in the soil after remediation. These forms are relatively stable and low toxicity, indicating that the remediation has significantly reduced the harm of Pb to the environment.

Investigation on the Properties and Distribution of Air Voids in Porous Asphalt with Relevance to the Pb(II) Removal Performance

In this study, one type of porous asphalt (PA) mixture was designed at two different air void (AV) contents. Direct information regarding both the dimensional properties and AV distribution within two PA specimens in their natural states were observed, compared, and analyzed based on the X-ray CT (computed tomography) and digital image analysis techniques and fractal geometry theory. The characteristics of AV distribution, including AV content, AV number, and AV volume were quantified by comparing pore structure at different specimen heights. The dimensional properties of voids at different specimen heights were characterized by parameters in terms of equivalent diameter, specific surface area, and fractal dimension. The Pb(II) removal performance of the two PA mixtures was examined by an artificial rainfall event. The relationship between the PA microstructure and Pb(II) removal rate was then determined. It is observed from this study that the overall distribution pattern of AV inside PA specimen is independent of AV content. The distributional parameters including AV content, AV number, and AV volume show good correlations with three dimensional parameters, respectively. The Pb(II) removal in general appears to be independent of AV content because both PA mixtures have the same level of performance in removing Pb(II) during the rainfall period. The removal rate of Pb(II) shows good correlation with AV content, AV number, AV volume, and equivalent diameter of AV, indicating that a perfect distribution of AV within PA mixture is more important than the complex geometries of voids for getting a higher Pb(II) removal during rainfall event and without providing a temporary storage of stormwater in PA mixture. These findings provide an effective evidence to reveal that the AV distribution and properties characteristics have significant implications for pollutant removal in field PA pavement system.