Reutilization of carbon of waste filter cartridge after its surface modification for the fluoride removal from water by continuous flow process.

In the present study, the waste carbon cartridge of the water filter was modified and reutilized for defluoridation of water. The modified carbon was characterized by particle size analysis (PSA), Fourier transformed infrared spectroscopy (FTIR), zeta potential, pHzpc, energy-dispersive X-ray (EDS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray crystallography (XRD). The adsorptive nature of modified carbon was investigated with pH (4-10), dose (1-5 g/L), contact time (0-180 min), temperature (25-55 °C), fluoride concentration (5-20 mg/L), and the effect of the competitive ions. Adsorption isotherm, kinetics, thermodynamics, and breakthrough studies were evaluated for fluoride uptake on surface-modified carbon (SM*C). Fluoride adsorption on the carbon accepted Langmuir model (R2 = 0.983) and pseudo-second-order kinetic (R2 = 0.956). The presence of HCO3- in the solution reduced the elimination of fluoride. The carbon was regenerated and reused four times; the removal percentage was decreased from 92 to 31.7%. This adsorption phenomenon showed exothermic behavior. The maximum fluoride uptake capacity of SM*C achieved 2.97 mg/g at 20 mg/L of initial concentration. The modified carbon cartridge of the water filter was successfully employed for fluoride removal from water.

Synthesis of nZnO from waste batteries by hydrometallurgical method for photocatalytic degradation of organic pollutants under visible light irradiation.

Waste zinc carbon (Zn-C) batteries are generated worldwide in a large amount. They are non-rechargeable and costly to recycle. Therefore, they end up in the landfills where they create hazards for humans and for environment as well. Zn-C batteries are rich in concentration of different heavy metals so they can be subjected for the recovery of metals for the development of valuable new materials. In this study authors have proposed an easy hydrometallurgical method for the recovery of zinc from waste Zn-C batteries to synthesize nano zinc oxide (nZnO) photocatalyst. The prepared nZnO particles were irregular in shape, highly crystalline in nature with crystallite size 23.94 nm. The band gap of the photocatalyst was 3.1 eV. The photocatalytic activity of the synthesised nZnO was tested for the degradation of three organic pollutants namely; phenol, p-nitrophenol (PNP) and crystal violet dye (CV) in an aqueous solution under visible light irradiation. nZnO showed a good catalytic efficiency for the degradation of all the three pollutants, however, the crystal violet (CV) removal was best in comparison with the other pollutants, it was minimally effected by the increase in CV concentration. The maximum degradation of phenol, PNP and CV was found to be 95.03 ± 0.2%, 88.63 ± 0.1% and 97.87 ± 0.4%, respectively. The degradation data was fitted best with pseudo-first-order kinetic model. The photocatalyst was recyclable and its regeneration ability was higher for initial three cycles. The intermediate compounds formed in the process of degradation were determined by liquid chromatography and mass spectroscopy (LC-MS) analysis.

Photocatalytic Degradation of Orange G Dye by Using Bismuth Molybdate: Photocatalysis Optimization and Modeling via Definitive Screening Designs.

In the current study, Bismuth molybdate was synthesized using simple co-precipitation procedure, and their characterization was carried out by various methods such as FT-IR, SEM, and P-XRD. Furthermore, the photocatalytic degradation of Orange G (ORG) dye using synthesized catalyst under visible light irradiation was studied. Response surface Method was used for the optimization of process variables and degradation kinetics evaluated by modeling of experimental data. Based on the experimental design outcomes, the first-order model was proven as a practical correlation between selected factors and response. Further ANOVA analysis has revealed that only two out of six factors have a significant effect on ORG degradation, however ORG concentration and irradiation time indicated the significant effects sequentially. Maximum ORG degradation of approximately 96% was achieved by keeping process parameters in range, such as 1 g L-1 loading of catalyst, 50 mg L-1 concentration of ORG, 1.4 mol L-1 concentration of H2O2 at pH 7 and a temperature of 30 °C. Kinetics of ORG degradation followed the pseudo first order, and almost complete degradation was achieved within 8 h. The effectiveness of the Bi2MoO6/H2O2 photo-Fenton system in degradation reactions is due to the higher number of photo-generated e- available on the catalyst surface as a result of their ability to inhibit recombination of e- and h+ pair.

Adsorption of As(III) and As(V) from aqueous solution by magnetic biosorbents derived from chemical carbonization of pea peel waste biomass: Isotherm, kinetic, thermodynamic and breakthrough curve modeling studies.

The purpose of this research was to investigate the adsorption of arsenic (As) from aqueous solutions using MPAC-500 and MPAC-600 (magnetic-activated carbons synthesized from the peel of Pisum sativum (pea) pyrolyzed at 500 °C and 600 °C temperatures, respectively). The potential of both biosorbents for As adsorption was determined in batch and column mode. The characterization of both biosorbents was performed by energy dispersive spectroscopy, scanning electron microscope, pHZPC, particle size distribution, X-ray diffraction, zeta potential and Fourier-transform infrared spectroscopy. It was found that the efficiency of MPAC-600 was better than MPAC-500 for the adsorption of As(III) and As(V) ions. The adsorption capacities of MPAC-500 and MPAC-600 in removing As(III) were 0.7297 mg/g and 1.3335 mg/g, respectively, while the values of Qmax for As(V) on MPAC-500 and MPAC-600 were 0.4930 mg/g and 0.9451 mg/g, respectively. The Langmuir isotherm model was found to be the best fit for adsorption of As(III) by MPAC-500 and MPAC-600, as well as adsorption of As(V) by MPAC-500. The Freundlich isotherm model, on the other hand, was optimal for As(V) removal with MPAC-600. With R2 values close to unity, the pseudo-second-order kinetics were best fitted to the adsorption process of both As species. The Thomas model was used to estimate the breakthrough curves. The effects of coexisting oxyanions and regeneration studies were also carried out to examine the influence of oxyanions on As adsorption and reusability of biosorbents.

Performance of a novel iron infused biochar developed from Raphanus sativus and Artocarpus heterophyllus refuse for trivalent and pentavalent arsenic adsorption from an aqueous solution: mechanism, isotherm and kinetics study.

Fabrication of magnetic biochar was done by pyrolysis of waste leaves of Raphanus sativus (MRB) and Artocarpus heterophyllus (MJB) peel pretreated with FeCl3 was examined for As(III and V) adsorption from an aqueous solution. The synthesized bioadsorbents were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), particle size analysis (PSA), scanning electron microscope (SEM), energy dispersive x-ray (EDX), zeta potential, Vibrating sample magnetometer (VSM) and point of zero charge (pHZPC). MRB-800 exhibits greater efficiency toward the removal of both As species with qmax value 2.08 mg/g for As(III) and 2.03 mg/g for As(V). Whereas, the qmax value was 1.13 mg/g for As (III) and 1.26 mg g-1 for As (V) adsorption using MJB-800. Temkin and Freundlich isotherm were best fitted to the adsorption of As(III) and As(V) by MRB-800, respectively. Langmuir isotherm was best followed to the adsorption of As (III and V) by MJB-800. Pseudo-second-order kinetics was well simulated by the experimental data of As adsorption using both the bioadsorbents. Surface complexation and electrostatic attraction was dominant mechanism for As (III) and As (V) adsorption. Thermodynamic study shows that removal of As (III) was exothermic while the As (V) adsorption was endothermic for MRB-800 and MJB-800.

Based on the available literature, it was revealed that no work has been reported yet for the utilization of Raphanus sativus (Radish leaves) and Artocarpus heterophyllus (Jackfruit peel) waste for the preparation of magnetic biochar and its application for As(III) and As(V) removal for aqueous solution.

Removal of arsenic from aqueous solution by novel iron and iron-zirconium modified activated carbon derived from chemical carbonization of Tectona grandis sawdust: Isotherm, kinetic, thermodynamic and breakthrough curve modelling.

The aim of the present study was: development of activated carbon modified with iron (Fe@AC) and modified with iron and zirconium (Fe-Zr@AC) from the Tectona grandis sawdust (TGS) waste biomass and its potential applicability for the removal of As (III) from contaminated water by batch and column mode. The biomass waste was pre-treated with ferric chloride (FeCl3) and the mixture of FeCl3 and zirconium oxide (ZrO2) and then pyrolyzed at 500 °C for 2 h. The properties of both bioadsorbents were comprehensively characterized by using Scanning electron microscopy (SEM), Energy dispersive X-ray (EDX), Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), Particle Size analysis (PSA), point of zero charge (pHZPC), Brunauer-Emmett-Teller (BET) to prove successful impregnation of the Fe and Zr on the surface of AC of TGS. FTIR analysis clearly indicates the Fe and Fe-Zr complexation on biosorbents surface and biosorption of As (III). The results revealed that maximum As (III) removal was achieved 86.35% by Fe-Zr@AC (3 g/L dose, pH-7.0, temperature-25 °C and concentration 0.5 mg/L). However, maximum removal of As (III) was attained ~75% by Fe@AC (with dose-4g/L, pH-7.0, temperature-25 °C and concentration 0.5 mg/L) at the initial concentration of 0.5 mg/L of As (III). Fe-Zr@AC exhibits higher efficiency with qmax value 1.206 mg/g than Fe@AC with the qmax value 0.679 mg/g for the removal of As(III). While in the column study, Fe-Zr@AC exhibited 98.8% removal at flow rate of 5 mL/min and bed height of 5 cm. Biosorption Isotherm and Kinetics were fitted good with Langmuir isotherm (R2 ≥ 0.99) and followed pseudo-second-order (R2 ≥ 0.99). The regeneration study indicates that the prepared biosorbents efficiently recycled up to five cycles. Therefore, Fe@AC and Fe-Zr@AC derived from TGS has been showed to be novel, effective, and economical biosorbent. The collective benefits of easy development, good affinity towards As (III), good separability, reusability, and inexpensive of magnetized Fe@AC and Fe-Zr@AC make it a novel biosorbent. The application of Fe-Zr@AC for the removal of As (III) from the water was very efficient its concentration in the solution after treatment was found below the 10 µg/L as per the guideline WHO.

Development of adsorbent from Mentha plant ash and its application in fluoride adsorption from aqueous solution: a mechanism, isotherm, thermodynamic, and kinetics studies.

In the present study, Mentha plant ash was modified by Na and Al for the synthesis of adsorbent and applied for the removal of Fluoride from an aqueous solution. Mixture of acid washed Mentha plant ash (MPA) and NaOH (in the ratio 1:1.3) thermally treated at 600°C in a muffle furnace then treated with aqueous solution of sodium aluminate. The characterization of sodium aluminum modified ash (Na-Al-MA) powder was done such as SEM (Scanning Electron Microscopy), Particle Size Analysis (PSA), Fourier transformed spectroscopy (FTIR), Zeta Potential, XRD (X-ray Diffraction) analysis, and Brunauer-Emmett-Teller (BET) analysis. The removal of fluoride from an aqueous solution carried out with Na-Al-MA by batch adsorption process. The Na-Al-MA was found to be very effective as adsorbent. The maximum removal of fluoride was achieved Ì´ 86% at neutral pH and at room temperature. It was investigated that Langmuir adsorption isotherm and pseudo-second-order kinetic was best fitted for fluoride adsorption. The fluoride adsorption on Na-Al-MA was an exothermic process. A possible mechanism including electrostatic attraction, hydrogen bonding, and metal-fluoride interaction for fluoride adsorption on Na-Al-MA have described in this study. Novelty statement: Utilization of Mentha plant ash for the development of adsorbent and its application in adsorptive removal of fluoride from aqueous solution is the novelty of this work. Adsorbent preparation may be the better way of waste biomass management.

Bacterial degradation of distillery wastewater pollutants and their metabolites characterization and its toxicity evaluation by using Caenorhabditis elegans as terrestrial test models.

Distillery wastewater has significant amount of coloring compounds and organic substances even after the secondary treatment process, which poses many severe environmental and health threats. However, the recalcitrant coloured compounds have not yet been clearly identified. In this study, two bacterial strains DS3 and DS5 capable to decolorize distillery wastewater (DWW) pollutants were isolated and characterized as Staphylococcus saprophyticus (MF182113) and Alcaligenaceae sp. (MF182114), respectively. Results showed that mixed bacterial culture was found more effective decolorizing 71.83% DWW compared to axenic culture DS3 and DS5 resulting only 47.94% and 50.67% decolorization, respectively. The FT-IR and LC-MS/MS analysis of untreated DWW showed the presence of many recalcitrant compounds having different functional groups, but after bacterial treatment, most of compounds get diminished and the toxicity of DWW was reduced significantly. Further, the Nile red staining of Caenorhabditis elegans exposed to untreated and bacteria treated DWW for evaluation of toxicity assay and results revealed that the worms exposed to untreated DWW showed sharp reduction in total fat content having more profound effects, suggesting the diminished nAchR signaling as compare to bacterial treated DWW. Hence, this study revealed that inadequate disposal of untreated DWW may cause transfer of toxic substances into the environment and receiving water bodies.

As(III) and As(V) removal by using iron impregnated biosorbents derived from waste biomass of Citrus limmeta (peel and pulp) from the aqueous solution and ground water.

Now a day's biosorbents with magnetic properties have been applied for water and wastewater treatment process, because of its magnetic nature it can be easily separated and can be reused more than one time. In the present study, two magnetic biosorbents were synthesized from waste biomass of Citrus limetta (peel and pulp) at 500 °C temperature represented as PAC-500 and PPAC-500. These biosorbents were effectively used for the removal of As(III) and As(V) from an aqueous solution and groundwater samples. The prepared biosorbents were characterized by using Brunauer Emmett Teller (BET), Zeta potential, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Energy Disperssive X-ray (EDS), X-ray Diffraction (XRD) and Particle Size Analyzer (PSA). Isotherms, kinetics and thermodynamics were also applied to the obtained experimental data. The regeneration study revealed that the biosorbent can be recycled up to four cycles. The adsorbent capacity of PAC-500 and PPAC-500 for the sorption of As(III) was 714.28 µg/g and 526.31 µg/g, respectively, whereas the qmax value for As(V) sorption was 2000 µg/g for both the biosorbents (PAC-500 and PPAC-500). The effect of competitive ions was also studied that shows that the presence of H2PO4- and CO32 have negative effects on the sorption of As(III) and As(V). Arsenic is very toxic and it is a more important subject for consideration, therefore it is necessary to develop a low cost material that is very efficient in removing As from ground water contaminated with As water.

Synthesis of novel biochar from waste plant litter biomass for the removal of Arsenic (III and V) from aqueous solution: A mechanism characterization, kinetics and thermodynamics.

The present study is focusing on utilization of a new feedstock material for the preparation of biochar. The dry waste leaves litter of Tectona and Lagerstroemia speciosa was used for synthesizing the biochar at 800 °C for 1 h in muffle furnace represents as TB 800 and LB 800 and then used for the removal of As(III) and As(V) from aqueous solution. The prepared biochar materials had a crystalline structure and was characterized by using Scanning electron microscopy (SEM), Energy dispersive X-ray (EDX), Brunaur emmit teller (BET), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Zeta potential, particle size and X-ray photoelectron spectroscopy (XPS). In regeneration study it was observed that prepared biochar material could be used up to four times with good removal percentage of Arsenic (III and V). The experimental data fitted well by Langmuir model for As(V) removal using TB 800 and LB 800, Freundlich model for As(III) removal by LB 800 and Temkin model for As(III) removal by TB 800. Pseudo-second-order kinetics was followed and best fitted with the obtained data of As(III) and (V) removal. Thermodynamics study revealed that the process of adsorption was endothermic for the removal of As(III) and exothermic for the adsorption of As(V) using TB 800 and LB 800. The adsorption capacity obtained for the removal of As(III) was 666.7 µg/g and 454.54 µg/g for TB 800 and LB 800, respectively and adsorption capacity for As(V) was 1250 µg/g for TB 800 and 714.28 µg/g was attained by LB 800.

Corn husk derived magnetized activated carbon for the removal of phenol and para-nitrophenol from aqueous solution: Interaction mechanism, insights on adsorbent characteristics, and isothermal, kinetic and thermodynamic properties.

In this study, waste corn husk was used for the synthesis of an effective adsorbent (cornhusk activated carbon, CHAC) and by treating at two different temperatures, 250 °C (CHAC-250) and 500 °C (CHAC-500) to check adsorption efficiency. The synthesized adsorbents were characterized with the help of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy, Particle size analysis and x-ray diffraction (XRD), which revealed the different properties of the two adsorbents. The synthesized adsorbents were applied for the removal of phenol and p-nitrophenol (PNP) from aqueous solution. CHAC-500 was more efficient than the CHAC-250. The maximum adsorptions of phenol and PNP by CHAC-500 were ∼96% and ∼94%, respectively, while the maximum adsorptions of phenol and PNP by CHAC-250 were ∼81% and ∼84%, respectively. The adsorption processes were best fitted with the Langmuir adsorption isotherm and the pseudo-second-order kinetic model. The adsorption of phenol was an exothermic process, while that of PNP was an endothermic process, on both adsorbents.

Adsorptive Removal of Fluoride from Aqueous Solution by Biogenic Iron Permeated Activated Carbon Derived from Sweet Lime Waste.

In this study, biogenic activated carbon were successfully synthesized from Citrus limetta pulp residue, and applied to remove fluoride from an aqueous solution. For the synthesis activated carbon of biosorbents, raw materials were heated in muffle furnace at two different temperatures i.e. (250 °C and 500 °C) and were noted as ACP-250 and ACP-500. The prepared biosorbents were characterized through scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and X-ray diffraction (XRD). Batch adsorption studies were performed with varying temperature, dosage, pH, and various initial concentrations. Adsorption isotherms and the reaction kinetics were also analyzed in order to understand the adsorption mechanism. The results of this study shows that the maximum removal achieved was approximately (86 and 82) % of ACP-500 and ACP-250, respectively. The isotherm results show that the Langmuir isotherm model fitted better, with monolayer adsorption capacity of 12.6 mg/g of fluoride. However, for kinetic study, the pseudo-second-order kinetics fitted well. The synthesized materials at different temperature were highly effective for the removal of fluoride from water, with reusability of three to four times.

Adsorptive Removal of Selected Anionic and Cationic Dyes by Using Graphitic Carbon Material Prepared from Edible Sugar: A Study of Kinetics and Isotherms.

Graphitic carbon-like material (GCM) derived from edible sugar under a nitrogen environment was applied as an adsorbent for the removal of anionic and cationic dyes (methyl orange, MO) and methylene blue (MB) from wastewater. The physico-chemical characterization of GCM was analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The plate-like morphology with an average size of 50-100 nm was measured from the SEM images. The measured BET 'surface area and pore volume were 574 m2/g and 0.248 cm3/g, respectively with pore diameter (d), 1.8 47 (< 2 nm) indicates that the GCM classified as a microporous. The effects of dosage, pH, contact time and concentration on the adsorption of MB and MO onto GCM were studied to unveil the adsorption process. The experimental isotherm data concurred with the Langmuir isotherm model (R2 = 0.990) for MB, while the MO isotherm data concurred with Freundlich model (R2 = 0.995). The maximum adsorption capacity achieved from the Langmuir isotherm equation at 25 °C was 38.75 and 43.48 mg/g for MB and MO, respectively, which indicates that GCM is a suitable adsorbent for the adsorption of both anionic and cationic dyes. The kinetic study demonstrated that the adsorption of both dyes onto GCM was the pseudo-second-order diffusion kinetics. The thermodynamic parameters reveal the adsorption of both dyes was endothermic spontaneous through chemical interactions. The GCM was found to be a potential adsorbent for the removal of MB and MO from an aqueous solution.

Rapid degradation of phenol by ultrasound-dispersed nano-metallic particles (NMPs) in the presence of hydrogen peroxide: A possible mechanism for phenol degradation in water.

The present study was carried out to investigate the degradation of phenol by ultrasonically dispersed nano-metallic particles (NMPs) in an aqueous solution of phenol. Leaching liquor from automobile shredder residue (ASR) was used to obtain the NMPs. The prepared NMPs were analyzed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and by X-ray diffraction (XRD). The SEM images show that the diameters of the NMPs were less than 50 nm. An SEM-EDX elemental analysis reveals that Fe was the most commonly found element (weight %) in the NMPs. The FTIR and XRD peaks indicate the presence of metals oxides on the surfaces of the NMPs. The results of the XPS analysis indicate that various elements (e.g., C, O, Zn, Cu, Mn, Fe) are present on the surfaces of the NMPs. The effects of the NMP dose, the initial solution pH, and of different concentrations of phenol and H2O2 on the phenol degradation characteristics were evaluated. The results of this study demonstrate that phenol degradation can be improved by increasing the amount of NMPs, whereas it is reduced with an increase in the phenol concentration. The degradation of phenol by ultrasonically dispersed NMPs followed the pseudo-first-order kinetics. The probable mechanism of phenol degradation by ultrasonically dispersed NMPs was the oxidation of phenol caused by the hydroxyl radicals produced during the reaction between H2O2 and the NMPs during the ultrasonication process.

Influence of nano-TiO2 particles on the bioaccumulation of Cd in soybean plants (Glycine max): A possible mechanism for the removal of Cd from the contaminated soil.

Phytoremediation is a highly efficient technique for the elimination of trace elements from contaminated soils through the shoots and roots of plants. This study was carried out to investigate the effects of nano-titanium dioxide (TiO2) on Cd uptake by soybean plants. The objective of the present research was to examine the potential to improve the phytoextraction of Cd by the application of nano-TiO2 particles. The results showed that an addition of Cd to the soil significantly decreased plant growth and the biomass, pigment and protein contents. Increases in the proline content and malondialdehyde (MDA) indicate that Cd toxicity stresses the plants. Fourier transform infrared spectroscopy (FTIR) was used to determine variations in functional groups due to the Cd taken up into the shoot and root tissues of plants. An application of nano-TiO2 particles restricts Cd toxicity by increasing the photosynthetic rate and growth parameters of the plants. The uptake of Cd was also increased from 128.5 to 507.6 µg/plant with an increase in the nano-TiO2 concentration from 100 to 300 mg/kg in the soil. The application of nano-TiO2 significantly enhanced Cd uptake in the plants. The results of this study thus demonstrate that an application of nano-TiO2 can increase Cd uptake and minimize Cd stress in soybean plants.

Recovery of precious metals from low-grade automobile shredder residue: A novel approach for the recovery of nanozero-valent copper particles.

The presence of precious metals (PMs) in low-grade automobile shredder residue (ASR) makes it attractive for recycling. This study investigated the leaching and recovery characteristics of two PMs (Cu and Ag) and two heavy metals (Mn and Co) from ASR. The effects of H2O2, leaching temperature, liquid to solid (L/S) ratio, and particle size on metal leaching were determined in an aqueous solution of 0.5M nitric acid. The metal leaching rate was increased with increasing nitric acid concentration, amount of H2O2, L/S ratio and temperature. The leaching kinetics was analyzed by using a second-order reaction model. In the analysis of leaching kinetics, the metal leaching data were well fitted (R(2)⩾0.99) with the second-order reaction model. The activation energy (kJ/mol) for metal leaching was 39.6 for Cu, 17.1 for Ag, 17.3 for Mn and 29.2 for Co. Metal recovery was carried out by fractional precipitation with the addition of advanced Fenton's regent. Metal recovery efficiency was increased to 99.95% for Cu, 99.8% for Mn, 90.0% for Ag and 96.46% for Co with the advanced Fenton's regent. In particular, a novel finding of the PM recovery is that Cu can also be recovered directly from the leachate of ASR in the form of zero-valent copper (ZVC) nanoparticles (NPs). Hydrometallurgical recovery of the metals from ASR using nitric acid is highly efficient.

Quantitative analysis and reduction of the eco-toxicity risk of heavy metals for the fine fraction of automobile shredder residue (ASR) using H2O2.

Automobile shredder residue (ASR) fraction (size <0.25mm) can be considered as hazardous due to presence of high concentrations of heavy metals. Hydrogen peroxide combined with nitric acid has been used for the recovery of heavy metals (Zn, Cu, Mn, Fe, Ni, Pb, Cd and Cr) from the fine fraction of ASR. A sequential extraction procedure has also been used to determine the heavy metal speciation in the fine fraction of ASR before and after treatment. A risk analysis of the fine fraction of ASR before and after treatment was conducted to assess the bioavailability and eco-toxicity of heavy metals. These results showed that the recovery of heavy metals from ASR increased with an increase in the hydrogen peroxide concentration. A high concentration of heavy metals was found to be present in Cbio fractions (the sum of the exchangeable and carbonate fractions) in the fine fraction of ASR, indicating high toxicity risk. The Cbio rate of all selected heavy metals was found to range from 8.6% to 33.4% of the total metal content in the fine fraction of ASR. After treatment, Cbio was reduced to 0.3-3.3% of total metal upon a treatment with 2.0% hydrogen peroxide. On the basis of the risk assessment code (RAC), the environmental risk values for heavy metals in the fine fraction of ASR reflect high risk/medium risk. However, after treatment, the heavy metals would be categorized as low risk/no risk. The present study concludes that hydrogen peroxide combined with nitric acid is a promising treatment for the recovery and reduction of the eco-toxicity risk of heavy metals in ASR.

Hydrometallurgical recovery of heavy metals from low grade automobile shredder residue (ASR): An application of advanced Fenton process (AFP).

To investigate the leaching and recovery of heavy metals from low-grade automobile shredder residue (ASR), the effects of nitric acid (HNO3) and hydrogen peroxide (H2O2) concentrations, liquid/solid (L/S) ratio, leaching temperature and ASR particle size fractions on the heavy metal leaching rate were determined. The heavy metals were recovered by fractional precipitation and advanced Fenton process (AFP) at different pHs. The toxicity characteristic leaching procedure (TCLP) test was also performed in the residue remaining after heavy metal leaching to evaluate the potential toxicity of ASR. The heavy metal leaching efficiency was increased with increasing HNO3 and H2O2 concentrations, L/S ratio and temperature. The heavy metal leaching efficiencies were maximized in the lowest ASR size fraction at 303 K and L/S ratio of 100 mL/g. The kinetic study showed that the metal leaching was best represented by a second-order reaction model, with a value of R(2) > 0.99 for all selected heavy metals. The determined activation energy (kJ/mol) was 21.61, 17.10, 12.15, 34.50, 13.07 and 11.45 for Zn, Fe, Ni, Pb, Cd and Cr, respectively. In the final residue, the concentrations of Cd, Cr and Pb were under their threshold limits in all ASR size fractions. Hydrometallurgical metal recovery was greatly increased by AFP up to 99.96% for Zn, 99.97% for Fe, 95.62% for Ni, 99.62% for Pb, 94.11% for Cd and 96.79% for Cr. AFP is highly recommended for the recovery of leached metals from solution even at low concentrations.

Pollution control and metal resource recovery for low grade automobile shredder residue: a mechanism, bioavailability and risk assessment.

Automobile shredder residue (ASR) is considered as hazardous waste in Japan and European countries due to presence of heavy metals. This study was carried on the extraction characteristics of heavy metals (Mn, Fe, Ni, and Cr) from automobile shredder residue (ASR). The effects of pH, temperature, particle size, and liquid/solid ratio (L/S) on the extraction of heavy metals were investigated. The recovery rate of Mn, Fe, Ni, and Cr increased with increasing extraction temperature and L/S ratio. The lowest pH 2, the highest L/S ratio, and the smallest particle size showed the highest recovery of heavy metals from ASR. The highest recovery rates were in the following order: Mn > Ni > Cr > Fe. Reduction of mobility factor for the heavy metals was observed in all the size fractions after the recovery. The results of the kinetic analysis for various experimental conditions supported that the reaction rate of the recovery process followed a second order reaction model (R(2) ⩾ 0.95). The high availability of water-soluble fractions of Mn, Fe, Ni, and Cr from the low grade ASR could be potential hazards to the environment. Bioavailability and toxicity risk of heavy metals reduced significantly with pH 2 of distilled water. However, water is a cost-effective extracting agent for the recovery of heavy metals and it could be useful for reducing the toxicity of ASR.

Reduction of bioavailability and leachability of heavy metals during vermicomposting of water hyacinth.

Vermicomposting of water hyacinth is a good alternative for the treatment of water hyacinth (Eichhornia crassipes) and subsequentially, beneficial for agriculture purposes. The bioavailability and leachability of heavy metals (Zn, Cu, Mn, Fe, Ni, Pb, Cd, and Cr) were evaluated during vermicomposting of E. crassipes employing Eisenia fetida earthworm. Five different proportions (trials 1, 2, 3, 4, and 5) of cattle manure, water hyacinth, and sawdust were prepared for the vermicomposting process. Results show that very poor biomass growth of earthworms was observed in the highest proportion of water hyacinth (trial 1). The water soluble, diethylenetriaminepentaacetic acid (DTPA) extractable, and leachable heavy metals concentration (percentage of total heavy metals) were reduced significantly in all trials except trial 1. The total concentration of some metals was low but its water soluble and DTPA extractable fractions were similar or more than other metals which were present in higher concentration. This study revealed that the toxicity of metals depends on bioavailable fraction rather than total metal concentration. Bioavailable fraction of metals may be toxic for plants and soil microorganisms. The vermicomposting of water hyacinth by E. fetida was very effective for reduction of bioavailability and leachability of selected heavy metals. Leachability test confirmed that prepared vermicompost is not hazardous for soil, plants, and human health. The feasibility of earthworms to mitigate the metal toxicity and to enhance the nutrient profile in water hyacinth vermicompost might be useful in sustainable land renovation practices at low-input basis.