Leaching Of Cr Research Articles

Effects of Basicity and Mesh on Cr Leaching of EAF Carbon Steel Slag

The slag’s chromium leaching is one of the most pressing concerns in Electric Arc Furnace (EAF) carbon and stainless steels production. In recent years, many studies have aimed at understanding which properties (basicity, cooling speed) and phases (spinels, wustite, silicates) determine the Cr leaching, defining different indices (sp-factor, cs-factor) in order to forecast the slag’s behavior compared to the leaching of this toxic metal. The literature suggests that spinel formation is usually a good way to fix Cr and prevent its leaching. However, in some conditions (high basicity, low amount of spinel-forming species) soluble Cr-bearing phases can be formed, i.e., Ca-chromite or unstable spinel. In these conditions, Cr can be leached easily, even if it is bound in a spinel structure. In this paper, the effects of basicity and impurities (Ca, Si) on the instability of Cr-spinel was investigated, with respect to slag mesh. The influence of basicity was also studied on Mg-wustite stability, which might contribute to the leaching of Cr. Different samples of carbon steel slag, suspected of forming unstable spinels, belonging to different steel grade production, were also investigated. Both granulated (4 mm) and milled (<100 μm) slag were analyzed. Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM-EDS) analyses were carried out to measure the local chemical composition of Cr-bearing phases. This data was correlated with slag basicity (by X-Ray Fluorescence: XRF), spinel fraction (by X-Ray Diffraction: XRD), and Cr leaching (by Inductively Coupled Plasma Mass Spectrometry: ICP-MS). The main results indicate that the increase of the slag basicity implies an increase of the impurity content (Ca, Si) in the spinel, also over-saturated by Cr. This aspect, coupled with spinel geometrical features, seems to justify the unexpected Cr leaching of some slag samples. Basicity does not influence the chemistry of wustite, thus excluding it as an additional Cr leaching source.

Immobilization of hexavalent chromium in contaminated soil using nano-magnetic MnFe2O4.

Nano-magnetic MnFe2O4 was prepared and examined to immobilize Cr(VI) in the soil. According to the results of scanning electron microscopy (SEM) and X-ray diffraction (XRD) the formation of nano-magnetic MnFe2O4 with the particle size of less than 200 nm was demonstrated. Compared with the untreated soil, the leachability of Cr(VI) was reduced from 70.95% to 4.22% through toxicity characteristic leaching procedure (TCLP) at a dosage of 2 g/L of nanoparticles and 192 h remediation time. At the same condition, the physiologically based extraction test (PBET) human bioaccessibility of chromium was reduced from 86.76% to 4.42%. Moreover, the plant bioavailability of hexavalent chromium (using EDTA) was reduced from 83.72% to 5.53%. According to the sequential extraction procedure (SEP) the loosely bounds Cr (90.28%) was converted to the relatively strong bound (Fe-Mn oxides fraction, 92.09%) revealed the significant decrease in risk of release and availability of chromium after immobilization procedure. Further, results of column experiments of Cr(VI) elution revealed that almost all of the water-soluble chromium was converted to the associated synthesized nanoparticles phase. Overall, the present study proved that nano-magnetic MnFe2O4 significantly enhanced the hexavalent chromium immobilization through a decrease in leachability, plant bioavailability, human bioaccessibility, and risk of release.

Effect of ferrous sulfate dosage and soil particle size on leachability and species distribution of chromium in hexavalent chromium‐contaminated soil stabilized by ferrous sulfate

Ferrous sulfate (FeSO4) is widely used to effectively stabilize hexavalent chromium (Cr(VI))‐contaminated soil. The leaching behavior, Cr(VI) content, and chromium speciation distribution in the stabilized soil are the most important indexes for determining the effectiveness of reduction treatment. Numerous factors, such as reductant dosage and soil particle size, affect the stabilization process; these factors are relatively important. This study investigated the influence of FeSO4 dosage and soil particle size on leachability and speciation distribution of chromium in contaminated soil. Results showed that the increase in FeSO4 significantly reduced the leachability and Cr(VI) content in the soil given the increased reducible species that stem from an acid soluble fraction of chromium. The small particle size of the soil that contains a large surface area facilitated the reaction between Cr(VI) and FeSO4, thereby resulting in low leachability and high reducible species of Cr(VI) in the stabilized soil. The leached Cr(VI) concentration was exponentially correlated to Cr(VI) content in the stabilized soil, and the leachability of Cr from the stabilized soil was linearly correlated to the exchangeable phase of Cr. In addition, the leached Cr(VI) concentration from the stabilized soil conform to the US Environmental Protection Agency and China regulatory limits; meanwhile, considerable Cr(VI) remained in a few stabilized soil and exceeded the environmental quality standards for soil in China. These results illustrated the importance of a comprehensive assessment of Cr(VI)‐contaminated soil, which is treated by reductants for enabling flexible future land use. © 2018 American Institute of Chemical Engineers Environ Prog, 38: 500–507, 2019

Electrodialytic treatment of Greenlandic municipal solid waste incineration fly ash

In Greenland, fly ash could contribute as a local resource in construction as a substitute for cement in concrete or clay in bricks, if the toxicity of the ash is reduced. In this study, fly ash from three different Greenlandic waste incinerators were collected and subjected to electrodialytic treatment for removal of heavy metals with the aim of enabling reuse of the fly ashes. Seven electrodialytic experiments treating up to 2.5 kg of fly ash in a 10 L suspension were made. The heavy metal removal was mostly dependent on the initial concentration in the fly ash. Heavy metal leaching was examined before and after treatment and revealed overall a significant reduction in leaching of Cd, Cr, Cu, Pb and Zn; however, Cr and Pb leaching were above Danish guideline levels for reuse purposes. Hg leaching was also reduced to below Danish guideline levels, although only investigated for one fly ash. Hexavalent Cr was not the dominant speciation of Cr in the fly ashes. Ettringite formed during electrodialytic treatment in the fly ash suspensions at pH above 12. The total concentration of eligible components for reuse such as CaO, SiO2 and Al2O3, increased during the electrodialytic treatment.

Potential Leaching of Heavy Metals from Pristine and Accelerated Weathered Slag from Recycling of Automobile Lead-Acid Batteries

Recycling of automotive lead-acid batteries generates large qualities of potentially toxic slag. The current study investigated heavy metal leaching and partitioning in spent lead-acid battery slag (LaBS) as a function of pH, liquid/solid (L/S) ratio, and pore volume. LaBS was highly alkaline (pH: 12.22) and contained high total concentrations (mg/kg) of Pb (101,300), Cu (2508), Cr (1238), Zn (589), Cd (515) and Ni (110), indicating poor metal recovery in the recycling processes. pH-dependent leaching results showed that maximum leaching of Pb, Cu, Cr, Zn, Cd and Ni occurred under acidic conditions (pH 2–6), but dropped under neutral and alkaline conditions (pH 7–13) due to precipitation as insoluble compounds. Heavy metal leaching at high L/S (5–10) was significantly higher (p < 0.05) than those at low L/S ratios (0.5–2.0), suggesting that the greatest risk of release of these heavy metals occurs in the long-term following disposal into the environment. Heavy metal breakthrough curves exhibited washout behaviour of highly soluble fractions, generally characterized by an initial rapid release of heavy metals within the first pore volumes, followed by a drop in concentration. Accelerated weathering of LaBS significantly reduced heavy metal leaching in both batch and column experiments except in very few cases. Heavy metal partitioning showed that total cumulative leaching in column experiments was very low, accounting for just 0.1–7.7%, while 92.3–99.9% occurred as the residual fraction. Despite high total concentrations of heavy metals in LaBS, the risk of heavy metal leaching under neutral-to-alkaline conditions or natural pH of the LaBS was very low, but could be high if the material is exposed to acidic conditions.

Speciation analysis and leaching behaviors of selected trace elements in spent SCR catalyst

This study investigated heavy metal chemical speciation and leaching behavior from a board-type spent selective catalytic reduction (SCR) catalyst containing high concentrations of vanadium, chromium, nickel, copper, zinc, and lead. A three-step sequential extraction method, standard toxicity characteristic leaching procedure (TCLP), and leaching characteristic tests have been performed. It was found that the mobility of six heavy metals in the spent SCR catalyst was significantly different. The mobility of the six heavy metals exhibited the following order: Ni > Zn > V > Cr > As > Cu. Meanwhile, TCLP test results revealed relatively high Zn and Cr leaching rate of 83.20% and 10.35%, respectively. It was found that leaching rate was positively correlated with available contents (sum of acid soluble, reducible and oxidizable fractions). Leaching characteristics tests indicated that pH substantially affected the leaching of these heavy metals. In particular, the leaching of Cr, Ni, Cu, and Zn was positively influenced by strong acid, while V and As were easily released in the presence of strong acid and strong alkali (pH < 3 or pH > 11). In terms of kinetics, the leaching of Cr, Ni, Cu, Zn, and As within the spent catalyst was dominated by erosion and dissolution processes, which were rapid reaction processes. V was released in large amounts within 1 h, but its leaching amount sharply decreased with time due to readsorption.

Stainless steel tailings accelerated direct carbonation process at low pressure: Carbonation efficiency evaluation and chromium leaching inhibition correlation analysis

Chromium leaching from stainless steel tailings is an urgent problem risking of the environments, calcite integument of tailings by accelerated direct gas-solid carbonation process can be formed and the inhibition factor of carbonation degree on chromium leaching rate is discussed in detail. Stainless steel tailings accelerated direct gas-solid carbonation process is investigated at 300 °C–700 °C and 0.2–0.4 MPa, and the effect of temperature, reaction time, particle size and CO2 pressure on carbonation degree are analyzed by TGA-DSC, FTIR, SEM-EDS analysis. The results show that the maximum CO2 uptake obtained (8.2%), corresponding to 16% carbonation degree can be obtained when 48–75 μm stainless steel tailings are carbonated for 90 min at 300 °C and 0.4 MPa. Tailings particle size, carbonation time, and carbon dioxide pressure display a positive relationship with carbonation degree, but carbonation temperature has a negative relationship. 48–75 μm carbonated tailings with varied carbonation degree and original tailings are investigated for the inhibitory factor between carbonation degree and Cr leaching rate, when leaching process is at 60 °C for 90min on the condition that L/S ratio equals 20 ml/g. The results show the inhibitory factor is fitted by random function better, and the value decreases from 31.5% to 9.7%, when carbonation degree is from 2% to 8%, and then keeps stable, when carbonation degree is still increases from 8% to 14%, which illustrates that carbonation process as a better strategy of tailings innocuous treatment at high temperature is valid for restricting Cr leaching behavior.

Occurrence of Fibrous Chrysotile and Tremolite in the Çankiri and Ankara Regions, Central Anatolia, Turkey

AbstractNumerous occurrences of asbestos minerals, notably chrysotile and tremolite, are to be found on fracture surfaces in thrust fault deformation zones of Cretaceous dunite-harzburgite and pyroxenite in the Çankırı and Ankara regions, central Anatolia, Turkey. Consequently, potential exists for the development of regional malignant mesothelioma. The means of serpentinization, such as reaction of seawater during accretion of the upper ophiolitic mantle crust in a subduction zone and/or following uplift of ophiolitic units and the influence of hydrothermal/meteoric fluids along fractures, were investigated. Cretaceous dunite-harzburgite and localized pyroxenite rocks are mainly composed of serpentinized olivine and pyroxene associated with opaque minerals and Fe-(oxyhydr)oxide phases. Smectite, chlorite, illite, kaolinite, hydromagnesite, goethite, quartz, and opal-CT are also present. Chrysotile and localized tremolite occur either as a mesh, a suboriented to oriented long-fiber bundle, or as fiber-filling millimetric micro-vein textures on relicts of olivine and pyroxene (enstatite, augite). The chrysotile and tremolite have non-pseudomorphic textures developed under high pressure and temperature. The textures suggest authigenic formation of chrysotile and tremolite via a dissolution and precipitation mechanism. Additionally, spherical structures of opal-CT and locally platy hydromagnesite crystals either enclose or are developed within chrysotile/tremolite fiber bundles. The leaching of MgO, Fe2O3, Al2O3, Ni, Cr, and Nb, an increase in the LREE/HREE ratio, and negative Eu anomalies in the dunite-harzburgite and pyroxenite, and asbestos samples suggest that the chrysotile and tremolite were derived from the serpentinization of olivine and pyroxene. The chrysotile and tremolite were developed along fractures by hydrothermal fluid alteration during accretion and/or following the uplift of ophiolitic units of the region under high pressure and temperature conditions. This interpretation is also supported by isotope data and the calculated formation temperature of 170–555°C for chrysotile and tremolite. The average structural formulae for chrysotile and tremolite are (NanK0.03)(Mg5.54Fe0.09Al0.05Ca0.01Mn0.001) (Si3.96Al0.03)O10(OH)8 and (Na0.17K0.07)(Ca1.59Mg0.19Mn0.002)(Mg4.72Fe0.28)(Si7.86Al0.1Fe0.06)O22(OH)2, respectively.

Effective Remediation of Groundwater Fluoride with Inexpensively Processed Indian Bauxite.

India represents one-third of the world's fluorosis burden and is the fifth global producer of bauxite ore, which has previously been identified as a potential resource for remediating fluoride-contaminated groundwater in impoverished communities. Here, we use thermal activation and/or groundwater acidification to enhance fluoride adsorption by Indian bauxite obtained from Visakhapatnam, an area proximate to endemic fluorosis regions. We compare combinatorial water treatment and bauxite-processing scenarios through batch adsorption experiments, material characterization, and detailed cost analyses. Heating Indian bauxite above 300 °C increases available surface area by > 15× (to ∼170 m2/g) through gibbsite dehydroxylation and reduces the bauxite dose for remediating 10 ppm F- to 1.5 ppm F- by ∼93% (to 21 g/L). Additionally, lowering groundwater pH to 6.0 with HCl or CO2 further reduces the average required bauxite doses by 43-73% for ores heated at 300 °C (∼12 g/L) and 100 °C (∼77 g/L). Product water in most examined treatment scenarios complies with EPA standards for drinking water (e.g., As, Cd, Pb, etc.) but potential leaching of Al, Mn, and Cr is of concern in some scenarios. Among the defluoridation options explored here, bauxite heated at 300 °C in acidified groundwater has the lowest direct costs ($6.86 per person per year) and material-intensity.

Controlling the mobility of chromium and molybdenum in MSWI fly ash in a washing process

Fly ash from a cogeneration plant near Sundsvall in Sweden was treated in an ash-washing facility. The leaching of chromium (Cr) and molybdenum (Mo) from the ash residue exceeded the limit values for non-hazardous landfills. In this study factors that influence the leaching of Cr and Mo were identified and methods that can reduce the leaching were evaluated. The results revealed that the mobility of Cr and Mo are mainly controlled by pH and redox reactions and sequential extraction tests also showed that the fraction of highly soluble species of Cr and Mo increased after washing due to pH reactions in the ash during the process. Stabilization of the pH at ∼8 through carbonation of the washed ash and a lowering of the redox potential by adding ferrous iron to the process resulted in decreased leaching. Treatment with carbon dioxide yielded a decrease (from 10.7 to 8.2) in the pH and, hence, the leaching of Cr and Mo by 93 and 91%, respectively. And the addition of ferrous iron reduced the leaching of Cr by 50%. Carbonation of the ash can be achieved via treatment with flue gases from the power plant or treatment with landfill gas at the disposal site.

In situ remediation of hexavalent chromium contaminated soil by CMC-stabilized nanoscale zero-valent iron composited with biochar.

In this study, the remediation experiments were performed outdoors in natural conditions. Carboxymethyl cellulose (CMC)-stabilized nanoscale zero-valent iron (CMC-nZVI), biochar (BC) and CMC-stabilized nanoscale zero-valent iron composited with biochar (CMC-nZVI/BC) were synthesized and investigated for their effect on the in situ remediation of hexavalent chromium [Cr(VI)] contaminated soil and the concentration of available iron was tested after the remediation, compared with the untreated soil. The results of toxicity characteristic leaching procedure (TCLP) test showed that CMC-nZVI and CMC-nZVI/BC used as remediation materials could obviously improve the remediation rate of Cr contaminated soil and when the ratio of CMC-nZVI to Fe0 was 2.5 g/Kg, the leachability of Cr(VI) and Crtotal can be reduced by 100% and 95.8% simultaneously. Moreover, sequential extraction procedure (SEP) showed that most exchangeable Cr converted to carbonate-bound and Fe-Mn oxides-bound, reducing the availability and leachability of Cr in the soil.

Closing the material cycle of biomass-derived fly ashes: a regional case study of natural ageing in Finland

The amount of biomass-derived ashes is expected to rise in the EU due to targets to increase the use of renewable energy resources. To promote the reuse of biomass ashes, a regional case study of natural ageing of approximately 1 year was carried out on two landfill fly ash materials originating from wood and wood/peat. The results showed that leaching behaviour differed considerably between the fly ashes. Natural ageing had beneficial effects on the leaching properties of wood fly ash. The leached concentrations of sulphate, chloride, Cr and Mo decreased significantly in this residue. In peat and wood-derived fly ash, natural ageing decreased the leaching of Cr, but had no significant effect on the leaching of Mo and chloride. It was also notable that the leaching of sulphate increased in wood/peat fly ash by more than 130%, exceeding the upper limit value given in national legislation for a paved structure. To comply with the limit values of national legislation concerning the recovery of waste in earth construction, natural ageing alone was not shown to be a sufficient method to reduce the leaching of harmful elements in biomass-derived fly ashes and, thus, further treatments are required.

Comparative leaching of six toxic metals from raw and chemically stabilized MSWI fly ash using citric acid

The leaching behavior of six typical toxic metals (Pb, Zn, Cr, Cd, Cu and Ni) from raw and chemically stabilized (phosphate and chelating agent) municipal solid waste incineration (MSWI) fly ash were investigated using citric acid. Leaching tests indicated that phosphate stabilization can effectively decrease the leaching of Zn, Cd and Cr; whereas chelating agent stabilization shows a strong ability to lower the release of Pb, Cd and Cu, but instead increases the solubility of Zn and Cr at low pH conditions. Sequential extraction results suggested that the leaching of Pb, Zn and Cd in both the stabilized MSWI fly ash samples led to the decrease in Fe/Mn oxide fraction and the increase in exchangeable and carbonate fractions. The leaching of Cr was due to the decrease in exchangeable, carbonate and Fe/Mn oxide fractions in phosphate-stabilized and chelating agent-stabilized MSWI fly ash. The leaching of Cu in both stabilized MSWI fly ash was greatly ascribed to the decrease in Fe/Mn oxide and oxidisable fractions. Moreover, predicted curves by geochemical model indicated that both stabilized MSWI fly ash have the risk of releasing toxic metals under strong acid environment.

Electrodialytic extraction of Cr from water-washed MSWI fly ash by changing pH and redox conditions

Electrodialytic process offers a range of possibilities to waste management by electrodialytic separation (EDS) of heavy metals, depending on how the process is designed. Using three EDS cell setups (two two-compartment and one three-compartment) and their combinations, the extraction of Cr from municipal solid waste incineration fly ash by changing pH and redox conditions was investigated in the present work. The experiments were designed into single, two and three steps, based on the number of setups (by changing EDS cells) or effective setups (by shifting working electrode pairs) used. Prior to EDS the ash studied went through pretreatments such as water-washing and dry-sieving with a 50 µm sieve. The results showed that Cr was strongly bound in the ash, and the major fraction remained bound after the different treatments. Two/three-step treatment, which obtained the maximum Cr extraction rate of 27.5%, is an improvement on the single-step that extracted maximum 3.1%. The highest extraction was obtained due to the combined extraction of Cr(III) under low pH (accompanied with high redox) conditions and Cr(VI) under high pH (low redox) conditions subsequently. The Cr leaching from the treated ashes with acidic pH was lower than from those with alkaline pH; after the three-step treatment, Cr leaching was much lower from the coarse fraction (> 50 µm), as compared to the fine (≤ 50 µm) or the unsieved ash. As for the coarse fraction, two/three-step treatment reduced the leaching of Cr compared to the single-step in the same pH range (either acidic or alkaline).

Chemical vs bio-mediated reduction of hexavalent chromium. An in-vitro study for soil and deep waters remediation

The removal of hexavalent chromium, Cr(VI), from a water-sediment system has been studied in vitro in different condition of soil water saturation, in order to simulate different possible occurring real scenarios. Two different approaches have been compared: the bio-mediated and the chemical Cr(VI) reduction. In the first technique three organic nutrients have been tested: glucose, trehalose and β-cyclodextrin. For the chemical remediation reducing agents such as sodium sulphite, sodium metabisulphite and ascorbic acid were considered.Both bio-mediated and chemical remediation approach yielded to the total abatement of Cr(VI) from a contaminated soil. No relevant drawbacks were observed in term of release of metal ions in solution or pH perturbation. Among the organic nutrients glucose showed the best performances while the best chemical reducing agent was ascorbic acid. Ascorbic acid can be considered more advantageous because its reaction with Cr(VI) is very fast (total Cr(VI) abatement in 24h) and allows a better control of the process parameters, not involving the action of microorganisms; moreover its higher cost compared to glucose, is compensated by the much lower amount necessary to attain 100% of Cr(VI) reduction.In case of in-situ remediation of groundwater, the spreading on soil of ascorbic acid would contribute to reduce the leaching of Cr(VI), helping the overall site remediation.

Removal of metallic Al and Al/Zn alloys in MSWI bottom ash by alkaline treatment

In order to reduce the leaching of pollutants and remove the Al and Zn/Al alloy from municipal solid waste incineration bottom ash (MSWIBA), an optimized alkaline pre-treatment procedure was developed in this study. The influences of alkaline conditions on the removal rate of Al and Zn/Al alloy were investigated, including [OH]− concentration, temperature, particle size, liquid/solid ratio and treatment duration. The experimental results showed that the optimized alkaline pre-treatment conditions to efficiently remove the Al and Zn/Al alloy was by using a minimum of 1.0mol/l [OH]−, at 55°C and with a minimal liquid/solid ratio of 5. The removal rate of Al and Zn/Al alloy followed an S-shape curve, in which the slow beginning stage was attributed to the protection of the oxidation layer and the quenched product around the Al and Al/Zn alloy. After 3h of the optimized alkaline pre-treatment, the leaching of Cr, Cu, Pb and Zn of the treated MSWIBA was reduced by more than 90% of that of the original MSWIBA. The alkali-silica reaction test further indicated that the expansion of concrete prepared with the pre-treated MSWIBA was significantly reduced and there was no macro-crack or spalling damage on the surface of the tested specimens.

Comparison of different MSWI fly ash treatment processes on the thermal behavior of As, Cr, Pb and Zn in the ash

To reduce heavy metal leaching and stabilize municipal solid waste incineration (MSWI) fly ash, different methods and combination of methods were tested: water washing, electrodialytic separation and thermal treatment at 1000°C. A comparison of heavy metal concentration and leaching levels of As, Cr, Pb and Zn for the different untreated and treated ashes was made. The results showed that minimizing leaching to meet the limiting values of the all the studied heavy metals can be obtained at the same time by combining water washing, electrodialytic separation and thermal treatment. The ash subjected to this combination had lower Cr than the ash solely subjected to thermal treatment or subjected to water washing prior to thermal treatment. The electrodialytic separation (EDS) of the washed ash lowered pH from alkaline to acidic, which resulted in elevated leaching of Cd and Zn, while the Cr leaching was reduced. Up to 58.6% of Zn and 5.5% of Pb were extracted by EDS compared to less than 0.6% extraction by water washing. During thermal treatment of the EDS treated ash, the ash was re-alkalized. Due to solidification and possibly evaporation, most heavy elements left in the thermally treated ash were stabilized and immobilized. However, leaching of As and/or Cr was still problematic and did not meet the limit value for the thermally treated ash being recycled in construction work. The removal of Ca and decomposition of Ca oxides and minerals during EDS was linked to the leaching patterns of As and Cr after thermal treatment.

Heavy Metal Leaching as Affected by Long-Time Organic Waste Fertilizer Application.

The recycling of urban waste products as fertilizers in agriculture may introduce contaminants such as heavy metals into soil that may leach and contaminate groundwater. In the present study, we investigated the leaching of heavy metals from intact soil cores collected in the long-term agricultural field trial CRUCIAL. At the time of sampling, the equivalent of >100 yr of urban waste fertilizers following Danish legislation had been applied. The leaching of Cu was significantly increased in the treatments receiving organic waste products compared with the unfertilized control but remained below the permissible level following Danish drinking water guidelines. The leaching of Cu was controlled primarily by the topsoil Cu content and by the leaching of dissolved organic carbon (DOC) but at the same time significantly correlated with leaching of colloids in soils that had not received fertilizer or had received an organic fertilizer with a low concentration of Cu. The leaching of Zn, Cd, and Co was not significantly increased in urban waste-fertilized treatments. The leaching of Mo was elevated in accelerated waste treatments (both agricultural and urban), and the leaching of Mo was linked to the leaching of DOC. Since leaching of Cr and Pb was strongly linked to the level of colloid leaching, leaching of these metals was reduced in the urban waste treatments. Overall, the results presented should not raise concern regarding the agricultural use of urban waste products in agriculture as long as the relevant guidelines are followed.

Solidification and Biotoxicity Assessment of Thermally Treated Municipal Solid Waste Incineration (MSWI) Fly Ash.

In the present work, thermal treatment was used to stabilize municipal solid waste incineration (MSWI) fly ash, which was considered hazardous waste. Toxicity characteristic leaching procedure (TCLP) results indicated that, after the thermal process, the leaching concentrations of Pb, Cu, and Zn decreased from 8.08 to 0.16 mg/L, 0.12 to 0.017 mg/L and 0.39 to 0.1 mg/L, respectively, which well met the limits in GB5085.3-2007 and GB16689-2008. Thermal treatment showed a negative effect on the leachability of Cr with concentrations increasing from 0.1 to 1.28 mg/L; nevertheless, it was still under the limitations. XRD analysis suggested that, after thermal treatments, CaO was newly generated. CaO was a main contribution to higher Cr leaching concentrations owing to the formation of Cr (VI)—compounds such as CaCrO4. SEM/EDS tests revealed that particle adhesion, agglomeration, and grain growth happened during the thermal process and thus diminished the leachability of Pb, Cu, and Zn, but these processes had no significant influence on the leaching of Cr. A microbial assay demonstrated that all thermally treated samples yet possessed strong bactericidal activity according to optical density (OD) test results. Among all samples, the OD value of raw fly ash (RFA) was lowest followed by FA700-10, FA900-10, and FA1100-10 in an increasing order, which indicated that the sequence of the biotoxicity for these samples was RFA > FA700-10 > FA900-10 > FA1100-10. This preliminary study indicated that, apart from TCLP criteria, the biotoxicity assessment was indispensable for evaluating the effect of thermal treatment for MSWI fly ash.

Corrosion and radiation resistant nanoceramic coatings for lead fast reactors

Bare and Al2O3-coated austenitic steel samples are exposed to lead-fast-reactor relevant corrosive conditions. Selective leaching of Ni, Mn and Cr is observed in bare samples exposed to high temperature stagnant lead (550°C, 10−8wt.% oxygen, 1000 and 4000h). By contrast, corrosion is not observed in either pristine (4000h) or irradiated (1000h) coated samples. Further characterization and testing methods include SEM, TEM, STEM, EDS, cyclic nanoimpact, microindentation, scratch, and thermal cycling. Overall, the results show that the coatings retain structural integrity under the conditions investigated, which is a crucial prerogative for corrosion protection with ceramic coatings.