Leaching Of Zn Research Articles

Accumulation of heavy metals in soil and maize after 17-year pig manure application in Northeast China

Application of composted pig manure (PM) is a traditional practice to improve soil fertility, whereas generally leads to some environmental questions. The effects of PM application on Cd, Cu and Zn accumulation in soil and maize were investigated based on a long-term field trial in Northeast China, including control (CK), PM<sub>L</sub>, PM<sub>M</sub>, and PM<sub>H</sub>, receiving 0, 100, 250 and 500 kg total N/ha/year from 2002 to 2008 and 0, 10, 25 and 50 t fresh weight/ha/year from 2009 to 2018, respectively. Results showed that long-term soil application of PM increased maize grain yield, soil organic carbon (SOC) contents, coupled with significant accumulation and availability of Cd, Cu, and Zn in soil (0–15 cm). Compared with CK, the soil total Cd, Cu and Zn concentrations significantly increased by 105, 287 and 108% at high PM rate, respectively. Notably, the increments enhanced these heavy metals storage in maize roots rather than in grains. Moreover, the application of PM confirmed vertical transport of heavy metals in the tested soil, particularly for Cd and Cu in PM<sub>H</sub> treatment. Overall, the repeated application of PM can cause the accumulation and leaching of Cd, Cu and Zn in soil.

Contrasting effects of biochar and hydrothermally treated coal gangue on leachability, bioavailability, speciation and accumulation of heavy metals by rapeseed in copper mine tailings.

The purpose of this research was to examine the influence of hydrothermally treated coal gangue (HTCG) with and without biochar (BC) on the leaching, bioavailability, and redistribution of chemical fractions of heavy metals (HMs) in copper mine tailing (Cu-MT). An increase in pH, water holding capacity (WHC) and soil organic carbon (SOC) were observed due to the addition of BC in combination with raw coal gangue (RCG) and HTCG. A high Cu and other HMs concentration in pore water (PW) and amended Cu-MT were reduced by the combination of BC with RCG and/or HTCG, whereas individual application of RCG slightly increased the Cu, Cd, and Zn leaching and bioavailability, compared to the unamended Cu-MT. Sequential extractions results showed a reduction in the exchangeable fraction of Cu, Cd, Pb, and Zn and elevation in the residual fraction following the addition of BC-2% and BC-HTCG. However, individual application of RCG slightly increased the Cu, Cd, and Zn exchangeable fractions assessed by chemical extraction method. Rapeseed was grown for the following 45 days during which physiological parameters, metal uptake transfer rate (TR), bioconcentration factor (BCF), and translocation factor (TF) were measured after harvesting. In the case of plant biomass, no significant difference between applied amendments was observed for the fresh biomass (FBM) and dry biomass (DBM) of shoots and roots of rapeseed. However, BC-2% and BC-HTCG presented the lowest HMs uptake, TR, BCF (BCFroot and BCFshoot), and TF for Cu, Cd, Cr, Ni, Pb, and Zn in rapeseed among the other amendments compared to the unamended Cu-MT. Overall, these findings are indicative that using biochar in combination with RCG and/or HTCG led to a larger reduction in HMs leaching and bioavailability, due to their higher sorption capacity and could be a suitable remediation strategy for heavy metals in a Cu-MT.

Mass balance of heavy metals in a non-operational incinerator residue landfill site in Japan

To better understand the general behavior of heavy metals in semi-aerobic incinerator residue landfills, we developed a general equation for calculating the mass balance of heavy metals (cadmium, lead, copper, zinc, mercury, and chromium) based on monitoring data from incineration plants and landfill sites. The mass balance results showed that 0.0042%, 0.001%, 0.0004%, 0.0019%, 0.022%, and 0.0065% of the disposed Cd, Pb, Cu, Zn, Hg, and Cr, respectively, were washed out by rainfall from 1975 to 2015. Heavy metals (Cd, Cr, and Hg) with a lower total mass in the landfill had a relatively high total leaching rate. This may be because of the high pH of the landfill, which affected the leaching of Pb, Zn, and Cu. According to our analysis of the changes in annual leaching rates at this landfill site, there was an obvious change in those of Cu, Zn, and Pb after 1989, when the pH of the leachate increased suddenly. The overall annual leaching rate became more stable, at around 0.00002%, following closure of the landfill site, and it is believed that the dissolvable fraction and heavy metal concentration in the leachate are expected to reach a limit under the current conditions.

Metal–organic framework-5 as a novel phosphorescent probe for the highly selective and sensitive detection of Pb(II) in mussels

Lead ion (Pb(II)) has emerged as a major mussel pollutant in recent decades, thus the development of sensors capable of detecting Pb(II) is of considerable interest. In this work, a novel, rapid, and “turn-on” phosphorescent sensor was developed to monitor Pb(II) using metal-organic framework-5 (MOF-5, Zn4O(TPA)3, TPA: terephthalic acid) as a highly selective and sensitive luminescent probe. A mechanism describing the leaching of Zn(II) from Zn4O complexes and self-assembly of TPA after Pb(II) coordination is proposed for the MOF-5-Pb(II) system. Using enhanced phosphorescence, the sensor displays a wide linear detection range of 0.01−10 μmol/L and a low detection limit of 2 nmol/L for the determination of Pb(II). Moreover, it is noteworthy that when immobilized in a polyethylene glycol (PEG) film, the MOF-5 probe exhibited a visually distinct color change at 1.0 μmol/L Pb(II) under 365 nm UV light. From these results, a test strip was prepared for semi-quantitative analysis of Pb(II) content. Finally, the proposed phosphorescent sensor was successfully utilized to detect Pb(II) content in mussel. This study demonstrates the first MOF-based “turn-on” phosphorescent sensor for monitoring Pb(II), from which future high-performance phosphorescent sensors to determine food pollutants may be developed.

Improved chemical water oxidation with Zn in the tetrahedral site of spinel-type ZnCo2O4 nanostructure

Spinel oxides with the composition of AIIBIII2O4 (A and B are metal ions) represent an important class of anode material for water splitting to replace the currently used noble-metal catalysts. Although spinel electrocatalysts have widely been investigated for electrochemical water oxidation, the role of octahedral and tetrahedral sites influencing catalytic performance has been a topic of discussion for a long time and still under debate. Lately, this issue has been addressed by substituting redox-inert cation to the tetrahedral sites of cobalt spinels and comparing the electrochemical activity between them. However, rapid surface structural transformation of the catalysts under operating electrochemical conditions makes it difficult to infer the exact contribution of tetrahedral and octahedral sites for water oxidation. Herein, for the first time, we utilize the oxidant-driven water oxidation approach to reveal the responsible active sites using two spinel-type nanostructures, ZnIICo2IIIO4 and CoIICo2IIIO4 (Co3O4), synthesized by using a single-source precursor approach. Strikingly, a superior O2 production rate (0.98 mmolO2 molCo−1 s−1) following first-order reaction kinetics was achieved for ZnCo2O4 in the presence of CeIV as sacrificial electron acceptor compared to Co3O4 spinel (0.29 mmolO2 molCo−1 s−1). The structural and morphological stability of the ZnCo2O4 and Co3O4 post water oxidation catalysis confirms that the catalytic activity is strictly controlled by the geometry and electronic structure of the active site of the spinel structure. The higher performance of ZnCo2O4 over Co3O4 further indicates that the presence of CoII is not essential for catalytic water oxidation. The presence of redox inert ZnII at the tetrahedral site of ZnCo2O4 can facilitate the stabilization of a high-valent CoIV intermediate via oxidation of CoIII (situated at the octahedral site), and this intermediate can be regarded as the active species for water oxidation catalyst along with structural defects caused by surface Zn leaching.

Microwave assisted alkaline roasting-water leaching for the valorisation of goethite sludge from zinc refining process

Microwave (MW) alkaline roasting followed by water leaching was studied to selectively extract valuable (Zn, Pb) and hazardous (As) elements for the decontamination of the goethite sludge. During alkaline roasting stable ZnFe2O4 was decomposed to ZnO. The influence of alkali source (KOH, NaOH) and the heating source (conventional vs. microwave) were systematically investigated. Generally, ZnFe2O4 decomposed better upon increasing roasting temperatures.For the water leaching step, different liquid-to-solid ratios (L:S = 10, 3, 2) and addition of alkaline agents (KOH, NaOH) were tested to enhance Zn extraction. NaOH addition to the leaching solution (60 °C, 30 min, L:S = 10) gave the best extractions for Zn and Pb for both MW KOH roasted (84.3 ± 0.4% Zn and 38 ± 3% Pb) and MW NaOH roasted (83 ± 1% Zn and 36.3 ± 0.3% Pb extraction) materials (400 °C, 60 min). Alternatively, decreasing the L:S of water leaching to 2 gave a similar Zn extraction (83 ± 1%) and reduced alkali consumption. By increasing the set MW roasting temperature to 450 °C, Zn leachability was 87 ± 3% (NaOH roasting, water leaching L:S = 2, 60 °C, 30 min). Additionally, As removal in the studied system was 98–100%. Interestingly, roasting with KOH increased the Mn solubility as (per)manganate and decreased Zn leachability by consuming OH– for disproportionation reactions of manganate. The leachability of matrix elements Ca and Fe was negligible.

The effect of humic acid and bovine serum albumin on the adsorption and stability of ZnO nanoparticles on powdered activated carbon

Abstract Natural organic matter (NOM) can influence the properties and behavior of metal nanoparticles (MNPs) in aquatic environments. Thus, understanding the effect of NOM on MNPs’ physiochemical properties is critical for identifying an effective water treatment processes, and controlling the potential risk they pose to ecological and human health. In this study, adsorption and leaching experiments were performed with powder activated carbon (PAC), to investigate the effect of humic acid (HA) and bovine serum albumin (BSA) on the removal of ZnO nanoparticles (ZnONPs) from an aqueous environment and their stability on the adsorbed PAC. The different ZnONPs forms— particulate, colloidal, and dissolved Zn fractions, were respectively considered. The adsorption experiments demonstrated that both colloidal and dissolved Zn fractions can adsorb on the PAC’s surface. As the HA concentration increased from 0 to 20 mg/L, the colloidal Zn fraction’s adsorption efficiency decreased from 74.49% to 61.24%. However, BSA did not significantly influence the colloidal Zn fraction’s adsorption. The leaching experiments showed that the colloidal Zn fraction would release from the PAC’s surface, and most of them transferred to the dissolved Zn fraction. As the HA concentration increased from 0 to 20 mg/L, the Zn concentration leached from the PAC adsorbed ZnONPs reduced from 0.956 to 0.694 mg/g. Comparatively, the leached Zn concentration varied only slightly with an equal increase in BSA concentration.

Freezing/thawing effects on geochemical behavior of residues from acid mine drainage passive treatment systems

Passive systems are promising for the treatment of acid mine drainage (AMD) but generate metal-rich solids or residues. In subarctic climate, freezing/thawing (F/T) cycles may influence the chemical stability of waste, including residues from AMD passive treatment. The objective of this study was to assess and better understand the effect of F/T cycles on contaminants (metal and sulfates) leaching from AMD post-treatment residues. To do so, samples of residues WA50 (50 % wood ash and 50 % wood chips), PBR (30 % inorganic materials and 70 % organic substrate) and C50 (50 % calcite and 50 % wood chips) were collected from a laboratory tri-unit passive treatment system for iron-rich AMD (Fe-AMD) operated for over 1-year. To better understand the effect of freezing upon contaminant leaching, kinetic tests in weathering cells under wetting/drying (W/D) and F/T cycles were performed. Results showed that F/T cycles are likely to enhance the potential of metal leaching from post-treatment residues. The Fe leaching was 1.6-(for WA50), 3.2-(for C50) and 5.2-(for PBR) times higher under F/T cycles relative to the W/D cycles. Similarly, Zn leaching was 2.4-(for WA50), 4.9-(for PBR) and 5-(for C50) times higher under F/T cycles compared to the W/D cycles. Finally, Mn leaching was 2.4-(for WA50) and 5.2-(for PBR) times higher under F/T cycles relative to the W/D cycles but no difference in Mn concentration was observed for C50 residues. These findings suggest that during snow melt or early spring significant metal concentrations could be released while disposing AMD passive treatment residues.

Bioretention cell age and construction style influence stormwater pollutant dynamics

In urbanized landscapes, green infrastructure is proposed as a method for using relatively small plots of land to manage stormwater and protect receiving ecosystems from pollutants. Bioretention cells can infiltrate stormwater from roads and parking lots, and as stormwater passed through the soils, metals can be removed. Metal removal and storage has been demonstrated in laboratory media columns and field-scale test cells, but we have an incomplete understanding of metal removal and accumulation in aging bioretention cells in the field. We surveyed 25 bioretention cells (0–7 years of service) for soil physicochemistry to determine which characteristics related to soil metal (Cu, Pb, and Zn) concentrations. We collected soil cores and treated them with simulated stormwater to measure potential rates of metal removal under different metal and salt concentrations. Older bioretention cells had higher Cu, Pb, and Zn concentrations in soil, which indicates accumulation and storage over time. The oldest cells had metal concentrations that were not a risk to human health but which approached screening thresholds for potential impairment of plants. Soil organic matter content (OM) was positively associated with metal concentrations which highlights the importance of OM in the functioning of cells. Retrofit bioretention cells were younger with less OM and more clay than cells built concurrently with new parking lot construction (i.e., de novo), but after 2.7 years of service, soil OM was similar between retrofit and de novo builds. Soil cores from de novo bioretention cells retained more stormwater metals than soil cores from retrofit cells, and this was likely due to differences in soil OM. Elevated road salt in stormwater was associated with less effective metal removal and leaching of Zn from soils. Overall, these data suggest that management (e.g., salting) and design (e.g., construction) decisions can greatly influence metal removal function of bioretention cells.

Nano zerovalent zinc catalyzed peroxymonosulfate based advanced oxidation technologies for treatment of chlorpyrifos in aqueous solution: A semi-pilot scale study

Chlorpyrifos (CPY), an organophosphate pesticide is largely used throughout the world on different crops for the control of pests and causes severe health and environmental issues. In this study, highly efficient, crystalline, and nm-rang sized zerovalent zinc (nZVZn) catalyst was synthesized and used for removal of chlorpyrifos at semi-pilot scale. The nZVZn showed high activity and caused 55% removal of CPY at 90 min time under the conditions of [CPY] 0 = 10 mg/L, [nZVZn] 0 = 1.0 g/L, and flow rate of the reactor = 0.2 L/min. Using identical conditions of [CPY] 0 , [nZVZn] 0 and flow rate, the use of peroxymonosulfate (PMS) promoted the performance of nZVZn and caused 99.5% removal of CPY at [PMS] 0 = 40 mg/L. The electron spin resonance (ESR) spectroscopy studies revealed that nZVZn catalyzed PMS reactions yield hydroxyl and sulfate radicals that degraded CPY and removal of CPY was suppressed by applying radical scavengers. The nZVZn catalyzed PMS based removal of CPY was optimum at high [PMS] 0 , [nZVZn] 0 and low pH of solution. The flow rate of the pilot plant reactor also influenced the degradation efficiency of CPY. High pH of solution, high [CPY] 0 as well as use of alcohols, NOM, and some inorganic ions inhibited removal of CPY by nZVZn catalyzed PMS. The analysis of degradation products (DPs) of CPY were used to propose degradation pathways of CPY. The high TOC removal of CPY, low leaching of Zn 2+ from Zn 0 into aqueous solution, and toxicity reduction of CPY suggest the nZVZn catalyzed PMS process to be highly effective and environmental benign for treatment of CPY. • Nano zerovalent zinc was used for removal of chlorpyrifos at semi-pilot scale. • Removal of chlorpyrifos by zerovalent zinc was promoted by peroxymonosulfate. • Hydroxyl and sulfate radical rate constants with chlorpyrifos were calculated. • Proposed degradation pathways of chlorpyrifos were suggested. • Toxicities of treated chlorpyrifos solutions and zinc ion leaching were evaluated.

Life cycle assessment of the reuse of fly ash from biomass combustion as secondary cementitious material in cement products

In this study, we performed a life cycle assessment of the reuse of biomass fly ash as secondary cementitious material in cement mortars as alternative to a reference landfill scenario of the ash. Since biomass ash does contain enhanced levels of elements that are of potential concern for the environment or human exposure, the performed Life Cycle Assessment (LCA), in addition to CO2 savings, takes into account the impact on all non-toxic categories and human toxicity/carcinogenicity during service and second life stages. Results showed that utilization of biomass ash in cement is preferable over landfill for all the non-toxic categories at both cement replacements rates of 20 and 40 wt%. In detail, the reduction of CO2-eq. was found to be between 11 and 26% when biomass ash was blended with cement instead of being landfilled. The hydraulic activity of biomass ashes was found to be a critical parameter in this scenario, as it had impacts on the global warming potential (and all other investigated non-toxic categories), and it is therefore crucial to consider the uncertainty related to this aspect in LCA studies. Cement containing biomass ash performed better, on average, when compared with the reference landfill scenario regarding the impact to human toxicity (carcinogenic) category. Contrary, only the utilization in cement for one particular ash type (from paper sludge combustion) showed a better performance than the reference scenario for the ecotoxicity (ET) category. The impact to human toxicity carcinogenic (HTc) and ecotoxicity (ET) was mainly dominated by the leaching of Cr from landfilling of pure biomass fly ash (reference scenario) and the leaching of Ba, Cu, Cr (VI) and Zn from the second life stage of cement products (i.e., reuse of the crushed cement after service life in road base applications). However, this impact was acceptable when emissions are compared to existing EU landfill directive and regulations on the reuse of secondary materials in construction works. The novel LCA approach performed in this study, which includes impacts of leached contaminants during both the service and second life phase of cement, has shown that the reuse of biomass ash as secondary cementitious materials has a beneficial effect on the majority of the impact categories, with no unacceptable leaching risks.

Novel process for decontamination and additional valorization of steel making dust processing using two-step correlative leaching

Recycling of steel making dusts often targets Zn removal. Other heavy metals such as Mo, W or Cr do not receive as much attention, and the decontamination of the dusts from these constituents is scarcely addressed in the literature. This study presents a novel approach of the selective separation of Mo from steel making dusts using alkaline solutions with low concentrations, before Zn removal using concentrated alkaline medium. Such an approach has never been reported before and can contribute to more efficient decontamination of the steel making dusts and will increase the value of recovered components since Mo can be significantly preconcentrated. Two samples originating from two steel producers were investigated. One sample contained 2.65% of Mo and 1.87% of Zn, and the second sample had 0.61% of Mo and 35.9% of Zn. Temperature was found to have a low impact on the leaching efficiency of Mo, while increased NaOH concentration promoted leaching of Zn. Excellent pre-concentration of Mo was achieved by using a S:L ratio of 1:3. Almost 5170 mg/L Mo, 1000 mg/L W, no Fe and only 2 mg/L Zn were present in the solution after leaching at 30 °C for 30 min. For the samples containing lower concentrations of Mo and high concentrations of Zn, the selectivity of the process was affected when using higher concentrations of NaOH. A final leachate containing 797 mg/L of Mo and only 11 mg/L Zn was obtained after leaching with 0.05 M NaOH. DFT computations showed that the 2D layered structures of MoO3 and WO3 are decisive factors that account for their high solubilites.

Zero-waste approach in municipal solid waste incineration: Reuse of bottom ash to stabilize fly ash

Abstract In this paper a simple method for all waste recovery through municipal solid waste incineration (MSWI) is presented. For the first time, MSWI fly ash (FA) is treated using MSWI bottom ash (BA), which is considered as a new urban mining source due to its pozzolanic characteristics. The proposed technology involves mixing these ashes with two other components: flue gas desulphurization residue and coal fly ash. Thermal annealing at a low temperature (120 °C for 4 h) can also be performed, to accelerate some reactions, but it is not necessary for stabilization. The efficacy of the process is demonstrated by the comparison of elemental concentrations in leaching solutions that are detected in the untreated ashes and the obtained stabilized materials, which show the reduced solubility of leachable Zn and Pb (with respect to the starting MSWI FA). The chemical, morphological, and structural characterization of the obtained materials makes it possible to propose and discuss a stabilization mechanism, which was attributed to carbonation and formation of calcium silicate hydrate (C–S–H). In particular, for the stabilized sample, X-ray Diffraction analysis confirmed the formation of calcite, whereas the sample morphology shows some fibrils that may be due to amorphous C–S–H with a Ca/Si ratio that is slightly smaller than 1.5. Because the proposed method employs wastes produced at the same location, it is reasonable to conclude that the method may be directly applied to incinerator plants due to the simplification of the MSWI FA waste management strategy, which generally involves its transport and stabilization treatment before landfilling. Finally the saved carbon dioxide emissions and the economic benefits that are a result of the new urban mining proposed approach have been evaluated for Europe. In particular the avoid of MSWI FA landfilling was evaluated to save approximately 1.6 M€/day, and the saved carbon dioxide emissions introduced into the atmosphere is approximately 960 kt/year.

Synergistic immobilization of potentially toxic elements (PTEs) by biochar and nanoparticles in alkaline soil

Biochar and nanoparticle (NP) have the ability to sorb potentially toxic elements (PTEs) from soil and reduce toxicity and leaching into water bodies. However, there is need to tailor biochar formulations to soil types. In this study, we investigate the mobility and chemical forms of Cd, Cr, Cu, Ni, and Zn in a spiked, alkaline soil after amendment with combination of NPs (nano-Fe (NF), nano-clay (NC)) and biochars (almond shell 500 °C, walnut shell 400 °C) in different doses (0, 2.5, 5, and 10%). Many previous studies concluded biochar immobilized PTEs due to an increase in soil pH, which can be disregarded here (soil pH 7.9). In a twenty-week column leaching experiment biochar addition significantly decreased PTE leaching and NP addition further immobilized PTEs in most cases. On average almond biochar more effectively reduced Zn leaching and walnut biochar was more effective in decreasing the leaching of Cd, Cr, and Ni (e.g. 5% biochar reduced Cr leaching by 68%). Copper was immobilized effectively by both biochars. Nano-clay combined with walnut biochar performed best in all treatments, in particular for Cd, Ni, and Zn (e.g. 10% walnut biochar only and in combination with NC reduced Zn leaching by 14.2% and 58.5%, respectively). After amendment, PTEs were present in the Fe-Mn oxides, organic and residual fractions and less in the exchangeable fraction, reducing PTE availability and leachability. The results demonstrate that even for cationic PTEs that behave similarly in the environment optimal biochar-mineral formulations can differ.

Long-term leaching of As, Cd, Mo, Pb, and Zn from coal fly ash in column test.

Globally, millions of tons of coal fly ash (CFA) are generated per year, and the majority of this material is usually stored in stock piles or landfills, and in a long-term, it can be an environmental hazard if rainwater infiltrates the ashes. Long-term leaching studies of Brazilian ashes are scarce. The purpose of this study was to evaluate arsenic, cadmium, molybdenum, lead, and zinc leaching behavior from a Brazilian CFA by a column experiment designed to simulate field conditions: slightly acid rain considering seasonality of precipitation and temperature for a long-term leaching period (336 days). All elements were leached from CFA, except lead. Elements leaching behavior was influenced by leaching time, leaching volume, and temperature. Higher leachability of As and Cd from CFA during warm and wet season was observed. Results indicate a potential risk to soil and groundwater, since ashes are usually stored in uncovered fields on power plants vicinity.

The effect of temperature on the leaching of Cr, Cu, Fe, Ni and Zn from tailings, Ballangen deposit, Norway

The effect of temperature on the leaching of Cr, Cu, Fe, Ni and Zn from tailings, Ballangen deposit, Norway

Simultaneous Immobilization of Zn(II) and Cr(III) in Spinel Crystals from Beneficial Utilization of Waste Brownfield-Site Soils

AbstractWaste brownfield-site soils contaminated with heavy metals such as Zn and Cr are of critical environmental concern because of the rapid urbanization and industrialization that is occurring in China. Thermal treatment can fix heavy metals in specific mineral structures, which might be a promising technology for remediation and reutilization of the metal-contaminated soils. The objective of the present study was to elucidate the stabilization mechanisms of Zn and Cr through thermal treatment of mixtures of ZnO + Cr2O3 to form ZnCr2O4 and to confirm that Zn and Cr were incorporated simultaneously into the spinel structure. The incorporation efficiency for Zn was quantified, with the value ranging from 70.6 to 100% over the temperature range 700–1300°C. Leaching results further confirmed that ZnCr2O4 spinel was a superior product for Zn and Cr immobilization. Then, by artificially sintering Zn- and Cr-enriched soils, both Zn and Cr were immobilized effectively (with three orders of magnitude reduction in Zn leachability) in the ZnCr2O4 spinel as the predominant product phase. In addition, multiple heavy metals such as Zn, Cu, and Cr in the actual brownfield-site soils were well immobilized after sintering, which confirmed the potential for practical application of the thermal treatment technology utilized in this study.

Insights into the speciation of heavy metals during pyrolysis of industrial sludge.

The purpose of this study was to determine the mechanisms in heavy metals immobilisation during pyrolysis of industrial sludge (IS). Pyrolysis was conducted in a fixed-bed unit at the temperature range between 400 and 800°C. Conventional and advanced analytical techniques were employed to assess the influencing parameters on the transformation of heavy metals during pyrolysis process. The examined heavy metals (i.e. Mn, Ni, Cu, Zn, Cd, and Pb) were effectively immobilised in the char derived at ≤600°C. In contrast, for the char derived at ≥700°C, Mn, Cu, and Zn leaching efficiencies were significantly increased. According to BCR sequential extraction procedure (SEP) results, pyrolysis of IS conducted at ≤600°C transformed heavy metals into stable fractions (i.e. associated with Fe-Mn nodules, and organics and sulphides), while Mn, Cu, and Zn bound in these fractions decomposed into easily soluble forms at higher temperatures. Advanced analytical characterisation (XRD, EDX, XPS, and FTIR) of the derived char and anion concentrations in the leachate have demonstrated that the increase in metal leaching was probably due to the formation of metal halides.

Pilot-scale field investigation of ex situ solidification/stabilization of soils with inorganic contaminants using two novel binders

Recently, two novel binders, one by-product-based binder named as GM and one phosphate-based binder named as KMP, have emerged that can stabilize soils spiked with mixed lead and zinc contaminants. However, field evaluations of the stabilization of actual soils that contaminated with mixed zinc (Zn) and inorganic chloride (Cl−) using GM and KMP have not been performed yet. This study presents a pilot-scale field test to evaluate the performance of GM and KMP to stabilize these inorganic contaminants in soils at two locations in an abandoned industrial plating plant site. The field soils were stabilized and cured for 1, 3, 7, and 28 days and tested for dry density, dynamic cone penetration, soil pH, and leachability. Laboratory unconfined compression tests were performed, and the relationship between unconfined compressive strength and dynamic cone penetrometer index was assessed. The results showed that the strength of both the GM- and KMP-stabilized soils after 28-day curing improved significantly, and the leached Zn and Cl− concentrations were well below the corresponding remediation limits. In general, the KMP-stabilized soil demonstrated superior performance in terms of higher dry density, unconfined compressive strength, average dynamic cone penetration resistance, lower dynamic cone penetrometer index in the early curing stage (7 days), and lower leached Zn concentration under all curing times. In contrast, the GM exhibited superior immobilization of Cl− in the contaminated soil irrespective of the curing time. The results demonstrate that GM and KMP are promising binders for treating Zn- and Cl−-contaminated soils at plating and other industry sites with similar contaminants.

The Impact of Physical Properties on the Leaching of Potentially Toxic Elements from Antimony Ore Processing Wastes.

This study reports on the assessment of the impact of antimony mine wastes from Xikuangshan (XKS) Antimony Mine in Lengshuijiang City, Hunan Province. We focus on the leaching of a number of potentially toxic elements (PTEs) from residues from the processing of antimony ore. The PTE content of ore processing waste and solutions generated by leaching experiments were determined for a suite of PTEs associated with the ore mineralization. These were Sb, As, Hg, Pb, Cd and Zn. As anticipated, high concentrations of the PTEs were identified in the waste materials, far exceeding the standard background values for soil in Hunan Province. For Sb and As, values reached >1800 mg·kg−1 and >1200 mg·kg−1, respectively (>600 and >90 times higher than the soil background). The leaching of Sb, As, Hg, Pb, Cd and Zn decreased with an increase in grain size and leachable portions of metal ranged between 0.01% to 1.56% of total PTE content. Leaching tests identified the release of PTEs through three stages: a. alkaline mineral dissolution and H+ exchanging with base cation; b. oxidation and acid production from pyrite and other reducing minerals; and c. the adsorption and precipitation of PTEs.