Leaching Of Zn Research Articles

Dynamic leaching behaviors of heavy metals from recycled coal gangue aggregate under loading conditions during solid backfill mining

In solid backfill coal mining, recycled coal gangue aggregate (RCGA) is subject to the combined effects of overlying strata stress and leaching by mine water in the goaf. This process causes heavy metals to be leached and released from RCGA, which can lead to groundwater contamination. In this study, the release patterns of heavy metals in RCGA under the coupled effects of stress, solution pH, and solution flow rate were investigated, and the interactions between RCGA and the surrounding environment were explored. The findings indicate that: (1) The combined action of effective stress and mine water promotes the leaching of heavy metals. Specifically, the leaching of Pb, Zn, and Mn of RCGA is primarily influenced by the pH value of the leaching solution, while the leaching of Cu and Cr of RCGA is more closely related to the stress level; (2) Acidic environments accelerate the release of carbonate-bound fraction (CAR) in elements, facilitating the transformation of Fe/Mn oxide-bound fraction (XXI) into soluble forms; (3) The leaching ratios (Lr) of heavy metals follow the order: LrZn > LrPb > LrMn > LrCu > LrCr. This research provides guidance for the safe application of RCGA in solid backfill coal mining.

Stabilization of Pb/Zn mine tailings by modified fly ash: characterization, performance, and mechanism.

The presence of heavy metals in mine tailings poses a serious threat to the surrounding environment. In this study, we aimed to stabilize Pb/Zn-containing mine tailings using modified fly ash (FA) with various alkali solutions. Notably, the modification of FA with Na2SiO3 (NaSi-FA) resulted in the most significant structure changes. To understand the adsorption mechanism of Pb and Zn by modified FA, batch adsorption experiments were conducted. Doubling the adsorption capacity for both Pb and Zn was observed in the modified FA samples compared to unmodified samples. These results could be attributed to the enhanced surface area and porous structure, providing more anchor sites for the heavy metal ions. Additionally, the adsorption of Pb and Zn was found to follow the Langmuir isotherm and pseudo-second order kinetic. Molecular dynamics simulations further supported the notion that Pb and Zn ions could effectively exchange with Na ions within the N-A-S-H gel network, ultimately solidifying them in its structure. Stabilizing Pb/Zn tailings with NaSi-FA resulted in a significant decrease in the leaching of Pb and Zn. Specifically, the leading amount decreased by 55.2% for Pb and 35.3% for Zn, showcasing the superior performance of this stabilization method. This reduction in leaching indicates effective compliance with environmental regulations regarding the containment of Pb and Zn.

Copper leaching behaviour during oxygen pressure leaching of zinc sulfide concentrate

ABSTRACT To optimise copper (Cu) leaching, this study investigated Cu behaviour during a two-stage oxygen pressure leaching process of zinc sulfide concentrate (ZnS). The results indicated that maintaining low temperature, low sulfuric acid (H2SO4) concentration, and low oxygen partial pressure during the first stage of leaching the reduction of ferric iron (Fe3+) by ZnS and the weak leaching of Cu. In the second stage, increasing the temperature, H2SO4 concentration, and oxygen partial pressure enabled efficient Cu leaching while converting iron (Fe) back to Fe3+ and returning it to the first stage. This two-stage process effectively mitigated Fe hydrolysis precipitation, resulting in a small residue yield and preventing Cu incorporation into jarosite. Cyclic validation experiments were conducted under optimum experimental conditions with a residue yield of 36.1%, the dissolution rates of Zn, Cu, and Fe impurity of 98.76%, 91.65%, and 81.05%, and the Zn, Cu, and silver (Ag) contents of leaching residue were 1.61%, 0.17%, and 0.524%, respectively. The primary phases in the leach residue included lead (Pb) sulfate, sulfur, and pyrite. This approach allowed for deep leaching of Zn and Cu as well as achieving efficient Pb and Ag enrichment.

Leaching behavior of Cu, Zn, Fe and Pb from polymetallic tailings

ABSTRACT Copper tailings are a common byproduct of copper production, containing high levels of heavy metals which are released into the environment. Conventional methods have historically prioritized copper recovery, and often overlooking the leaching of other valuable elements. However, the rising demand for nonferrous metals necessitates understanding their leaching behavior from copper tailings. This study examined the atmospheric leaching of Cu, Fe, Pb, Zn, and CuO from a polymetallic tailing ore. Leaching recoveries of 63.5% for Cu, 97.5% for CuO, 1% for Fe, and 100% for Zn were achieved under the optimum conditions of 0.5 M sulfuric acid concentration, 25% solids percentage, 65°C, stirring speed of 100rpm, particle size of 75 µm within 30 minutes. Results indicated that the dissolution of oxide minerals such as CuO and ZnO was significant; however, copper sulfides need oxidant to be dissolved. In this condition, iron oxides and silicates were partially reacted by sulfuric acid, and Pb-bearing minerals formed lead sulfate. The presence of iron and lead-bearing minerals in the leaching residue was confirmed by XRF, XRD, and SEM analyses, and was in agreement with the information displayed in the Eh-pH diagrams.

Recycling Process of Spent Alkaline and Zn-C Batteries for the Re-Utilization in Rechargeable Zn-Ion Battery

The Zn, Mn and C extraction processes from spent primary batteries and the synthesis of recycled Zn film, MnO2 and MnO2/C for Zn-ion battery application were developed in the project. The Zn, Mn and C extraction process involved the acid leaching of Zn and Mn ions from the spent alkaline and Zn-C battery electrodes in the lab-scale was initially investigated using various leaching conditions. The acid leaching using 0.5-2 M HCl and H2SO4 at ambient temperature providing Zn extraction efficiencies in a range of 72.3-95.3%. By introducing an inexpensive reducing agent namely sodium sulfide (Na2S), sodium metabisulfite (Na2S2O5) or hydrogen peroxide (H2O2) in 2M H2SO4, the Mn extraction efficiency for Mn was increased from 21.9% (with no reducing agent) up to 48.4%, 82.8% and 98.9%, respectively. The upscale leaching study was subsequently performed in a 100-L pilot scale reactor demonstrated the Zn and Mn extraction efficiencies of 71% and 65%, respectively. Using the leaching solutions from the upscale hydrometallurgical route, Zn-film fabrication via electrodeposition process, and the MnO2 and MnO2/C synthesis via hydrothermal techniques were performed. Additionally, the one-step synthesis of MnO2/C via one-step hydrothermal method with no acid leaching was also explored in this study. The recycled Zn, MnO2, MnO2/C and C residual were subsequently used as the anode and cathode main components in the CR2032 and pouch-cell rechargeable Zn-ion batteries. The recycled MnO2 and MnO2/C provided similar performance as the commercial products, which indicating the recycled MnO2, MnO2/C could be effectively utilized in the Zn-ion battery, while the utilization of recycled Zn-film provided slightly lower performance compared to that of the commercial Zn foil.

Fractionation and leaching of Cd, Cu, Fe, Pb, and Zn from smelter residues of an old environmental liability in Argentina

An integrated chemical and mineralogical characterization approach was applied to smelter wastes collected from 50-year-old dump sites in Argentina. Characterization included pseudo-total element concentrations, acid generation/neutralization potential, sequential extractions, pH-dependent leaching kinetics, and mineralogical analysis of all residues. These analyses provided detailed information on the reactivity of the minerals in the waste material and associated metal release. Cadmium and Zn were the elements of greatest environmental concern due to their high mobility. On average, the release of Zn and Cd in pH-dependent leaching essays reached 17.6% (up to 5.24 mg g−1) and 52.7% (up to 0.02 mg g−1) of the pseudo-total content, respectively. Moreover, Cd and Zn were also the metals that showed the higher proportions of labile fractions associated to the adsorbed and exchangeable fraction (60–92% for Cd and 19–38% for Zn). Since Cd and Zn concentrations in the residue are not high enough to form their own minerals, a large proportion of these elements would be weakly adsorbed on Fe oxyhydroxides. In contrast, the low release of Cu, Pb and Fe would be associated with these elements being incorporated into the crystalline structure of insoluble or very poorly soluble minerals. Lead is incorporated into plumbojarosite and anglesite. Copper was mainly in association with Fe oxyhydroxides and may also have been incorporated into the plumbojarosite structure. The latter could act as a sink especially for Pb under the acidic conditions of the smelter residue. Despite the elevated concentrations of Pb observed in the residue, it showed a very low mobility (≈0.1%), indicating that it is mostly stabilized. Nevertheless, the smelter residue is a continuous source of metals requiring remediation.

Heavy metal removal by porous asphalt in cyclical wetting and drying

Porous asphalt pavement (PAP) is subjected to wetting and drying cycles involving storms of varying intensity and inter-event drying periods to study the impact of continuous weather systems on heavy metal removal in runoff. Four physical models: a complete PAP system, a PAP surface, a geotextile fabric and a reservoir of cobblestone aggregate, were created at the lab-scale and tested with stormwater contaminated with dissolved Mn(Ⅱ), Zn(Ⅱ), Cu(Ⅱ), and Cr(Ⅵ). The models were exposed to repeated wetting and drying cycles spanning over 27 days in triplicate. Wetting involved light, moderate and heavy rainfall intensities. All pavement material designs performed well at removing Cu(Ⅱ) and Cr(Ⅵ). The PAP system had an overall better performance at removing Mn(Ⅱ), Zn(Ⅱ), Cu(Ⅱ), and Cr(Ⅵ) than any of the individual pavement materials but was unable to remove all of the heavy metals simultaneously to sufficiently high levels. The materials used in the filter layer and reservoir structure and their adsorption and desorption capacities should be assessed for potential contamination (leaching) of Zn(Ⅱ) and Mn(Ⅱ), respectively, prior to construction. Wetting and drying cycles had the greatest impacts on the reservoir structure’s performance versus any of the other layers. Leaching of Mn(II) observed from cobblestone aggregate was affected by the solution composition and pH. Removal of selected heavy metals was rapid in first flush and fluctuated with storm event intensity.

Environmental Behaviour of Synthesized and Commercial Agricultural Zinc Products: Leaching, Migration, and Availability in Soils

The aim of this paper is to examine the environmental effect of different chemical characteristics of Zinc (Zn) sources, assessing the transport, leaching and accumulation in the environment in sand, acidic (AS) and calcareous (CS) soils. Comparative short- and long-term studies applying ZnO sources [bulk, laboratory-synthesized and commercial nanoparticles (NP)], ZnSO4, complexed Zn (Zn-lignosulfonate) and chelated Zn (Zn-diethylenetriamine-pentaacetate, Zn-hydroxy-ethylenediamine-tetraacetate and Zn-ethylenediamine-tetraacetate) were carried out. For all treatments and media, the medium- and long-term dissolution kinetic model was fitted to a logistic function. The applied Zn in the form of ZnO was mainly retained at the upper half (0–7.5 cm) of the columns and in very available form (ranging 40–61% of added Zn in AS and 29–31% in CS). Leached Zn reached values below 6% in AS and 3% in CS. The use of chelated Zn in both soils and complexed Zn, and ZnSO4 in AS resulted in excessive leaching of Zn (around 70%). The amount of Zn available at the upper half of the column was less than 5%. In the CS, these fertilizers showed a higher aging than ZnO sources, negatively affecting its availability as a nutrient for crops. ZnO NP showed short- and medium-term dissolution kinetics that allow gradual nutrient release and high availability at the medium-term. These products provide an effective solution for plant nutrition while mitigating the environmental problems observed with more traditional sources related to leaching.Graphical

Assessing viability and leachability in fly ash geopolymers incorporated with rubber sludge

This study explores the innovative use of rubber sludge (RS) from glove manufacturing as a partial replacement for fly ash (FA) in geopolymer production. The research investigates the physical properties, functional group analysis, microstructural analysis, phase analysis and compressive strength. The partial replacement of different types of RS, such as activated sludge (AS), pre-leaching sludge (PLS) and coagulant sludge (CS), will affect differently on the geopolymer integrity and performance. CS enriched with high calcium content, facilitated the formation of a denser geopolymer matrix with C(N)-A-S-H gel in conjunction with C-S-H, C-A-S-H and N-A-S-H gels, enhancing the compressive strength of FA/CS geopolymers up to 70.4 MPa, surpassing FA/AS and FA/PLS geopolymers. The fly ash/rubber sludge geopolymers exhibited compressive strengths ranging from 20.5 to 70.4 MPa, not only meeting ASTM standards for construction but also effectively immobilizing hazardous metals, particularly Zn (>98.4 %), the Zn leaching in geopolymers was reduced by more than 87.4 % compared to the rubber sludge itself, thereby mitigating environmental toxicity. This utilization addresses significant industrial waste management issues, providing a cost-effective and environmentally friendly alternative for construction. The findings contribute to advancing sustainable building materials and advocate for equitable utilization of industrial waste resources.

Radiation Techniques for Tracking the Progress of the Hydrometallurgical Leaching Process: A Case Study of Mn and Zn

With advancements in hardware and software, non-destructive radiometric analytical methods have become popular in a wide range of applications. A typical case is the study of the leaching process of metals from mineral ores and mine tailings. The objective of the current study was to develop a radiometric method based on neutron activation analysis (NAA), in particular, delayed gamma neutron activation analysis (DGNAA), to monitor the process of Mn and Zn leaching from Ti ore, Cu mine tailings, and Zn-Pb mine tailings. The DGNAA method was performed using a neutron source: a deuterium-tritium (D-T) neutron generator for Mn and a MARIA research nuclear reactor for Zn. Laboratory-scale Mn leaching from Ti ores, Cu tailings, and Zn-Pb tailings was investigated using delayed gamma-rays of 56Mn (half-life of 2.6 h). The dissolution efficiencies of Mn were found to increase with interaction time and HCl concentration (1 to 5 M) and to vary with the leaching temperature (22.5 to 110 °C). Such results were found to agree with those obtained by total reflection X-ray fluorescence (TXRF) spectrometry for the same samples. 65Zn (half-life of 244 days) was chosen to investigate real-time/online leaching of Zn in Ti ore, Cu tailings, and Zn-Pb tailings. During online monitoring, Zn recovery was also reported to increase with increased leaching time. After approximately 300 min of leaching, 80%, 79%, and 53% recovery of Zn in Zn-Pb tailings, Ti ore, and Cu tailings, respectively, were reported. Theoretically, developed mathematical prediction models for 65Zn radiotracer analysis showed that the spherical diffusion model requires much less time to attain saturation compared to the linear diffusion model. The results of NAA for Zn were compared with those obtained by handheld X-ray fluorescence (handheld-XRF) and TXRF analysis. The analyzed samples encompassed leached Ti ore, Cu tailings, and Zn-Pb tailings which were subjected to different conditions of leaching time, temperature, and HCl concentrations. The XRF analysis confirmed that the leaching efficiencies of Zn rise with the increase in leaching time and HCl concentration and fluctuate with leaching temperature. The developed approach is important and can be applied in laboratories and industrial setups for online monitoring of the recovery of any element whose isotopes can be activated using neutrons. The efficiency of the metal-recovery process has a direct impact on the normal operation and economic advantages of hydrometallurgy.

Photocatalytic Removal of the Endocrine Disruptor Chlorpyrifos using a ZnO.MoO3 Composite Supported on Al2O3

AbstractChlorpyrifos is an endocrine disruptor pesticide that induces breast cancer cell proliferation through Estrogen receptor alpha pathway in humans. It also has toxic effects on some beneficial insects like bees, wasps, and arthropods, even low levels of CP can kill fish in water. Thus, it is important to efficiently remove this compound from wastewaters to get rid of its hazardous effects. Al2O3 supported ZnO.MoO3 composite was prepared as an efficient material for photo‐degradation of chlorpyrifos under UV irradiation and characterized by SEM‐EDX, XRD and TG techniques. The XRD analysis showed the orthorhombic structures with band gap of 2.86 eV for ZnO.MoO3/Al2O3 which was 2.96 eV for MoO3/Al2O3. The kinetics of degradation depicted that ZnO.MoO3/Al2O3 afforded a complete degradation of chlorpyrifos with half life of only 3 minutes which otherwise was 24 minutes in the presence of MoO3/Al2O3. The complete mineralization of chlorpyrifos was confirmed by GC/MS analysis, where no peaks of intermediates were recorded. The prepared material also exhibited good recyclability without any leaching of Zn and Mo metals. Thus, ZnO.MoO3/Al2O3 is an efficient and cost effective material for removal of chlorpyrifos. Its potential may also be explored for the removal of other hazardous organic pollutants.

Cation-induced formation of highly active γ -NiFeOOH for efficient oxygen evolution reaction

The oxygen evolution reaction (OER) activity of Ni-based oxyhydroxides greatly hinges on their phase structures, which are mainly γ and β phases: the former has higher intrinsic activity than the latter. However, it is still a grand challenge to purposefully generate γ phase, rather than β phase. Here, we propose a cation-doping strategy to generate γ phase by taking Zn-doped NiFeP/N-doped C (Z-NFP/N-C) precatalyst as a model. In contrast to the case of NFP/N-C that can only be reconstructed into β-NiFeOOH, Zn dopant will induce the formation of γ-NiFeOOH during an electrochemical process. Specifically, the doped Zn cation will promote the dissolution of NiFeP and redeposition of NiFeOOH on the surface. Simultaneously, the cation defects generated by Zn leaching will force the surrounding Ni valence state to rise for charge balance and will attract more K+ in the solution to intercalate into the interlayer of NiFeOOH, resulting in the formation of γ-NiFeOOH. As a result, the γ-NiFeOOH/Z-NFP/N-C exhibits superior OER performance: a low overpotential of 216 mV at 10 mA cm−2 and satisfactory stability (100 h at 17 mA cm−2). Our study offers a practical approach to produce highly active “true catalyst” for efficient water splitting.

Roles of the SOM and clay minerals in alleviating the leaching of Pb, Zn, and Cd from the Pb/Zn smelter soil: Multi-surface model and DFT study

Soil organic matter (SOM) and clay minerals are important sinks for reactive heavy metals (HMs) and exogenous hydrogen ions (H+). Therefore, HMs are likely to be released into soil porewater under acid rainfall conditions due to the competitive adsorption of H+. However, negligible Lead, Zinc, and Cadmium (<6 ‰) in the Pb/Zn smelter soil were leached, and the effects of SOM and clay minerals on HMs leaching were unclear. Herein, the H+ consumption and HMs redistribution on SOM and clay minerals were quantitated by the multi-surface model and density functional theory calculations to reveal the roles of SOM and clay minerals in alleviating HMs' leaching. Clay minerals consumed 43.2 %–52.0 % of the exogenous H+, serving as the dominant sink for the exogenous H+ due to its high content and hindering H+ competitive adsorption on SOM. Protonation of the functional groups constituted >90 % of the total H+ captured by clay minerals. Meanwhile, some H+ also competed with HMs for adsorption sites on clay minerals due to its 0.497-fold to 1.54-fold higher binding energies than HMs, resulting in the release of HMs. On the contrary, SOM served as an accommodator for taking over the released HMs from clay minerals. The HMs complexation on the low-affinity sites (R-L−) of SOM was responsible for the recapture of HMs. In Ca-enriched soil, the released HMs were also recaptured by SOM via ion exchange on the R-L-Ca+ and the high-affinity sites (R-H-Ca+) sites due to the 30.8 %–178 % higher binding energies of HMs on these sites than those of Ca. As a result, >63.4 % of the released HMs from clay minerals were transferred to the SOM. Thus, the synergy of SOM and clay minerals in alleviating the leaching of HMs in Pb/Zn smelter soils cannot be ignored in risk assessment and soil remediation.

Advances in the Sustainable Production of Fertilizers from Spent Zinc-Based Batteries

Wastes from spent batteries are a secondary source of raw materials. To ensure this, it is mandatory to design sustainable and low-cost processes. In the case of alkaline and zinc–carbon-based batteries, the high content of Zn and Mn makes them of interest in the development of fertilizers. The main objective of this research is to study the fertilizers production from spent zinc-based batteries, using sulfuric acid, citric acid (CIT) and glycine (GLY) solutions as leaching agents. Leaching with glycine at alkaline pHs shows a high selectivity of Zn over Mn, whereas the use of citric and sulfuric solutions leads to recoveries of Zn and Mn. Solutions with the highest Zn recoveries were tested in sand columns. Commercial ZnSO4 heptahydrate was used as a control. For sulfuric acid, two solutions (H2SO4 2M and 0.25M) were used. The elution of leached Zn and Mn in sand columns depended on the solution added. The Zn-Mn-CIT treatment showed a slight but steady increase in the leachates, reaching 70% and 75% of the total leached Zn and Mn, respectively, in the medium term. The Zn-Mn-H2SO4 2M and ZnSO4 treatments showed a similar behavior in Zn release. Both Zn-Mn-GLY and Zn-Mn-H2SO4 0.25M treatments showed similar amounts of leached Mn in the medium term (77% of total leached Mn), differing in the leached Zn. Solutions from the leaching of spent black mass batteries, especially Zn-Mn-CIT or Zn-Mn-GLY, showed promising behavior as fertilizer from the point of view of Zn and Mn availability as nutrients.

Heavy metal leaching from wood ash before and after hydration and carbonation

AbstractWood ashes can be used, e.g., as soil fertilizer or in construction materials; however, it is important to ensure that such use will not cause spreading of heavy metals and subsequent harm to the environment. Wood fly ashes (WFAs) generally have higher concentrations of heavy metals than wood bottom ashes. This paper focuses on the leaching of heavy metals from WFA, specifically identifying WFA characteristics that influence the leaching and changes in leaching caused by hydration and carbonation in ambient air. Chemometric modeling based on characteristics for eight different WFAs suggested that the leaching of Cr and Zn was associated with the concentration of K and the leaching of SO42−, indicating a connection to the soluble K2(SO4) commonly found in WFAs. During the aging, both pH and conductivity of the WFAs decreased showing the formation of new phases. The leaching of Cd, Cu, Ni, and Pb was low initially and decreased to non-measurable after the aging. So did the leaching of Zn except from one of the WFAs. Thus, the part of the heavy metals, which were leaching originally, was built into the newly formed phases. The Cr leaching also showed a general decrease during the aging, however, not to similarly low levels. This means that the leaching Cr fraction was either not influenced by the aging processes or the formed phases contained water-soluble Cr. The continued leaching of Cr needs more attention as it may be the toxic and carcinogenic Cr(IV). As the chemistry and mineralogy of WFAs, inclusive of the mobility of the heavy metals, are subject to changes, increased knowledge on the chemistry determining these changes is needed to choose environmentally sound recycling options.

Kinetics of zinc leaching from intermediate feedstocks

The aim of the work was to study the leaching kinetics of zinc from the compound CaO. ZnO, formed during the sintering of dust from electric arc furnaces with limestone, as well as to identify the mechanisms by means which such chemical interactions occur. The object of the study was the dust sinter of electric arc furnaces with limestone obtained at the Chelyabinsk Zinc Plant. It was found that zinc is contained in sinter in the form of readily soluble CaO. ZnO. The elemental composition of the initial dusts and sinter was determined by the spectral atomic emission method using inductively coupled plasma on a Spectroblue optical emission device and spark spectrometry. The phase composition of the materials was studied on a Bruker D8 Advance X-ray diffractometer. The initial sinter was milled to apowder state having a particle size of ~0.04 mm and with a yield of ~97% of the composition, %: 11.9 Zn; 28.5 Ca; 16.6 Fe; 0.38 Mg; 0.14 Pb; 0.05 Cl. Experiments on the leaching of Zn with NaOH solution were carried out at the following parameters: the initial concentration of zinc in the pulp was 0.202 g-ion/dm3 ; alkali concentration – 5‒9 mol/dm3 NaOH; L:S = 9:1; pulp mixing rate – 10‒20 rad. c-1; temperature – 333‒363 K; duration – 0.5–2.5 hours. It has been shown that zinc from sinter passes into solution as sodium tetrahydroxozincate Na2[Zn(OH)4], while calcium remains in the cake, mainly as insoluble Ca(OH)2, which reacts with carbon dioxide to form insoluble calcium carbonate CaCO3. The process of dissolving zinc from the sinter corresponds to the external diffusion mode of mutual transfer of the initial reagents and reaction products through the surface layer of the liquid at the interface of the “liquid–solid” phases with an activation energy value equal to 12.44 kJ/mol. Thus, with the studied parameters of zinc leaching with NaOH solution, the process proceeds in an external diffusion mode. The results are of interest when identifying conditions corresponding to the intradiffusion and kinetic modes of zinc leaching.

Nano zerovalent Fe did not reduce metal(loid) leaching and ecotoxicity further than conventional Fe grit in contrasting smelter impacted soils: A 1-year field study

The majority of the studies on nanoscale zero-valent iron (nZVI) are conducted at a laboratory-scale, while field-scale evidence is scarce. The objective of this study was to compare the metal(loid) immobilization efficiency of selected Fe-based materials under field conditions for a period of one year. Two contrasting metal(loid) (As, Cd, Pb, Zn) enriched soils from a smelter-contaminated area were amended with sulfidized nZVI (S-nZVI) solely or combined with thermally stabilized sewage sludge and compared to amendment with microscale iron grit. In the soil with higher pH (7.5) and organic matter content (TOC = 12.7 %), the application of amendments resulted in a moderate increase in pH and reduced As, Cd, Pb, and Zn leaching after 1-year, with S-nZVI and sludge combined being the most efficient, followed by iron grit and S-nZVI alone. However, the amendments had adverse impacts on microbial biomass quantity, S-nZVI being the least damaging. In the soil with a lower pH (6.0) and organic matter content (TOC = 2.3 %), the results were mixed; 0.01 M CaCl2 extraction data showed only S-nZVI with sludge as remaining effective in reducing extractable concentrations of metals; on the other hand, Cd and Zn concentrations were increased in the extracted soil pore water solutions, in contrast to the two conventional amendments. Despite that, S-nZVI with sludge enhanced the quantity of microbial biomass in this soil. Additional earthworm avoidance data indicated that they generally avoided soil treated with all Fe-based materials, but the presence of sludge impacted their preferences somewhat. In summary, no significant differences between S-nZVI and iron grit were observed for metal(loid) immobilization, though sludge significantly improved the performance of S-nZVI in terms of soil health indicators. Therefore, this study indicates that S-nZVI amendment of soils alone should be avoided, though further field evidence from a broader range of soils is now required.

Effect of acidic and basic leachants on the synthesis of ZnO nanoparticles from Egyptian zinc ore, their optical/surface characteristics and photocatalytic performance

It is of pivotal significance to optimize the parameters affecting the extraction of metals from natural ores to convert them to value-added products. Owing to their semiconducting nature, most metal oxides, including ZnO, have various electronic, optical, and photocatalytic applications. Hence, we are investigating the leaching of Zn from Smithsonite (an Egyptian ore) using acidic/basic leaching agents (leachants). The leached salts were employed in a co-precipitation method followed by calcination to obtain crystalline ZnO nanoparticles. Both photocatalytic performance of the ZnO nanoparticles obtained from acid leaching and basic leaching were investigated toward the photodegradation of Rhodamine B dye. The ZnO(A) prepared using the acid leaching route has achieved about 5.6-fold enhancement in the dye photodegradation% and 5.3-fold enhancement in the observed rate constant compared to ZnO(B) prepared from basic leaching. Finally, the superior photocatalytic activity of the ZnO(A) is attributed to the smaller particle size, larger surface area, and existence of some defects that enhanced the photocatalytic performance.

Comparative study of chemical speciation and leaching feature of typical heavy metals in coarse and fine slags from the entrained-flow coal gasification

ABSTRACT The dissimilarity in chemical speciation and release properties of heavy metals will result in varying levels of environmental hazards and potential applications of coal gasification coarse and fine slags. The distribution, chemical speciation, leaching features, and potential environmental risks of heavy metals (Cr, Cu, Cd, Zn, Pb, and Mn) in coarse and fine slags from different coal gasification processes were revealed and compared by the sequential chemical extraction method, Horizontal vibration method, and pH-dependent leaching experiments. The results show that Cr (516.78 mg/kg) in coarse slag, Zn (348.50 mg/kg) and Pb (214.78 mg/kg) in fine slag are highly enriched and the content exceeds the screening value, indicating the need for better management during stockpiling and landfilling. The distribution of Cr, Cu, Pb, and Mn in residual state, Zn in Fe-Mn oxide bound state, and Cd in unstable bound state is the highest in both coarse slag and fine slag. The leaching toxicity of heavy metals (HMs) does not exceed the standard, but the leachate is classified as Level V surface water or groundwater quality due to the leaching concentration of Pb exceeding 0.1 mg/L. Furthermore, leaching of Cr, Zn, Cd, and Pb in fine slag is much more dependent on pH compared to coarse slag, and the concentrations of Zn and Pb exceed emission standards at pH < 3.0. The high concentration of heavy metals caught on the surface of fine slag is more harmful to the environment. The properties of HMs in the slags and pH of the application environment must be comprehensively considered before coal gasification slag disposal, especially fine slag.

Cadmium, zinc, and copper leaching rates determined in large monolith lysimeters

Soil mass balances are used to assess the risk of trace metals that are inadvertently applied with fertilizers into agroecosystems. The accuracy of such balances is limited by leaching rates, as they are difficult to measure. Here, we used monolith lysimeters to precisely determine Cd, Cu, and Zn leaching rates in 2021 and 2022. The large lysimeters (n = 12, 1 m diameter, 1.35 m depth) included one soil type (cambisol, weakly acidic) and distinct cropping systems with three experimental replicates. Stable isotope tracers were applied to determine the direct transfer of these trace metals from the soil surface into the seepage water. The annual leaching rates ranged from 0.04 to 0.30 for Cd, 2.65 to 11.7 for Cu, and 7.27 to 39.0 g (ha a)−1 for Zn. These leaching rates were up to four times higher in the year with several heavy rain periods compared to the dry year. Monthly resolved data revealed that distinct climatic conditions in combination with crop development have a strong impact on trace metal leaching rates. In contrast, fertilization strategy (e.g., conventional vs. organic) had a minor effect on leaching rates. Trace metal leaching rates were up to 10 times smaller than fertilizer inputs and had therefore a minor impact on soil mass balances. This was further confirmed with isotope source tracing that showed that only small fractions of Cd, Cu, and Zn were directly transferred from the soil surface to the leached seepage water within two years (< 0.07 %). A comparison with models that predict Cd leaching rates in the EU suggests that the models overestimate the Cd soil output with seepage water. Hence, monolith lysimeters can help to refine leaching models and thereby also soil mass balances that are used to assess the risk of trace metals inputs with fertilizers.