Ni Release Research Articles

Comprehensive evaluation of the antibacterial and antibiofilm activities of NiTi orthodontic wires coated with silver nanoparticles and nanocomposites: an in vitro study.

Fixed orthodontic appliances act as a niche for microbial growth and colonization. Coating orthodontic wires with antimicrobial silver nanoparticles (AgNPs) and nanocomposite was adopted in this study to augment the biological activity of these wires by increasing their antibacterial and antibiofilm properties and inhibiting bacterial infections that cause white spot lesions and lead to periodontal disease. Three concentrations of biologically synthesized AgNPs were used for coating NiTi wires. The shape, size, and charge of the AgNPs were determined. Six groups of 0.016 × 0.022-inch NiTi orthodontic wires, each with six wires, were used; and coated with AgNPs and nanocomposites. The antimicrobial and antibiofilm activities of these coated wires were tested against normal flora and multidrug-resistant bacteria (Gram-positive and Gram-negative bacterial isolates). The surface topography, roughness, elemental percentile, and ion release were characterized. AgNPs and nanocomposite coated NiTi wires showed significant antimicrobial and antibiofilm activities. The chitosan-silver nanocomposite (CS-Ag) coated wires had the greatest bacterial growth inhibition against both Gram-positive and Gram-negative bacteria. The surface roughness of the coated wires was significantly reduced, impacting the surface topography and with recorded low Ni and Ag ion release rates. NiTi orthodontic wires coated with AgNPs, and nanocomposites have shown increased antimicrobial and antibiofilm activities, with decreased surface roughness, friction resistance and limited- metal ion release.

Kinetic and equilibrium analysis of penguin guano trace elements release to Antarctic seawater and snow meltwater

The present work extends the scope of prior studies through analysis, modelling and simulation of the As, Cd, Co, Cu, Fe Mn, Mo, Ni and Zn release from Gentoo (Pygoscelis papua) and Chinstrap (Pygoscelis antarcticus) penguin guano to the Southern Ocean seawater and to Antarctic snow meltwater. Laboratory experimental results have been modelled considering kinetic processes between water and guano using two element pools in the guano compartment; its application allows us to interpret behaviours and predict release concentrations of dissolved trace elements from guano which are potentially useful for incorporation as elements source into biogeochemical models applied in the Southern Ocean. Variations in quantities and release patterns depending on the type of guano and aqueous medium in contact have been identified. The release percentages from the guano to the aqueous medium, once the steady state has been reached, vary depending on the water medium and guano type in the ranges of 100–2.9 % for Mo; 91.5–68.6 % for Ni; 81.8–22.8 % As; 52.0–43.9 % Cu; 26.9–7.4 % Mn; 24.9–5.4 for Co; 4.4–3.2 % for Zn and 0.94–0.51 % for Fe. Considering a penguin population of 774,000 Gentoo and 8,000,000 Chinstrap, the estimated annual mass released to the both seawater and freshwater would be ≈18,500 kg for Cu, ≈1710 kg for Zn, ≈1944 kg for Fe, ≈1640 kg for Mn, ≈499 kg for As, ≈289 kg for Ni, ≈155 kg for Mo, ≈36.7 kg for Cd and ≈8.1 kg for Co. These contributions can be locally significant both in promoting phytoplankton growth and in their role as inhibitors of primary productivity.

All-In-One solution for simultaneous phosphonate degradation and orthophosphate recovery by NiFe-Layer double Hydroxide/PDS

Phosphate recovery presents an effective solution to address the conflicting problems of phosphorus pollution and scarcity. However, recovering organic phosphates, such as 1-hydroxyethane 1,1-diphosphonic acid (HEDP), is comparatively complex, which involves multiple processes. Herein, we developed an innovative all-in-one solution to simplify these processes by combining NiFe-layered double hydroxides (NiFe-LDH) and peroxydisulfate (PDS). This combination achieved approximately 90 % conversion of HEDP to orthophosphate, with 100 % of the resulting orthophosphate recovered in 120 min. The exceptional performance in simultaneous HEDP degradation and recovery can be attributed to dual roles of Ni and Fe in NiFe-LDH/PDS. The polyvalent Ni functions as an electron shutter (Ni2+ ⇋ Ni3+ ⇋ Ni2+) in the redox cycles between PDS and HEDP, accounting for effective HEDP degradation. The high complexation stability between Fe(Ⅲ) and orthophosphate (log K = 9.92) allows Fe(Ⅲ) to serve as binding sites for orthophosphate recovery. Moreover, NiFe-LDH/PDS effectively treats HEDP across wide pH ranges (3–––10), which can be ascribed to pH buffers originating from protonation/deprotonation in NiFe-LDH layers. The recovered phosphorus with NiFe-LDH exhibited a slow-release property under soil water solution without notable Ni release, which highlighted its potential usage as a slow-release fertilizer. These features—catalytic and binding sites, and high compatibility—allow NiFe-LDH to achieve concurrent degradation and recovery of organic phosphate in a single solution.

Sulfide mediated zero valent iron for enhanced nickel removal under neutral condition: Reaction kinetic, mechanism, and stability

The application of sodium sulfide (Na2S) as sulfidation reagent of zero valent iron (ZVI) has been well studied, however, the effect of Na2S existence on ZVI reactivity remains obscure. In this study, Ni(II) removal performance, mechanism, and stability by ZVI with Na2S were investigated at neutral condition. The results showed that Ni(II) removal sharply increased from < 5–100% by ZVI within 60 min with the increase of Na2S concentration, but the subsequent Ni(II) release occurred. In addition to the slight Ni(II) removal by Na2S in aqueous phase, Ni(II) was mainly removed by the adsorption and reduction by Na2S mediated ZVI system. Characterization analysis indicated that Na2S could lead to the severe Fe0 corrosion and the main corrosion product on ZVI was lepidocrocite, which played the dominant role for Ni(II) immobilization. Meanwhile, the formation of iron sulfides on ZVI surface would enhance Ni(II) reduction and partially transform the adsorbed Ni(II) to NiS. Moreover, the higher ionic strength could further enhance the initial Ni(II) removal rate but the stability became poor. Regardless of the additive methods, the Ni(II) removal significantly enhanced in the system of ZVI and Na2S combination. Overall, this work reveals the sulfide mediated Fe0 corrosion and provides a potential method for enhancing the reactivity of ZVI in the treatment of Ni(II) pollution.

An XPS and TEM study of the composition and structure of native oxides on the inner surface of as-received Ni base alloy steam generator tubes

Ni based alloys steam generator (SG) tubes in pressurized water reactors may suffer generalized corrosion and Ni release in primary water. The processes of corrosion and oxidation are strongly dependent on the surface properties. In particular, the chemical composition and structure of the native oxide films present at the surface of the SG tubes are crucial and improving the passive properties of the surface could contribute to reduce the corrosion damage and Ni release. The native oxides on the inner surface of two as-received Ni base alloy SG tubes were investigated using two main techniques, namely X-ray photoemission spectroscopy and transmission electron microscopy. The chemical elements present in the native film for the two tubes were identified and the structure and composition of the native film at the nanoscale was determined. A duplex oxide structure was identified for both samples, but with differences in the chemical composition of the inner and outer oxide layer. Chemical heterogeneities such as alumina, Ti oxides and Cr oxides were also detected; they are considered to play a role in the evolution of the surface exposed to primary water. The two techniques used allowed a multi-scale description of the surface and led to complementary results.

Investigation of Ion Release and Antibacterial Properties of TiN-Cu-Nanocoated Nitinol Archwires

Background: The use of nitinol (NiTi) archwires in orthodontic treatment has increased significantly due to unique mechanical properties. The greatest obstacle for safe orthodontic treatment is chemically or microbiologically induced corrosion, resulting in nickel (Ni) release. The aim of this investigation was to enhance corrosion resistance and introduce antibacterial properties to NiTi archwires by coating them with copper (Cu) doper titanium nitride (TiN-Cu). Methods: NiTi archwires were coated with TiN-Cu using cathodic arc evaporation (CAE) and direct current magnetron sputtering (DC-MS). The morphology of the sample was analyzed via field emission scanning electron microscopy (FESEM) and chemical composition was assessed using energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transformed infrared spectroscopy (FTIR). Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to estimate the ion release. The biocompatibility of samples was investigated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Antibacterial activity was tested against Streptococcus mutans and Streptococcus mitis. Results: Physicochemical characterization revealed well-designed coatings with the presence of TiN phase with incorporated Cu. TiN-Cu-nanocoated archwires showed a statistically lower Ni release (p &lt; 0.05). Relative cell viability was the highest in 28-day eluates of TiN-Cu-nanocoated archwires (p &lt; 0.05). The most remarkable decrease in Streptococcus mitis concentrations was observed in the case of TiN-Cu-coated archwires (p &lt; 0.05). Conclusion: Taking into account biocompatibility and antibacterial tests, TiN-Cu-nanocoated archwires may be considered as a good candidate for further clinical investigations.

Enhanced olivine dissolution in seawater through continuous grain collisions

Carbon dioxide removal (CDR) technologies at a gigaton scale need to be developed and implemented within the next decades to keep global warming below 1.5 °C. Coastal enhanced silicate weathering is one of the proposed CDR techniques that aims to accelerate the natural process of CO2-sequestration during marine chemical weathering of silicate minerals. To this end, finely ground rock containing olivine (MgxFe2−xSiO4) could be dispersed in dynamic coastal environments, where local biotic and abiotic factors potentially enhance the weathering process. However, accurate predictions of the olivine dissolution rate and the associated CO2 sequestration under in situ conditions are currently lacking and ecosystem impacts remain to be assessed. Previously, it has been hypothesized that in situ grain collisions, induced by bed load transport due to currents and waves, could accelerate the in situ chemical weathering of olivine particles. To examine this, we investigated the effects of continuous grain tumbling on olivine dissolution in natural seawater. A 70-day experiment was conducted in which forsterite olivine sand was continuously tumbled in filtered seawater at different rotation speeds, and dissolution rates were measured on a weekly basis. Results showed that continuously tumbled olivine dissolved 8 to 19 times faster compared to stagnant (no rotation) conditions. Olivine dissolution was complete and stoichiometric (except for Ni release), air-seawater CO2 exchange was not significantly rate limiting, and minimal particle fragmentation and secondary mineral formation were observed. Hence, we infer that olivine weathering was mainly enhanced via advective pore water flushing, which limits saturation effects at the grain scale. Overall, this study provides evidence that ambient physical stresses in coastal environments could enhance marine silicate weathering, which has implications for both the natural silicon cycle as well as the use of enhanced coastal weathering of silicates as a CDR technique.

Evaluation of Galvanic and Crevice Corrosion of Watch Case Middle (1.4435 Steel) and Bottom (Panacea® Steel) Assembly Supposed to Be in Prolonged Contact with the Skin

Today, laws protecting the population at the global level aim to minimize the induction risk of allergies to type IV contact dermatitis. In the European population, the prevalence of nickel allergy is at 10%–15% of adult females and 1%–3% of adult males. A total of 30% of nickel-sensitive people in the general population develop hand eczema. This study concerns the possibility of assembling a bottom of nickel-free austenitic steel (Panacea®) in a watch case middle made of a grade of austenitic steels, steel 316L (DIN 1.44359), to avoid the risks of Ni release and to develop a galvanic pile between these two dissimilar materials. Two types of methods were used: direct measurements and prediction techniques (mixed potentials theory). For the degradation of thbottom-middle watch assembly, Nielsen–Tuccillo tests were performed, and Ni release measurements according to EN 1811 completed the study. All direct electrochemical investigations and galvanic current prediction measurements show low current values of 40–400 nA. Measurements of nickel release of Panacea® and 316L reveal small quantities of nickel, much lower than the 0.5 µg/cm2 per week that the European legislation enforces. The nickel-free steel Panacea® in the work hardening conditions 280, 427, and 510 HV0.1s were also studied. The cation extractions reveal the large quantities released from Cr, Mo, Mn, and Fe, so there is a risk of toxicity in contact with the skin.

Multi-scale characterization of the inner surface of as-received steam generator tubes and correlation with the Ni release in primary water

The inner surface of two as-received steam generator (SG) tubes made of nickel base alloy 690 was analyzed to explain the differences in nickel release obtained for the tubes in a loop simulating the primary environment of pressurized water reactors. The roughness, microstructure and chemical heterogeneities were characterized; differences that could explain the specific behavior of the two tubes in primary water were noted. In particular, the presence of alumina particles at the surface of SG tubes influences the nickel release: their dissolution in the primary coolant induces a change in roughness and a local breakdown of the passive film.

Transformation kinetics of exogenous nickel in a paddy soil during anoxic-oxic alteration: Roles of organic matter and iron oxides

Nickel is generally released from flooded soils; however, the key Ni transformation processes in soils that are freshly contaminated by Ni2+ during anoxic–oxic alteration remain unclear. We developed a kinetic model to investigate the Ni transformation in paddy soils under anoxic and oxic conditions based on the results of the seven-step sequential extraction, determination of dissolved and soil organic matter, and surface site quantification, which provide the kinetic data of different Ni fractions, organic matter, and reactive sites for modeling. The dissolved, exchangeable, and specifically adsorbed Ni was gradually transferred to fulvic complex, humic complex, Fe–Mn oxide bound, and sulfide bound Ni after 40 d of anoxic incubation due to the increase in pH and soil surface sites, which were mainly induced by Fe(III) oxide reduction and soil organic matter release. The introduction of oxygen triggered a rapid release of Ni, which was ascribed to the decrease in pH and soil surface sites caused by Fe(II) oxidation and carbon re-immobilization. Kinetic modeling demonstrated that complexation with soil organic matter dominated Ni immobilization under anoxic conditions, while organic matter and Fe–Mn oxides contributed similarly to Ni release under oxic conditions, although the majority of Ni remained complexed with soil organic matter. These findings are important for the evaluation and prediction of Ni behavior in paddy soils with exogenous Ni during flooding-drainage practices.

Nickel and copper ion release, deflection and the surface roughness of copper-nickel-titanium orthodontic archwire in sodium fluoride solution.

Sodium fluoride (NaF) is commonly used in oral hygiene products, leading to corrosion and reduced archwire properties. In addition, ion release can cause allergies and become toxic to the oral environment. This research aimed to observe the Nickel (Ni) and Copper (Cu) ions released that affected initial corrosion as deflection and surface roughness changed in the Copper-Nickel-Titanium (CuNiTi) archwire. The total samples were 54 copper-nickel-titanium (CuNiTi-Tanzo, American orthodontic®) archwires immersed in three solutions. Artificial saliva was used in the control group NaF 0.05%, and a NaF 0.15% solution was used in the intervention groups (n = 6). The groups were divided into three observation times (two, four, and six weeks). Cu and Ni ions released, deflection, the surface roughness of the archwires, and solution acidities were recorded and analyzed. Ni and Cu ion release and surface roughness of the CuNiTi archwires significantly increased as the NaF concentration increased. The Ni ion release improved along the immersion period; the opposite was true for the Cu ion release. The solutions became more alkaline after the CuNiTi archwires were immersed. The pH and the archwires' deflections of the three solutions did not show significant differences. The NaF increased Cu-Ni ion release and surface roughness but not the deflection force of the CuNiTi. The increase was affected by the concentration and duration of immersion.

THE METAL BRACKETS STAINLESS STEEL SURFACE ANALYSIS OF THE NICKEL (Ni) AND MANGAN (Mn) ION RELEASE

Background: The installation of stainless steel metal brackets on the patient's teeth in a long phase will interact with the oral cavity environment which causes the release of ions such as Ni and Mn ions. Their release in the metal bracket can impact the body in the form of hypersensitivity reactions while the impact on the bracket is the bracket surface changes shown by the gap in it. These changes can reduce the effectiveness of orthodontic and aesthetics treatments, quality and the strength of the bracket, and can provide an attachment place for Streptococcus mutans microbe. The aim of this study was to determine the release of the ions (Ni and Mn) on the stainless steel metal bracket surface. Method: This study was a descriptive research. The research sample used a stainless steel metal bracket with 0.22" lower jaw premolar slots which was marked by the American Orthodontic (AO) brand which experienced the ions release. The observation of ion Ni, Mn, Fe and Cr release on the bracket was carried out by using a Scanning Electron Microscope- Energy Dyspersive X-Ray Spectroscopy’s tool (SEM-EDX). Result: The results showed that the mean percentage of Ni ions decreased by 0.758 % while the mean percentage of Mn ions decreased by 0.324 %. The percentage of ion release is calculated from all ion Ni, Mn, Fe and Cr. Conclusion: The results can be concluded that there were differences of ion release` (Ni and Mn) on the stainless steel metal bracket surface. Their release was demonstrated by the presence of microscopic gaps due to pitting corrosion.

Using recoverable sulfurized magnetic biochar for active capping to remediate multiple heavy metal contaminated sediment

Due to anthropogenic activities, heavy metals are discharged into the hydrosphere and deposit onto the sediment. Heavy metals remobilize through physical disturbance and change in environmental conditions, posing a risk to environments and human health. Among several remediation methods, active layer capping is considered to be more feasible due to its financial and technical advantages; however, its long-term effects remain unknown. To overcome this problem, this work applied a novel, recoverable amendment, sulfurized magnetic biochar (SMBC), to remediate multiple heavy metal (Cu, Ni, Zn, Cr, Hg, and MeHg) contaminated sediment. Physiochemical characterization shows magnetite (Fe3O4) crystalline in both magnetic biochar (MBC) and SMBC, with such characteristics resulting in a greater surface area (324.9 and 346.3 m2/g) than BC (39.6 m2/g) and SBC (65.0 m2/g). FeS crystalline was also observed in SMBC, which plays an important role in controlling heavy metal release from sediment. Microcosm experiments indicated the effectiveness of SMBC in lowering aquatic Cu, Ni, Zn, Hg, and MeHg releases was significantly greater than the other three biochar materials. Notably, the recovery of SMBC by magnetism was 87%, demonstrating the exceptional recoverability of SMBC from seawater and sediment. Based on its robust capability in lowering Cu, Ni, Zn, Hg, and MeHg release and excellent recoverability from seawater and sediment, this technique represents a practical alternative to conventional approaches for heavy metal immobilization from sediment.

Estimating Ni, Cr, Co, and Mo release from 3 dental casting alloys in saliva and blood at 6 and 12 months by using inductively coupled plasma mass spectroscopy

Statement of problemThe leaching of elements from long-term definitive prostheses, with saliva acting as an electrolyte, poses a biological concern. The approximate concentration in the biological samples that are considered clinically toxic ranges from 1 to 5000 nmol/L for Cr and Co, 1 to 200 nmol/L for Ni, and 1 to 20 nmol/L for Mo. While in vitro studies are available regarding the leaching of elements in artificial saliva, solutions containing protein, solutions of different pH, and different culture media, the in vivo effects of leaching in the biological sample with increasing time are unknown. PurposeThe purpose of this clinical study was to quantify the Ni, Co, Cr, and Mo metals in saliva and blood before and after restoration with prostheses made from 3 different brands of dental casting alloy at 6 and 12 months. Material and methodsThree popular brands of Ni-Cr alloy with different compositions were evaluated. A total of 150 participants requiring a definitive prosthesis were enrolled and divided into 3 groups (n=50). Heavy metal levels from saliva and blood were measured by using the inductively coupled plasma mass spectroscopy method before cementation of the prosthesis and after 6 and 12 months. ResultsThe presence of Ni in saliva was in the range of 10.34 to 12.12 μg/L, Cr was 1.04 to 1.22 μg/L, and Mo was 1.04 to 1.08 μg/L over a period of 6 and 12 months after cementation of the metal prosthesis. The presence of Ni in blood was in the range of 6.35 to 14.45 μg/L and that of Cr was 9.09 to 16.16 μg/L over a period of 6 and 12 months after cementation. Co levels were not detected from any brands in saliva or blood, and Mo was detected only in the saliva samples. ConclusionsIncreased levels of Ni and Cr in saliva and blood from all 3 brands of base metal alloy at 6 and 12 months were observed at higher than threshold values.

Cellular and molecular mechanisms of NiONPs toxicity on eel hepatocytes HEPA-E1: An illustration of the impact of Ni release from mining activity in New Caledonia.

Anthropic activities such as open pit mining, amplify the natural erosion of metals contained in the soils, particularly in New Caledonia, leading to atmospheric emission of nickel oxide nanoparticles (NiONPs). These particles are produced during extraction end up in aquatic ecosystems through deposition or leaching in the rivers. Despite alarming freshwater Ni concentrations, only few studies have focused on the cellular and molecular mechanisms of NiONPs toxicity on aquatic organisms and particularly on eels. Those fish are known to be sensitive to metal contamination, especially their liver, which is a key organ for lipid metabolism, detoxification and reproduction. The objective of this study was to assess in vitro the cytotoxic effects of NiONPs on Anguilla japonica hepatocytes, HEPA-E1. HEPA-E1 were exposed to NiONPs (0.5-5μg/cm2) for 4 or 24h. Several endpoints were studied: (i) viability, (ii) ROS production, SOD activity and selected anti-oxidant genes expression, (iii) inflammation, (iv) calcium signalling, (v) mitochondrial function and (vi) apoptosis. The results evidenced that NiONPs induce a decrease of cell viability and an increase in oxidative stress with a significant superoxide anion production. An increase of mitochondrial calcium concentration and a decrease of mitochondrial membrane potential were observed, leading to apoptosis. These results underline the potential toxic impact of NiONPs on eels living in mining areas. Therefore, eel exposure to NiONPs can affect their migration and reproduction in New Caledonia.

Investigating the effect of nickel concentration on phytoplankton growth to assess potential side-effects of ocean alkalinity enhancement

Abstract. Ocean alkalinity enhancement (OAE) is a proposed method for removing carbon dioxide (CO2) from the atmosphere by the accelerated weathering of (ultra-)basic minerals to increase alkalinity – the chemical capacity of seawater to store CO2. During the weathering of OAE-relevant minerals relatively large amounts of trace metals will be released and may perturb pelagic ecosystems. Nickel (Ni) is of particular concern as it is abundant in olivine, one of the most widely considered minerals for OAE. However, so far there is limited knowledge about the impact of Ni on marine biota including phytoplankton. To fill this knowledge gap, this study tested the growth and photo-physiological response of 11 marine phytoplankton species to a wide range of dissolved Ni concentrations (from 0.07 to 50 000 nmol L−1). We found that the phytoplankton species were not very sensitive to Ni concentrations under the culturing conditions established in our experiments, but the responses were species-specific. The growth rates of 6 of the 11 tested species showed generally limited but still significant responses to changing Ni concentrations (36 % maximum change). Photosynthetic performance, assessed by measuring the maximum quantum yield (Fv/Fm) and the functional absorption cross-section (σPSII) of photosystem II (PSII), was sensitive to changing Ni in 3 out of 11 species (35 % maximum change) and 4 out of 11 species (16 % maximum change), respectively. The limited effect of Ni may be partly due to the provision of nitrate as the nitrogen source for growth as previous studies suggest higher sensitivities when urea is the nitrogen source. Furthermore, the limited influence may be due to the relatively high concentrations of synthetic organic ligands added to the growth media in our experiments. These ligands are commonly added to control trace metal bioavailability and therefore for example “free Ni2+” concentrations by binding the majority of the dissolved Ni. Our data suggest that dissolved Ni does not have a strong effect on phytoplankton under our experimental conditions, but we emphasize that a deeper understanding of nitrogen sources, ligand concentrations, and phytoplankton composition is needed when assessing the influence of Ni release associated with OAE.

Diavik Waste-Rock Project, Northwest Territories, Canada: Predicting Field-Scale Waste-Rock Drainage Quality from Humidity-Cell Experiments

Abstract The prediction of water quality from waste-rock stockpiles is an important aspect of mine planning and closure. These predictions are complex, and a well-documented mechanistic approach can provide greater confidence in the results. In this study, humidity-cell experiments (1-kg sample) conducted at 5° and 22°C were used to estimate the effluent water quality and release rates of oxidation products from small-scale (12 t) field-based lysimeters. A comparison between estimated total mass loadings from laboratory humidity cells and total mass loadings from field lysimeters at the Diavik diamond mine, Northwest Territories, Canada, was completed for a five-year period. Measured temperature, S content, and surface area values were used as the primary scaling variables in these estimates. The release rate of SO42− from humidity cells with varying S content (ranging from 0.02–0.18 wt % total S) were normalized to the surface area of sulfide (mol m–2 sulfide S–1 sec–1) from each humidity cell. The resulting variability in SO42− release rates for waste-rock types were within one order of magnitude. The release rates of SO42− from the humidity cells were used to estimate the release rates from waste rock in the field with an average of 0.053 wt % total S. The results suggest that the measured annual total mass loading in the field was within the range predicted from the normalized annual total mass loadings using the surface area of sulfide from the humidity cells, with some discrepancies. Variation in annual loading at the field scale, presumably due to variability in precipitation and flushing, resulted in year-to-year discrepancies. Predictions of Fe and Ni release rates did not capture the field lysimeter results well, likely as a result of variations in geochemical conditions between laboratory and field-scale experiments (i.e., pH, mineral solubility) and also physical and geochemical heterogeneity that is not fully captured in the material characterization at each scale. The results indicate that, at this scale, annual total mass loadings can be estimated using small-scale humidity cells with a mechanistic approach if a thorough characterization of the waste rock is completed to better refine the release rates.

Kinetics of cadmium (Cd), nickel (Ni), and lead (Pb) release from fulvic acid: Role of re-association reactions and quantitative models

Dissolved organic matter (DOM), a ubiquitous ligand for heavy metals, plays a crucial role in regulating the bioavailability and fate of heavy metals in the environment. However, owing to complex structure and heterogeneity of DOM, it is still challenging to develop kinetics models to predict the rates of heavy metal reactions with DOM. In this study, we investigated the kinetics of Cd, Ni, and Pb release from a typical fulvic acid (FA) under a wide range of experimental conditions using a competing ligand exchange (CLE) method. Among three metals, Cd showed the fastest release from FA while Ni and Pb had slower release rates. Reaction pH also had different impact on the release rates of the three metals, presumably attributed to different proton/metal exchange ratios for the metal ion complexation with FA. We formulated a kinetics model for Cd, Ni, and Pb release from FA by considering metal ions dissociation from FA, re-association of metal ions with FA, and metal ion uptake by the resin in the CLE experiments. The chemical speciation model WHAM 7 was used to predict the local equilibrium status that the kinetic reactions were away from, which help to derive the kinetic parameters based on the equilibrium parameters. For both Cd and Pb, model calculations were sensitive to the re-association rates, especially at high pH, while for Ni, the impact of the re-association rates was less significant. Based on the model parameters obtained in this study, our model simulations have also demonstrated that metal-FA complexes may undergo different rates of dissociation in the environment, affecting the dynamic speciation and transfer of metals to other biological processes. This work has provided a quantitative tool for predicting metal release from DOM, which would be useful for predicting the bioavailability and fate of heavy metals in the environment.

Chemical speciation and release kinetics of Ni in a Ni-contaminated calcareous soil as affected by organic waste biochars and soil moisture regime.

Biochars vary widely in properties and have been shown to have variable effects on potentially toxic element(s) stabilization in soil. This is the first study to examine the interaction effects of biochar and soil moisture regime on Ni stabilization in a Ni-contaminated calcareous soil. Three different organic waste (cow manure, municipal compost and licorice root pulp) biochars produced at two temperatures (300 and 600°C) were applied (3% wt.) to a Ni-contaminated calcareous soil and incubated at field capacity and saturated conditions for 70 d. Sequential chemical fractionation and Ni release kinetics were then performed. All applied biochars, especially the high-temperature biochars, were significantly able to enhance Ni stabilization in the studied soil. In particular, the biochars significantly decreased Ni content in the water-soluble and exchangeable fractions (10-42% decrease), while increasing the immobile residual fraction (13-38% increase). The biochars also significantly decreased the rate and cumulative amount of EDTA-extractable Ni from the calcareous soil. Among the studied biochars, the cow manure and municipal compost biochars produced at 600 °C were the most effective at reducing Ni mobility factor (27-28% decrease) and initial release rate (42-49% decrease), likely due to their high ash content and pH, which promotes Ni sorption in soil. Soil moisture regime was not found to significantly affect the Ni mobility factor or rates of Ni release from the calcareous soil but did, however, affect certain soil Ni chemical fractions. Soil water saturation significantly decreased Ni in the Mn (4%) and non-crystalline Fe oxides (17%) fractions, while increased the crystalline Fe oxide fraction (3%), attributed to reductive dissolution of Mn and Fe oxide crystallinity enhancement. Saturation also significantly enhanced Ni in the residual fraction (4%), attributed to the associated pH increase and potential sulfide formation. The results of this study demonstrate that high temperature, ash-rich, and alkaline biochars are most effective at Ni immobilization, and that soil water saturation can further enhance Ni in the residual fraction.

Nickel behavior as affected by various physical-chemical modified biochars of cypress cones in a calcareous nickel-spiked soil

ABSTRACT This study aimed to investigate the effects of cypress cone biochar (RB) and its modifications (chitosan-coated biochar (CB), acid-modified biochar (AB), alkali-modified biochar (ALB), humic acid-coated biochar (HB), walnut shell residue extraction-coated biochar (WB), ball-milled biochar (BMB)) on the behavior of nickel (Ni) in Ni-spiked calcareous soil. The biochars were added separately to the soil at the rates of 1.5% and 3%, and the Ni behavior was investigated using methods of desorption kinetics and sequential extraction. The modification process significantly changed the specific area and functional groups of BMB, CB and HB compared to RB. Application of CB (26.3%), HB (28.7%), ALB (28.8%), BMB (30.7%), AB (31.9%) and RB (32.6%) showed the most effects on reduction of Ni mobility factor compared to control soil sample (38.8%). The results of Ni desorption showed high effectiveness of CB, BMB, ALB and HB, in reducing the Ni release compared to the control soil sample. Overall, our findings indicated that among the modified biochars, BMB, CB and HB showed a good performance in Ni stabilization, due to the simple and low-cost process of physical modification. BMB can be suggested as a suitable amendment for soil Ni immobilization.