Nickel speciation in aqueous chloride solutions

Transport Properties in Multicomponent Systems Containing Cyclodextrins and Nickel Ions

In this work, we propose a comprehensive experimental study of the diffusion of nickel ions in combination with different cyclodextrins as carrier molecules for enhanced solubility and facilitated transport. For this, ternary mutual diffusion coefficients measured by Taylor dispersion method are reported for aqueous solutions containing nickel salts and different cyclodextrins (that is, α-CD, β-CD, and γ-CD) at 298.15 K. A combination of Taylor dispersion and other methods, such as UV-vis spectroscopy, will be used to obtain complementary information on these systems. The determination of the physicochemical properties of these salts with CDs in aqueous solution provides information that allows us to understand solute-solvent interactions, and gives a significant contribution to understanding the mechanisms underlying diffusional transport in aqueous solutions, and, consequently, to mitigating the potential toxicity associated with these metal ions. For example, using mutual diffusion data, it is possible to estimate the number of moles of each ion transported per mole of the cyclodextrin driven by its own concentration gradient.

Enhanced photoelectrocatalytic oxidation of hypophosphite and simultaneous recovery of metallic nickel via carbon aerogel cathode

Carbon aerogel (CA) cathode was adopted to an undivided-chamber photoelectrocatalytic system with TiO₂ nanotube arrays (TNA) photoanode to enhance the oxidation of hypophosphite (H₂PO₂^-) and simultaneous recovery of metallic nickel (Ni). Both the efficiencies of H₂PO₂^- oxidation and Ni recovery were significantly enhanced after replacing Ti or carbon fiber paper cathode with CA cathode. With 1.0 mM H₂PO₂^- and 1.0 mM Ni²⁺, the ratio of PO₄^3- production increased from ∼41% or ∼54% to ∼100%, and the ratio of Ni recovery increased from ∼20% or ∼ 37% to ∼93% within 180 min at 3.0 V. H₂PO₂^- was finally oxidized to PO₄^3- by •OH radicals, which was speculated to be generated from UV/H₂O₂ and bound on TNA photoanode. Meanwhile, Ni²⁺ was eventually electro-reduced to metallic Ni by a two-electron reduction reaction. The efficiencies of H₂PO₂^- oxidation and Ni recovery were favored at higher cell voltage, faintly acid conditions and larger H₂PO₂^- concentration. The stability of this system exhibited that the ratio of PO₄^3- production increased significantly in each cycle, which was attributed to the increase of H₂O₂ in-situ-generation via CA cathode caused by deposition of metallic Ni. Finally, the treatment of actual electroless nickel plating effluents was demonstrated.

The Use of Polymer Membranes for the Recovery of Copper, Zinc and Nickel from Model Solutions and Jewellery Waste

A polymeric inclusion membrane (PIM) consisting of matrix CTA (cellulose triacetate), ONPPE (o-nitrophenyl pentyl ether) and phosphonium salts (Cyphos 101, Cyphos 104) was used for separation of Cu(II), Zn(II) and Ni(II) ions. Optimum conditions for metal separation were determined, i.e., the optimal concentration of phosphonium salts in the membrane, as well as the optimal concentration of chloride ions in the feeding phase. On the basis of analytical determinations, the values of parameters characterizing transport were calculated. The tested membranes most effectively transported Cu(II) and Zn(II) ions. The highest recovery coefficients (RF) were found for PIMs with Cyphos IL 101. For Cu(II) and Zn(II), they are 92% and 51%, respectively. Ni(II) ions practically remain in the feed phase because they do not form anionic complexes with chloride ions. The obtained results suggest that there is a possibility of using these membranes for separation of Cu(II) over Zn(II) and Ni(II) from acidic chloride solutions. The PIM with Cyphos IL 101 can be used to recover copper and zinc from jewellery waste. The PIMs were characterized by AFM and SEM microscopy. The calculated values of the diffusion coefficient indicate that the boundary stage of the process is the diffusion of the complex salt of the metal ion with the carrier through the membrane.

Phytoremediation of nickel and chromium-containing industrial wastewaters by water lettuce (Pistia stratiotes)

This study was conducted to assess the phytoremediation potential of Pistia stratiotes for post-treatment of Ni(II) and Cr(III)-containing industrial wastewater effluents in mono (synthetic wastewater) and bimetallic systems (real wastewater). Differences were seen in metal uptake, growth performance, and metal accumulation of the plants. In the monometallic system, the highest removal efficiency was calculated as 77.50% for Cr(III) and 70.79% for Ni(II) at 5 mg L^-1 concentration. At 1.25 mg L^-1 concentration, the bioconcentration factor of P. stratiotes was calculated as 734.2 for Ni(II) and 799.0 for Cr(III). To assess the effects of metal stress on plants, photosynthetic pigments and percent growth rates were also investigated. The percent growth rate increased from 38.22 to 81.74% for Ni and decreased from 87.53 to 43.18% for Cr(III) when the metal concentrations increased from 1.25 to 5 mg L^-1. Toxicity symptoms were less severe in plants exposed to low Ni concentrations. The greatest reduction in chlorophyll was observed at 5 mg L^-1 Ni concentration. P. stratiotes showed better performance in the monometallic system. It was concluded based on present findings that P. stratiotes could potentially be used for the post-treatment of wastewaters containing Ni and Cr.Novelty Statement Previous phytoremediation studies were mostly conducted only in either mono- or multi-metallic systems. In this study, mono- and bimetallic systems were assessed together and the feasibility of research findings on a large scale was investigated in detail. Present findings may also aid in the development of phyto-remedial strategies and the identification of Ni and Cr toxicity in macrophytes. Pistia stratiotes are already known for its incredible potential in removing metals and other contaminants from wastewater effluents. However, most studies only present data regarding the plant performance in laboratory studies (synthetic wastewater), while this study provides some important additional information on natural effluent conditions, which transform the presented data more interesting from a practical point of view.

Recovery of nickel from electroless nickel plating wastewater based on the synergy of electrocatalytic oxidation and electrodeposition technology

Nickel exists primarily as a stable complex in electroless nickel plating wastewater, and the Ni recovery from it cannot be achieved solely through electrodeposition. As the electrocatalytic oxidation has excellent oxidation potential to break down the complex, an efficient and stable electrochemical system using the synergy of electrocatalytic oxidation and electrochemical deposition technology was developed for the recovery of nickel from electroless nickel plating wastewater. In the present study, the effects of initial pH, current density, and initial nickel ion concentration on the treatment performance of the electrochemical system was investigated. The highest Ni recovery (94.84%) and total organic carbon removal (63.94%) were achieved at a current density of 83.3 mA/cm² , initial pH of 3.0, and initial Ni concentration of 0.01 M. At the same time, the recovered nickel product was confirmed by scanning electron microscopy, energy dispersive X-ray, X-ray powder diffraction, and X-ray photoelectron spectroscopy. Furthermore, the electrochemical system displayed good stability and economic benefits, thereby suggesting its excellent application potential for the treatment of electroless nickel plating wastewater. PRACTITIONER POINTS: An efficient and stable electrochemical system was developed for the recovery of nickel from electroless nickel plating wastewater. In an acidic medium, the nickel recovery rate and TOC removal ratio were 94.84% and 63.94%, respectively. The system displayed good stability, thereby suggesting its excellent application potential for the treatment of nickel plating wastewater.

Electrochemical deposition of nickel targets from aqueous electrolytes for medical radioisotope production in accelerators: a review

This paper reviews reported methods of the electrochemical deposition of nickel layers which are used as target materials for accelerator production of medical radioisotopes. The review focuses on the electrodeposition carried out from aqueous electrolytes. It describes the main challenges related to the preparation of suitable Ni target layers, such as work with limited amounts of expensive isotopically enriched nickel; electrodeposition of sufficiently thick, smooth and free of cracks layers; and recovery of unreacted Ni isotopes from the irradiated targets and from used electrolytic baths.

Recovery of phosphorus and metallic nickel along with HCl production from electroless nickel plating effluents: The key role of three-compartment photoelectrocatalytic cell system

A three-compartment photoelectrocatalytic (PEC) cell system combined with ion exchange and chemical precipitation was proposed to recover phosphorus and nickel from electroless nickel plating effluents containing hypophosphite (H₂PO₂^-) and nickel ions (Ni²⁺). Ion exchange was used to concentrate and separate Ni²⁺ and H₂PO₂^-. As a key unit, the established PEC system consisted of TiO₂/Ni-Sb-SnO₂ photoanode and Ti cathode. With 25.8 mM NaH₂PO₂ and 500 mM NiCl₂, 100 % H₂PO₂^- was oxidized to PO₄^3- in the anode cell, 78 % Ni²⁺ was recovered as metallic Ni in the cathode cell, and 900 mM HCl was obtained in the middle cell within 24 h at 3.0 V. Based on quenching experiments and ESR technique, OH radicals were mainly responsible for H₂PO₂^- oxidation. In situ Raman spectroscopy indicated that Ni²⁺ initially reacted with OH^- to form α-Ni(OH)₂, which was gradually reduced to metallic Ni. Fortunately, a slight pH decrease in the cathode cell in the three-compartment cell system was beneficial for Ni²⁺ reduction to Ni°. The obtained PO₄^3- was recovered by chemical precipitation. Finally, recovery of phosphorus and metallic nickel along with HCl production from an actual electroless nickel plating effluents in terms of efficiency, cost-benefit, and stability assessment were demonstrated.

Synthesis of super hydrophilic cellulose-alpha zirconium phosphate ion exchange membrane via surface coating for the removal of heavy metals from wastewater

In this study, commercial cellulose membranes were surface coated with alpha‑zirconium phosphate nanoparticles (α-ZrP-n) to study their impact on the overall removal efficiency of heavy metals from synthetic metal mixture wastewater solution. A total of four homogeneous solutions (0.25, 0.50, 0.75, and 1.00 wt%) of α-ZrP-n were prepared by sonicating the nanoparticles in deionized water. These solutions were used to surface coat the commercial cellulose membranes. The Scanning Electron Microscopy (SEM) along with Energy Dispersive Spectroscopy (EDS) were used to confirm the attachment of α-ZrP-n on the cellulose membrane surface. Furthermore, the structural characteristics of the α-ZrP-n modified cellulose membranes were also studied. The water contact angle results showed that all coated membranes remained super-hydrophilic. The porosity of the membranes decreased to 48% with the addition of 1.00 wt% α-ZrP-n compared to 65% for the pristine membrane. The mechanical strength has improved from 3.4 MPa for the pristine membrane to about 4 MPa for the 1.00 wt% α-ZrP-n membrane. Similarly, the thermal stability was found to be slightly enhanced as evidenced by the increase in decomposition temperature to 280 and 285 °C in the 0.75 and 1.00 wt% α-ZrP-n membranes, respectively. Furthermore, a removal efficiency of 97.0 ± 0.6, 98.0 ± 0.5, 99.5 ± 0.2, and 91.5 ± 2.0% for Cu (II), Zn (II), Ni (II), and Pb (II), respectively, was observed with the 0.50 wt% α-ZrP-n membrane. This removal was achieved at a flux of 41.85 ± 0.87 × 10³ LMH. Increasing the α-ZrP-n concentration further did not show any improvement in the overall removal efficiency. However, it led to 46% flux reduction in the 1.00 wt% α-ZrP-n membrane. The mechanism of removal of the heavy metal ions was postulated to be a combination of ion exchange and electrostatic attraction of the strong negatively charged α-ZrP-n membranes and the free metal ions in the wastewater solution.

Ultramicroelectrode Studies of Self-Terminated Nickel Electrodeposition and Nickel Hydroxide Formation upon Water Reduction

The interaction between electrodeposition of Ni and electrolyte breakdown, namely the hydrogen evolution reaction (HER) via H₃O⁺ and H₂O reduction, was investigated under well-defined mass transport conditions using ultramicroelectrodes (UME's) coupled with optical imaging, generation/collection scanning electrochemical microscopy (G/C-SECM), and preliminary microscale pH measurements. For 5 mmol/L NiCl₂ + 0.1 mol/L NaCl, pH 3.0, electrolytes, the voltammetric current at modest overpotentials, i.e., between -0.6 V and -1.4 V vs. Ag/AgCl, was distributed between metal deposition and H₃O⁺ reduction, with both reactions reaching mass transport limited current values. At more negative potentials, an unusual sharp current spike appeared upon the onset of H₂O reduction that was accompanied by a transient increase in H₂ production. The peak potential of the current spike was a function of both [Ni(H₂O)₆]²⁺_(aq) concentration and pH. The sharp rise in current was ascribed to the onset of autocatalytic H₂O reduction, where electrochemically generated OH^- species induce heterogeneous nucleation of Ni(OH)_2(ads) islands, the perimeter of which is reportedly active for H₂O reduction. As the layer coalesces, further metal deposition is quenched while H₂O reduction continues albeit at a decreased rate as fewer of the most reactive sites, e.g., Ni/Ni(OH)₂ island edges, are available. At potentials below -1.5 V vs. Ag/AgCl, H₂O reduction is accelerated, leading to homogeneous precipitation of bulk Ni(OH)₂·xH₂O within the nearly hemispherical diffusion layer of the UME.

Insights into the equilibrium, kinetic and thermodynamics of nickel removal by environmental friendly Lansium domesticum peel biosorbent

Lansium domesticum peel (LDP), a waste material generated from the fruit consumption, was evaluated as a biosorbent for nickel removal from aqueous media. The effects of dosage, contact time, initial pH, initial concentration and temperature on the biosorption process were investigated in batch experiments. Equilibrium data were fitted by the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich models using nonlinear regression method with the best-fit model evaluated based on coefficient of determination (R(2)) and Chi-square (χ(2)). The best-fit isotherm was found to be the Langmuir model exhibiting R(2) very close to unity (0.997-0.999), smallest χ(2) (0.0138-0.0562) and largest biosorption capacity (10.1mg/g) at 30°C. Kinetic studies showed that the initial nickel removal was rapid with the equilibrium state established within 30min. Pseudo-second-order model was the best-fit kinetic model indicating the chemisorption nature of the biosorption process. Further data analysis by the intraparticle diffusion model revealed the involvement of several rate-controlling steps such as boundary layer and intraparticle diffusion. Thermodynamically, the process was exothermic, spontaneous and feasible. Regeneration studies indicated that LDP biosorbent could be regenerated using hydrochloric acid solution with up to 85% efficiency. The present investigation proved that LDP having no economic value can be used as an alternative eco-friendly biosorbent for remediation of nickel contaminated water.

Evaluation of carbon-based nanosorbents synthesised by ethylene decomposition on stainless steel substrates as potential sequestrating materials for nickel ions in aqueous solution

The present work covers the preparation of carbon-based nanosorbents by ethylene decomposition on stainless steel mesh without the use of external catalyst for the treatment of water containing nickel ions (Ni2+). The reaction temperature was varied from 650 to 850 degrees C, while reaction time and ethylene to nitrogen flow ratio were maintained at 30 min and 1:1 cm3/min, respectively. Results show that nanosorbents synthesised at a reaction temperature of 650 degrees C had the smallest average diameter (75 nm), largest BET surface area (68.95 m2/g) and least amount of impurity (0.98 wt.% Fe). A series of batch-sorption tests were performed to evaluate the effects of initial pH, initial metal concentration and contact time on Ni2+ removal by the nanosorbents. The equilibrium data fitted well to Freundlich isotherm. The kinetic data were best correlated to a pseudo second-order model indicating that the process was of chemisorption type. Further analysis by the Boyd kinetic model revealed that boundary layer diffusion was the controlling step. This primary study suggests that the prepared material with Freundlich constants compared well with those in the literature, is a promising sorbent for the sequestration of Ni2+ in aqueous solutions.

Identifying the causes of oil sands coke leachate toxicity to aquatic invertebrates

A previous study found that coke leachates (CL) collected from oil sands field sites were acutely toxic to Ceriodaphnia dubia; however, the cause of toxicity was not known. Therefore, the purpose of this study was to generate CL in the laboratory to evaluate the toxicity response of C. dubia and perform chronic toxicity identification evaluation (TIE) tests to identify the causes of CL toxicity. Coke was subjected to a 15-d batch leaching process at pH 5.5 and 9.5. Leachates were filtered on day 15 and used for chemical and toxicological characterization. The 7-d median lethal concentration (LC50) was 6.3 and 28.7% (v/v) for pH 5.5 and 9.5 CLs, respectively. Trace element characterization of the CLs showed Ni and V levels to be well above their respective 7-d LC50s for C. dubia. Addition of ethylenediaminetetraacetic acid significantly (p ≤ 0.05) improved survival and reproduction in pH 5.5 CL, but not in pH 9.5 CL. Cationic and anionic resins removed toxicity of pH 5.5 CL only. Conversely, the toxicity of pH 9.5 CL was completely removed with an anion resin alone, suggesting that the pH 9.5 CL contained metals that formed oxyanions. Toxicity reappeared when Ni and V were added back to anion resin-treated CLs. The TIE results combined with the trace element chemistry suggest that both Ni and V are the cause of toxicity in pH 5.5 CL, whereas V appears to be the primary cause of toxicity in pH 9.5 CL. Environmental monitoring and risk assessments should therefore focus on the fate and toxicity of metals, especially Ni and V, in coke-amended oil sands reclamation landscapes.

Effects of nickel chloride and oxygen depletion on behaviour and vitality of zebrafish (Danio rerio, Hamilton, 1822) (Pisces, Cypriniformes) embryos and larvae

We examined acute (2 h exposure of 5-day-old larvae) and subchronic (exposure from fertilization up to an age of 11 days) effects of NiCl(2).6H2O on embryos and larvae of zebrafish (Danio rerio), both alone and in combination with oxygen depletion. The following endpoints were recorded: acute exposure: locomotory activity and survival; subchronic exposure: hatching rate, deformations, locomotory activity (at 5, 8 and 11 days) and mortality. In acute exposures nickel chloride (7.5-15 mg Ni/L) caused decreasing locomotory activity. Oxygen depletion (<or=2.45+/-0.16 mg O2/L) also resulted in significantly reduced locomotory activity. In the subchronic test, exposure to >or=10 mg Ni/L resulted in delayed hatching at an age of 96 h, in decreased locomotory activity at an age of 5 days, and increased mortality at an age of 11 days (LC20=9.5 mg Ni/L). The observed LOEC for locomotory activity (7.5 mg Ni/L) is in the range of environmentally relevant concentrations. Since locomotory activity was already affected by acute exposure, this parameter is recommended to supplement commonly recorded endpoints of toxicity.