Initial Ammonia Concentration Research Articles

Application of Bioelectrochemical System in Nitrogen Removal via Simultaneous Autotrophic Nitrification and Denitrification from Wastewater

AbstractBioelectrochemical systems (BES) is a new and expanding technology that can simultaneously convert chemical energy into electrical energy by removing nutrients. The present study investigated the BES in removing nitrogen compounds and produce electricity. To this end, a BES reactor with two chambers of cathode and anode and nafion 117 membrane was used as a separator between the two chambers. Then, the BES performance at different concentrations of COD and primary ammonium at different retention times was investigated to remove nitrogen compounds and organic matter. Voltage, current and power density were measured. The results showed that the maximum COD removal efficiency was 73.2 % for the substrate concentration of 2000 mg/L, which decreased to 72.6 % when the substrate concentration increased to 10000 mg/L. The maximum removal efficiency of nitrogen compounds was 83.4 % at COD 10000 mg/L and the initial ammonium concentration was 50 mg/L. The maximum voltage, current and power density in this phase were 391 mV, 460 mA/m2, 63/48 mW/m2, respectively. The results of the study showed that BES can be used as a suitable method to remove high amounts of ammonium in wastewater and organic materials and simultaneously produce electricity.

Optimization of Electrodialysis for Ammonium Removal From NH4Cl-Doped Groundwater Samples Using the Response Surface Method.

This study aims to optimize ammonium removal from NH4Cl-enriched groundwater at different concentrations using an electrodialysis (ED) process. A customized design (CD) based on response surface methodology (RSM) was employed to develop predictive models and improve the performance of the demineralization system. Ion removal efficiency was evaluated in 32 unique experimental configurations, taking into account variations in three input parameters: voltage (A), initial ammonium concentration (B) and demineralization rate (C). These parameters were selected for their impact on two response variables: electric conductivity (Y1) and final ammonium concentration (Y2). An in-depth analysis of variance (ANOVA) was performed to examine the variables and their interactions. The results indicated that Y1 was significantly influenced by C, while Y2 was influenced by B. In addition, the predictive models demonstrated strong correlations, with a coefficient of determination (R2) greater than 0.88 for both response variables. The RSM approach applied to optimize the parameters studied identified the following optimum values: 14.17 V for A, 1 mg/L for B and 70 % for C, giving Y1 of 215.377 μS/cm and Y2 of 0.279 mg/L.

Bifunctional system constructed by NiCu-F/DSA electrode self-coupling for efficient removal of ammonia nitrogen from landfill leachate

ABSTRACT Landfill leachates containing high concentrations of ammonia nitrogen, due to its strong toxicity, large discharge and great environmental hazard, is in urgent need of efficient cleaning treatment. In this work, Ni1Cu0.25-F/DSA catalytic electrode was prepared via electrodeposition by means of fluorination-induced surface reconstruction. The surface of electrode was determined to be a porous sponge-like structure by physical characterizations. The electrode exhibited a superior ammonia oxidation reaction (AOR) activity and stability by a series of electrochemical tests. On this basis, a Ni1Cu0.25-F/DSA || Ni1Cu0.25-F/DSA bifunctional system was developed for efficient removal of ammonia nitrogen in landfill leachate. The results of denitrification experiment indicated that the removal efficiency of NH4 +-N and TN were 99.89% and 68.9%, respectively, when the electrolytic cell potential was 1.7 V, pH was 13 and the initial ammonia concentration was 600 mg L−1. The NH4 +-N removal efficiency remained above 95% after the cyclic denitrification experiment lasting for 6 days, which validates the robust stability of the electrode.

Efficient removal of ammonia from aqueous solution using coal-based carbon membrane via electrochemical oxidation in the present of chloride ion

To tackle the escalating issue of ammonia nitrogen water pollution, developing efficient removal technologies holds paramount significance. In this work, an electrochemical membrane reactor (EMR) was constructed for the decontamination of ammonia nitrogen wastewater using the coal-based carbon membrane (CCM) as the flow-through anode. The removal efficiency and degradation mechanism of ammonia nitrogen by EMR during the treatment were investigated. It was found that, under applied voltage and in the presence of chloride ions, the CCM exhibited excellent chlorine evolution performance, and as a result, the EMR had excellent ammonia nitrogen removal efficiency. The removal of ammonia nitrogen by the flow-through EMR was following the pseudo-first-order kinetics. Analysis revealed that various operating parameters, including applied voltage, chloride ion concentration, flow rate, pH value, and initial ammonia concentration, all significantly influenced the ammonia nitrogen treatment performance of EMR. At optimal operation conditions (feed concentration of 30 mg/L, applied voltage of 2.8 V, NaCl concentration of 0.1 mol/L and flow rate of 2 ml/min), the EMR achieved a removal rate of 100 % for ammonia nitrogen with a low energy consumption (EC) of 0.0380 kW•h/g-NH4-N. The degradation mechanism analysis revealed that the primary means of ammonia removal relied on indirect oxidation mediated by OCl·, which was generated by the oxidation of Cl- on the surface of CCM within the solution under the influence of the electric field. Furthermore, the EMR demonstrated good applicability across various water matrices. In conclusion, the EMR holds considerable potential for the decontamination of ammonia nitrogen-containing wastewater.

Steam Stripping for Recovery of Ammonia from Wastewater Using a High-Gravity Rotating Packed Bed

Steam stripping of ammonia from ammonia-rich wastewater (5000–20,000 mg/L) was conducted in a continuous-flow rotating packed bed (RPB) at a pH of 11. This study aimed to elucidate the influence of key operational parameters, including the steam-to-liquid ratio, rotational speed (ω), initial ammonia concentration, steam inlet temperature (TSi), and liquid inlet temperature (TLi), on critical performance metrics such as the ammonia removal efficiency (ARE), the volumetric liquid mass transfer coefficient (KLa), and the concentration of the recovered ammonia solution (CR). The findings revealed that a CR of 22.88 wt.% was achieved under the optimal conditions of a steam-to-liquid ratio of 0.175 kg/kg, an initial concentration of 20,000 mg/L, a TSi of 120 °C, and a TLi of 70 °C. Key experimental factors, including the initial ammonia concentration, TSi, and TLi, significantly impacted the achievement of higher ARE and CR values. The KLa values exhibited a decrease with the increase in the steam-to-liquid ratio, while they increased with ω. However, the KLa remained relatively consistent with ω values within the range of 600 to 1200 rpm. In comparison with prior studies, steam stripping of ammonia exhibits a higher ARE than air stripping with RPB and a higher CR than conventional stripping methods. Moreover, RPB requires a smaller size to achieve equivalent ARE compared to conventional stripping apparatuses. Thus, the steam stripping process with RPB equipment emerges as a suitable method for ammonia recovery from ammonia-rich wastewater.

Self-regenerable oxygen system using microalgae-bacterial consortium for ammonium removal from wastewater

This study investigated self-regenerable oxygen system using microalagae-bacterial consortium for ammonium removal from wastewater and its kinetic modeling based on a combined mechanistic and empirical approach. By mechanistic modeling using a simple microalgal-bacterial Monod model, based on algal growth due to NH4+, NO3− and NO2−, the nitrogen and DO profiles were accurately predicted under different nitrogen conditions (low, medium, and high NH4+ concentrations). The mathematical modeling results showed that sufficient oxygen was available for nitrification at low initial NH4+ ammonium concentration levels, even when dual nitrogen substrate (NH4+–NO2−, NH4+–NO3− or NO2−–NO3−) or all three in combination (NH4+–NO2−–NO3−) were used, compared with high initial ammonium concentration levels. The DO profile was successfully used to monitor N transformation and N uptake in the PSBR based on net O2 uptake rate, O2 production rate, and O2 saturation profile. By empirical modeling of the data obtained, the actual O2 produced by microalgae with the different N species was calculated based on N mass balance and empirical equations. The empirical model further revealed that low NH4+ concentration levels (up to 82.5 mg N/L) favored successful nitrification due to the sufficient production of O2 in the system. However, NH4+ concentration in the range 82.5–132.5 mg N/L affected the nitrification efficiency due to insufficient O2 produced in the system, whereas high ammonium concentration results in nitritation/partial nitrification due to the high demand of O2 by AOB and inhibition in the growth of NOB.

Severity-adjusted evaluation of initial dialysis on short-term health outcomes in urea cycle disorders

ObjectiveIn individuals with urea cycle disorders (UCDs) and neonatal disease onset, extracorporeal detoxification by continuous kidney replacement therapy is considered the therapeutic method of choice in addition to metabolic emergency treatment to resolve hyperammonemic decompensation. However, the indications for the initiation of dialysis are heterogeneously implemented transnationally, thereby hampering our understanding of (optimal) short-term health outcomes. MethodsWe performed a retrospective comparative analysis evaluating the therapeutic effects of initial dialysis on survival as well as neurocognitive outcome parameters in individuals with UCDs in comparison to a severity-adjusted non-dialyzed control cohort. Overall, 108 individuals with a severe phenotype of male ornithine transcarbamylase deficiency (mOTC-D), citrullinemia type 1 (CTLN1) and argininosuccinic aciduria (ASA) were investigated by stratification based on a recently established and validated genotype-specific disease prediction model. ResultsMortality is associated with the height of initial peak plasma ammonium concentration, but appears to be independent from treatment with initial dialysis in mOTC-D. However, improved survival after initial dialysis was observed in CTLN1, while there was a trend towards improved survival in ASA. In survivors, annual frequency of (subsequent) metabolic decompensations did not differ between the dialyzed and non-dialyzed cohorts. Moreover, treatment with initial dialysis was not associated with improved neurocognitive outcomes. InterpretationThe present severity-adjusted comparative analysis reveals that general practice of initial dialysis is neither associated with improved survival in individuals with mOTC-D nor does it differ with regard to the neurocognitive outcome for the investigated UCD subtypes. However, initial dialysis might potentially prove beneficial for survival in CTLN1 and ASA.Clinical trial registration: The UCDC database is recorded at the US National Library of Medicine (https://clinicaltrials.gov).

Direct Electrooxidation of Ammonia-Enriched Wastewater Using a Bipolar Membrane-Integrated Electrolytic Cell

The treatment of reject water containing concentrated ammonia and non-biodegradable organics is a challenging task in wastewater treatment plants. To address this problem, we propose a novel process consisting of a selective ammonium-exchange resin and an ammonia electrooxidation reaction (AmER-AOR). Because an alkaline condition is essential for direct ammonia oxidation, the use of a bipolar membrane (BPM) was helpful. Nonetheless, an initial pH of 13 and KOH addition were required to maintain a high alkalinity for the complete elimination of ammonia. The linear sweep voltammogram elucidated the high pH requirement and ammonia oxidation promotion. When the current density varied from 30 to 80 mA cm−2, 60 mA cm−2 showed the highest current efficiency (30.39%) and the lowest specific energy demand (95.3 kWh/kg-N), indicating the most energy-effective condition. Increasing the initial concentration of ammonia from 0.1 M to 0.5 M improved the current efficiency (51.57%), demonstrating an additional energy-effective strategy for the AmER-AOR. The energy efficiency of pure H2 production in the cathodic chamber was 30%. To estimate the viability for practical applications, reject water collected from a local wastewater treatment plant was applied in the AmER-AOR. Notably, no significant difference in the ammonia removal rate was observed with synthetic wastewater. To the best of our knowledge, this is the first study that employs a BPM as a separator and OH− supplier for direct ammonia oxidation. Our findings reveal that the AmER-AOR with a BPM has promising practical applicability in the treatment of reject water and energy production.

Photocatalytic degradation of ammonia to nitrogen by anatase TiO2 under microwave discharge electrodeless lamp irradiation

In this study, a microwave discharge electrodeless lamp (MDEL) photo-degradation system coupled with anatase TiO2 (P25) was constructed to improve the selective degradation of NH3 to N2. The MDEL system can generate abundant reactive oxygen species (ROS) with ultraviolet radiation at 185 nm and 254 nm during gas phase reaction. The species and content of ROS generated in the reaction system were determined by oxidation extraction spectrophotometry, and the effects of residence time, temperature, and relative humidity on the production of reactive oxygen species were investigated. In addition, the removal efficiency under different conditions such as initial ammonia concentration, relative humidity and residence time was explored. It was found that the removal rate could reach 83% when the initial ammonia concentration was 100 ppm, relative humidity was 55% and gas residence time was 5.16 s. The high-energy ultraviolet at 185 nm from MDEL could break NH3 molecules in advance and produced a large amount of ·NH2. Besides, NH3 was converted to N2 by generating large amounts of ROS, reducing NOx and nitrate generation. Our work presents a novel approach to construct a photocatalytic system for high efficiency degradation of NH3.

Physicochemical assessment of ammonium adsorption using a palm shell-based adsorbent activated with acetic acid: experimental and theoretical studies.

The adsorption of ammonium from water was studied on an activated carbon obtained using raw oil palm shell and activated with acetic acid. The performance of this adsorbent was tested at different operating conditions including the solution pH, adsorbent dosage, and initial ammonium concentration. Kinetic and equilibrium studies were carried out, and their results were analyzed with different models. For the adsorption kinetics, the pseudo-first order equation was the best model to correlate this system. Calculated adsorption rate constants ranged from 0.071 to 0.074 g/mg min. The ammonium removal was 70-80% at pH 6-8, and it was significantly affected by electrostatic interaction forces. Ammonium removal (%) increased with the adsorbent dosage, and neutral pH condition favored the adsorption of this pollutant. The best ammonium adsorption conditions were identified with a response surface methodology model where the maximum removal was 91.49% with 2.27 g/L of adsorbent at pH 8.11 for an initial ammonium concentration of 36.90 mg/L. The application of a physical monolayer model developed by statistical physics theory indicated that the removal mechanism of ammonium was multi-ionic and involved physical interactions with adsorption energy of 29 kJ/mol. This activated carbon treated with acetic acid is promising to depollute aqueous solutions containing ammonium.

UV/TiO2 photocatalysis as post-treatment of anaerobic membrane bioreactor effluent for reuse

Advanced oxidation processes have been widely applied as a post-treatment solution to remove residual organic compounds in water reuse schemes. However, UV/TiO2 photocatalysis, which provides a sustainable option with no continuous chemical addition, has very rarely been studied to treat anaerobically treated effluents. In the current study, the removal of organics and nutrients from an anaerobic membrane bioreactor (AnMBR) effluent is evaluated during adsorption and photocatalysis processes under various conditions of TiO2 dose and UV intensity and compared to the effluent from an aerobic membrane bioreactor (AeMBR). The sequence for preferential adsorption on TiO2 was found to be phosphorus, inorganic carbon and then ammonia/organic carbon were found. The competing effect between the organics and nutrients, along with the low UV transmission efficiency caused by the need for high doses of TiO2, ultimately compromise the organic removal efficiency in the AnMBR permeate. TiO2 dosage was found to have a greater impact than UV intensity on improving the overall removal performance as nutrients are competing for the adsorption site but are not photodegraded. Under the same operational condition, the UV/TiO2 photocatalysis displayed a higher removal efficiency of organic matter and phosphorus in the AeMBR effluent due to a lower initial organics concentration and absence of ammonia as compared to the AnMBR effluent.

Ammonia oxidation by in-situ chloride electrolysis in etching wastewater of semiconductor manufacturing using RuSnOx/Ti electrode: Effect of plating mode and metal ratio

The indirect chloride-mediated ammonia oxidation encounters challenges in maintaining the effectiveness of metal oxide anodes when treating wastewaters with complex compositions. This study aims to develop a highly stable anode with RuO2-SnO2 coatings for treating an etching effluent from semiconductor manufacturing, which majorly contains NH3 and organic compounds. The RuSnOx/Ti electrode was synthesized using wet impregnation and calcination processes. The metal oxide configuration on Ti plate substrate was tuned by varying the step-dipping process in RuCl3 and SnCl4 baths. A 10-day continuous-flow electrolysis was conducted for studying the ammonia removal and chlorine yield under variable conditions, including detention, pH, current density, and initial ammonia and chloride concentrations. In the RuSnOx coatings, the configuration comprising RuO2 nanorods as the surface layer and an intermediate layer of SnO2 crystallites (by plating Ru3+ for three times to cover one Sn4+ layer, denoted as the Ru3Sn/Ti electrode) exhibited the best durability for acid washing, along with relatively high Faradaic efficiency and low energy consumption. To further improve the treatability of real wastewater (NH3-N = 634 mg L−1, chemical oxygen demand (COD) = 6700 mg L−1, Cl- = 2000 mg L−1, pH 11), the duel-cell electrolyzers were constructed in series under a current density of 30 mA cm−2 and 45 min detention. Ultimately, removals of NH3 and COD reached 95.8% and 76.3%, respectively, with successful limitation of chloramine formation.

Ammonia absorption by water droplet in a small controlled atmosphere wind tunnel

The mass transfer characteristics during ammonia absorption into a sessile water droplet in a small controlled-atmosphere wind tunnel were investigated using particle tracking velocimetry (PTV) with polystyrene microspheres. The results showed that the flow field inside the droplet transformed from Marangoni convection to Rayleigh convection in the absence of gas flow. As the gas velocity increased, the drag force-induced circulation inhibited the Marangoni convection in the initial stage of the mass transfer process and Rayleigh convection in the advanced stage. However, the suppressed Marangoni convection cells recurred at high initial ammonia concentrations. Compared with the initial ammonia concentration in the wind tunnel and droplet size, the gas velocity significantly increased the gas-phase mass transfer coefficient. Furthermore, a calculation model for ammonia absorption by a moving droplet was derived based on the Colburn analogy and the two-film theory. The gas-phase mass transfer coefficients calculated using the model coincided with the experimental results. These results will help the design of water curtains.

Competition between ammonia-oxidizing archaea and complete ammonia oxidizers from freshwater environments.

Nitrification is a key process in the global nitrogen cycle. Aerobic ammonia oxidizers play a central role in the nitrogen cycle by performing the first step of nitrification. Ammonia-oxidizing archaea (AOA) and complete ammonia oxidizers (comammox) are the dominant nitrifiers in environments with low ammonium availability. While AOA have been studied for almost 20 years, comammox were only discovered 8 years ago. Until now, there has been a gap in our understanding of whether AOA and comammox can co-exist or if one strain would be dominant under ammonium-limiting conditions. Here, we present the first study characterizing the competition between freshwater AOA and comammox under varying substrate concentrations. Our results will help in elucidating the niches of two key nitrifiers in freshwater lakes.

Environmental factors militating against the activities of ammonia oxidizing archaea and ammonia oxidizing bacteria in soil

This review aims to scrutinize the effect of ammonia concentration, temperature, pH, drought and inhibitors on activity of AOA and AOB in soil. Ammonia concentration in soil increases during drought due to the reduced soil water content and, with desiccation stress or a combination of both factors result in greater inhibition of AOA than AOB during drought. AOA were more susceptible to increased desiccation stress than AOB, irrespective of initial soil ammonium concentration and AOA cultures were more sensitive than AOB to osmotic stress which represent an additional niche differentiating factor between AOA and AOB in soil. Activity and growth of AOA and AOB observed in soil amended with high ammonium concentration at different temperature, suggesting that AOA can contribute to nitrification in highly fertilized soil. The selective inhibition of AOA by simvastatin in culture and in soil provides evidence for oxidation of ammonia by AOB at low ammonium concentration. The findings advance our understanding of the influence of ammonium supply, temperature and osmotic stress on soil nitrification and its role in controlling the availability of ammonium-based fertilizers for plant uptake.

Biological denitrification inhibition (BDI) on nine contrasting soils: An unexpected link with the initial soil denitrifying community

Denitrification is considered the major pathway leading to soil gaseous (N) losses, affecting N availability for plants and consequently plant productivity. Biological denitrification inhibition (BDI) in Fallopia spp., a plant species complex with a high level of growth and competitiveness for mineral N, acts through procyanidin production. However, the soil factors governing BDI development are still unknown. Through a mesocosm experiment using two treatments – soil planted with Fallopia japonica and unplanted–, nine biologically and physically contrasting soils were studied with the aim to ascertain how each can affect BDI development. Microbial enzyme activities (respiration - SIR, denitrification - DEA), denitrifying functional gene abundance (nirK, nirS), total bacterial community abundance (rRNA 16S) and soil physicochemical parameters (N mineral forms, soil texture, moisture, pH) were measured before and after plant growth, and the DEA:SIR ratio was used as a BDI proxy. The DEA:SIR ratio decreased for six soils. BDI development is related to a small number of soil factors, mainly initial soil moisture and ammonium concentration, and unexpectedly, with the initial abundance of nirK(in), nirS(in) and rRNA 16S(in). The intensity of this decrease is positively correlated to the level of DEA in unplanted soil: the higher the DEA in unplanted soil, the more intense the BDI under F. japonica. The procyanidin concentration of the F. japonica belowground system was positively correlated to BDI intensity. These results suggest that a procyanidin assay from the plant belowground system could be a new proxy for measuring BDI intensity. Interestingly, this research shows that BDI is not systematic, and that few (a)biotic soil parameters influence its development. More importantly, this research is the first to highlight that biotic factors are relevant in explaining BDI. This paper also presents new perspectives on plant-microorganism interactions in terms of plant awareness of the soil microbial community.

The Effect of Foam-Recycle on Ammonium Removal by Aerobic Denitrification Using Alcaligenes faecalis No. 4

Aerobic denitrifier Alcaligenes faecalis No. 4 removes ammonium-nitrogen to nitrogen gas via denitrification in a single aerobic condition. In our previous studies, factors such as ammonium removal rate, denitrification ratio, and cell growth were tested in various conditions. The removal pathway from ammonium to nitrogen gas still needs to be determined in detail. To clarify this pathway of Alcaligenes faecalis No. 4, we in this study investigated the effects of several factors on ammonium removal, such as foam-recycle, initial pH, initial ammonium concentration, and airflow rate. Denitrification ratio was improved by up to 23% through foam-recycle. The improvement of the denitrification ratio was resulted by the higher enzyme activity of hydroxylamine oxidoreductase (HAO) in the produced foam, which was about 28 times higher than that in the culture broth (i.e., without foam-recycle). The stripped ammonia was significantly high (above pH 9). The initial ammonium concentration and airflow rate also influenced the denitrification ratio.

Manganese oxide-loaded activated carbon for ammonium removal from wastewater: the roles of adsorption and oxidation.

The urgent need to address the severe issue of nitrogen pollution has prompted the search for a functional and easy recycling material. In this study, manganese oxides (MnOx) were loaded on activated carbon (AC), resulting in a composite known as AC-MnOx, for efficient ammonium removal from aqueous solutions. The results indicated a remarkable 15.6-fold increase in ammonium removal efficiency and a fivefold enhancement in removal capacity for AC-MnOx (3.20mg/g) compared to AC. Under specific conditions (initial NH4+-N concentration of 15mg/L, adsorbent dose of 2.5g, pH of 6.5, and temperature of 35 ℃), the highest achieved ammonium removal efficiency reached 94.6%. Furthermore, the study distinguishes the contributions of catalytic oxidation and adsorption in the removal process. The adsorption process was effectively modeled using pseudo-second-order kinetics and Langmuir isotherm models. Interestingly, the amount of oxidation conversion (Ntur) exhibited a linear relationship with the dosage when the initial ammonium concentration was sufficiently high, while the relationship between initial ammonium concentration and the ratio of Ntur to adsorption capacity (Nsur) followed a negative exponential trend. The removal mechanisms involved electrostatic interaction between ammonium and the negatively charged dehydrogenated hydroxyl groups (- OHsur) or cation tunnel in crystal structures of MnOx, ion exchange adsorption, and the oxidation impact of MnOx. This research provides valuable insights into the application of immobilized MnOx media for ammonium removal. Moreover, filling AC-MnOx into constructed wetlands (CW) proved to be an effective method for reducing ammonium pollution, demonstrating its potential in the field of engineering wastewater treatment.

Study on recycle of granulated blast-furnace slag as an adsorbent for ammonium remediation in wastewater

Blast-furnace slag (BFS) is enormously generated each year and has been considered as hazardous solid waste which is posing a significant pressure on waste treatment in terms of storage and transportation. This study aims to recycle BFS as a material for ammonium adsorption from an aqueous solution. Natural-state BFS and acidic-modified by using HNO3 at various concentration of 0.5M, 1M, and 3M (A-BFS1, A-BFS2, and A-BFS3) was examined. The surface characteristics of the materials were examined by BET analysis and Scanning Electron Microscope. The adsorption of ammonium on the BFS materials was conducted in batch mode at various conditions of contact time, pH level, adsorbent dosage, and initial concentration of ammonium. The results indicated that the HNO3 modification exhibited pore creations and surface enhancement as the A-BFS3 has 25.7 times larger surface area and 10.3 times pore size improvement. The A-BFS3 showed good ammonium adsorption capacity compared to other materials, which is 1.81 mg/g at the optimum conditions of pH 6, contact time of 120 minutes, and dosage of 0.5 g in 50 mL of 20 mg/L ammonium solution. Langmuir and Freundlich adsorption isotherm models of the A-BFS3 material showed a relatively good correlation with R2 values of 0.999 and 0.9625, respectively.

Recovery of nickel oxide nanorods from a laterite-originated intermediate product by ammonia leach-deammoniation method

Extraction of nickel from laterites, especially low-grade limonitic ores has been facing challenges related to the lack of an effective beneficiation method. A chemo-physical laterite ore processing comprising oxalic acid leaching followed by size separation of the leach residue was recently introduced by the authors as a novel method to collect small amounts of nickel values dispersed in the ore matrix into distinct oxalate particles to form an intermediate product. In the present work, the ammonia leaching of such intermediate product containing about 12 wt% NiC2O4·2H2O was accomplished. Factors such as initial ammonia concentration (NH3: 2.5–25 wt%), temperature (T: 20–50 °C), pulp density (S/L: 50–200 g/L), and sonication were examined in a series of agitated leaching tests. It was found that under the conditions of 25% NH3, T = 50 °C, S/L = 200 g/L, and 15 min of sonication, about 93% of nickel is dissolved resulting in a pregnant leach solution (PLS) with a nickel content of 7.4 g/L. Besides, the activation energy for dissolution of nickel oxalate in ammonia solution was found to be about 71 kJ mol–1 from a kinetic analysis of leaching data. The PLS was subsequently deammoniated by either boiling or vacuum-assisted gentle heating to reclaim the nickel as an oxalate salt. Electron microscopic analysis of nickel oxalate precipitates formed from ammonia solutions exhibited rod-like morphology with high aspect ratio. Deammoniation under boiling led to well-shaped and distinct particles (∼150 nm width), while the precipitates obtained under partial vacuum were splintered and finer (∼40 nm width). The pyrolysis at 400 °C in an air atmosphere of the nickel oxalate particles from the boiling and the vacuum-assisted deammoniation methods generated mesoporous NiO nanorods with average widths of about 100 and 30 nm, and specific surface areas of about 45 and 70 m2 g−1, respectively.