Precipitation Of Metal Hydroxides Research Articles

Biodegradation of sulfate and elimination of heavy metals by immobilized-microbial bioaugmentation coupled with anaerobic membrane bioreactor

Sulfate-rich metal-laden wastewater (SRMLW) shows a significant threat on the ecological environment and human health. Sulfate-reducing bacteria (SRB) can remove sulfate from wastewater in anaerobic membrane bioreactor (AnMBR). This study constructed recombinant genetic engineered SRB (rSRB) and investigated the sulfate and heavy metals removal efficiency for treating SRMLW by immobilized-microbial bioaugmentation using rSRB (IMrSRB) coupled with AnMBR (Bio-AnMBR). The results show that Bio-AnMBR removed sulfate (99.4%) from SRMLW by upregulating key genes (Sat, DsrAB, AprAB, QmoABC, DsrC and DsrMKJOP) and enzymes (APS reductase, Dissimilatory sulfite reductase, Trithionate reductase and Thiosulfate reductase) in dissimilatory sulfite and sulfate respiration processes. Bio-AnMBR achieved synergistic biodegradation of sulfate and nitrogen by stimulating the activity of these bacteria related to the conversion of nitrogen and sulfate. Microbial analysis indicated that the relatively high abundance of rSRB (79.2%) and functional genes (70.1%) upregulated the activities of key enzymes associated with sulfate metabolism system, thus increasing the production of S (66.4 mg/L) and H2S (23.8 mg/L). Bio-AnMBR significantly improved the tolerance to heavy metals by increasing concentrations of CO32–, S2-, and HS-, which was configured to reduce heavy metals (95.6%) via precipitation of metal sulfide (81.3 mg/L), metal carbonates (30.7 mg/L) and metal hydroxides (18.7 mg/L). Bio-AnMBR increased system stability, shorted hydraulic retention time (HRT), decreased the production of soluble microbial products (SMP), extracellular polymeric substances (EPS) and waste-sludge production (WSP), as well as improved effluent quality. In conclusion, data in this study indicate that application of Bio-AnMBR is a feasible strategy for the treatment of SRMLW.

Imaging the Footprint of Nanoscale Electrochemical Reactions for Assessing Synergistic Hydrogen Evolution

AbstractThis work proposes a novel method for measuring the intrinsic activity of single metal‐based nanoparticles towards water reduction in neutral media at industrially relevant current densities. Instead of using gas nanobubbles as proxy, the method uses optical microscopy to track the local footprint of the reaction through the precipitation of metal hydroxide, which is associated to the local pH increase during electrocatalysis. The results show the electrocatalytic activities of different types of metal nanoparticles and bifunctionnal core‐shell nanostructures made of Ni and Pt, and demonstrate the importance of metal hydroxide nano‐shells in enhancing electrocatalysis. This method should be generalizable to any electrocatalytic reaction involving pH changes such as nitrate or CO2 reduction.

Imaging the Footprint of Nanoscale Electrochemical Reactions for Assessing Synergistic Hydrogen Evolution.

This work proposes a novel method for measuring the intrinsic activity of single metal-based nanoparticles towards water reduction in neutral media at industrially relevant current densities. Instead of using gas nanobubbles as proxy, the method uses optical microscopy to track the local footprint of the reaction through the precipitation of metal hydroxide, which is associated to the local pH increase during electrocatalysis. The results show the electrocatalytic activities of different types of metal nanoparticles and bifunctionnal core-shell nanostructures made of Ni and Pt, and demonstrate the importance of metal hydroxide nano-shells in enhancing electrocatalysis. This method should be generalizable to any electrocatalytic reaction involving pH changes such as nitrate or CO2 reduction.

A comparative study of thermodynamic modeling and experimental measurement of precipitation titration curves for single- and multi-component sulfate systems

The current study is focused on the thermodynamic modeling and experimental measurement of metal hydroxide precipitation titration curves for the single- and multi-component sulfate systems. The systematic analytical model is developed based on Bromley-Zemaitis's theory and H. E. Wirth's theory to accurately predict the precipitation behavior of sulfate systems under different operating conditions and to simulate the precipitation titration curve. The titration curves established using the analytical model are compared with the curves built using the numerical mixed-solvent electrolyte model provided in OLI software along with the experimental measurement. The results demonstrate a good agreement between the analytical model, numerical model, and experimental approach while unveiling the limitations of the developed analytical model such as the disregard of multi-species ions, constant solution density, and constant water activity. The effect of three key operating parameters, namely initial solution pH, initial metal ion concentration, and reaction temperature, on the precipitation behaviors is investigated with emphasis on the ion interaction, precipitation pH, the amount of precipitant required, and species equilibrium.

The Effect of Sorbent Composition on Sorption Properties of Materials Based on Ti-Ca-Mg Phosphates.

Individual titanium and calcium-magnesium phosphates are widely known as effective sorbents. The sorption processes on these phosphates are based on different mechanisms. The sorption efficiency towards different cations depends on the phase composition of the sorbent. Composite materials with various ratio Ti:(Ca+Mg) have been synthesized. The sorption properties of samples obtained towards Cs+, Sr2+, Co2+, Cd2+, Zn2+, Cu2+, and Pb2+ have been studied to establish the effect of sorbent composition on metal removal. The adsorption isotherms have been analyzed using the Langmuir, Freundlich, and Redlich-Peterson models. The composition of sorbents has no effect on the level of removal of readily hydrolyzable Pb2+ and Cu2+ cations. Removal of lead occurs preferentially via the precipitation of metal phosphates and hydroxides. Copper precipitates as hydroxide in case of a high share of Ca-Mg phosphates in the composite sorbent. The removal of cesium proceeds according to the ion exchange mechanism only. For Cd2+, Co2+, Sr2+, and Zn2+ cations, the sorption efficiency on the composite materials synthesized is found to increase with the increase in titanium phosphate's share in the sample. All composite sorbents synthesized demonstrated a considerable increase in the level of purification of solutions studied compared with individual Ti and Ca-Mg phosphates due to the synergism of the components.

Bitumen–solids attachment induced by cation activation

AbstractInteractions between negatively charged bitumen and fine solids under oil sands extraction conditions were simulated using mature fine tailings (MFT) and hydrocarbon oil with dissolved carboxylic acids. Their attachment induced by cation activation was evaluated with different types of cations by simple dynamic attachment tests. The results revealed that solid hydrophobization by adsorbing surfactants was key for oil–solid attachment. Activation by multivalent metal cations was due to surface precipitation of metal hydroxides, followed by chemisorbing anionic surfactants on metal‐activated solids to form metal carboxylate complexes/precipitates, thereby hydrophobizing the solids. Activation by cationic surfactants depended on their hydrocarbon chain lengths. For short hydrocarbon chains, where hydrophobic interaction is weaker than electrostatic interaction between the added cationic and anionic surfactants, the added cations promote the adsorption of anionic surfactants by electrostatic interaction to render the solids hydrophobic. For long hydrocarbon chains where hydrophobic interaction is stronger than electrostatic interaction between the added cationic and anionic surfactants, the adsorption of anionic surfactants occurs through the hydrophobic association of the hydrocarbon chains, posing the head group towards water, thereby making the solids less hydrophobic. Activation by cationic flocculants was purely physical (hydrogen bonding and electrostatic): when the solids were turned positive by the added cationic flocculants, the added anionic surfactants then adsorbed onto the solids to render them hydrophobic. It appeared that soluble multivalent metal species (e.g., Ca2+ and Mg2+) were much less harmful to bitumen extraction than those heavy metals coated on the solids, either in the form of surface precipitates or hydrolyzed ionic species.

Removal of Heavy Metals from Acid Mine Drainage by Red Mud-Based Geopolymer Pervious Concrete: Batch and Long-Term Column Studies.

Various metal ions in acid mine drainage (AMD) cause environmental pollution. Due to the unique advantages of heavy metal treatment and gelling properties, previous concretes incorporating red mud have attracted extensive attention in AMD passive treatment, which utilises naturally occurring chemicals to cleanse contaminated mine waters with low operating costs. This study aims to develop red mud-based geopolymer pervious concrete as an eco-friendly method to remove heavy metals in AMD. Compared with raw pervious concrete, red mud-based geopolymer pervious concrete improves the purification efficiency of heavy metals. The high rate of acid reduction and metal removal by the geopolymer is attributed to the dissolution of portlandite in red mud. Precipitation of metal hydroxides seems to be the dominant metal removal mechanism. Under optimal conditions (influent pH = 4.0 and the hydraulic retention time = 24 h), red mud-based geopolymer pervious concrete could completely remove Cu(II), Mn(II), Cd(II) and Zn(II) by up to 10 mg/L, 10 mg/L, 1.6 mg/L and 16 mg/L, respectively. When the influent pH is 2.5, the hydrolysis of Fe(III) released from red mud increases the consumption of OH-. Moreover, when the influent pH is 4.0, the precipitation of CaSO4 promotes the dissolution of portlandite and metal removal. Therefore, red mud has demonstrated feasibility in the manufacturing of geopolymer-based pervious concrete for purification AMD.

A kinetic descriptor to optimize Co-precipitation of Nickel-rich cathode precursors for Lithium-ion batteries

This work proposes a kinetic descriptor, reaction quotient to equilibrium constant ratio ( Q / K ), to optimize co-precipitation of nickel-rich hydroxides. Ammonia concentration of 1.0 M rendered the Q / K close to 1, where the crystals can grow efficiently by Ostwald ripening. The enhanced morphological uniformity and performances of the nickel-rich cathode validate the effectiveness of this methodology. • A descriptor to optimize co-precipitation of precursors for nickel-rich cathodes. • Well-ordered hydroxide particles can grow by Ostwald ripening if Q / K approaches 1. • The enhanced morphology and performances validate the suggested descriptor. Nickel-rich cathodes are advantageous for lithium-ion batteries (LIBs) due to their exceptional energy densities at lower cost. In general, particles' shape and crystal structure greatly influence the electrochemical performances of cathode active materials. In this regard, co-precipitation can afford secondary particles made of highly crystalline primary particles with uniform composition. Auxiliary complexing agent such as ammonia provides sufficient time for the well-ordered nucleation and growth of primary and secondary particles by retarding the hydroxide formation. Herein we suggest the reaction quotient ( Q ) to equilibrium constant ( K ) ratio, as a kinetic descriptor for the effective nucleation and crystal growth of metal hydroxide. Based on the cumulative formation constant and the solubility product values of each metal ion, about 1.0 M NH 3 concentration rendered the Q / K ratio close to 1, which implies balanced precipitation and dissolution of metal hydroxide that provides sufficient time for the crystal growth. In accordance with the theoretical expectation, co-precipitation at 1 M NH 3 rendered particles with uniform shape and size. And the resultant nickel-rich cathode outperformed other samples co-precipitated at different NH 3 concentrations, in terms of significantly higher discharge capacity, cycle stability, and rate capability.

Biochar admixture cement mortar fines for adsorptive removal of heavy metals in single and multimetal solution: Insights into the sorption mechanisms and environmental significance

The combined action of biochar and C-S-H (calcium-silicate-hydrate) in the cement mortars as adsorbents was explored for treating heavy metals from water. The biochar admixture cement mortars were ground to fines for use as adsorbents with the rationale that combined action of Ca, Si, Al etc. based industrial waste with conventional adsorbent biochar could enhance the removal efficiency of contaminants and therefore the overarching aim was to study the removal capacity for three selected heavy metals (Pb2+, Cu2+ and Zn2+) commonly found in the aqueous waste stream. Batch adsorption was carried out on single and multi-metal systems to determine the removal efficiency under varied conditions such as pH, dosage of adsorbent, the effect of contact time and the initial concentration of the adsorbate. For Pb(II), Cu (II) and Zn(II), pH 5 was optimized for single and multi-metal batch sorption studies. A dosage of 20 mg for single metal and 70 mg for multi-metal of an adsorbent dose was found to be sufficient to remove about 70–90% of the three heavy metals in 25 mL solution. Langmuir model best described the isotherm data with maximum adsorption capacities of 476, 81, 123 mg/g for Pb2+, Cu2+ and Zn2+ for BC-40 during single metal adsorption, which were quite comparable to other C-S-H and cement-based adsorbents. The metal hydroxides precipitation, the ion exchange between the Ca2+ and metal ions and metal complexation were explained as plausible mechanisms for the heavy metal removal.

A Pitfall in Heavy Metal Separation with Amino-modified Silica Adsorbents from Aqueous Solution: The Occurring pH Shift.

Selective separation of heavy metal ions from acidic aqueous solutions is of strong interest for certain industrial processes, such as electroplating, as well as environmental protection, for example battery recycling. Amino‐functionalized adsorbents are often discussed as suitable material for this purpose. Herein, two silica‐based adsorbents functionalized with 3‐aminopropyl‐ and 3‐[2‐[2‐aminoethylamino]‐ethylamino]‐propyl‐ligands resulting in adsorbents MonoA and TriA, respectively, were investigated regarding their separation behavior with focus on nickel(II) and cobalt(II) in batch as well as continuous flow experiments in acidic aqueous solutions. For both adsorbents, pH shifts into the alkaline range were observed in the process solutions, causing precipitation of metal hydroxides mainly in the particle pores in case of adsorbent MonoA and a combination of precipitation and adsorption regarding adsorbent TriA.Contrary to prior studies, our findings evidence that amino‐functionalized adsorbents are not applicable for nickel(II) and cobalt(II) in selective adsorption processes and additionally demonstrate that, besides batch investigations, continuous flow experiments are essential for well‐founded adsorbent selections in process development.

Application of Electrodialysis for the Selective Lithium Extraction Towards Cobalt, Nickel and Manganese from Leach Solutions Containing High Divalent Cations/Li Ratio

The present work aims at investigating the potentialities of implementation of electrodialysis for the recycling of spent lithium-ion batteries. In this work, the use of highly-selective membrane toward lithium(I) in electrodialysis was investigated to recover selectively lithium(I) toward cobalt(II), nickel(II) and manganese(II) by means of monovalent ion-selective membranes. It was shown that the presence of divalent cations in the leach solution is responsible for a significant decrease of the limiting current despite an increase in ionic conductivity. Therefore, monitoring the ionic conductivity was not sufficient to operate electrodialysis under optimal conditions, especially when highly selective membranes were used. Furthermore, it was demonstrated that the current has to be lower than the limiting current to avoid metal hydroxide precipitation into the membrane porosity by monitoring the limiting current over time.

Novel Zn-Fe engineered kiwi branch biochar for the removal of Pb(II) from aqueous solution

In this study, a novel adsorbent made from kiwi branch biochar modified with Zn-Fe (KB/Zn-Fe) was compared with original biochar to the Pb(II)'s adsorptivity from waste water. The adsorbent was synthetized by liquid-phase deposition. Batches of sorption tests were performed, and the biochars' representative properties were tested. Characterizations revealed the physicochemical properties of biochars and showed that the KB/Zn-Fe composites were successfully synthesized. The Langmuir model and pseudo-second-order kinetic model were proven to satisfactorily fit the original biochar and KB/Zn-Fe. The KB/Zn-Fe showed Langmuir maximum adsorption ability to Pb (II) in aqueous solution of 161.29 mg g-1, compared with 36.76 mg g-1 for original biochar. The adsorption ability of Pb(II) decreased and the Pb(II) removal efficiency increased with increasing biochar dose. The effect of co-existence of NO3- to the absorptive capacity of KB/Zn-Fe on Pb(II) was unremarkable, but Cl- could increase the absorptive capacity. Multiple Pb(II) adsorption mechanisms by KB/Zn-Fe include surface precipitation of metal hydroxides, complexation with active functional groups and ion-exchange. This work provides guidance for future production of biochar with efficient adsorption ability, which could be used to remove Pb(II) ions from wastewater.

PRECIPITATION OF METAL HYDROXIDES FROM AQUEOUS SOLUTIONS AS A RESULT OF SPONTANEOUS CONDENSATION OF POLYNUCLEAR HYDROXOCOMPLEXES

Background. Generally, it is assumed that the formation of a solid phase (precipitate) happens when the activities of the involved ions would exceed those defined by the thermodynamic solubility product. However, in case of precipitation of metal hydroxides, this is a simplification, and the real pattern is more complicated, since metal ions form strong mono- and polynuclear hydroxocomplexes in a solution. Formation of such complexes, especially those with zero charge, should result in the deviation from the common solubility product rule. Objective. The aim of this paper is to develop a precipitation model, which takes into account the effect of the formation of the hydroxocomplexes on the solubility of a metal hydroxide. Eventually, this solubility includes the sum of the concentrations of metal ions, and all neutral, positively and negatively charged hydroxocomplexes involved in all equilibria in aqueous solution. Methods. We assume that formation of the solid precipitate is the result of spontaneous condensation of polynuclear neutral hydroxocomplexes when their concentrations in a solution exceed a certain critical value. These critical concentrations can be estimated from the consideration of all equilibria with the assumption that the equilibrium constants for the formation of neutral polynuclear complexes when their nuclearity increases by one are approximately equal and do not significantly depend on the size of the particle. Results. Using this approach, we developed the model, which predicts spontaneous condensation with formation of a precipitate. Also, we calculated the dependencies of pH-logCM for precipitation of various divalent cation hydroxides. It was shown that there exist minimal concentrations, below which no precipitates are formed at any pH value. Conclusions. Such approach also explains the nature of linear correlations between logarithms of solubility products and stability constants of neutral complexes described in literature. These results are important for the development and optimization of industrial wastewater treatment processes.

Effective removal of Cu(II), Pb(II) and Cd(II) by sodium alginate intercalated MgAl-layered double hydroxide: adsorption properties and mechanistic studies.

To improve the adsorption efficiency of layered double hydroxides (LDHs) for heavy metals, a novel sodium alginate (SA) intercalated MgAl-LDH (SA-LDH) was synthesized in this work. SA-LDH was characterized by XRD, FTIR, XPS and employed as adsorbent for Cd(II), Pb(II), Cu(II) elimination. Adsorbent dosage, initial pH and contact time, which are regarded as several key parameters, were optimized. The results showed that SA-LDH exhibited better adsorption performance compared with the pristine MgAl-LDH. The maximum adsorption capacities of SA-LDH for Cu(II), Pb(II) and Cd(II) reached 0.945, 1.176 and 0.850 mmol/g, respectively. The possible mechanisms were analyzed by XPS, XRD and FTIR. The results showed that Cd(II), Pb(II) and Cu(II) may be removed by SA-LDH via (i) bonding or complexation with Sur-OH or Sur-O- of SA-LDH, (ii) precipitation of metal hydroxides or carbonates, (iii) isomorphic substitution, and (iv) chelation with -COO- in the interlayers. This work provides an effective method for the development of LDH-based adsorbent and the treatment of wastewater containing heavy metals.

Al-doped yttrium iron garnets Y3AlFe4O12: Synthesis and properties

A method to synthesize nanosize particles of Y3AlFe4O12 garnet ferrite by precipitation in aqueous solutions at constant pH during the synthesis has been demonstrated. The effect of the sequence of the metal hydroxides precipitation on the filtration coefficient is studied. The filtration coefficient is found to be three times greater in the case of simultaneous precipitation of iron and aluminum hydroxides compared to the one observed for the case of simultaneous precipitation of all hydroxides. Synthesized precipitates are established to be amorphous and crystalline nanoparticles are formed in one stage after the treatment at 800 °C. The average particles size is around 60–70 nm. The ceramics obtained after a proper heat treatment of the nanoparticles is shown to be characterized by the high density and good electrophysical properties.

Reactivity of Zinc Cations under Spontaneous Accumulation of Hydrophobic Coexisting Cations in Hydrophobic Nanoporous Silicon.

The ion enrichment behavior due to surface-induced phase separation and the concomitant phase transition of electrolyte solutions between a liquid and a solid confined within nanopores of porous silicon is examined using concentrated aqueous solutions. We performed open-circuit potential measurements and differential scanning calorimetry (DSC) while varying the concentration of aqueous tetraethylammonium chloride (TEACl) solution. Open-circuit potential measurements revealed that the local OH– concentration within the nanopores increases as the bulk TEACl concentration increases. DSC measurements indicated that TEA+ cations are enriched within the nanopores and an extremely high concentration of TEA+ remarkably increases the local OH– concentration. This increase in the local pH should realize the selective precipitation of metal hydroxides within the nanopores. However, such precipitation was not observed in our investigations using aqueous solutions containing zinc cations. The experimental results suggest that ionic species within the nanopores of porous silicon are more stable than those in a bulk solution due to the formation of ion pairs with enhanced stability as well as kinetic factors that increase the activation energy for precipitation.

Basic Sulfate Precipitation of Zirconium from Sulfuric Acid Leach Solution

H2SO4 was ensured to be the best candidate for Zr leaching from the eudialyte. The resulting sulfuric leach solution consisted of Zr(IV), Nb(V), Hf(IV), Al(III), and Fe(III). It was found that ordinary metal hydroxide precipitation was not feasible for obtaining a relatively pure product due to the co-precipitation of Al(III) and Fe(III). In this reported study, a basic zirconium sulfate precipitation method was investigated to recover Zr from a sulfuric acid leach solution of a eudialyte residue after rare earth elements extraction. Nb precipitated preferentially by adjusting the pH of the solution to around 1.0. After partial removal of SO42− by adding 120 g of CaCl2 per 1L solution, a basic zirconium sulfate precipitate was obtained by adjusting the pH to ~1.6 and maintaining the solution at 75 °C for 60 min. Under the optimum conditions, the loss of Zr during the SO42− removal step was only 0.11%, and the yield in the basic zirconium sulfate precipitation step was 96.18%. The precipitate contained 33.77% Zr and 0.59% Hf with low concentrations of Fe and Al. It was found that a high-quality product of ZrO2 could be obtained from the basic sulfate precipitate.

PH evolution during water washing of incineration bottom ash and its effect on removal of heavy metals

Incineration bottom ash (IBA) of municipal solid waste is a potential construction material for civil engineering. However, the possible leaching of trace heavy metals from IBA is a concern. Water washing is a simple and economic method to remove heavy metals from IBA. In order to optimize the water washing process of IBA, this study investigated the pH evolution during washing and its effect on the removal of several heavy metals, including lead (Pb), zinc (Zn), nickel (Ni), cadmium (Cd), copper (Cu), and chromium (Cr), through a small-scale laboratory experiment. The results show that the pH of washing water increases quickly in the first 1–3 h mainly due to the dissolution of quicklime and portlandite, and then decreases with the increasing of washing time might be due to consumption of OH− by precipitation of metal hydroxides. The concentrations of Pb, Zn, and Ni in the washing water show a similar trend as that of the pH with time, whilst the concentrations of Cd, Cu, and Cr increase with the increase of washing time. Hence, the optimum washing time should be determined accordingly based on the most concerned metal(s), as well as the pH evaluation during washing.

Hydrometallurgical Recovery of Cobalt(II) from Spent Industrial Catalysts

The work presents studies on the application of hydrometallurgical recovery of cobalt(II) from solutions after leaching spent industrial catalysts used in process of hydrodesulfurization. A four-stage process was proposed, which consists of: leaching, precipitation of metal hydroxides accompanying Co(II), extraction of Co(II) with bis(2,4,4-trimethylpentyl)phosphinic acid and Co(II) stripping from the organic phase. The results indicate that by using the proposed method it is possible to leach Co(II) and Mo(VI) from spent catalyst, and remove main impurities such as Al(III), Fe(III) in hydroxide precipitation step and separate Co(II) from Mo(VI) by extraction and stripping.

Evaluation of charcoal ash nanoparticles pollutant removal capacity from acid mine drainage rich in iron and sulfate

Abstract Acid mine drainage is globally recognized as one of the environmental pollutants, due to its highly toxic metals and sulfate concentration. In this study, the effect of metal and sulfate removal capacity of Namibian hardwood charcoal ash from acid mine drainage was investigated. The experimental results have shown that charcoal ash has dual pollutant removal capacity via adsorption and precipitation. For adsorption, insoluble charcoal ash minerals and precipitates produced during treatment are responsible. While soluble metal oxides and sparingly soluble carbonates are essential for neutralization of the acid mine drainage and metal hydroxide precipitation. Based on the treated acid mine drainage analysis results, almost complete and partial removal of toxic metals and sulfate from acid mine drainage was observed, respectively. Unlike commonly used lime or limestone obtained by purchasing and also which requires crushing to form a powder, charcoal ash obtained for free, need no modification due to its nanoparticle size (20–96 nm) and environmentally friendly nanomaterials. Collection and use of charcoal ash for pollution remediation is one way of creating a clean environment. Overall, charcoal ash performed well in metals and sulfate removal and has been found an attractive and novel-alternative for acid mine drainage treatment, with an added-value of resource recovery.