Precipitation Of Ca Research Articles

Triple-function carbon-based Ca2+ ion-selective pH ring microelectrode to study real-time bacteria-mediated hydroxyapatite corrosion

BackgroundThe local pH change mediated by the pathogenic bacterial species Streptococcus mutans plays a significant role in the corrosion of hydroxyapatite (HA) present in the tooth in the dynamic oral cavity. The acid produced by the bacteria decreases the local pH and releases Ca2+ ions from the HA. We studied the bacteria-mediated demineralization of HA by scanning electrochemical microscopy (SECM) after growing S. mutans biofilm on HA for 7 days. ResultsWe notably developed a triple-function SECM-compatible tip that could be positioned above the biofilm. It can also measure the pH and [Ca2+] change simultaneously above the biofilm-HA substrate. The triple-function SECM tip is a combination of a potentiometric pH sensor deposited with iridium oxide and a dual-function carbon-based Ca2+ ion-selective membrane electrode with a slope of 67 mV/pH and 34.3 mV/log [Ca2+], respectively. The distance-controlled triple-function SECM tip monitored real-time pH and [Ca2+] changes 30 μm above the S. mutans biofilm. The high temporal resolution pH data demonstrated that after approximately 20 min of sucrose addition, S. mutans started to produce acid to titrate the solution buffer, causing a pH change from 7.2 to 6.5 for HA and from 7.2 to 5 for the glass substrate. We observed that, after 30 min of acid production, ∼300 μM of Ca2+ ions were increased at pH 6.5 above the biofilm surface as a result of the pH change in the local microenvironment. After the release of Ca2+ from HA, the pH environment again shifted toward the neutral side, from 6.5 to 7.2. Therefore, precipitation of Ca2+ happens at the top of the biofilm, thus corroding the HA from underneath. For a glass substrate, in contrast, no Ca2+ ions were released, and the pH did not change back to 7.2. We were able to observe the dynamics of the HA demineralization–remineralization process simultaneously with our newly developed triple-function SECM tip or microprobe. SignificanceThis technique could notably advance the study of similar complex processes, such as bacteria-mediated corrosion in biomedical and environmental contexts.

Fate of calcium, magnesium, and phosphate during Fe electrocoagulation: An investigation for mitigating cathodic scaling in phosphate removal process

Fe electrocoagulation (Fe-EC) is efficient for the removal of phosphate (PO43−-P). The fate of Ca2+, Mg2+, and PO43−-P during the Fe-EC process is unclear, resulting in the difficulty for mitigating the cathodic scaling. After Fe-EC treatment for 10 min at 10 mA/cm2, PO43−-P was mainly distributed in the sediment (>90 %). Ca and Mg was mainly distributed in the solution (54 % − 97 %), followed by in the sediment (2 % − 44 %) and on the cathode (0 % − 6 %). Although only a small amount of Ca and Mg was precipitated on the cathode, with a long term operation, cathodic scaling would still occur. The precipitation of Ca on the cathode was mainly caused by the presence of HCO3− with other precipitates which directly precipitated with OH− as crystal seeds, because the precipitation of CaCO3 did not depend on the local pH near the cathode. The precipitation of Mg on the cathode was mainly caused by a lower applied current, because Mg(OH)2 which formed on the cathode would be prevented by H2 evolution with a higher current. Accordingly, the strategies for preventing cathode scaling are proposed. The precipitation of Ca can be prevented by increasing the current both with HCO3− and crystal seeds, and by increasing the current only with PO43−-P. It is hard to prevent the precipitation of Ca by controlling the current only with HCO3−. The precipitation of Mg can be prevented by increasing the current. With the initial concentrations of PO43−-P, HCO3−, Ca2+, and Mg2+ in the real wastewater 1.0 mg/L, 48 mg/L, 150 mg/L, and 30 mg/L, respectively, the amounts of Ca and Mg deposited on the cathode were much less at 10 mA/cm2 (5.8 ± 2.9 mg/L, 1.1 ± 0.3 mg/L) than those at 1 mA/cm2 (28.6 ± 4.6 mg/L, 5.0 ± 0.4 mg/L). With the above controlling strategies, the cathode scaling can be alleviated under different water quality conditions.

Granular sludge characterization and microbial response in a hydroxyapatite (HAP)- anammox coupled process at different nitrogen loading rates

To enhance the treatment capacity and operational stability of the anammox process for nutrient-rich wastewater disposal, a hydroxyapatite (HAP)-anammox coupled process was developed in a granular sludge-based upflow bioreactor. The impact of nitrogen loading rate (NLR) on process performance was investigated by gradually increasing the NLR from 1 to 1.5, 3, and 5 kgN/m3/d for 264 days continuous operation. TN and TP removal rates of 82.51 ± 3.58 % and 60.49 ± 2.82 % were achieved at the NLR of 5 kgN/m3/d. The precipitation of Ca and phosphorus resulted in HAP crystals formation evidenced by sludge morphology and component analysis, which enhanced sludge settling properties and facilitated biomass enrichment. The HAP-anammox granular sludge was characterized by the outer layer HAP crystals formed on inner anammox granules, while highly mineralized granular sludge with higher density distributed at the bottom of the reactor is conducive to HAP-based phosphorus recovery. After a long-term accumulation, the abundance of Planctomycetota phylum gradually increased (from 7.7 % to 14.1 %), consisting of three species of anammox bacteria, namely Candidatus_Brocadia_sapporoensis, Candidatus_Brocadia_sinica and Candidatus_Kuenenia_stuttgartiensis. Nitrogen metabolic pathway analysis illustrated that denitrification was also present except the anammox reaction, synergistically contributing to superior nitrogen removal in the HAP-anammox process.

Effect of electrochemical treatment in mitigating OH− leaching from cement paste and its microscopic analysis at BSE imaging

The present study concerns the electrochemical treatment between steel embedment and an external mesh in mitigating OH− ion leaching from the cement paste into external water, which was ensured by a microscopic observation on the surface of the cement paste specimen at the backscattered electron (BSE) image analysis and by measuring the leaching rate for OH− ions with time. The electrochemical properties for the treatment included 1000 mA/m2 current density and 4 weeks duration. As a result, the pH at the electrochemical treatment in the external water accounted for 9.32 in the pH, while the untreated specimen indicated 13.46, implying a quite reduction of OH− ion leaching to a water environment. The porosity on the surface was reduced to lower the access of external water, while the decomposition of C–S–H gel was lowered. Due to the precipitation of Ca(OH)2, a further solidification of hydration phases could lower OH− ion leaching.

Calcium-decorated biochar modified with phosphorus from wastewater to promote U(VI) removal: Adsorption behavior and mechanism

In this study, waste shrimp shell and phosphorous-containing wastewater were used to synthesize calcium-decorated biochar modified with phosphorus (Ca-BC-P) and utilized to remove uranium from aqueous solutions. The results from static adsorption experiment demonstrated that Ca-BC-P exhibited good U(VI) adsorption performance in acidic environments, with a maximum theoretical adsorption capacity of 1074.29 mg g−1. The adsorption behavior perfectly fit Langmuir isotherm and the pseudo-second-order kinetic models, which revealed the nature of monolayer chemical adsorption by Ca-BC-P. Thermodynamic analysis showed that this process was spontaneous and endothermic. Ca-BC-P also displayed excellent selectivity and could be reused for several times while keeping a high U(VI) removal efficiency. When treating simulated acidic uranium mine wastewater, the removal efficiency of uranium reached 99.9 % with Ca-BC-P. The U(VI) removal mechanism was attributed to the precipitation of Ca(UO2)2(PO4)2·6H2O and surface complexation, nHAP on the surface of Ca-BC-P played a pivotal role during the adsorption process. Therefore, Ca-BC-P could be prepared economically and showed great potential for efficiently remove uranium from mining wastewater.

Synergy between Ca2+ and high ionic field‐strength cations during the corrosion of alkali aluminoborosilicate glasses in hyper‐alkaline media

AbstractOne major factor impeding the design of nuclear waste glasses with enhanced waste loadings is our insufficient understanding of their composition–structure–durability relationships, specifically in the environments the waste form is expected to encounter in a geological repository. In particular, the high field‐strength cations (HFSCs) are an integral component of most waste streams. However, their impact on the long‐term performance of the glassy waste form remains mostly undeciphered. In this context, the present study aims to understand the impact of some HFSCs (i.e., Nb5+, Zr4+, Ti4+, and La3+) on the dissolution behavior of alkali/alkaline‐earth aluminoborosilicate‐based model nuclear waste glasses in hyper‐alkaline media. At pH = 13, the studied glasses dissolve through the dissolution–reprecipitation mechanism, with Ca precipitation being the most vital step to passivation. In Ca‐free glasses, although the HFSCs slow down the forward rate, they do not seem to impact the residual rate behavior of glasses. The presence of Ca2+, however, initiates the rapid precipitation of network polymerizing HFSCs (i.e., Nb5+, Zr4+, and Ti4+) into a Ca2+/HFSCs‐based passivating layer, thus suggesting a synergy between Ca2+ and HFSCs that contributes to the enhanced long‐term durability of the glasses. Such synergy is not strongly evident for La3+, but instead, a potential La/Si affinity is observed upon the formation of the alteration layer.

Physical properties and enamel remineralization potential of arginine-fluoride varnishes

ObjectiveThe study objectives were to examine the physical properties and enamel remineralization potential of fluoride (F) varnishes incorporated with arginine (Arg). MethodsFour commercial F varnishes: 1) Duraphat®; 2) Flúor Protector®, 3) Fluor Protector S®, and 4) Fluorimax™ were supplemented with 2% w/v. Arg. The control/experimental varnishes underwent rheometric analysis to assess varnish density (δ), velocity (ν), and associated viscosity, both quantitatively (ν/δ) and qualitatively based on determined mass, volume, distance flow, and time under experimentation. The varnish wet/dry weights (at 2 h) were also analysed. Further, sound enamel specimens (T0) with artificial incipient caries-like lesions (T1) were treated with control/experimental varnishes and subjected to remineralization assay with artificial saliva for 6 h. Thereafter (T2), the specimens were characterized to estimate precipitated Ca and net enamel F uptake. Additionally, mineral density (MD) was assessed using micro-CT at T0, T1, and T2 to derive mineral gain (MG) and % remineralization for the treatment groups. ResultsWhen Arg is incorporated, the physical properties of the F-containing varnishes undergo a significant transformation, resulting in higher density, varnish weight, dry varnish weight, and viscosity compared to their respective control varnishes (p < 0.05). Incorporating Arg-in Duraphat®, Fluor Protector S®, and Fluorimax™ significantly improved both enamel Ca precipitation and F uptake compared to the respective controls (p < 0.05). Additionally, the enamel F uptake was significantly higher with all the tested varnishes when enriched with Arg (p < 0.05). The combined data for MD, MG, and % remineralization suggests that the remineralization potential of F-varnishes significantly increased when enriched with Arg (p < 0.05). ConclusionIncorporating Arg in inorganic F varnishes improves their physical properties and enhances the enamel remineralization potential of the varnishes. Clinical significanceThis study highlights the possibility of incorporating Arg in distinct F-source varnishes. The synergism between active components (Arg-F) aids in enhanced remineralization and superior varnish physical properties, demonstrating a promising approach for high caries-risk patients.

Cesium immobilization of high pH and low pH belite-rich cement under varying temperature

Low-pH cement is being studied in radioactive waste repositories. The belite-rich cement (BRC) recently gained attention due to its higher CO2 sequestration and low pH attainment under carbonation exposure. Therefore, this study evaluated the effects of pH and temperature on cesium immobilization of BRC. High pH (12.6) and low pH (9.9) BRC were produced via air curing and carbonation treatment, respectively. The high and low pH BRC samples were placed in a leaching environment at 25 °C and 45 °C for 90 days. An inverse correlation between pH and cesium mobilization of BRC was observed. The high pH BRC achieved the lowest effective diffusion coefficient (4.05E-09 cm2/s), whereas the highest value (2.64E-07 cm2/s) was achieved in case of low pH BRC. The physicochemical and morphological properties unveiled the decrease in Si/Ca ratio of gel, precipitation of Ca2+ ions in calcite formation, and increment in pore structure connectivity (pore size > 100 nm) in low pH BRC. However, the high pH BRC demonstrated the high Si/Ca ratio in C-S-H gel, hydroxide phases and higher disconnected pores. Thermodynamic modeling revealed the presence of significant carbonated phases beyond 15% CO2 uptake. The findings contributed to the BRC’s feasibility in developing nuclear waste storage facility.

Evaluation of the shear stability of aerobic granular sludge from a pilot-scale membrane bioreactor: Establishment of a quantitative method

This work established a quantitative method to access the shear stability of aerobic granular sludge (AGS) and validated its feasibility by using the mature AGS from a pilot-scale (50 tons/day) membrane bioreactor (MBR) for treating real municipal wastewater. The results showed that the changing rate (ΔS) of the peak area (S) of granule size distribution (GSD) exhibited an exponential relationship (R2≥0.76) with the shear time (y=a−b·cx), which was a suitable indicative index to reflect the shear stability of different AGS samples. The limiting granule size (LGS) was defined and proposed to characterize the equilibrium size for AGS after being sheared for a period of time, whose value in terms of Dv50 showed high correlation (R2=0.92) with the parameter a. The free Ca2+ (28.44–34.21 mg/L) in the influent specifically interacted with polysaccharides (PS) in the granule's extracellular polymeric substance (EPS) as a nucleation site, thereby inducing the formation of Ca precipitation to enhance its Young's modulus, while Ca2+ primarily interacted with PS in soluble metabolic product (SMP) during the initial granulation process. Furthermore, the Young's modulus significantly affected the parameter a related to shear stability (R2=0.99). Since the parameter a was more closely related (R2=1.00) to ΔS than that of the parameter b or c, the excellent correlation (R2=0.99) between the parameter a and the wet density further verified the feasibility of this method.

Magnesite everywhere: Formation of carbonates in the alkaline lakes and playas of the Cariboo Plateau, British Columbia, Canada

The Cariboo Plateau in central British Columbia, Canada, hosts the largest aerial extent of low temperature lacustrine magnesite in the world. Magnesite was the most abundant carbonate mineral in 21 of 33 sampled alkaline lakes and 20 of 22 sampled playas. Calcite, hydromagnesite and very high magnesium calcite (VHMC, also called disordered dolomite) were also found in closed basin alkaline lakes on the plateau. Carbonate mineralogy was strongly associated with lake water geochemistry, particularly total alkalinity. VHMC was the dominant carbonate mineral in lakes with the highest alkalinities (>1000 mEq/kg), magnesite was the dominant carbonate mineral in lakes in the middle range of alkalinities (generally 70 to 800 mEq/kg) and hydromagnesite with minor amounts of magnesite was the phase assemblage in lakes with lower relative alkalinities (<110 mEq/kg). The geochemical trends for the activity of CO32−, Ca2+ and Mg2+ suggest that these constituents in all Cariboo water bodies are controlled by the precipitation of Ca- and/or Mg‑carbonate minerals. The waters are near equilibrium with metastable crystalline Ca‑carbonate and Mg‑carbonate minerals. We hypothesize that carbonates present in the lakes likely formed via non-classical crystallization pathways based on the relationship between aqueous geochemistry and mineralogy and the chemical composition of the Ca-bearing magnesites. Non-classical crystallization offers new models for thinking about magnesite formation in lacustrine environments.

Kinetic analysis and mechanism of nitrate, calcium, and cadmium removal using the newly isolated Pseudomonas sp. LYF26

The co-existence of heavy metals and nitrate (NO3−-N) pollutants in wastewater has been a persistent global concern for a long time. A strain LYF26, which can remove NO3−-N, calcium (Ca(II)), and cadmium (Cd(II)) simultaneously, was isolated to explore the properties and mechanisms of synergistic contaminants removal. Different conditions (Cd(II) and Ca(II) concentrations and pH) were optimized by Zero-, Half-, and First-order kinetic analyses to explore the environmental parameters for the optimal effect of strain LYF26. Results of the kinetic analyses revealed that the optimal culture conditions for strain LYF26 were pH of 6.5, Cd(II) and Ca(II) concentrations of 3.00 and 180.00 mg L−1, accompanied by Ca(II), Cd(II), and NO3−-N efficiencies of 53.10%, 90.03%, and 91.45%, respectively. The removal mechanisms of Cd(II) using strain LYF26 as a nucleation template were identified as biomineralization, lattice substitution, and co-precipitation. The differences and changes of dissolved organic matter during metabolism were analyzed and the results demonstrated that besides the involvement of extracellular polymeric substances in the precipitation of Cd(II) and Ca(II), the high content of humic acid-like species revealed a remarkable contribution to the denitrification process. This study is hopeful to contribute a theory for further developing microbially induced calcium precipitation used to treat complex polluted wastewater.

Diisobutylamine mediated CO2 mineralization and CaCO3 production from municipal solid waste incineration fly ash as raw ingredient and regeneration reagent

The CO2 mineralization technology involving Ca leaching and subsequent mineralization has emerged in recent years. It is still plagued by slow mineralization rate and frequent pH swings, requiring the consumption of exogenous substances. In this study, a leaching-mineralization-regeneration process for CO2 sequestration and CaCO3 production from municipal solid waste incineration fly ash (MSWIFA) mediated by diisobutylamine was proposed. Ca could be effectively extracted into the leaching solution with a concentration of 37420 mg/L from fly ash while heavy metals could be left in the leached residue. Diisobutylamine, acted as an H+ extractant and a crystal form regulator, was mixed with 1-octnaol to form a novel extraction system. When diisobutylamine/1-octanol/leaching solution ratio was at 1:2:3, almost full precipitation of Ca and a high CaCO3 yield of 282.4 g/kgfly ash was achieved. The crystal form of the CaCO3 product was confirmed by scanning electron microscope to be spherical and identified by X-ray diffraction as vaterite. The product purity (99.1 %) met the standard requirement (HG/T 2226–2019) for industrial use. Fly ash acted as a regenerant and was able to fully regenerate the extraction system. The mineralization performance of the regenerated extraction system remained relatively stable in multiple cycles of mineralization-regeneration process. Given the fundamental nature of this research, it would provide a potential route for future CO2 mineralization and Ca-containing waste utilization.

Exploitation of ladle furnace iron slag for semiconductor borosilicate glass production

The supply consumption of ladle furnace slag (LFS) is a prominence of recent researches and is extensively considered. In this work LFS has the potential to be utilized as the main raw material for producing glass and glass-ceramics because of its chemical compositions similarities to the silicate glass materials. Three borosilicate glass samples were produced via melting – quenching technique. The three samples contained 10, 20, 30 wt % of slag waste materials, respectively. The second sample was heat treated at 625 °C, guiding by DTA studies, for 2, 6, 10, or 15 h. XRD studies showed traces precipitation of Ca(Mg,Al) (Si,Al)2O6 (diopside), Sodium Aluminum Silicate (NaAlSiO4), Sodium Aluminum Borate (Na2Al2B2O7) and Clinoenstatite (MgSiO3) phases. FTIR analysis demonstrated the same functional groups through glass and glass ceramics sample confirming that all prepared samples had the same structure. Ferrimagnetism property of a glass sample and its glass ceramic sample derivative was confirmed by vibrating sample magnetometer (VSM) analysis. Vickers microhardness and fracture toughness results indicated noticeable rising in toughness value and decreasing of hardness after using 100 g load by increasing slag percent in glass samples. The glass ceramic sample had little change, in hardness and toughness values, rather than its corresponding glass sample due to its lower crystallization behavior. The low dielectric constant values are very good indication for the availability of using these type of glass for electronic applications. X-ray photoelectron spectroscopy (XPS) studies indicate that manganese ions are found as MnO in both glass and glass ceramic samples.

Synthesis of Calcium Manganese Oxide Films Using a Sol–Gel Method and Evaluation of Color and Photocatalytic Properties

Herein, for developing colored photocatalysts, calcium manganese oxide (Ca–Mn–O) film and powder samples are synthesized by a sol–gel method using acetylacetone (acac) or citric acid as a chelating agent, and their color and photocatalytic properties are evaluated. Thin‐film X‐ray diffraction experiments clarify the precipitation of Ca–Mn–O phases, such as Ca3Mn2O7 (Ca/Mn = 1.5) and Ca2MnO4 (Ca/Mn = 2), in the film samples with drop‐cast coating. These films strongly absorb all visible light due to the interband transition between O 2p and Mn 3d orbitals, resulting in dark gray coloration. By testing photocatalytic activities using methylene blue dyes, it is revealed that the film sample (acac, 4‐drops) exhibits photocatalytic activities, which makes Ca–Mn–O films dual functional with photocatalytic functions and coloration.

The Influence of DOC on the Migration Forms of Elements and Their Sedimentation from River Waters at an Exploited Diamond Deposit (NW Russia)

The development of mineral deposits causes changes that are comparable to natural exogenous geological processes, and prevail over the latter in local areas of intensive mining activity. In this article, a diamond deposit is selected, developed by quarries of great depth, and a forecast is made of the impact of drainage water discharge on changes in the composition of surface water and bottom sediments during the entire period of development of the deposit. Modeling was performed according to various scenarios, taking into account changes in the total dissolved solids of groundwater from 0.5 to 21.7 g/kg H2O. Thermodynamic calculations were carried out using the HCh software package. The role of dissolved organic carbon in the migration of chemical elements and the effect of DOC on the precipitation of chemical elements from mixed solutions is given. It has been established that fulvic acid completely binds to Fe in the Fe(OH)2FA− complex in all types of natural waters and under all mixing scenarios. With humic acid, such a sharp competitive complex formation does not occur. It is distributed among the various elements more evenly. It was determined that the mass of precipitating iron in the presence of DOC decreases by 18–27%, and its precipitation in winter is more intense. In contrast to Fe, the precipitation of Ca, Mg, and C from solutions with DOC is higher in summer, and there are more of them in the solutions in winter. This study contributes to a better understanding of the behavior of heavy metals in surface waters and sediments under anthropogenic pressures in order to improve the sustainable management of water resources in the face of anthropogenic activities.

Chemical conditioning of drinking groundwater through Ca2+/Mg2+ ratio adjust as a treatment to reduce Ca precipitation: Batch assays and test bench experiments

Drinking groundwater sources can vary in their calcium (Ca)/magnesium (Mg) ratios, alkalinity levels, and temperatures. High levels of calcium relative to magnesium in water encourage Ca precipitation, causing pipe obstruction problems during water distribution. Ca/Mg ratio was studied in batch experiments using synthetic and real groundwater at different alkalinity levels, and temperatures to obtain an optimal condition that reduces Ca precipitation. The addition of magnesium salts to real drinking water was also investigated as a means of adjusting the Ca/Mg ratio and reducing Ca precipitation. A test bench was used to examine the effect of water velocity during its conduction on Ca precipitation, simulating an intermittent water supply. The results were analyzed and compared in terms of initial precipitation, rate of precipitation, and maximum precipitation of Ca using a modified model of Gompertz, and the precipitate was analyzed through X-ray Diffraction. The results of the present work found an optimal Ca/Mg ratio (1.1) that avoided Ca precipitation at batch conditions and during water conduction at different velocities, as well as Ca/Mg ratios that retarded or increased both the induction time and the maximum rate of Ca precipitation. Chemical conditioning by adjusting the Ca/Mg ratio is a viable option to minimize Ca precipitation in pipes.

Treatment of strong alkaline wastewater from neutral leaching of EAF dust by precipitation and ion exchange

Neutral leaching or water washing is used for Cl− and partially Ca2+ ion removal in order to save the leaching reagents for the next steps in hydrometallurgical treatment of electric arc furnace dust. This pre-treatment of the material leads to the generation of strong alkaline (pH = 11.9–12.7) leachate (wastewater), which underlies precipitation of Ca and other accompanying metals. This work presents results from the study of various economically differing (cost and time) techniques for elimination of these disadvantageous phenomena. The aim of the experimental study was to obtain water suitable for reuse in the leaching or for discharge into a recipient in accordance with valid legislation. The experiments were focused on the removal of precipitates, or metals which create the precipitates, and pH decreasing. Our results indicate that five-minute agitation of 4 g solid NaHCO3 and 1 L of neutral leachate and subsequent ion exchange in the sequence of strong-acid cation and strong-base anion exchange treatment led to the acquisition of water without creation of precipitates, with pH below 8.5 and conductivity approx. 0.03 mS. The removal of Cl− ions was not complete.

Experimental and economic evaluation of nanofiltration as a pre-treatment for added-value elements recovery from seawater desalination brines

Desalination brine mining emerges as a solution to supply raw materials to the European Union industry in a circular economy approach since valuable minerals and metals (e.g., B(III), Mg(II), Ca(II), Sc(III), V(V), In(III), Ga(III), Li(I), Mo(VI), Rb(I)) are present in seawater but in low concentrations. Brine pre-treatment is important to remove species that may impair the performance of other technologies involved and to increase recovery efficiencies. Hence, nanofiltration and calcium precipitation were proposed as pre-treatment stages. Nanofiltration was studied to separate monovalent from multivalent elements (Fonsalía desalination plant case study), while economically, it was evaluated whether it would be better to place it before (Scenario 1) or after (Scenario 2) a Ca(II) precipitation stage, considering that Ca(II) can produce scaling in membranes. Three commercial membranes were tested using synthetic brines at 30 bar. Experiments (65 % permeate recovery) showed that Fortilife XC-N and PRO-XS2 membranes presented higher Ca(II) and Mg(II) rejection than NF270. Heating the brine for Ca(II) precipitation jeopardizes the economic feasibility of the project. Scenario 1 was the best configuration since it presented lower total levelized cost (≈1.6 €/m3 inlet, without heating the brine for Ca(II) removal). In such scenario, PRO-XS2 reported the best selectivity between monovalent and multivalent elements.

A quantitative recovery process of rare earth in bastnaesite leachate for energy saving and emission reduction

Extraction-precipitation method is a novel separation strategy, a new extraction-precipitant N-lauroyl sarcosine (NLSA) is synthesized in this article. It was found that the extraction-precipitant has a task-specific precipitation ability for rare earth (RE). RE(III) can be recovered quantitatively in the presence of Ca(II), Mg(II), Al(III). When the precipitation rate of RE is 96 %, the precipitation rate of Al is only 6.8 %. The separation coefficient (βRE/Al) reaches 375, and the precipitation of Ca(II) and Mg(II) is negligible. The solid complex produced in the precipitation process has a large particle size which is easy to be separated. In addition, the precipitation can be completely stripped with 6 mol/L hydrochloric acid, and the REO concentration of stripping solution reaches 255 g/L. After 5 cycles of extraction-precipitation, the specific precipitation of NLSA on RE remains basically unchanged. Mechanism analyses indicate that the extraction-precipitation process is cation exchange. The specificity of the precipitation process can be attributed to the steric hindrance of amide bonds hindering the coordination of Al (III). Finally, a novel enrichment process of bastnaesite leachate is developed to enrich RE, which can effectively remove impurities, so as to effectively avoid the generation of impurity removal residue. Also the enrichment process can reduce energy consumption and carbon emission. The pulverized coal consumption in this process is only 6.25 % of the existing industrial process, and the carbon emission has been decreased by 93.75 %.

(Digital Presentation) Application of Polarity Reversal and Performance Analysis of Continuous Electrocoagulation

An important challenge for continuous treatment by electrocoagulation (EC) is the passivation and fouling of electrodes which increases during the longer operation (Ingelsson et al., 2020). The application of polarity reversal (PR) and treatment performance of EC was investigated using continuous flow reactor for simultaneous removal of silica and hardness (calcium and magnesium) from produced water. Polarity reversal times (PRT) from 30 s to 10 min were studied at a fixed charge loading of 2000 C L- 1 (i.e., the amount of charge passed per unit volume of produced water treated) using Fe and Al electrodes. Periodic PR was found to reduce the fouling and de-passivate the electrodes by changing the surface chemistry at the electrode-electrolyte interface (Ingelsson et al., 2020; Yasri et al., 2022). During 90 minutes of continuous treatment the chronopotentiometric data indicated that a PRT of 10 min was more effective in reducing the cell voltage for both Fe and Al electrodes [Fig. 1 (a & b)]. With a longer PRT of 10 min, there is more time for the acid boundary layer to form on the anode, which mitigates metal precipitation at the anode. In contrast the higher cell voltage that persists in direct current EC (DC-EC) could be due to the precipitation of Ca and Mg minerals in the alkaline solution on the cathode surface, leading to cathode passivation (Chow et al., 2021). After the first polarity reversal, both electrodes have been anodic, removing passivation layers from the surface and reducing the cell voltage. On reversing the polarity, the cathode becomes the anode, and the acidic pH on the formed at the electrode interface will facilitate the dissolution of Ca and Mg precipitates on the electrode surface, reducing the cell voltage significantly. For Fe-EC, the contaminant removal performance increased with PRT, and the highest removal was observed with DC-EC (Fig. 1c). The increasing removal performance with PRT for Fe-EC is consistent with the increase in faradaic efficiency observed of 55%, 68%, 85%, and 99.8% with 30 sec, 2 min and 10 min PRT, and DC respectively. The lower faradaic efficiencies for Fe-EC with short PRTs are likely due to redox reactions of iron species at the electrode surface (Chow et al. 2021).The contaminant removal at a charge loading of 2000 C L–1 using DC-EC with Al electrodes was similar to that for PR-EC with PRTs of 2 to 10 min (Fig. 1d). Slightly lower Si and hardness removal was observed for Al-EC at the shortest PRT of 30 s. For Al-EC, the faradaic efficiency was also observed to increase with PRT, with values of 150%, 220% and 287% obtained at 30 sec, 2 min and 10 min PRT respectively. The super-faradaic (>100%) efficiencies can be explained by dissolution of the Al from the cathode under the local alkaline conditions that develop on the electrode surface. With a short PRT, there is less time for the alkaline pH to develop at the surface and hence the faradaic efficiency was reduced.