Adsorptive seawater desalination using MOF-incorporated Cu-alginate/PVA beads: Ion removal efficiency and durability

Poor water availability with the fast-growing population creates crucial issues for universal water security, and efficient approaches ought to be accomplished to balance the demand and supply. One of the most energy- and cost-effective methods for removing NaCl is adsorption desalination. Metal–organic frameworks with ceramic and nanoparticles are a comparatively new research route that increases the desalination capacity. The synthesized composites were examined for efficient and rapid removal of NaCl from NaCl solution or artificial seawater. The adsorption desalination properties were analyzed based on adsorption isotherm, adsorption kinetics, contact time, NaCl, and adsorbent dosage. The adsorptive desalination rate of ZnO@MIL88A(Fe)@α-cordierite composite was only decreased by 4% as the maximum loss after 5 consecutive cycles.

Aoshio is hypoxic milky blue-green seawater observed in some eutrophic bays. Previous studies have shown that colloidal sulfur causes the coloration and that the source of aoshio water is attributed to coastal anoxic bottom water. Occurrences of aoshio have been reported in limited areas of coastal seawater, although hypoxic transparent water seems rather universal. Promotion in auto-oxidation of sulfide by metal ions in seawater was investigated to explain the occurrences of aoshio. Artificial seawater containing 10 μM metal ion was assayed for the sulfide oxidation rate. The velocity constant which represents the oxidation rate within the initial 30 min and the amount of reacted sulfide in 2 h were determined by oxygen monitoring and sulfide quantification, respectively. Fe2+ and Cu2+ enhanced the initial 30 min reaction. Fe2+, Fe3+ and Ni2+ increased the amount of reacted sulfide in 2 h, forming whitish turbid water. Seawater from a suspected source of aoshio water was also assayed for the auto-oxidation rate of sulfide. The oxidation rate in water from 12 m depth was 13-19 times higher than the artificial seawater without an addition of heavy metal ions. More than 15% of the oxidation rate in 12 m deep seawater was explained by dissolved iron in the seawater.

High sulfate content in seawater forms sulfate salts, which become impurities in sea salts. This study investigates the influence of lime juice in the adsorption of sulfate ions in seawater using commercial activated carbon. A full factorial experimental design was employed to optimize the level factors of activated carbon type, adsorbent dosage, and concentration of lime juice in response to the percentage reduction in sulfate concentration. Activated carbon (GCB) and acid-washed activated carbon (GCA) were two types of coconut shells granular activated carbon used for the experiment without further modification. The main effect and interaction effects were analyzed using analysis of variance (ANOVA) and p-values to define the influence of variables affecting sulfate ions adsorption. The adsorption of sulfate ions in seawater was affected by the interaction between the activated carbon type and the dosage, and the concentration of lime juice. The lime juice factor significantly enhanced the performance of activated carbon to adsorb the sulfate ions in seawater, and the factor's contribution was 58.2 %. The optimum sulfate ions reduction from seawater was attained at levels of factors activated carbon GCB, the dosage of 50mg, and the concentration of lime juice 50 µl. The interaction between lime juice and activated carbon pores are electrostatic. The impurities are attracted by the revealed polarity of the activated carbon pores. High electronegativity of lime juice acid pulls the negatively charged ions of the impurities. The more economical activated carbon, GCB, which performed better in sulfate ion adsorption, provides an alternative for reducing sea salt impurities. Hence, GCB can directly be mixed with the seawater to produce high quality sea-salt. Therefore, this study is suitable to improve sea salt product quality that processed with activated carbon

Harvesting the salinity gradient power (SGP) between concentrated brine discharged from seawater desalination installations and seawater and converting into electric energy by reverse electrodialysis (RED) is a promising technique. However, trace ions in brine and seawater may affect the performance of the RED stack, and little attention has been focused on this issue. Therefore, the influences of trace ions in seawater and concentrated brine are analyzed in this work. The effects of these ions on power density, open-circuit voltage, and internal resistance of the RED stack are analyzed by configuring manual seawater and concentrated brine including K1+, Mg2+, SO42-, and Ca2+. Experimental results show that divalent ions (Mg2+, SO42-, and Ca2+) can significantly increase the internal resistance of the RED stack and reduce power density. Mg2+ especially has the largest reduction in the output power of the stack. Oppositely, potassium ions (K1+) in feed solutions will reduce the internal resistance and improve power output. In addition, increasing the salinity gradient of feed solutions, temperature, and flow rate can increase open-circuit voltage and power density, and reduce inner power consumption of the RED stack. This study can provide references for the recovery of SGP in seawater desalination plants.

The advantages of matrix modification are explained in relation to the direct determination of trace metal ions in natural or artificial seawater. An experimental procedure is described leading to the determination of Mn2+ in seawater using matrix modification to eliminate interference effects from volatilized NaCl. The procedure is adaptable to the determination of other trace metal ions in seawater.

We describe capillary zone electrophoresis (CZE) for the simultaneous determination of bromide, nitrite and nitrate ions in seawater. Artificial seawater was adopted as the carrier solution to eliminate the interference of high concentrations of salts in seawater. The artificial seawater was free from bromide ion to enable the determination of bromide ion in a sample solution. For the purpose of reversing the electroosmotic flow (EOF), 3 mM cetyltrimethylammonium chloride (CTAC) was added to the carrier solution. A 100 microm ID (inside diameter) capillary was used to extend the optical path length. The limits of detection (LODs) for bromide, nitrite, and nitrate ions were 0.46, 0.072, and 0.042 mg/L (as nitrogen), respectively. The LODs were obtained at a signal to noise ratio (S/N) of 3. The values of the relative standard deviation (RSD) of peak area for these ions were 1.1, 1.5, and 0.97%. The RSDs of migration time for these ions were 0.61, 0.69, and 0.66%. Artificial seawater samples containing various concentrations of bromide, nitrite, and nitrate ions were analyzed by the method. The error was less than +/-12% even if the concentration ratio of bromide ion to nitrite or nitrate ion was 20-240. The proposed method was applied to the determination of bromide, nitrite, and nitrate ions in seawater samples taken from the surface and the seabed. These ions in other environmental waters such as river water and rainwater samples were also determined by ion chromatography (IC) as well as this method.

Porous Cu-based metal organic framework (Cu-MOF) for highly selective adsorption of organic pollutants

Determination of bromide ions in seawater by capillary zone electrophoresis using diluted artificial seawater as the buffer solution

Simultaneous determination of nitrate and nitrite ions in seawater by capillary zone electrophoresis using artificial seawater as the carrier solution

A thorough investigation of the adsorption of metal ions in seawater on d-glucose and its analogues: A theoretical study

The demand for fresh water is gradually and globally increasing due to the growth of population and water contamination. To meet this global demand, we fabricated metal-organic framework (MOF)-incorporated Cu-based alginate beads (Cu-MOF-Alg beads) for effective removal of water-dissolved salt ions from seawater. Alginic acid formed a matrix for preconfined Cu coordination. In this matrix, the MOFs were successfully in situ synthesized with organic ligands. The as-prepared Cu-MOF-Alg beads exhibited exceptional salt ion adsorption with the extraction of sedimented MOF particles. The adsorption characteristics of the fabricated Cu-MOF-Alg beads exhibited a linear isotherm according to the concentration of Na+ ions. In addition, the beads could be applied over a wide concentration range of target solutions and maintained their ion adsorption capacity after three repeated uses. The beads exhibited rapid adsorption kinetics, and their salt ion removal rate was approximately 94.3% through a multistage adsorption process. The MOF-treated seawater, which was desalinated to a low concentration of 1000 ppm, was filtered by a mangrove-inspired membrane, which yielded a total ion removal rate of 98.1%. Considering the low material cost compared to other adsorption-based desalination techniques and the absence of external energy supply, the proposed hybrid desalination system can produce purified water at an extremely low cost. Thus, this desalination technique could be economically and ecofriendly utilized for practical seawater desalination in a facile manner.

Collaborative disposal of problematic calcium ions in seawater and carbon and sulfur pollutants in flue gas by bipolar membrane electrodialysis

A new method for Li recovery from seawater by electrodialysis using a Li separation membrane with the ionic liquid PP13-TFSI was developed. Only Li ions can significantly permeate this membrane and thus pass from the anode side to the cathode side. Because the other ions (Na, Mg, Ca and K) in seawater are much less capable of permeating the membranes, Li becomes selectively concentrated on the cathode side. In the measurements of the ion concentration on the cathode side as a function of the duration of the applied dialysis voltage (2V), the Li concentration increased with time, reaching 24.5% after 2 h. The other ions in seawater did not permeate the membrane. This new recovery method shows good energy efficiency and is easily scalable. It should be suitable for use in seawater desalination plants and for the recycling of used Li-ion batteries.

Seawater used to Metakaolinite-based geopolymer preparation

Cadmium (II) ion adsorption of an industrial liquid waste-derived ferric oxide loaded with chitosan: Parameters optimization, isotherms, kinetics and thermodynamics