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In this study, we used three processes to synthesize magnesium sulfate from seawater. First, alkaline industrial wastes, cement kiln dust and paper sludge ash, were injected to the seawater to precipitate magnesium in the form of magnesium hydroxide (Mg(OH)2). Then, magnesium was eluted with a small amount of H2SO4 to make a high concentration magnesium solution. Finally, an organic solvent was added to precipitate magnesium sulfate (MgSO4). Over 90% of magnesium was recovered through the three processes. It is expected that 11.3 kg of magnesium sulfate (based on MgSO4 · 6H2O) can be synthesized from 1 ton of seawater. [ABSTRACT FROM AUTHOR]

Vaterite, a type of calcium carbonate, has recently raised the potential for use as a drug delivery material and a filler for bone defects due to its high specific surface area and solubility, low specific gravity, and high porosity. However, existing methods of producing fine-particle vaterite exhibit limitations that annexed processes such as adding excessive additives or irradiating ultrasound are necessary, and mass production is impossible. We developed a simple, chemical additive-free, low-cost technology with mass production capability that can overcome problems faced in conventional vaterite production. We found that seawater is favorable for vaterite production and enables the reduction of its particle size because of its supersaturation in CaCO 3 , absence of magnesium, and high viscosity, and the reduced surface energy of vaterite. Using seawater as a solvent for indirect carbonation, we succeeded in producing a vaterite content of 100% containing fine particles without additives or additional processing. Spherical or elliptical vaterite was separately formed by adjusting the ionic strength of seawater. In addition, the ionic strength of seawater controlled the surface area and pore size of vaterite. [Display omitted] • Seawater is favorable for vaterite production and reduction of its particle size. • Seawater is used as an indirect carbonation solvent to produce fine particle vaterite. • CaCO 3 supersaturation and absence of Mg in used seawater affect vaterite formation. • Spherical or elliptical vaterite is produced by adjusting the ionic strength of seawater. • The ionic strength of seawater controls the surface area and pore size of vaterite. [ABSTRACT FROM AUTHOR]

Indirect carbonation is a technology for carbon capture, utilization, and storage that is used to reduce the concentration of CO 2 , and it may be also used to produce vaterite for drug delivery materials. However, vaterite is difficult to produce at the sizes and production volumes required for these applications. In this study, we investigated the effects of sucrose additions to seawater in an indirect carbonation process to increase CO 2 storage, generate vaterite, and reduce CaCO 3 particle size. In addition, sucrose was added before and after Ca elution and the CO 2 storage, vaterite content, and CaCO 3 particle size results were compared. By adding sucrose to seawater, the CO 2 storage capability was doubled, the vaterite content increased by 34%, and the CaCO 3 particle size decreased by 41% compared to results using seawater alone. When the molar ratio of sucrose to Ca in the Ca eluate was 1:2, the vaterite content was at its highest and the particle size was the smallest. At this ratio, the supersaturation of the Ca eluate was maximized due to the high Ca concentration and pH. Adding sucrose before Ca elution had many advantages compared to adding sucrose after Ca elution: the vaterite content increased, the particle size decreased, and most significantly, CO 2 storage and CaCO 3 production doubled and the addition of NaOH for carbonation was unnecessary. Because seawater and sucrose used in this study are non-toxic and inexpensive, the economical mass production of small-sized pure vaterite using this technology is feasible. • Sucrose addition promotes the effect of seawater in indirect carbonation. • Seawater and sucrose work together to produce small-sized pure vaterite. • Highest vaterite content and smallest particle size occurs when sucrose:Ca is 1:2. • Adding sucrose before Ca elution is more advantageous than that after Ca elution. • Sucrose elutes Ca from CaO while forming a Ca-sucrate complex. [ABSTRACT FROM AUTHOR]

In this study, we developed a technology to recover Mg from seawater desalination brine in the form of high-purity MgSO 4 that did not contain Ca impurities. The MgSO 4 recovery consisted of pre-precipitation of Mg(OH) 2 using alkali, concentration of Mg using sulfuric acid, and precipitation of MgSO 4 using ethanol. The removal of Ca impurities by adding ethanol twice into the Mg concentrate in the precipitation process was subtle but a highly beneficial novelty. The first dosage of ethanol was added to the Mg concentrate by adjusting the quantity such that only Ca (without Mg) was precipitated in the form of CaSO 4. Then, the ethanol was further added to the Ca-free Mg concentrate to precipitate high-purity MgSO 4. This two-step ethanol addition ensures effective removal of Ca impurities without Mg loss using the difference in the solubility of CaSO 4 and MgSO 4 in ethanol. As the purity of the recovered MgSO 4 was up to 99.8%, it could be used to re-mineralize fresh water after the seawater desalination process. According to the cost assessment, high-purity MgSO 4 produced from seawater desalination brine is expected to be preferred over other products in pharmaceutical and food markets that require high purity and economic feasibility. • We develop a technology to produce pure MgSO 4 from seawater desalination brine. • Ca impurities are effectively removed without Mg loss by adding ethanol twice. • Purity of Ca-free MgSO 4 produced is very high up to 99.8%. • The technology uses the solubility difference between CaSO 4 and MgSO 4 in ethanol. • Mg recovery efficiency is 67%, producing 15.8 kg of MgSO 4 ·7H 2 O from 1 ton of brine. [ABSTRACT FROM AUTHOR]

The economic challenges arising from resource depletion and uneven distribution of Mg in land reserves have spurred interest in technologies for Mg extraction from seawater. Thus, this study introduces a novel method to recover high-purity magnesium carbonate, specifically hydromagnesite, from seawater through carbonation using Ca(OH)₂ as an alkali source. A significant achievement of this method is the production of high-purity hydromagnesite despite the presence of large amounts of Ca, realized only through carbonation without the need for expensive additives such as NaOH. Experimental results reveal that the Ca(OH)₂ content predominantly influences the Mg dissolution efficiency during carbonation and the overall Mg recovery rate. Maximizing the efficiency of this technology relies on using an appropriate amount of Ca(OH)₂. Notably, the appropriate amount of OH− supply enhances CO₂ dissolution, facilitating Mg dissolution. Conversely, an excess of Ca(OH)₂ impedes Mg dissolution. The overall Mg recovery rate reaches a peak of 67 %, enabling the recovery of 3.4 kg of hydromagnesite from one ton of seawater. The findings highlight the effectiveness of the proposed technology as a promising and cost-effective method for extracting high-purity Mg from seawater, utilizing Ca(OH) 2 , previously considered an impurity, as a cost-effective alkali source. • Recovered high-purity hydromagnesite from seawater via carbonation using Ca(OH) 2 • Used Ca(OH)₂, previously deemed an impurity, as a cost-effective alkali • Optimal amounts of Ca(OH)₂ enhanced Mg dissolution but excess content inhibited it • Mg recovery peaked at 67 %, yielding 3.4 kg hydromagnesite per ton of seawater [ABSTRACT FROM AUTHOR]

• Seawater and industrial by-product are used for CO 2 storage and CaCO 3 production. • Economic feasibility of the indirect carbonation is secured by nearly costless seawater. • Mg in seawater mainly contributes to eluting Ca from alkali industrial by-product. • CO 2 storage and CaCO 3 yield are 271 and 615 kg/ton-CKD, respectively. • Purity of CaCO 3 exceeds 99% despite the use of CKD and seawater with impurities. Indirect carbonation is one of the typical carbon capture, utilization, and storage technologies. It is well known, however, that the technology is very difficult to achieve economic feasibility because expensive chemical solvents used account for most of the cost. To overcome this limitation, we performed an experimental study to secure the economic feasibility of the technology by replacing such chemical solvents with nearly costless seawater. For the study, we used cement kiln dust (CKD), which is an alkali industrial by-product, together with seawater. In this paper, we attained CO 2 storage and CaCO 3 yield despite the use of seawater, which is comparable in both quantitative and qualitative respects to the existing studies using chemical reagents. The CO 2 storage and CaCO 3 yield were 185 kg-CO 2 /ton-CKD and 419 kg-CaCO 3 /ton-CKD, respectively. With the addition of Mg into the seawater, moreover, the amounts could significantly increase to reach 271 kg-CO 2 /ton-CKD and 615 kg-CaCO 3 /ton-CKD, respectively. Despite using CKD and seawater containing many impurities, the purity of CaCO 3 produced was as high as 99.4%. It was also found that Mg is one component, which can elute Ca from CKD, dissolved in seawater. The solid to liquid ratio was the most influential factor for the Ca elution efficiency, while the CO 2 flow rate and NaOH dosage had significant effects on the carbonation efficiency. [ABSTRACT FROM AUTHOR]

Previous studies on the utilization of seawater and brine have focused on either recovering Mg from seawater/brine using alkalis or extracting Ca from industrial byproducts using solvents. Therefore, the present study was aimed at recovering Mg and Ca simultaneously from simulated seawater/brine and slaked lime [Ca(OH) 2 ] using a simple process, with seawater/brine employed both as a Mg source and as a solvent for extracting Ca from the Ca source. Manipulating the concentration of the sucrose additive and the ionic strength of seawater/brine enabled Mg and Ca recovery with high efficiency and purity. The highest Mg recovery from brine was 75 %, and ~ 100 % pure MgSO 4 was produced; specifically, ~28 kg of MgSO 4 •7H 2 O was produced from 1 ton of brine. The impacts of sucrose concentration and seawater ionic strength on the Ca elution, carbonation efficiency, and size and shape of the resulting vaterite particles were analyzed. The purity of the vaterite produced was 94 %–100 %, and the maximum CaCO 3 yield per ton of the Ca(OH) 2 was estimated as 770 kg, with a carbonation efficiency of up to 92 %. Therefore, our cost-effective method—featuring the use of seawater/brine and Ca(OH) 2 —can concurrently produce economically demanding minerals such as MgSO 4 and vaterite, thereby facilitating resource conservation. • MgSO 4 and CaCO 3 are produced simultaneously from seawater and Ca(OH) 2. • The sucrose content and seawater ionic strength affect the mineral yield and form. • The Mg recovery efficiency is 75 %, and the MgSO 4 •7H 2 O yield is 28 kg/ton of brine. • The carbonation efficiency is 92 %, and the CaCO 3 yield is 770 kg/ton of Ca(OH) 2. • The MgSO 4 and vaterite powders obtained through the devised process are ~100 % pure. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nanosized 100 % vaterite was produced via organic-solvent-free indirect carbonation. • Seawater, sucrose, ultrasonication, and aging exhibited a synergistic effect. • An eluent with the highest free-Ca-ion concentration was prepared by controlling the sucrose concentration. • The carbonation end pH was optimized, and the stirring speed and ultrasound intensity were adjusted to minimize interference. • After carbonation, the CaCO 3 -containing suspension was floated and a stable dispersion was maintained. Nanosized vaterite, which exhibits characteristics such as high specific surface area, porosity, and biocompatibility, has attracted research attention for use as a drug delivery material. However, fatal drawbacks such as high costs, difficulty in mass production, and toxicity exist in conventional nanosized vaterite production owing to the use of a large amount of organic solvents to forcibly suppress the vaterite recrystallization and particle growth. Therefore, nanosized 100 % vaterite was produced in this study via indirect carbonation without using any organic solvent, which has rarely been achieved previously. Seawater, sucrose, ultrasonication, and aging—which facilitate vaterite production and particle size reduction—exhibited a synergistic effect in producing vaterite. To realize nanosized vaterite production via indirect carbonation, seawater was used as a solvent, sucrose was added when Ca was eluted, and CO 2 bubbling was performed under ultrasonication. Furthermore, the CaCO 3 -containing suspension obtained after the carbonation was aged. Ultrasonic waves were required to generate nanosized vaterite and reducing size at the carbonation stage. This nanosized-vaterite-production strategy involving organic-solvent-free indirect carbonation is meaningful, in that it highlights the potential of synthesizing vaterite in an economically sound, environmentally friendly manner for use as a pharmaceutical raw material. [ABSTRACT FROM AUTHOR]

We describe a simple hydrothermal process for synthesizing vaterite-type CaCO 3 microparticles with a hexagonal bipyramidal shape using seawater. Vaterite with a spherical morphology is synthesized at room temperature relatively frequently, and a few high-temperature synthetic methods have been reported. However, the majority of these procedures require specific conditions, such as the use of detrimental surfactants, ultrasonication, and microwave irradiation. In this study, we successfully synthesized vaterite in Mg-free seawater using Ca(NO 3) 2 and urea, which do not require surfactants/organic additives or complex experimental conditions. The obtained vaterite hexagonal bipyramids had sharp edges and facets and a purity of 96%. We investigated the effects of the solvent type, reaction temperature, reaction time, and the ratio of Ca2+ and CO 3 2−, on the crystallization and morphology of the CaCO 3 polymorph. The phase and morphology of the vaterite were primarily determined by the synergistic effects of seawater and the ammonium ions from urea. [Display omitted] • Vaterite CaCO 3 was synthesized by Mg-free seawater aided hydrothermal method. • Unique hexagonal bipyramidal morphology was observed for the vaterite particles. • No organic additive/solvent is used for hexagonal bipyramidal vaterite formation. • Temperature (T) and time (t) play major roles in the vaterite formation. • CaCO 3 polymorphs follow same phase transition route irrespective of T and t. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ca precursor anions play an important role in the morphology of CaCO 3 superstructures. • The synergistic effects of anions, seawater, and ammonium ions alter the morphology of CaCO 3. • No additives/organic solvent is used for metastable CaCO 3 phase formation. • Selective crystallization of CaCO 3 polymorph was done by seawater-aided hydrothermal method. This work provides crucial insights into the crystallization and morphogenesis of CaCO 3 polymorphs in seawater at elevated temperatures. Using Ca source anions as a controlling factor, we modify the crystallization of CaCO 3 and demonstrate that stable and intricate particle morphologies of CaCO 3 , such as hexagonal bipyramidal, disks, and twin structures, can be generated in seawater without surfactants. The synthesis of CaCO 3 was accomplished through a direct hydrothermal method utilizing water-soluble Ca salts (calcium chloride, calcium nitrate, and calcium acetate) as Ca source and urea as a carbonate source. Depending on the specific source anions used, various morphological changes were observed. The CaCO 3 prepared with the nitrate source yields vaterite as the major polymorph with hexagonal bipyramidal morphology. Pseudohexagonal prisms of aragonite were the primary product obtained with calcium acetate as the source. In contrast, chloride ions yielded vaterite and aragonite depending on the reaction temperature and time. The purity of CaCO 3 prepared with seawater was > 94 % regardless of the Ca source. We observe that the phase formation follows the order of gypsum-vaterite-aragonite with an increase in hydrothermal reaction time. Further, we propose the formation mechanism of vaterite hexagonal bipyramidal and aragonite pseudohexagonal prism superstructures where directional aggregation of particles occurs in the presence of ammonium ions and seawater solvent. These findings, obtained through the exploration of seawater and different Ca sources, offer a comprehensive understanding of how source anions influence the selective formation of CaCO 3 polymorph and its morphological tuning. This information can be applied to tailor the synthesis of CaCO 3 for specific applications. [ABSTRACT FROM AUTHOR]