Boron Removal Performance of a Solid Sorbent Derived from Waste Concrete

Advances in Technologies for Boron Removal from Water: A Comprehensive Review

Boron overabundance in aquatic environment raises severe concerns about the environment and human health because it is toxic to various crops and induces many human and animal diseases with long-term consequences. In response to the boron pollution of water resources and the difficulty of eliminating boron from water for production and living purposes, this article summarizes the progress in research on boron removal technology, addressing the following aspects: (1) the reasons for the difficulty of removing boron from water (boron chemistry); (2) ecological/biological toxicity and established regulations; (3) analysis of different existing processes (membrane processes, resin, adsorption, chemical precipitation, (electric) coagulation, extraction, and combined methods) in terms of their mechanisms, effectiveness, and limitations; (4) prospects for future studies and possible improvements in applicability and recyclability. The focus of this paper is thus to provide a comprehensive summary of reported deboronation processes to date, which will definitely identify directions for the development of boron removal technology in the future.

Removal of fluoride ions from aqueous solution by metaettringite

Fluoride contamination is a major problem in wastewater treatment. Metaettringite (which has previously shown enhanced anion adsorption) was investigated as a possible adsorbent to remove fluoride from low-concentration solution (25 mg-F/L). The fluoride removal properties of ettringite and metaettringite were first compared at pH 10, and metaettringite was found to be more effective. The dominant reaction mechanism for fluoride adsorption in metaettringite was found to be recrystallization of metaettringite by rehydration; this was accompanied by precipitation of calcium fluoride. The adsorption kinetics followed the pseudo-second order model. Metaettringite was also able to remove fluoride effectively in low pH environment (i.e., at pH 3.5). The influence of coexistence of sulfate ions in solution on the fluoride removal performance was investigated, and a small decrease in performance was noted. The residual fluoride concentrations obtained with higher doses of metaettringite were lower than those specified by the Japanese effluent standard (non-coastal areas: 8 mg-F/L; coastal areas: 15 mg-F/L). The fluoride removal capacity of metaettringite was compared with those of other solid materials. The observed maximum capacity was 174.7 mg-F/g-metaettringite. In the case of high fluoride concentration solution, the main removal mechanism will be changed to calcium fluoride precipitation. In general, metaettringite is regarded as promising material for fluoride removal in wastewater treatment.

Synthesis of metaettringite from blast furnace slag and evaluation of its boron adsorption ability

Blast furnace slag (BFS) is generated as a by-product in the ironmaking process, and hence, the development of a recycling system for BFS waste is important. In this study, the calcium component of BFS obtained from a steel company in Japan was successfully used as raw material of the synthesis of metaettringite. Metaettringite has been recently considered for as an adsorbent for boron, which is toxic to humans and animals. The BFS used was amorphous, and mainly consisted of CaO, SiO₂, Al₂O₃, and MgO; in particular, it contained 42.82 mass % CaO. The X-ray diffraction pattern and Fourier transform infrared spectrum of the synthesized sample indicated the formation of metaettringite. Field-emission scanning electron microscopy observations revealed its needle-like morphology. The synthesized metaettringite adsorbed 1.189 mg-B/g-adsorbent in 240 min, which was approximately 25 times greater than that achieved using the parent BFS. The metaettringite can reduce the boron concentration to below the uniform effluent standard in industrial wastewater in Japan (16 mg/L).

Removal of boron from water by GO/ZIF-67 hybrid material adsorption

With the development of the boron industry, boron pollution is getting more and more serious, and excessive boron will harm human health. In this paper, graphene oxide was used as a template to prepare ZIF-67, and GO/ZIF-67 was successfully prepared. GO/ZIF-67 was used for the first time to remove boron from water. SEM, XRD, and other characterization methods were used to confirm the structure. The adsorption kinetics, adsorption isotherm, adsorption thermodynamics, and adsorption mechanism of boron by GO/ZIF-67 were studied in this paper. The adsorption capacity of GO/ZIF-67 for boron is up to 66.65 mg·g^-1 at 25 °C, and adsorption process reaches equilibrium in 400 min. Adsorption kinetics indicates that the adsorption process conforms to the pseudo-first-order kinetic model, and adsorption thermodynamics indicates that the adsorption process is a spontaneous endothermic process controlled by entropy change. The adsorption capacity of boron by GO/ZIF-67 does not decrease significantly after four cycles. The adsorption of boron by GO/ZIF-67 has both chemical and physical adsorption. From Zeta potential and adsorption kinetics, it can be seen that there is physical adsorption during the adsorption process and boron mainly has positive charge on the surface of GO/ZIF-67 and graphene oxide hydroxyl bonding. Based on the adsorption thermodynamics and XPS, it is known that there is chemisorption during the adsorption process, and mainly the combination of boron and cobalt sites.

CO2 Utilization via Direct Aqueous Carbonation of Synthesized Concrete Fines under Atmospheric Pressure

Mineral carbonation using alkaline wastes is an attractive approach to CO₂ utilization. Owing to the difference between waste CO₂ and feedstock CO₂, developing CO₂ utilization technologies without CO₂ purification and pressurization is a promising concept. This study investigated a potential method for CO₂ utilization via direct aqueous carbonation of synthesized concrete fines under atmospheric pressure and low CO₂ concentration. The carbonation reaction with different solid-liquid ratios and different concentrations of introduced CO₂ was examined in detail. Under basic conditions, a CO₂ uptake of 0.19 g-CO₂/g-concrete fines demonstrated that direct aqueous carbonation of concrete fines under atmospheric pressure and low CO₂ concentration is effective. The CaCO₃ concentration, degree of carbonation, and reaction mechanism were clarified. Furthermore, characterization of the carbonated products was used to evaluate ways of utilizing the carbonated products.

Radiation synthesis and performance of novel cellulose-based microsphere adsorbents for efficient removal of boron (III)

A novel cellulose-based microsphere containing glucamine groups, referred as CVN, was successfully synthesized by radiation-induced graft polymerization of 4-vinylbenzyl chloride onto cellulose microspheres and subsequent functionalization with N-methyl-d-glucamine. The adsorption by CVN for boron (III) from aqueous solutions was evaluated systematically by batch adsorption technique. Langmuir models could fit well with the adsorption behavior of CVN. The CVN adsorbents exhibited a high adsorption capacity up to 12.4mgg^-1 towards boron (III) over the wide pH range of 5-8. After the addition of chloride salts, the boron uptake of CVN was enhanced that was attributed to the compensation of the surface charge generated by boron (III) adsorption leading to favor the adsorption. At high concentrations of salts, the ionic strength and different salts have no effect on the adsorption of boron(III). This work provides a new sustainable, cost effective material as a promising specific adsorbent for the removal of boron (III) from saline solutions.

Nitrogen-doped graphene oxide for effectively removing boron ions from seawater

Elemental boron exists in the form of boric acid or borate salts in aqueous solution. The human body is very sensitive to the amount of boron, and boron contamination in drinking water affects our health adversely. However, boron is not easily removed due to its small ionic size and is a problem to water treatment systems. Herein, we report a new method to remove boron using nitrogen-doped graphene oxide (N-GO). The maximum adsorption capacity we have obtained is 58.7 mg g^-1 and this makes N-GO one of the best materials to adsorb boron. Real seawater with 5 mg L^-1 as boron is used as a feed for testing and the absorption capacity is shown to be up to 2.42 mg g^-1. This high adsorption capacity is mainly attributed to the large amount of hydroxyl groups distributed across the high surface area of graphene oxide and the enhanced adsorption that results from nitrogen-doped sites. Once N-GO is saturated with boron ions, it can be easily regenerated via acid treatment. Our proposed technique has high commercial value and we believe that it is very valuable to the water treatment industry.