Hydroxyl-modified chitosan nanofiber beads for sustainable boron removal and environmental applications

The removal of boron from wastewater is essential for protecting environmental health and supporting sustainable urbanization by preventing toxic accumulation in ecosystems. Existing adsorption technologies face challenges such as limited capacity, slow kinetics, high regeneration costs, and reduced efficiency due to adsorbent saturation. This study develops an eco-friendly adsorbent (CGCNF beads) by modifying chitosan nanofibers with d-(+)-glucono-1,5-lactone (GL) to enhance boron removal. The adsorbents were characterized by 1H NMR, Cosy NMR, SEM, BET, TGA, FTIR, and colloidal titration. Notably, the hydroxyl functional groups grafted onto chitosan nanofibers (49.5%) were found to be three times higher than those on chitosan flakes (16.4%). The CGCNF beads followed the Langmuir model and pseudo-second-order model with a maximum boron adsorption capacity of 6.05 mg g-1, surpassing commercial Amberlite IRA-743 resin (5.73 mg g-1). The adsorption process of CGCNF beads was much faster, reaching equilibrium in 120 minutes, compared to 720 minutes for adsorbent-based chitosan flakes. The adsorption capacity is significantly enhanced by either elevating the pH levels or introducing salts such as NaCl, KCl, CaCl2, or MgCl2. The beads showed robust regeneration, maintaining 65.1% of their adsorption capacity after 20 cycles. The developed CGCNF beads also demonstrate simultaneous high-efficiency removal of B(iii) and As(iii) ions from local wet flue gas desulfurization (FGD) wastewater at rates of 94.5% and 100%, respectively, providing a sustainable solution for wastewater contamination.

Solvent extraction of boron from mildly alkaline salt lake brine in Tibet, China

Since the level of resource depletion is maintained at a high level, the recovery of boron from salt lake brine has become an effective way to meet the increasing demand for boron. This study investigates the optimization of boron extraction from the weakly alkaline brine of the Laguocuo Salt Lake (LGCSL) in Tibet, China, a representative of Tibetan weakly alkaline salt lakes. We evaluated the efficacy of 2,2,4-trimethyl-1,3-pentanediol (TMPD) as an extractant within a solvent mixture of 2-butyl-1-octanol (C12-OH) and sulfonated kerosene. The extraction performance was systematically assessed through single-stage and multi-stage counter-current extraction experiments, examining variables such as extractant type, concentration, pH, temperature, and the presence of co-existing ions. Our results demonstrate that optimal boron extraction is achieved under conditions of pH 8.0, an organic-to-aqueous phase ratio (O/A) of 1 : 1.5, and lower temperatures. Under these parameters, single-stage extraction efficiency surpassed 83%, while a three-stage process achieved an impressive 98.61% efficiency. Stripping experiments identified sodium hydroxide (NaOH) as an effective stripping agent, with a concentration of 0.3 mol L-1 and a phase ratio of 2 : 1 at room temperature yielding high stripping efficiency and significant boron concentration enrichment. To elucidate the extraction mechanism, Raman spectroscopy was employed to characterize the structural interactions between TMPD and boron complexes in the organic phase. Additionally, the influence of carbonate (CO3 2-) and bicarbonate (HCO3 -) ions, prevalent in alkaline brines, on boron extraction was investigated. These ions were found to affect the extraction efficiency, likely through competitive interactions or complex formation, highlighting the necessity of their consideration in optimizing the extraction process. This study provides both theoretical insights and practical experimental data essential for the efficient recovery of boron from weakly alkaline salt lake brines.

Enhanced boron removal via seed-induced crystal growth of barium perborate in sequential fluidized-bed crystallization

Chemical oxo-precipitation (COP) is an enhanced precipitation method for boron removal with the conversion of boric acid to perborate anions. When using barium-based precipitant, the boron can be effectively precipitated as barium perborates (BaPBs). The phase transformation of BaPBs from amorphous (A-BaPB, Ba(B(OH)3OOH)2) to crystalline (C-BaPB, BaB2(OO)2(OH)4) form is crucial for effective boron removal. However, scaling up this phase transformation of BaPBs is hindered by poor diffusion. This study aims to promote the growth of C-BaPB through seed-induced crystal growth, eliminating the need for phase transformation. By examining the relationship between crystal growth rate and supersaturation, surface spiral growth was identified as the rate-limiting step of the growth of micron-sized seeds near pHpzc. To enable continuous crystal growth, granular seeds of C-BaPB were prepared and employed as the medium for fluidized-bed crystallization (FBC). The system reached steady state 3 hydraulic retention times, achieving 90% boron removal. The effect of surface loading, ionic strength, and dosages on steady-state crystal growth rate was studied, revealing a shift of the rate-limiting step in FBC to diffusion. Lastly, the system that constituted of two FBCs in-series for sequential crystallization of A-BaPB and C-BaPB was demonstrated. The integrated system provided 97.8% of boron removal from synthetic wastewater containing 500 mg-B/L, with 92.3% of boron crystallized on the granular seeds of BaPBs.

Recent advances in adsorption and coagulation for boron removal from wastewater: A comprehensive review

The anthropogenic emission of boron to river has become a serious problem that deteriorates the water quality and endangers the ecosystem. Although boron is a micronutrient, it is toxic to plants, animals and humans upon exposure. In this review, we first present the sources of the boron-containing streams and their composition, and then summarize the recent progress of boron removal methods based on adsorption and coagulation systematically. The boron-spiked streams are produced from coal-fired and geothermal power plants, the manufacturing and the activities of oil/gas excavation and mining. The adsorbents for boron removal are classified into the ones functionalized by chelating groups, the ones on the basis of clays or metal oxide. Three subgroups reside in the coagulation approach: electrocoagulation, chemical precipitation and chemical oxo-precipitation. The hybrid technology that combines membrane process and adsorption/coagulation was covered as well. To provide a comprehensive view of each method, we addressed the reaction mechanism, specified the strength and weakness and summarized the progress in the past 5 years. Ultimately, the prospective for future research and the possible improvement on applicability and recyclability were proposed.

Simultaneous Recovery of Display Panel Waste Glass and Wastewater Boron by Chemical Oxo-precipitation with Fluidized-Bed Heterogeneous Crystallization

Silica-based carrier is a promising material for recovery of metal and nonmetal contaminants in chemical oxo-precipitation-fluidized bed crystallization (COP-FBC) system. Boron species are an essential element for plant growth and can cause health concerns in human beings at high concentrations in water environments. The composition of thin-film transistor liquid crystal display (TFT-LCD) contains a wide variety of metal oxides and can be tailored as promising functional mesoporous carriers for boron crystallization recovery in the presence of barium ions and hydrogen peroxide. In this study, waste-derived mesoporous aluminosilicate (MAS) nanomaterial in the presence of barium ions and hydrogen peroxide was used as a carrier for sustainable recovery of crystallized boron, a priority wastewaters pollutant. The MAS shows the hierarchically homogeneous distribution of nanostructured aluminosilicate particles with an average size of 12.8 ± 3.6 nm on the surface after the activation with Na₂CO₃ at 1000 °C. Moreover, the negatively charged surface and the mesoporous structure of MAS enhance the adsorption of Ba²⁺ onto MAS, and the Langmuir adsorption capacity of 105 mg/g is achieved, which is conducive to the enhancement of the recovery of boron species. Moreover, the recovery efficiency and crystallization ratio of boron by MAS can be up to 84.5 and 93.4%, respectively. The cross-sectional scanning electron microscopy images and the high-temperature X-ray diffraction results confirm the boron recovery mechanism that the negatively charged functional group as well as the mesoporosity of MAS triggers the rapid formation of needle-shaped precipitates of barium peroxoborate, and then converted to barium borate after calcination at 1050 °C. Results obtained in this study clearly demonstrate the possibility of fabricating environmentally benign mesoporous aluminosilicate adsorbents from TFT-LCD waste to sustainably recover and crystallize boron species from water and wastewater in COP-FBC.

One-dimensional controllable crosslinked polymers grafted with N-methyl-d-glucamine for effective boron adsorption

Modified one-dimensional crosslinked polymers exhibit good adsorption performances for boron, and magnetic separation is realized by doping Fe₃O₄ nanoparticles.