Recovery of Fluoride-Rich and Silica-Rich Wastewaters as Valuable Resources: A Resource Capture Ultrafiltration-Bipolar Membrane Electrodialysis-Based Closed-Loop Process

Environmental and economic sustainability of the novel photovoltaic industrial wastewater treatment systems from life cycle perspective

As the global photovoltaic industry expands, the production of solar cells generates significant quantities of wastewater, characterized by high concentrations of ammonia-nitrogen and fluorine. To sustainably manage this wastewater, it is crucial to evaluate and optimize existing treatment systems. In this study, three innovative photovoltaic wastewater treatment routes that integrate resource utilization processes are proposed. A comparative assessment of the sustainability performance of these three routes, alongside a conventional treatment route, was conducted using pilot-scale data. The findings reveal that recycling cryolite and ammonium chloride is the most environmentally friendly approach, whereas recycling fluorspar and ammonium chloride proves to be the most economically feasible. Chemical usage emerges as the predominant contributor to nearly all environmental impacts, although the recovery of high-value components offers certain benefits. Among the resource products recovered, cryolite yields the highest environmental benefits, followed by ammonium chloride, with fluorspar providing the least. Furthermore, the adoption of alternative green chemicals, precise control of chemical dosages, and maximization of energy efficiency are identified as key strategies for reducing both the environmental burden and economic costs. In conclusion, this study quantitatively evaluated the potential environmental impacts and economic benefits of a conventional treatment method and three novel resource utilization approaches, thereby providing a scientific foundation for the improvement and selection of wastewater treatment technologies in the photovoltaic industry.

Fast-selective electro-driven membrane reactor in fluoride/silica crystallization for microelectronic wastewaters recycling

Rapid growth of the microelectronic industry leads to a significant increase in the generation of microelectronic wastewaters containing complex pollutants. Resource recovery technologies offer promising solutions for effective wastewater reuse in the microelectronics sector. However, how to simultaneously achieve high-efficiency crystallization and high crystal purity of ionic resources from complex wastewater remains a challenge. Here, for the first time, we propose an electro-driven membrane reactor (EMR) for the ex-situ crystallization of fluoride/silica from microelectronic wastewaters as high-purity fluorosilicates. This EMR with independent chambers combines a bipolar membrane to produce protons for SiF62- generation from the reaction between fluoride and silica. An internal ultrafiltration membrane is used to reject nanoparticles/organics while providing ion channels for protons and SiF62- migration. Selective recovery of Na2SiF6 from the coexisting ions (Cl-, SO42-, NO3- and PO43-)/nanoparticles (SiO2, Al2O3 and CeO2)/organics (tetramethylammonium hydroxide, isopropyl alcohol, bovine serum albumin, sodium alginate and humic acid) is demonstrated. Over 99.5 % Na2SiF6 purity and 64.5 % crystallization rate are verified under the optimal conditions (voltage of 8 V, UH050 membrane, operation mode Ⅰ, and forward permeate flux of 1 mL min-1). This EMR with the advantages of accurate capture capability may be an innovative strategy for enlarging the scale of pollutant elimination, ionic resources and fresh water recovery from micro-electronic wastewaters.

Unravelling the cleavage-rate relationship from both the experimental and theoretical standpoint: The instance of fluorite dissolution

The phenomenon of solid dissolution into a solution constitutes a fundamental aspect in both natural and industrial contexts. Nevertheless, its intricate nature at the microscale poses a significant challenge for precise quantitative characterization at a foundational level. In this work, the influence across three specific cleavage planes, namely (100), (111), and (110) on the dissolution kinetics of fluorite in aqueous environments was examined from both experimental and theoretical standpoints. For the very first time, the surface potential of fluorite planes during dissolution was measured by means of a fluorite single-crystal electrode. Experimental results indicate that the dissolution of fluorite leads to a marked increase in surface roughness as well as an augmentation in the surface area of all analyzed surfaces. The most significant alteration in roughness is observed on the (111) plane, whereas the most substantial increase in surface area occurs on the (110) plane. In comparison to the (100) crystallographic plane, which demonstrates the slowest dissolution kinetics, the (111) and (110) planes display dissolution at a comparatively expedited rate. Theoretical simulations corroborate this trend, concurrently facilitating an effective examination of the system's free-energy landscape to analyze the dynamics and rates associated with the attachment and detachment of ions to the fluorite surface. Notably, the presence of interfacial defects has the potential to influence the free energy landscape, thereby altering the transition of ions into the bulk solution. Ultimately, the interplay of correlations and discrepancies between experimental findings and theoretical predictions is critically examined.

Dual-ion permeation Janus membrane-assisted element reconstitution system enables fluorosilicate-oriented recovery from fluoride-rich and silica-rich wastewaters

Rapid development of semiconductor manufacturing and photovoltaic industry leads to significant generation of fluoride-rich and silica-rich wastewaters. Due to the emphasis on circular economy and resource recovery, there is a shift from regarding wastewater as waste to a recoverable resource. In this study, we present a uniquely designed dual-ion permeation Janus membrane (DPM)-assisted element reconstitution system (MERS) for selective recovery of high-value fluorosilicates from fluoride-rich and silica-rich wastewaters. The MERS with a configuration of cation-exchange membrane/bipolar membrane/DPM/anion-exchange membrane/cation-exchange membrane achieved HF formation in silica chamber and further SiF62- generation from the reaction of HF with SiO2. Driven by the electric field, SiF62- was then transported through DPM into acid chamber for fluorosilicates selective recovery. The DPM with positively-charged nanoporous substrate/negatively charged active layer enhanced electrostatic interaction for SiF62-/H+ transport and steric exclusion for coexisting foulants rejection. Ion transport mechanism analysis demonstrated DPM enhanced SiF62- migration while inhibiting back diffusion by electrostatic interaction and steric exclusion. Through the application of DPM, MERS showed rejections over 99 % for nanoparticles and over 90 % for organics. Thus, MERS stably selectively recovered SiF62- with recovery rate over 85 % and fluorosilicates purity over 99.5 %. Compared to traditional technologies, MERS achieved valuable resource recovery with the advantages of simple operation, small footprint and no secondary pollutant generation. Overall, this study provides a new strategy for simultaneous recovery of fluoride and silica from different waste streams, enabling a more sustainable strategy for semiconductor and photovoltaic industries development.

Bipolar membrane electrodialysis integrated with in-situ CO2 absorption for simulated seawater concentrate utilization, carbon storage and production of sodium carbonate

In the context of carbon capture, utilization, and storage, the high-value utilization of carbon storage presents a significant challenge. To address this challenge, this study employed the bipolar membrane electrodialysis integrated with carbon utilization technology to prepare Na2CO3 products using simulated seawater concentrate, achieving simultaneous saline wastewater utilization, carbon storage and high-value production of Na2CO3. The effects of various factors, including concentration of simulated seawater concentrate, current density, CO2 aeration rate, and circulating flow rate of alkali chamber, on the quality of Na2CO3 product, carbon sequestration rate, and energy consumption were investigated. Under the optimal condition, the CO32- concentration in the alkaline chamber reached a maximum of 0.817 mol/L with 98 mol% purity. The resulting carbon fixation rate was 70.50%, with energy consumption for carbon sequestration and product production of 5.7 kWhr/m3 CO2 and 1237.8 kWhr/ton Na2CO3, respectively. This coupling design provides a triple-win outcome promoting waste reduction and efficient utilization of resources.

Rice husk biochar - A novel engineered bio-based material for transforming groundwater-mediated fluoride cycling in natural environments

Biochar, a promising carbon-rich and carbon-negative material, can control water pollution, harness the synergy of sustainable development goals, and achieve circular economy. This study examined the performance feasibility of treating fluoride-contaminated surface and groundwater using raw and modified biochar synthesized from agricultural waste rice husk as problem-fixing renewable carbon-neutral material. Physicochemical characterizations of raw/modified biochars were investigated using FESEM-EDAX, FTIR, XRD, BET, CHSN, VSM, pH_pzc, Zeta potential, and particle size analysis were analyzed to identify the surface morphology, functional groups, structural, and electrokinetic behavior. In fluoride (F-) cycling, performance feasibility was tested at various governing factors, contact time (0-120 min), initial F- levels (10-50 mg L^-1), biochar dose (0.1-0.5 g L^-1), pH (2-9), salt strengths (0-50 mM), temperatures (301-328 K), and various co-occurring ions. Results revealed that activated magnetic biochar (AMB) possessed higher adsorption capacity than raw biochar (RB) and activated biochar (AB) at pH 7. The results indicated that maximum F- removal (98.13%) was achieved using AMB at pH 7 for 10 mg L^-1. Electrostatic attraction, ion exchange, pore fillings, and surface complexation govern F- removal mechanisms. Pseudo-second-order and Freundlich were the best fit kinetic and isotherm for F- sorption, respectively. Increased biochar dose drives an increase in active sites due to F- level gradient and mass transfer between biochar-fluoride interactions, which reported maximum mass transfer for AMB than RB and AB. Fluoride adsorption using AMB could be described through chemisorption processes at room temperature (301 K), though endothermic sorption follows the physisorption process. Fluoride removal efficiency reduced, from 67.70% to 53.23%, with increased salt concentrations from 0 to 50 mM NaCl solutions, respectively, due to increased hydrodynamic diameter. Biochar was used to treat natural fluoride-contaminated surface and groundwater in real-world problem-solving measures, showed removal efficiency of 91.20% and 95.61%, respectively, for 10 mg L^-1 F- contamination, and has been performed multiple times after systematic adsorption-desorption experiments. Lastly, techno-economic analysis was analyzed for biochar synthesis and F- treatment performance costs. Overall, our results revealed worth output and concluded with recommendations for future research on F- adsorption using biochar.