Highly selective extraction of metal ions from dilute solutions by hybrid electrodialysis technology

Advanced membrane-based high-value metal recovery from wastewater

Considering the circular economy and environmental protection, sustainable recovery of high-value metals from wastewater has become a prominent concern. Unlike conventional methods featuring extensive chemicals or energy consumption, membrane separation technology plays a crucial role in facilitating the sustainable and efficient recovery of valuable metals from wastewater due to its attractive features. In this review, we first briefly summarize the sustainable supply chain and significance of sustainable recovery of aqueous high-value metals. Then, we review the most recent advances and application potential in promising state-of-the-art membrane-based technologies for recovery of high-value metals (silver, gold, rhenium, platinum, ruthenium, palladium, iridium, osmium, and rhodium) from wastewater effluents. In particular, pressure-based membranes, liquid membranes, membrane distillation, forward osmosis, electrodialysis and membrane-based hybrid technologies and their mechanism of high-value metal recovery is thoroughly discussed. Then, engineering application and economic sustainability are also discussed for membrane-based high-value metal recovery. The review finally concludes with a critical and insightful overview of the techno-economic viability and future research direction of membrane technologies for efficient high-value metal recovery from wastewater.

Modified coconut shell biochars (MCSBCs): Fabrication and their adsorptions for Pb(II)

The modified coconut shell biochars (MCSBCs) were fabricated and their adsorptions for Pb(II) were evaluated, in which waste coconut shell was used as the raw material, both ZnCl2 and KMnO4 were applied as the inorganic modifiers. FT-IR spectra, TGA, SEM and BET techniques were utilized to characterize their properties. It was spotted that the thermal stability of UCSBC could arrive at 500 °C. The BET specific surface areas of both Zn- and Mn-modified MCSBCs (485.137, 476.734 m2/g) were highly decreased as compared with that of UCSBC (3528.78 m2/g). In contrast, the average pore diameters of both Zn- and Mn-modified MCSBCs (3.295, 3.803 nm) were smaller than that of UCSBC (3.814 nm). These findings reveal that the modification of CSBC didn't change its pore size. Their adsorptions for Pb(II) were performed and some controlling factors involving pH, contact time, starting concentration and temperature were explored. Moreover, the experiment data were fitted via linear and non-linear techniques. It was found that the Langmuir maximal adsorption amounts of un-modified coconut shell biochar (UCSBC), Zn-modified and Mn-modified MCSBCs for Pb(II) could reach 31.653, 86.547 and 93.666 mg/g, respectively. Two-parameter kinetic models exposed that Pb(II) adsorption on UCSBC, Zn-modified and Mn-modified MCSBCs obeyed both the Lagergren first-order (non-linear R2 = 0.990, 0.954, 0.953, respectively) and Avrami fractional-order (non-linear R2 = 0.989, 0.946, 0.945, respectively) kinetic models. Two-parameter and three-parameter isotherm models verified that Pb(II) adsorption on UCSBC, Zn-modified and Mn-modified MCSBCs followed the Langmuir (non-linear R2 = 0.992, 0.997, 0.993, respectively) as well as Sips (non-linear R2 = 0.992, 0.997, 0.992, respectively) isotherm models. The computation of thermodynamic parameters evidenced that the modification of UCSBC via KMnO4 and ZnCl2 can effectively rise its adsorption for Pb(II), exhibiting promising applications in the handling of metal-bearing water.

Composite Anion Exchange Membranes Based on Quaternary Ammonium-Functionalized Polystyrene and Cerium(IV) Phosphate with Improved Monovalent-Ion Selectivity and Antifouling Properties

The possibility of targeted change of the properties of ion exchange membranes by incorporation of various nanoparticles into the membranes is attracting the attention of many research groups. Here we studied for the first time the influence of cerium phosphate nanoparticles on the physicochemical and transport properties of commercial anion exchange membranes based on quaternary ammonium-functionalized polystyrenes, such as heterogeneous Ralex^® AM and pseudo-homogeneous Neosepta^® AMX. The incorporation of cerium phosphate on one side of the membrane was performed by precipitation from absorbed cerium ammonium nitrate (CAN) anionic complex with ammonium dihydrogen phosphate or phosphoric acid. The structures of the obtained hybrid membranes and separately synthesized cerium phosphate were investigated using FTIR, P31 MAS NMR, EDX mapping, and scanning electron microscopy. The modification increased the membrane selectivity to monovalent ions in the ED desalination of an equimolar mixture of NaCl and Na₂SO₄. The highest selectivities of Ralex^® AM and Neosepta^® AMX-based hybrid membranes were 4.9 and 7.7, respectively. In addition, the modification of Neosepta^® membranes also increased the resistance to a typical anionic surfactant, sodium dodecylbenzenesulfonate.

Electrodialysis Applications in Wastewater Treatment for Environmental Protection and Resources Recovery: A Systematic Review on Progress and Perspectives

This paper presents a comprehensive review of studies on electrodialysis (ED) applications in wastewater treatment, outlining the current status and the future prospect. ED is a membrane process of separation under the action of an electric field, where ions are selectively transported across ion-exchange membranes. ED of both conventional or unconventional fashion has been tested to treat several waste or spent aqueous solutions, including effluents from various industrial processes, municipal wastewater or salt water treatment plants, and animal farms. Properties such as selectivity, high separation efficiency, and chemical-free treatment make ED methods adequate for desalination and other treatments with significant environmental benefits. ED technologies can be used in operations of concentration, dilution, desalination, regeneration, and valorisation to reclaim wastewater and recover water and/or other products, e.g., heavy metal ions, salts, acids/bases, nutrients, and organics, or electrical energy. Intense research activity has been directed towards developing enhanced or novel systems, showing that zero or minimal liquid discharge approaches can be techno-economically affordable and competitive. Despite few real plants having been installed, recent developments are opening new routes for the large-scale use of ED techniques in a plethora of treatment processes for wastewater.

A thiourea cross-linked three-dimensional graphene aerogel as a broad-spectrum adsorbent for dye and heavy metal ion removal

A honeycomb-like three-dimensional graphene-based aerogel applied to remove pollutants was assembled via a mild, easy-to-operate hydrothermal synthesis method.

Zinc Recovery through Electrolytic Refinement Using Insoluble Ir + Sn + Ta + PdOx/Ti Cathode to Reduce Electrical Energy Use

In this study, an alumina (Al) anode, a lead cathode, and insoluble catalytic cathodes (IrOx, PdOx, TaOx, and SnOx) were used as electrodes to enhance zinc recovery. The traditionally used iron electrode and insoluble catalytic electrodes were also used to compare the recovery yield when different types of electrodes were subjected to the same amount of energy. The lead electrode showed over 5000 Ω higher electrode resistance than did the insoluble catalytic electrode, leading to overpotential requiring higher electrical energy. As electrical energy used by the lead and the insoluble catalytic electrodes were 2498.97 and 2262.37 kwh/ton-Zn, respectively, electrical energy can be reduced by 10% when using an insoluble catalytic electrode compared to that when using a lead electrode. Using recovery time (1-4 h) and current density (100-500 A/m²) as variables, the activation, concentration polarization, and electrode resistance were measured for each condition to find the optimum condition for zinc recovery. A recovery yield of about 77% was obtained for up to 3 h of zinc recovery time at a current density of 200 A/m², which is lower than that (about 80%) obtained at 300 A/m². After 3 h of recovery time, electrode resistance (Zn concentration reduction, hydrogen generation on electrode surface) and overpotential increase with time decreased at a current density of 200 A/m², leading to a significant increase in zinc recovery yield (95%).

Fractionating magnesium ion from seawater for struvite recovery using electrodialysis with monovalent selective membranes

As the consumption of global phosphorus reserves accelerates, recovering phosphorus as struvite (MgNH₄PO₄·6H₂O) from wastewater is an important option for phosphorus recycling. However, magnesium source is one of the major limiting factors for struvite recovery. In this work, different from previous studies where seawater was used directly as magnesium source in struvite precipitation, an electrodialysis stack equipped with monovalent selective cation-exchange membranes was designed to fractionate Mg²⁺ from seawater for struvite recovery. Results revealed that Mg²⁺ fractionation was achieved effectively. The comparison on applying the driving force for ionic transport showed that constant voltage was more preferable than constant current due to its higher Mg²⁺ separation efficiency, current efficiency and lower energy consumption. Increasing voltage from 7 V to 13 V would improve Mg²⁺ permeation ratio from 72.9% to 80.5% into the product stream but simultaneously increased the energy consumption from 5.40 (kWh/kg MgCl₂) to 11.69 (kWh/kg MgCl₂). In addition, the investigation on the influence of Ca²⁺ co-existence and further struvite recovery experiments revealed that the variation of Ca²⁺ concentrations in seawater did not influence Mg²⁺ fractionation significantly, nevertheless it might reduce struvite recovery efficiency through forming calcium phosphate.

Electroplating wastes

Electroplating and other metal finishing industries, like every metal and metallurgical industry, are associated with the generation of waste. Spent electroplating baths, waste pickle liquors, etching solutions and rinse waters from electroplating units and steel finishing operations are complex solutions containing acids and several hazardous metals. It is compulsory, for environmental and economic reasons, to treat these solutions for recovering acid, metals and/or reusing these solutions/waters. This article is a review on the characterization of the wastes that are generated in electroplating industry, steel processing and copper etching in printed circuit boards manufacture, as well as on the treatment and regeneration methods of such streams. Various techniques, such as neutralization, crystallization, evaporation, pyrohydrolysis, electrodialysis, ion exchange, classical solvent extraction and membrane-based solvent extraction are presented, their advantages and disadvantages being scrutinized.