Purification of residual leach liquors from hydrometallurgical process of NiMH spent batteries through micellar enhanced ultra filtration

Ecofriendly recovery of copper from spent telecommunication printed circuit boards using an indigenous cyanogenic bacterium

In recent years, electronic waste (e-waste) production has increased due to the population's growth and high consumption. As a result of the high concentration of heavy elements in these wastes, their disposal has posed many environmental problems. On the other hand, due to the non-renewability of mineral resources and the presence of valuable elements such as Cu and Au in electronic waste, these wastes are considered secondary minerals for recovering valuable elements. Among electronic waste, recovery of metals from spent telecommunication printed circuit boards (STPCBs) is significant, which has not been addressed despite their high production worldwide. This study isolated an indigenous cyanogenic bacterium from alfalfa field soil. The 16S rRNA gene sequencing results showed that the best strain has 99.8% phylogenetic affinity with Pseudomonas atacamenisis M7DI(T) with the accession number SSBS01000008 with 1459 nucleotides. The effect of the culture medium, initial pH, glycine concentration, and methionine on the cyanide production of the best strain was investigated. The results showed that the best strain could produce 12.3 ppm cyanide in NB medium with an initial pH of 7 and a concentration of glycine and methionine of 7.5 g/L and 7.5 g/L, respectively. The one-step bioleaching method was performed, which led to the recovery of 98.2% of Cu from STPCBs powder after 5 days. Finally, XRD, FTIR, and FE-SEM analyses were performed to investigate the structure of the STPCBs powder before and after the bioleaching process, confirming the high Cu recovery.

Solubilization and separation of o-toluidine and tricyclazole in sodium dodecyl sulfate micelles in micellar enhanced ultrafiltration

The solubilization laws of pollutants in micelles and their separation efficiency are very important in the successfully efficient application of micellar enhanced ultrafiltration (MEUF). The solubilization behavior of o-toluidine (OT) and tricyclazole (TC) into sodium dodecyl sulfate (SDS) micelles in MEUF was studied using nonlinear equation sets for concentration analysis, which resolved the issue on the overlap of absorption spectra of multicomponent compounds restricting the application of conventional ultraviolet (UV) spectroscopic method. The solubilization isotherms for both pollutants could be best explained by the Langmuir-Freudlich model (R²>0.99) followed by the modes of Langmuir and Freudlich, inferring the complexity of solubilization mechanism and solubilization advantage of monolayer over multilayer. The calculated thermodynamic parameters (ΔG⁰, ΔH⁰ and ΔS⁰) indicated that this process was endothermic and spontaneous. The solubilization of OT and TC well followed the pseudo second-order and pseudo first-order kinetics, respectively. The separation and recovery of SDS solubilizing these two pollutants were also investigated through lowering solution temperature to 2 °C followed by centrifugation. The best recovery rate of about 66% for SDS was achieved containing 10 and 5% of each initial amount of OT and TC, respectively, at near-neutral solution pH value. The recovery of SDS could decrease to some extent under alkaline and acidic conditions.

Separation and concentration of o-toluidine and tricyclazole from water with micellar enhanced ultrafiltration based on sodium dodecyl sulfate surfactant

Micellar enhanced ultrafiltration (MEUF) of o-toluidine and tricyclazole in aqueous stream using polyethersulfone (PES) hollow-fibre membrane of 6 kDa molecule weight cut-off (MWCO) and sodium dodecyl sulfate (SDS) as anionic surfactant was studied. It was found that the concentration ratio and adsorption ratio were better for the determination of the optimal pollutant or surfactant concentration than the rejection rate. The excessive dosage of surfactant had only limited effect on the separation and concentration of o-toluidine and tricyclazole but could further decrease the permeate flux. The transmembrane pressure had a significantly positive effect on the permeate flux and recovery ratio. o-Toluidine was significantly separated and concentrated by lowering the solution pH, while tricyclazole reached the best treatment efficiency in near-neutral pH condition. The sodium salts (i.e. Na₂SO₄, NaCl and Na₂CO₃) could lead to the increase in the adsorption ratio of SDS. However, Na₂CO₃ could result in the decrease in both the rejection rates and adsorption ratios of o-toluidine and tricyclazole. The distribution coefficient, micellar loading and micelle binding constant were evaluated to confirm the effectiveness for the MEUF treatment of these two pollutants.

Reuse of manganese sulfate as raw material by recovery from pesticide's wastewater using nanofiltration and electro-electrodialysis: process simulation and analysis from actual data

Reuse of wastewater, as well as recovery of valuable, toxic or harmful products in industrial discharges, still represents an important issue, not only because it reduces the effect on receiving water bodies, but also because of the economic resources it represents for industry itself. In this research, in situ regeneration of Mn₂SO₄ is evaluated, for its reuse as the main raw material in the original process of a fungicide plant. The regeneration is evaluated by selective recovery of Mn²⁺, Zn²⁺ and SO₄ ⁼ present in the wastewater produced by the industrial plant, and utilizing nanofiltration, electro-electrodialysis and chemical precipitation as separation alternatives. Each alternative was designed and evaluated technically and economically through simulations in Aspen Plus^®, with data and information of the real process supplied by the company. Because zinc concentration is relatively low, its selective recovery was not attractive. The resulting Mn₂SO₄ solution and treated water quality in conventional alternatives were significantly poor with high costs. In contrast, nanofiltration and electro-electrodialysis alternatives generate water and by-products of higher quality and reuse potential with significantly lower costs. However, their viability depends on the membrane performance. The results were satisfactory, but future experimental studies are required to optimize the alternatives and define the correct pretreatment process.

Optimized bioleaching of copper by indigenous cyanogenic bacteria isolated from the landfill of e-waste

In this study, indigenous cyanogenic bacterial strains were isolated on nutrient, minimal salt, and soil extract media at various culture conditions from two distinct landfills of e-waste, Iran. Based on their cyanide formation profiles, five most potent isolates were selected for optimization and to this end, the influence of the most effective factors on cyanide production including pH, glycine concentration and temperature were assessed using one-factor at a time method (OFAT). Initial pH of 7, glycine concentration of 2 g/L and temperature of 30°C were obtained as optimal conditions for most of the isolates. Additionally, two bioleaching processes were applied for each bacteria to detect the effect of optimal conditions on bioleaching and to assay their potential in the mobilization of copper. Under optimal conditions and pulp density of 1 g/L, copper recoveries were recorded as 96.73%, 82.49%, 81.17%, 41.72%, and 31.52% by S22, N13, N37, N23, and N41 respectively during 10 days which is approximately 1.5-5 times higher than the recovery obtained without optimization. During the optimization and the bioleaching process, the pH fluctuation of the flasks was monitored which validated the activity of the microorganisms.

Valorization of waste NiMH battery through recovery of critical rare earth metal: A simple recycling process for the circular economy

The process flowsheet consists of three main circuits, i.e., metal extraction by acid leaching, critical rare earth metal (REM) recovery from leach liquor and pure Co/Ni recovery by solvent extraction. Quantitative metal extraction using 1 M H₂SO₄, pulp density of 25 g/L at 90 °C from waste NiMH battery was achieved. From leach liquor using 10 M NaOH, at pH 1.8, more than 99% REM was precipitated out and isolated through calcination at 600 °C. Undesired metals like Mn, Al, Zn, and Fe were scrubbed out from the leach liquor using 0. 7 M D2EPHA at the equilibrium pH of 2.30. From the scrubbed raffinate Co and Ni was separated using 0.5 M Cyanex 272 at pH 4.70 through solvent extraction. At pH 4.70 Co was completely extracted from solution leaving Ni in solution, which can be recovered completely. From Co loaded Cyanex 272, the Co was stripped by 1 M H₂SO₄ and regenerated Cyanex 272 can be reused and close the loop. Similarly, the undesired metal loaded D2EPHA can be regenerated and reused and close the loop. As the process is close-loop process recovers critical REMs, Co, and Ni, the valorization process efficiently addresses the circular economy and recycling challenges associated with waste NiMH battery.

Roles of surfactants in pressure-driven membrane separation processes: a review

Surfactants widely exist in various kinds of wastewaters which could be treated by pressure-driven membrane separation (PDMS) techniques. Due to the special characteristics of surfactants, they may affect the performance of membrane filtration. Over the last two decades, there are a number of studies on treating wastewaters containing surfactants by PDMS. The current paper gives a review of the roles of surfactants in PDMS processes. The effects of surfactants on membrane performance were discussed via two aspects: influence of surfactants on membrane fouling and enhanced removal of pollutants by surfactants. The characteristics of surfactants in solution and at solid-liquid interface were summarized. Surfactants in membrane filtration processes cause membrane fouling mainly through adsorption, concentration polarization, pore blocking, and cake formation, and fouling degree may be influenced by various factors (feed water composition, membrane properties, and operation conditions). Furthermore, surfactants may also have a positive effect on membrane performance. Enhanced removal of various kinds of pollutants by PDMS in the presence of surfactants has been summarized, and the removal mechanism has been revealed. Based on the current reports, further studies on membrane fouling caused by surfactants and enhanced removal of pollutants by surfactant-aided membrane filtration were also proposed.

Study on the efficiency of ultrafiltration technology in dealing with sudden cadmium pollution in surface water and ultrafiltration membrane fouling

In this paper, the application of ultrafiltration (UF) technology to treat cadmium (Cd) pollution in surface waters is investigated. The effect of the UF membrane molecular weight cut-off (MWCO), Cd ion (Cd²⁺) concentration, solution pH and ionic strength on the removal, and mass balance of Cd were explored. In addition, the effect of the solution pH on UF membrane fouling was analyzed. The results indicated that UF membranes with a low MWCO resulted in an improved Cd removal rate. In addition, as the Cd²⁺ concentration in feedwater increased, the Cd removal rate decreased, while the Cd concentration in the permeate increased. Since the solution pH and ionic strength had a notable impact on the Cd removal rate, a high pH value and low ionic strength led to a higher removal rate of Cd. Under optimal Cd removal conditions, UF reduced the influent Cd concentration from 1.0 to 0.019 mg/L. For membrane fouling, increasing the solution pH led to more serious membrane fouling. This phenomenon was the result of Cd²⁺ reacting with OH^- and forming a Cd (OH)₂ precipitate. The precipitate and humic acid formed compact cakes on the membrane surface and blocked membrane pores. These results provided adequate evidence for the higher removal of Cd with increasing solution pH. In addition, SEM images under different pH conditions were in agreement with the conclusion mentioned above, which provided further support for the effect of the solution pH on Cd removal and membrane fouling.