Bioelectrochemical technology for recovery of silver from contaminated aqueous solution: a review

One-step functionalization of chitosan with rich sulfur and nitrogen adsorption sites for efficient recovery of silver ions from actual wastewater

The recovery of silver ions from wastewater is of great importance due to their adverse environmental impact and significant economic value. This paper introduces a novel adsorbent (CS-AHMT) that can be easily synthesized via a one-step functionalization of chitosan with 4-Amino-3-hydrazino-1,2,4-triazol-5-thiol to efficiently recover silver ions from actual wastewater. CS-AHMT demonstrated superior adsorption performance, achieving an adsorption capacity of 241.4 mg·g-1 at pH 5 and 318 K, and the adsorption equilibrium was rapidly attained within 60 to 120 min. Kinetic and isotherm studies indicate that the adsorption process conforms to the pseudo-nth-order (PNO) and Sips models, suggesting a monolayer adsorption that incorporates both physical and chemical processes, with internal mass transfer being the primary rate-limiting step. Electrostatic and coordination interactions are primarily involved in the adsorption mechanism of silver ions on CS-AHMT, as further validated by density functional theory (DFT) calculations. The selectivity and practical applicability of CS-AHMT were confirmed in real wastewater containing high concentrations of competing ions. The findings underscore the potential of CS-AHMT as an effective adsorbent for silver ion recovery in wastewater treatment applications.

Synthesis of AgNPs from waste mobile phone circuit boards using an emulsion liquid membrane method

The disposal of mobile phone print circuit boards (WMPCBs) has now been a problem because of the continually increasing production of mobile phones. It could be considered a new source of precious metal but may jeopardize the environment and human health without proper management. An emulsion liquid membrane (ELM) method is applied and improved to recover silver from WMPCBs and prepare AgNPs. The effects of significant operating parameters were studied for a better understanding of the ELM process. Under the optimized conditions i.e., 0.25 % (v/v) Cyanex 302, 6 % (v/v) Span 80, 5 % (w/v) ASC, 3500 rpm emulsification speed, 10 min emulsification time, 300 rpm extraction stirring speed, 10 min extraction stirring time and 3 (v/v) phase ratio, 98.7 % silver was extracted. AgNPs produced were flower structures assembled by a group of individual nanosheets with a diameter of 800-1400 nm and a thickness of 10-14 nm. The purity was 98.7 % and the yield was 96.6 %. AgNPs of oblate spheroidal structure with a diameter of 30-50 nm could be synthesized by controlling the concentration of Span 80 in ELM. The current study intends to fulfill the gap by exploring the recovery of silver from WMPCBs by the ELM method.

Feather-weight cryostructured thiourea-chitosan aerogels for highly efficient removal of heavy metal ions and bacterial pathogens

Designing of economically feasible and recyclable polysaccharide-based materials with thiourea functional groups for removal of specific metal ions such as Ag(I), Au(I), Pb(II) or Hg(II) remains a major challenge for environmental applications. Here, we introduce ultra-lightweight thiourea-chitosan (CSTU) aerogels engineered by combining successive freeze-thawing cycles with covalent formaldehyde-mediated cross-linking and lyophilization. All aerogels exhibited outstanding low densities (0.0021-0.0103 g/cm³) and remarkable high specific surface areas (416.64-447.26 m²/g), outperforming the common polysaccharide-based aerogels. Benefitting from their superior structural features (honeycomb interconnected pores and high porosity), CSTU aerogels demonstrate fast sorption rates and excellent performance in sorption of heavy metal ions from highly-concentrated single or binary-component mixtures (1.11 mmol Ag (I)/g and 0.48 mmol Pb(II)/g). A remarkable recycling stability was observed after five sorption-desorption-regeneration cycles when the removal efficiency was up to 80 %. These results support the high potential of CSTU aerogels in the treatment of metal-containing wastewater. Moreover, the Ag(I)-loaded CSTU aerogels exhibited excellent antimicrobial properties against Escherichia coli and Staphylococcus aureus bacterial strains, the killing rate being around 100 %. This data points towards the potential application of developed aerogels in circular economy, by employing the spent Ag(I)-loaded aerogels in the biological decontamination of waters.

Bioelectrochemical systems-based metal removal and recovery from wastewater and polluted soil: Key factors, development, and perspective

Bioelectrochemical systems (BES) are considered efficient and sustainable technologies for bioenergy generation and simultaneously removal/recovery metal (loid)s from soil and wastewater. However, several current challenges of BES-based metal removal and recovery, especially concentrating target metals from complex contaminated wastewater or soil and their economic feasibility of engineering applications. This review summarized the applications of BES-based metal removal and recovery systems from wastewater and contaminated soil and evaluated their performances on electricity generation and metal removal/recovery efficiency. In addition, an in depth review of several key parameters (BES configurations, electrodes, catalysts, metal concentration, pH value, substrate categories, etc.) of BES-based metal removal and recovery was carried out to facilitate a deep understanding of their development and to suggest strategies for scaling up their specific application fields. Finally, the future intervention on multifunctional BES to improve their performances of mental removal and recovery were revealed.

Application of a combined response surface methodology (RSM)-artificial neural network (ANN) for multiple target optimization and prediction in a magnetic coagulation process for secondary effluent from municipal wastewater treatment plants

In this study, an enhanced coagulation-flocculant process incorporating magnetic powder was used to further treat the secondary effluent of domestic wastewater from a municipal wastewater treatment plant. The purpose of this work was to improve the discharged water quality to the surface water class IV standard of China. A novel approach using a combination of the response surface methodology and an artificial neural network (RSM-ANN) was used to optimize and predict the total phosphorus (TP) pollutant removal and turbidity. This work was first evaluated by RSM using the concentrations of coagulant, magnetic powder, and flocculant as the controllable operating variables to determine the optimal TP removal and turbidity. Next, an ANN model with a back-propagation algorithm was constructed from the RSM data along with the non-controllable variables, raw TP concentration, and raw water turbidity. Under the optimized experimental conditions (28.42 mg/L coagulant, 623 mg/L magnetic powder, and 0.18 mg/L flocculant), the TP and turbidity removal reached 88.79 ± 5.45% and 63.48 ± 9.60%, respectively, compared with 83.28% and 59.80%, predicted by the single RSM model, and 87.71 ± 5.74% and 64.62 ± 10.75%, predicted by the RSM-ANN model. The treated water were 0.17 ± 6.69% mg/L of TP and 2.46 ± 5.09% NTU of turbidity, respectively, which completely met the surface water class IV standard (TP < 0.3 mg/L; turbidity < 3 NTU). Therefore, this work demonstrated that the discharged water quality was completely improved using the magnetic coagulation process. In addition, the combined RSM-ANN approach could have potential application in municipal wastewater treatment plants.