Green Deep Eutectic Solvents (DESs) for Sustainable Metal Recovery from Thermally Treated PCBs: A Greener Alternative to Conventional Methods.

Waste PCBs the core of e-waste is rich in copper, tin, zinc, iron, and nickel. Leaching base metals from PCB used to be done in toxic, corrosive acidic/alkali mediums. In this work, an environmentally friendly method for leaching metals from thermally treated PCBs (TPCBs) of mobile phones was proposed using choline chloride based deep eutectic solvents (DES). DES selectivity and solubility of metals from metal oxides were the main screening criteria. FA-ChCl had the maximum solubility of Cu, Fe, and Ni, while Urea-ChCl had high Zn selectivity and solubility. Oxalic acid has high selectivity for Sn. FA-ChCl extracted Cu and Fe best at 16 h, 100 °C, and 1/30 g/mL. Urea-ChCl extracted Zn (90.4±2.9 %) from TPCBs at 100 °C, 21 h, 1/20 g/mL, and 400 rpm. Oxalic acid (1 M) removed 92.3±2.1 % Sn from TPCBs in 1 h at 80 °C and 1/20 g/mL. The shrinking core model-based kinetic investigation of FA-ChCl for Cu extraction showed a diffusion-controlled process. The proposed method is greener than mineral acids utilized for metal extraction.

A feasible approach for the treatment of waste computer casing plastic using subcritical to supercritical acetone: Statistical modelling and optimization.

Electronic waste (e-waste) usage has increased tremendously with the rapid evolution of technologies. The accumulated e-waste has now emerged as one of the crucial concerns regarding environmental pollution and human health. Recycling e-waste is commonly focused on metal recovery; nevertheless, a significant fraction of plastics (20-30%) are in e-waste. There is an indispensable need to focus on e-waste plastic recycling in an effective way, which has been mostly overlooked to date. An environmentally safe and efficient study is conducted using subcritical to supercritical acetone (SCA) to degrade the real waste computer casing plastics (WCCP) in the central composite design (CCD) of response surface methodology (RSM) to achieve the maximum oil yield of the product. The experiment parameters were varied in the temperature span of 150-300 °C, residence time between 30 and 120 min, solid/liquid ratio between 0.02 and 0.05 (g/ml), and NaOH amount from 0 to 0.5 g. Adding NaOH into the acetone helps to achieve efficient degradation and debromination efficiency. The study emphasized the attributes of oils and solid products recovered from the SCA-treated WCCP. The characterization of feed and formed products is performed with different characterization techniques such as TGA, CHNS, ICP-MS, FTIR, GC-MS, Bomb calorimeter, XRF, and FESEM. The highest oil yield achieved is 87.89% from the SCA process at 300 °C, in 120min, 0.05 S/L ratio, and 0.5 g of NaOH. GC-MS results disclose that the liquid product (oil) comprises single- and duplicate-ringed aromatic and oxygen-containing compounds. Isophorone is the significant component of the liquid product obtained. Furthermore, SCA's possible polymer degradation mechanistic route, bromine distribution, economic feasibility, and environmental aspect were also explored. This present work represents an environmentally friendly and promising approach for recycling the plastic fraction of e-waste and recovering valuable chemicals from WCCP.

A sustainable route for the recovery of metals from waste printed circuit boards using methanesulfonic acid.

The rapid increase in electronic waste (e-waste) generation and its unsustainable management pose a threat to the environment and human well-being. However, various valuable metals are present in e-waste, which makes it a potential secondary source to recover metals. Therefore, in the present study, efforts were made to recover valuable metals (Cu, Zn, and Ni) from waste printed circuit boards (WPCB) of computers using methanesulfonic acid (MSA). MSA is contemplated as a biodegradable green solvent and has a high solubility for various metals. The effect of various process parameters (MSA concentration, H2O2 concentration, stirring speed, liquid to solid ratio, time, and temperature) was investigated on metal extraction to optimize the process. At the optimized process conditions, 100% extraction of Cu and Zn was achieved, while Ni extraction was around 90%. The kinetic study for metal extraction was performed using a shrinking core model and findings showed that MSA-aided metal extraction is a diffusion-controlled process. Activation energies were found to be 9.35, 10.89, and 18.86 kJ/mol for Cu, Zn, and Ni extraction, respectively. Furthermore, the individual recovery of Cu and Zn was achieved using the combination of cementation and electrowinning, which resulted in 99.9% purity of Cu and Zn. The current study proposes a sustainable solution for the selective recovery of Cu and Zn from WPCB.

A sustainable approach for material and metal recovery from E-waste using subcritical to supercritical methanol.

The heterogeneous nature of e-waste, which is a rich source of metals, polymers, glass fibres and ceramics, is troublesome. Multi-step processes are employed to effectively treat e-waste with minimum environmental impact. In this research, a subcritical to supercritical methanol environment was investigated to pre-treat e-waste, recovering non-metallic fractions and eventually concentrate metals from e-waste. Experiments were conducted in the temperature range of 150 °C to 300 °C at an autogenous pressure with initial atmospheric pressure. The mechanism of depolymerization was investigated by varying reaction time from 30 min to 240 min; solid to liquid ratio of 1:10 to 1:30 g/ml in a batch reactor under N2 environment. Comparative analysis of liquid products obtained after Supercritical Methanol (SCM) treatment for both Waste Random Access Memory (WRAM) and Waste Printed Circuit Board (WPCB) was done with pyrolyzed oil/liquid product. This research briefly illustrates oil and solid product compositional changes with operating temperature, pressure, and solid/liquid ratio range. The metal concentrations of copper, nickel, silver, zinc, and gold are greater than 90% after SCM treatment. For comparison, the feed material was pyrolyzed under the same condition, the difference in oil and solid products are assessed. In the end section, the environmental and economic benefits of SCM were also discussed compared to other supercritical and conventional technologies. An efficient and greener approach of supercritical solvent is proposed via this research for e-waste recycling.

Microwave-assisted extraction of lignin from coconut coir using deep eutectic solvents and its valorization to aromatics.

Lignin is a rich renewable source of aromatics present in lignocellulosic biomass (LCB). The extraction of lignin from the intricate LCB network is a challenging task for successful commercialization of sustainable biorefineries. In the present study, a series of choline chloride (ChCl)-carboxylic acid based deep eutectic solvents (DESs) were used for the extraction of lignin from coconut coir under microwave irradiation. Among the synthesized DESs, ChCl: lactic acid (LA) (1:4) gave the highest lignin yield of 82% with >95% purity. Interestingly, the severity factor (H factor) for the pretreatment process was found to be a significantly lower (55.5) as compared to reported studies due to efficient microwave heating. Moreover, the DES showed good recyclability for four recycle runs thus making it a promising candidate for the delignification of LCB. Finally, the extracted lignin was converted to aromatics via catalytic transfer hydrogenation (CTH) using Ru/C and isopropanol as in-situ hydrogen donor.

Comparison of Airway Ultrasound Indices and Clinical Assessment for the Prediction of Difficult Laryngoscopy in Elective Surgical Patients: A Prospective Observational Study.

BACKGROUND: Ultrasound is evolving as a probable tool in airway assessment. The upper airway is a superficial structure and has sonographically identifiable structures which makes it ideal for evaluation with the ultrasound. AIMS: The aim of this study was to evaluate the role of skin to hyoid and skin to thyrohyoid membrane distance in prediction of difficult laryngoscopy. SETTINGS AND DESIGN: This is a prospective observational study included 150 patients aged 18-60 years of American Society of Anesthesiologists Physical Status I and II scheduled to undergo surgery under general anesthesia requiring laryngoscopy and endotracheal intubation. MATERIALS AND METHODS: The modified Mallampati score, mouth opening, mentohyoid distance, thyromental distance were noted. Skin to hyoid bone distance and skin to thyrohyoid membrane distance were measured by ultrasound. Patients were clubbed retrospectively into easy and difficult laryngoscopy groups on the basis of Cormack Lehane grading, and the characteristics of both groups were compared. STATISTICAL ANALYSIS: Statistical Package for the Social Sciences, Version 23 was used for statistical analysis. Independent samples t-test was used to compare the means between difficult and easy laryngoscopy patients. Diagnostic accuracy of the significant (P < 0.05) variables between difficult and easy laryngoscopy patients was calculated using receiver operating characteristics curve in terms of their area under curve. Appropriate cutoff values (with corresponding sensitivity, specificity, and overall accuracy) were also identified. RESULTS: Out of 150 patients, 13 (8.7%) were identified as difficult laryngoscopy whereas 137 patients (91.3%) were identified as easy laryngoscopy. The demographics of both groups were comparable. Mentohyoid distance, skin to hyoid bone distance, and skin to thyrohyoid distance were statistically different between easy and difficult laryngoscopy patients, with lower mentohyoid distance and higher skin to hyoid bone distance and skin to thyrohyoid distance in difficult laryngoscopy patients. Diagnostic accuracy of the mentohyoid distance (70.3%) was slightly superior to skin to hyoid bone distance (67.1%) and skin to thyrohyoid distance (68.1%). CONCLUSION: Ultrasound measurements of skin to hyoid bone and skin to thyrohyoid membrane distance fail to eclipse clinical parameters in accurately predicting a difficult laryngoscopy.

High quality liquid fuel production from waste plastics via two-step cracking route in a bottom-up approach using bi-functional Fe/HZSM-5 catalyst.

Plastic waste is a serious menace to the world due to its fastest growth rate of ~ 5% per annum and requires efficient technologies for its safe disposal. Plastic liquefaction producing liquid hydrocarbons is an effective way to dispose waste plastics in an eco-friendly manner. In present study, high quality liquid fuel is produced from waste plastics via two-step bottom-up cracking approach. A comparative analysis of liquid products obtained in thermal and catalytic cracking performed at relatively lower temperature (350 °C) with minimal catalyst to plastic feed ratio (1:30) has been studied. Catalytic cracking via two-step bottom-up route provides higher fraction of fuel range hydrocarbons in comparison to the thermal cracking. Catalytic cracking is performed using two different catalysts; HZSM-5 and 5%Fe/HZSM-5 in which later results in higher liquid yield (76 wt%) than former (60 wt%) having comparable fuel characteristics. GC-MS results confirm that liquid product obtained via catalytic cracking contains higher fraction of fuel range hydrocarbons (C6-C20); 66.39% for 5%Fe/HZSM-5 and 47.33% for HZSM-5 which is comparatively higher than that obtained in thermal cracking (27.39%). FT-IR, 1H and 13C NMR spectroscopic studies confirm that liquid hydrocarbons obtained via catalytic cracking have comparable chemical characteristics with fuel range hydrocarbons. Physiochemical properties of catalysts are studied using XRD, XPS, BET, FE-SEM, HR-TEM, NH3-TPD and H2-TPR techniques and correlated with activity results. Analysis of commercial diesel fuel is also incorporated to compare the fuel characteristics of liquid products.

Controlling liquid hydrocarbon composition in valorization of plastic waste via tuning zeolite framework and SiO2/Al2O3 ratio.

Abundance of plastic waste has become threat to the mankind and aquatic life and thus needs to be recycled or converted into value added products. Liquefaction of waste plastics via catalytic cracking is one the efficient routes towards plastic waste management. Concerning this, in present study, conversion of polymer mixture containing polypropylene, low-density polyethylene and high-density polyethylene (PP, LDPE and HDPE) was done for the production of gasoline and diesel range hydrocarbons using two-step cracking approach. MWW and MFI (12 and 10 member ring structures respectively) type zeolites having different pore structure and acidity were used for catalytic cracking of polymer feed at 350 °C. Investigations revealed that MWW type zeolite having two independent pore channels selectively provides gasoline range of hydrocarbons (C7-C12, 99.12%) in polymer cracking reaction as compared to MFI type which results in C13-C20 range of hydrocarbons (73.19%). Hydrocarbon compositions were confirmed from GC-MS, 1H, 13C NMR and FT-IR techniques. In activity results it was observed that acidity of zeolites affects the liquid yield and hydrocarbon distribution as analysed by using zeolites of two different SiO2/Al2O3 (SAR) ratio (30 and 55) which directs that zeolite (MFI/MWW) with lower SAR (30) having higher acidity results in higher yield of fuel range liquid hydrocarbons as compared to higher SAR (55) zeolite. Characterization studies such as XRD, N2-physisorption, NH3-TPD, FE-SEM and EDX were performed to check the physiochemical properties of zeolite and correlated with the activity. Overall, the present investigation provides detailed comparative study on plastic degradation using MFI and MWW type zeolites resulting into different range of liquid hydrocarbons.

Efficient recovery of Cu and Ni from WPCB via alkali leaching approach.

The large generation of electronic waste (e-waste) is posing a serious threat to society. It is important to develop sustainable technology for the effective management of e-waste and the recovery of valuable metals from it. The present study employed hydrometallurgical approach for Cu and Ni extraction from waste printed circuit boards (WPCB) of mobile phones. This study demonstrates the application of ammonia-ammonium sulfate leaching for the maximum recovery of Cu and Ni. Investigations revealed that the most favourable reaction parameters for efficient metal extraction are - ammonia concentration - 90 g/L, ammonium sulfate concentration - 180 g/L, H2O2 concentration - 0.4 M, time - 4 h, liquid to solid ratio - 20 mL/g, temperature - 80 °C and agitation speed - 700 rpm. Under these conditions, 100% Cu and 90% Ni were extracted. Furthermore, the kinetic study was performed using the shrinking core model which revealed that the internal diffusion is the rate-controlling step for Cu and Ni extraction. The activation energies for Cu and Ni extraction were found out to be 4.5 and 5.7 kJ/mol, respectively. Finally, Cu was recovered with 98.38% purity using electrowinning at a constant DC voltage of 2.0 V at Al cathode. The present study provides a solution for concurrent extraction of Cu and Ni from the raw WPCB of mobile phones and selective recovery of Cu from metal leached solution. The process has the potential to recover the resources from WPCB while minimising the pollution caused by mismanagement of WPCB.

Pretreatment of lignocellulosic biomass: A review on recent advances.

Depleting fossil reserves and growing energy needs have raised the demand for an alternative and clean energy source. The use of ubiquitously available lignocellulosic biomass for developing economic and eco-friendly large scale biorefinery applications has provided the much-needed impetus in this regard. The pretreatment process is a vital step for biomass transformation into added value products such as sugars, biofuels, etc. Different pretreatment approaches are employed to overcome the recalcitrance of lignocellulosic biomass and expedite its disintegration into individual components- cellulose, hemicellulose, and lignin. The conventional pretreatment methods lack sustainability and practicability for industrial scale up. The review encompasses the recent advances in selective physical and chemical pretreatment approaches such as milling, extrusion, microwave, ammonia fibre explosion, eutectic solvents etc. The study will allow a deeper understanding of these pretreatment processes and increase their scope as sustainable technologies for developing modern biorefineries.