A carbothermic hybrid synthesized using waste halogenated plastic in sub/supercritical CO2 and its application for lithium recovery.

Facile fabrication of porous carbon materials from waste halogenated plastic is highly attractive but frequently hampered due to potential release of halogenated organic pollutants. In this study, a novel type of carbon hybrid was tentatively synthesized from a real-world halogenated plastic as an inexpensive carbon source by sub/supercritical carbon dioxide carbonization technique. It was found that halogen-free carbon carrier was advantageously synthesized through carbonization of halogenated plastic without using catalysts due to zip depolymerization, random chain cracking and free radical reactions induced by sub/supercritical carbon dioxide technique. Exhibiting with more abundant functional groups including C-O, CO groups than pyrolytic carbon carrier, the derived carbon carrier demonstrated excellent performance in selective recovery of lithium from cathode powder with highest recovery efficiency of 93.6%. Mechanism study indicated that cathode powder was transformed into low-valence states of transition metals/metal oxides and released lithium as lithium carbonate due to collapse of oxygen framework via carbothermic reduction. This work provides an applicable and green process for synthesis of alternative carbon carrier from waste halogenated plastic and its application as carbothermic reductant in lithium recovery.

Degradation of organic compounds in hypersaline wastewater concentrate by a supercritical oxidation approach.

Hypersaline wastewater is a typical industrial wastewater produced by iron and steel metallurgy, food material processing and other industries. Aiming at a waste liquid produced by mechanical vapour recompression evaporation and concentration in Tianjin coastal industrial zone, an environment-friendly supercritical water oxidation technology was used to efficiently remove the high-content organic matter in the hypersaline wastewater concentrate (HWC). A comparison of the degradation effects of various oxidants in the supercritical state showed that hydrogen peroxide (H2O2) could be used as a suitable agent for processing the HWC. The reaction parameters were systematically optimised by single-factor experiment and response surface design. The degradation mechanism and reaction characteristics were analyzed using gas chromatography mass spectrometry. Solid residues were characterised by field emission scanning electron microscope. The results indicated that when the dosage of hydrogen peroxide was 6.39%, the reaction temperature was 380°C, the reaction time was about 90 min and the optimal total organic carbon removal rate was 96.22%. Furthermore, it was found that hydroxyl radicals produced by hydrogen peroxide initiated the bond breaking and ring-opening reactions in organic matter, which eventually degraded organic matter into water and carbon dioxide.

A sequential leaching procedure for efficient recovery of gold and silver from waste mobile phone printed circuit boards.

The present study reports a sequential, non-acid process for effective recovery of copper and precious metals from mobile phone printed circuit boards. In this process, gold and silver were first enriched during the synthesis process of cuprous chloride and then leached by thiosulfate method. Results indicated that the distribution of gold and silver in the liquid and solid phases during the synthesis of cuprous chloride process was affected by the [Cu]/[Cu2+] ratio. Enrichment of gold and silver in the residue after the cuprous chloride synthesis could be achieved by the adjusting the [Cu]/[Cu2+] ratio. The silver and gold leaching rates of the residue after cuprous chloride synthesis (93.8 % silver and 99 % gold) were much higher than those of the raw PCB sample (27.0 % silver and 14.2 % gold) under the same conditions. This process has the advantages of high leaching efficiency, high leaching rate and avoiding the use of HNO3 or aqua regia commonly used for copper, gold and silver recovery. Thus, this study offers a promising and environmentally friendly method for recovering valuable metals from e-waste.

Upcycling of blending waste plastics as zwitterionic hydrogel for simultaneous removal of cationic and anionic heavy metals from aqueous system.

Upcycling of waste plastics as functional materials is a new approach for synthesizing low-cost and durable adsorbents with zwitterionic property. Herein, a facile process for recycling blending waste plastics to fabricate zwitterionic plastic-g-hydrogel (ZPH) for simultaneous adsorbing cationic and anionic heavy metals was developed. ZPH possessed high affinities for cations and anions in both acid and alkaline conditions owing to its zwitterionic property, and the maximum adsorption capacities of Pb2+, Cd2+, Ba2+, and Cr(VI) (Cr2O72-) were 132.13, 85.58, 69.92 and 85.15 mg/g, respectively. Mechanism study indicated the incompatibility of blending plastics was skillfully overcome through the crosslinking between sodium alginate (SA)/chitosan (CTS) and plastics. Cations were adsorbed onto ZPH via electrostatic interaction, cation exchange and coordination interactions with Cl/N/O-containing groups. Furthermore, the reduction of Cr(VI) to Cr(III) was another important path for ZPH to capture anionic Cr2O72-, and subsequently Cr(III) was adsorbed via coordination interaction and cation exchange. Moreover, the regeneration experiment showed ZPH possessed excellent reusability and stable structure. Accordingly, this research provides a profitable approach for recycling blending plastics, and ZPH has potentials for industrial application in wastewater treatment or contaminated site remediation with complex heavy metals pollution.

Synthesis of graphene and recovery of lithium from lithiated graphite of spent Li-ion battery.

Recycling of spent Li-ion batteries is crucial for achieving sustainable development of battery industry. Current recycling processes mainly focus on valuable metals but less attention has been paid to spent graphite, which generally ends up as secondary waste. In this study, a process for preparing graphene and recovering Li in anode as a by-product from spent graphite was developed. The key point was to re-charge the spent LIBs to generate lithium graphite intercalation compounds. The lithium graphite intercalation compounds were then subjected to a hydrolysis procedure and graphene could be produced through ultrasonic treatment via the expansion/micro-explosion mechanism. Experimental results demonstrated that 1-4 layered graphene could be efficiently produced when spent Li-ion batteries with beyond 50% capacity were re-charged. The prepared graphene showed high quantity containing few defects (ID/IG = 0.33, C/O = 13.2 by energy dispersive spectroscopy and C/O = 8.8 by X-ray photoelectron spectroscopy). In addition, Li was simultaneously recovered in the form of battery-grade lithium carbonate in the above process. Economic analysis indicated that the graphene production cost was extremely low ($540/ton) compared to that of commercial graphene.

A green process for phosphorus recovery from spent LiFePO4 batteries by transformation of delithiated LiFePO4 crystal into NaFeS2.

Recovery of high-content and valuable elements including phosphorus (P) is critical for recycling of spent LiFePO4 battery, but P recovery is challengeable due to the poor solubility of lithium phosphate and iron phosphate. This study compared two strategies to recover P by adopting sulfide salt to induce P dissolution, i.e., recovery of P directly from LiFePO4, and step-by-step recovery of Li then P. The results revealed that the second strategy was more efficient because of the higher recovering efficiency and selectivity. Accordingly, an acid-free process to recover P was successfully demonstrated. Li-recovery efficiency of 97.5 % was reached at a leaching time of 65 min, and nearly 100 % P-recovery efficiency was reached at 5 h. Mechanism analysis revealed that the transforming of delithiated LiFePO4 crystal to NaFeS2 was mainly responsible for P dissolution. Thermodynamic analysis and density functional theory calculation further proved the transformation reaction, and a stepwise-transformation mechanism was proposed. In addition, P was reclaimed in the form of soluble phosphate salts. The process is especially appealing due to its environmental and economic benefits for recycling spent LiFePO4 batteries.

Enhanced dehalogenation and coupled recovery of complex electronic display housing plastics by sub/supercritical CO2.

Electronic display housing plastics contain a high amount of halogenated compounds such as brominated flame retardants (BFRs) and polyvinyl chloride (PVC). Compared with moderate critical conditions of conventional eco-friendly sub/supercritical carbon dioxide (Sc-CO2), a novel and sustainable procedure by using improved Sc-CO2 was developed for disposal of this type of plastic. The main merit of the process was that complex halogen-containing plastics were safely disposed and halogen-free products were recycled without using catalysts or additives. It was discovered that additive BFRs were initially extracted by Sc-CO2 technique and then it decomposed accompanied with PVC rapidly to form HBr and HCl, which could be separated by traditional bromine stripping techniques from seawater. Based on response surface methodology (RSM), the maximum debromination and dechlorination efficiencies were achieved at 99.51% and 99.12% respectively. After the treatment, halogen-free products such as solid carbon materials and organic chemical feedstocks were obtained. Mechanism study elucidated that free radicals reaction involving chain initiation, growth and termination induced the polymer decomposition to form these products. This study provides an applicable and green approach for disposal and recovery of halogen-containing plastics.

Selectively peeling of spent LiFePO4 cathode by destruction of crystal structure and binder matrix for efficient recycling of spent battery materials.

Impurity Fe could severely damage the performance of resynthesized cathode material, and therefore, LiFePO4 cathode should be removed from the mixed spent LIBs for materials recycling. In this research, a non-hydrometallurgy method has been developed to separate LiFePO4 by selectively peeling-off the LiFePO4 cathode material and the peeling-off process was well explained by theoretical modeling. The peeling-off efficiency of LiFePO4 was approximate 100 % and that of LiMn2O4/LiCoO2/Li(Ni, Co, Al)O2/Li(Ni, Mn, Co)O2 was only 0.08 %. That is, the separating selectivity was 1250. Mechanism study revealed that the peeling-off was achieved through selective destruction of the LiFePO4 crystal and the matrix of polyvinylidene fluoride (PVDF) binder. Particularly, the crystal structure of LiFePO4 was firstly destructed by sulfide, thus LiFePO4 particles were detached from the matrix of PVDF binder. Then, the PVDF binder without LiFePO4 particles filling were more susceptible to be brittlely peeled off by the micro-explosion force of hydrogen from the reaction of Al foil with water due to the weakened mechanical strength. The process is suitable for recycling varied types of spent LIBs, having a strong potential for industrial application.

A green process for exfoliating electrode materials and simultaneously extracting electrolyte from spent lithium-ion batteries.

Recycling of spent lithium-ion batteries (LIBs) has aroused extensive attentions with the expanding demand of electric vehicles. Two considerable challenges of LIBs recycling were separating electrode materials from metallic foils and reclaiming hazardous electrolyte. In the current study, an environmentally benign process was developed to recovery electrode materials and hazardous electrolyte. The main merits were that no strong acid or alkali was applied in the process, and the electrode materials were reclaimed in flaky form. A special complex aqueous peeling agent, namely exfoliating and extracting solution (AEES) was manufactured and applied in the process. The results indicated that cathode material could be exfoliated from Al foil by weakening the mechanical interlocking force and Coulomb force between cathode materials and foils. Ethylene carbonate (EC) and propylene carbonate (PC) could be extracted from electrodes and separators and recovered via distillation. LiPF6 could be precipitated from EC and PC and recovered via filtration. The conditions could be precisely controlled by optimizing the concentration of AEES. The recovery efficiencies of electrolyte, Al foil, Cu foil and electrode materials were 95.6%, 99.0%, 100% and near 100%, respectively. The process efficiently avoided infiltration of impurities into the electrode materials and is environmentally friendly for industrial application.

A novel process for preparing fireproofing materials from various industrial wastes.

In the current study, the possibility of incorporating various industrial wastes into fireproofing materials was investigated. It was found that the newly developed materials showed excellent air sealing and fireproofing performance, with air permeability coefficients 3 to 4 orders of magnitude smaller than traditional fire prevention materials. The influence of different parameters on the air permeability was investigated, and the air sealing mechanisms were clarified through microstructure analysis. In addition, the workability and mechanical properties of the fireproofing materials for practical application in coal mine were studied. The new materials derived from industrial wastes had a compact and monolithic structure, and the excellent air tightness could be attributed to the pozzolanic activity of the industrial wastes and the film-forming property of organic polymers. Among the industrial wastes examined, a special coal fly ash with high pozzolanic activity and little free calcium oxide derived the best product with air permeability coefficient, tensile strength and breaking elongation of 4.17 × 10-8 m2/s, 2.14 MPa and 48.90%, respectively. This study provides an economical, environmentally friendly and promising approach for industrial wastes recycling.

An environmentally friendly ball milling process for recovery of valuable metals from e-waste scraps.

The present study reports a mechanochemical (MC) process for effective recovery of copper (Cu) and precious metals (i.e. Pd and Ag) from e-waste scraps. Results indicated that the mixture of K2S2O8 and NaCl (abbreviated as K2S2O8/NaCl hereafter) was the most effective co-milling reagents in terms of high recovery rate. After co-milling with K2S2O8/NaCl, soluble metallic compounds were produced and consequently benefit the subsequent leaching process. 99.9% of Cu and 95.5% of Pd in the e-waste particles could be recovered in 0.5mol/L diluted HCl in 15min. Ag was concentrated in the leaching residue as AgCl and then recovered in 1mol/L NH3 solution. XRD and XPS analysis indicated that elemental metals in the raw materials were transformed into their corresponding oxidation state during ball milling process at low temperature, implying that solid-solid phase reactions is the reaction mechanism. Based on the results and thermodynamic parameters of the probable reactions, possible reaction pathways during ball milling were proposed. Suggestion on category of e-waste for ball milling process was put forward according to the experiment results. The designed metal recovery process of this study has the advantages of highly recovery rate and quick leaching speed. Thus, this study offers a promising and environmentally friendly method for recovering valuable metals from e-waste.

Recycling of spent lithium-ion battery with polyvinyl chloride by mechanochemical process.

In the present study, cathode materials (C/LiCoO2) of spent lithium-ion batteries (LIBs) and waste polyvinyl chloride (PVC) were co-processed via an innovative mechanochemical method, i.e. LiCoO2/PVC/Fe was co-grinded followed by water-leaching. This procedure generated recoverable LiCl from Li by the dechlorination of PVC and also generated magnetic CoFe4O6 from Co. The effects of different additives (e.g. alkali metals, non-metal oxides, and zero-valent metals) on (i) the conversion rates of Li and Co and (ii) the dechlorination rate of PVC were investigated, and the reaction mechanisms were explored. It was found that the chlorine atoms in PVC were mechanochemically transformed into chloride ions that bound to the Li in LiCoO2 to form LiCl. This resulted in reorganization of the Co and Fe crystals to form the magnetic material CoFe4O6. This study provides a more environmentally-friendly, economical, and straightforward approach for the recycling of spent LIBs and waste PVC compared to traditional processes.

A novel recovery method of copper from waste printed circuit boards by supercritical methanol process: Preparation of ultrafine copper materials.

In this study, supercritical methanol (SCM) process was successfully used for the preparation of ultrafine copper materials from waste printed circuit boards (PCBs) after nitric acid pretreatment. Waste PCBs were pretreated twice in nitric acid. Sn and Pb were recovered by the first nitric acid pretreatment. The leach liquor with a high concentration of copper ions after the second nitric acid leaching was subjected to SCM process. The mixture of Cu and Cu2O with poor uniformity of particle size was formed due to the effect of ferric iron contained in the leach liquor of waste PCBs, while more uniform and spherical Cu particles with high monodispersity and smaller size could be prepared after the removal of Fe. The size of Cu particles increased obviously with the decline of SCM temperature, and particles became highly aggregated when the reaction temperature decreased to 300°C. The size of Cu particles decreased markedly with the decrease of initial concentration of copper ion in the leach liquor of waste PCBs. It is believed that the process developed in this study is simple and practical for the preparation of ultrafine copper materials from waste PCBs with the aim of recycling these waste resources as a high value-added product.

Direct extraction of palladium and silver from waste printed circuit boards powder by supercritical fluids oxidation-extraction process.

The current study was carried out to develop an environmental benign process for direct recovery of palladium (Pd) and silver (Ag) from waste printed circuit boards (PCBs) powder. The process ingeniously combined supercritical water oxidation (SCWO) and supercritical carbon dioxide (Sc-CO2) extraction techniques. SCWO treatment could effectively enrich Pd and Ag by degrading non-metallic component, and a precious metal concentrate (PMC) could be obtained, in which the enrichment factors of Pd and Ag reached 5.3 and 4.8, respectively. In the second stage, more than 93.7% Pd and 96.4% Ag could be extracted from PMC by Sc-CO2 modified with acetone and KI-I2 under optimum conditions. Mechanism study indicated that Pd and Ag extraction by Sc-CO2 was a complicated physiochemical process, involving oxidation, complexation, anion exchange, mass transfer and migration approaches. Accordingly, this study established a benign and effective process for selective recovery of dispersal precious metals from waste materials.

Advanced degradation of brominated epoxy resin and simultaneous transformation of glass fiber from waste printed circuit boards by improved supercritical water oxidation processes.

This work investigated various supercritical water oxidation (SCWO) systems, i.e. SCWO1 (only water), SCWO2 (water+H2O2) and SCWO3 (water+H2O2/NaOH), for waste printed circuit boards (PCBs) detoxification and recycling. Response surface methodology (RSM) was applied to optimize the operating conditions of the optimal SCWO3 systems. The optimal reaction conditions for debromination were found to be the NaOH of 0.21g, the H2O2 volume of 9.04mL, the time of 39.7min, maximum debromination efficiency of 95.14%. Variance analysis indicated that the factors influencing debromination efficiency was in the sequence of NaOH>H2O2>time. Mechanism studies indicated that the dissociated ions from NaOH in supercritical water promoted the debromination of brominated epoxy resins (BERs) through an elimination reaction and nucleophilic substitution. HO2, produced by H2O2 could induce the oxidation of phenol ring to open (intermediates of BERs), which were thoroughly degraded to form hydrocarbons, CO2, H2O and NaBr. In addition, the alkali-silica reaction between OH(-) and SiO2 induced the phase transformation of glass fibers, which were simultaneously converted into anorthite and albite. Waste PCBs in H2O2/NaOH improved SCWO system were fully degraded into useful products and simultaneously transformed into functional materials. These findings are helpful for efficient recycling of waste PCBs.

A novel reutilization method for waste printed circuit boards as flame retardant and smoke suppressant for poly (vinyl chloride).

In this study, a novel reutilization method for waste printed circuit boards (PCBs) as flame retardant and smoke suppressant for poly (vinyl chloride) (PVC) was successfully testified. A supercritical water oxidation (SCWO) process was applied to treat waste PCBs before they could be used as flame retardants of PVC. The results indicated that SCWO conditions had a significant effect on the flame retarding and smoke suppressing properties of waste PCBs for PVC. Cu2O, CuO, and SnO2 were the main active ingredients in waste PCBs-derived flame retardants. A conversion of Cu elements (Cu(0)→Cu(+)→Cu(2+)) during SCWO process with the increase of reaction temperature was found to be the key influence factor for the flame retarding properties of SCWO-treated PCBs. The experiment results also showed that there was a synergistic effect of flame retardancy between Cu(+) and Cu(2+). After the optimized SCWO treatment, SCWO-treated PCBs significantly improved the flame retardancy and smoke suppression of PVC. Limiting oxygen index (LOI) and char yield (CY) increased with increasing SCWO-treated PCBs content in PVC, while smoke density rating (SDR) and maximum smoke density (MSD) decreased markedly. The mechanical properties of PVC samples were influenced in different degree by adding different content SCWO-treated PCBs.

Innovative leaching of cobalt and lithium from spent lithium-ion batteries and simultaneous dechlorination of polyvinyl chloride in subcritical water.

In this work, an effective and environmentally friendly process for the recovery of cobalt (Co) and lithium (Li) from spent lithium-ion batteries (LIBs) and simultaneously detoxification of polyvinyl chloride (PVC) in subcritical water was developed. Lithium cobalt oxide (LiCoO2) power from spent LIBs and PVC were co-treated by subcritical water oxidation, in which PVC served as a hydrochloric acid source to promote metal leaching. The dechlorination of PVC and metal leaching was achieved simultaneously under subcritical water oxidation. More than 95% Co and nearly 98% Li were recovered under the optimum conditions: temperature 350°C, PVC/LiCoO2 ratio 3:1, time 30min, and a solid/liquid ratio 16:1 (g/L), respectively. Moreover, PVC was completely dechlorinated at temperatures above 350°C without any release of toxic chlorinated organic compounds. Assessment on economical and environmental impacts revealed that the PVC and LiCoO2 subcritical co-treatment process had significant technical, economic and environmental benefits over the traditional hydrometallurgy and pyrometallurgy processes. This innovative co-treatment process is efficient, environmentally friendly and adequate for Co and Li recovery from spent LIBs and simultaneous dechlorination of PVC in subcritical water.

Effect of probiotics on the incidence of ventilator-associated pneumonia in critically ill patients: a randomized controlled multicenter trial.

PURPOSE: To evaluate the potential preventive effect of probiotics on ventilator-associated pneumonia (VAP). METHODS: This was an open-label, randomized, controlled multicenter trial involving 235 critically ill adult patients who were expected to receive mechanical ventilation for ≥48 h. The patients were randomized to receive (1) a probiotics capsule containing live Bacillus subtilis and Enterococcus faecalis (Medilac-S) 0.5 g three times daily through a nasogastric feeding tube plus standard preventive strategies or (2) standard preventive strategies alone, for a maximum of 14 days. The development of VAP was evaluated daily, and throat swabs and gastric aspirate were cultured at baseline and once or twice weekly thereafter. RESULTS: The incidence of microbiologically confirmed VAP in the probiotics group was significantly lower than that in the control patients (36.4 vs. 50.4 %, respectively; P = 0.031). The mean time to develop VAP was significantly longer in the probiotics group than in the control group (10.4 vs. 7.5 days, respectively; P = 0.022). The proportion of patients with acquisition of gastric colonization of potentially pathogenic microorganisms (PPMOs) was lower in the probiotics group (24 %) than the control group (44 %) (P = 0.004). However, the proportion of patients with eradication PPMO colonization on both sites of the oropharynx and stomach were not significantly different between the two groups. The administration of probiotics did not result in any improvement in the incidence of clinically suspected VAP, antimicrobial consumption, duration of mechanical ventilation, mortality and length of hospital stay. CONCLUSION: Therapy with the probiotic bacteria B. Subtilis and E. faecalis are an effective and safe means for preventing VAP and the acquisition of PPMO colonization in the stomach.

An environmental benign process for cobalt and lithium recovery from spent lithium-ion batteries by mechanochemical approach.

In the current study, an environmental benign process namely mechanochemical approach was developed for cobalt and lithium recovery from spent lithium-ion batteries (LIBs). The main merit of the process was that neither corrosive acid nor strong oxidant was applied. In the proposed process, lithium cobalt oxide (obtained from spent LIBs) was firstly co-grinded with various additives in a hermetic ball milling system, then Co and Li could be easily recovered by a water leaching procedure. It was found that EDTA was the most suitable co-grinding reagent, and 98% of Co and 99% of Li were respectively recovered under optimum conditions: LiCoO2 to EDTA mass ratio 1:4, milling time 4h, rotary speed 600r/min and ball-to-powder mass ratio 80:1, respectively. Mechanisms study implied that lone pair electrons provided by two nitrogen atoms and four hydroxyl oxygen atoms of EDTA could enter the empty orbit of Co and Li by solid-solid reaction, thus forming stable and water-soluble metal chelates Li-EDTA and Co-EDTA. Moreover, the separation of Co and Li could be achieved through a chemical precipitation approach. This study provides a high efficiency and environmentally friendly process for Co and Li recovery from spent LIBs.

Leaching of Au, Ag, and Pd from waste printed circuit boards of mobile phone by iodide lixiviant after supercritical water pre-treatment.

Precious metals are the most attractive resources in waste printed circuit boards (PCBs) of mobile phones. In this work, an alternative process for recovering Au, Ag, and Pd from waste PCBs of mobile phones by supercritical water oxidation (SCWO) pre-treatment combined with iodine-iodide leaching process was developed. In the process, the waste PCBs of mobile phones were pre-treated in supercritical water, then a diluted hydrochloric acid leaching (HL) process was used to recovery the Cu, whose leaching efficiency was approximately 100%, finally the resulting residue was subjected to the iodine-iodide leaching process for recovering the Au, Ag, and Pd. Experimental results indicated that SCWO pre-treatment temperature, time, and pressure had significant influence on the Au, Ag, and Pd leaching from (SCWO+HL)-treated waste PCBs. The optimal SCWO pre-treatment conditions were 420°C and 60min for Au and Pd, and 410°C and 30min for Ag. The optimum dissolution parameters for Au, Pd, and Ag in (SCWO+HL)-treated PCBs with iodine-iodide system were leaching time of 120min (90min for Ag), iodine/iodide mole ratio of 1:5 (1:6 for Ag), solid-to-liquid ratio (S/L) of 1:10g/mL (1:8g/mL for Ag), and pH of 9, respectively. It is believed that the process developed in this study is environment friendly for the recovery of Au, Ag, and Pd from waste PCBs of mobile phones by SCWO pre-treatment combined with iodine-iodide leaching process.