Lead extraction and glass-ceramics synthesis from waste cathode ray tube funnel glass through cooperative smelting process with coal fly ash

Carbon nanotubes synthesis over coal ash based catalysts using polypropylene waste via CVD process: Influence of catalyst and reaction temperature

Coal ash containing significant amount of SiO2 and Al2O3 is utilized as a catalyst substrate for carbon nanotubes (CNTs) synthesis. Three different types of catalysts were made by impregnating coal ash with cobalt, iron, and nickel. These catalysts were used to produce CNTs through pyrolysis of waste polypropylene followed by chemical vapor deposition. The influence of catalyst type and reaction temperature (700, 800 and 900 °C) on CNTs yield and its quality was studied in detail. The produced CNTs were characterized by thermogravimetric analysis (TGA), Raman scattering and electron microscopes (FESEM and HRTEM). The TGA results revealed that the Ni catalyst produced CNTs with highest yield (266 %) compared to those synthesized over and Fe (96 %) and Co (95 %). However, the yield of the CNTs from all three metal impregnated coal ash based catalysts was found to have decreased with increase in reaction temperature. The thermal stability of CNTs obtained over different catalysts followed the order of Fe (570 °C) > Ni (550 °C) > Co (530 °C). Further, the Raman analysis demonstrated that the produced CNTs over different catalysts showed increasing degree of graphitization with the rise in reaction temperature. Additionally, the ID/IG ratios indicated that CNTs produced from Fe catalyst showed highest degree of graphitization followed by Co and Ni. FESEM and HRTEM analysis showed that the coal ash based catalysts produced multiwalled CNTs and the diameter of the CNTs was increasing with the rise in catalysis temperature. Therefore, co-utilization of coal ash and waste plastic for production of high value CNTs can be a sustainable approach to waste management while actively contributing in circular economy.

Recovery of nickel and preparation of ferronickel alloy from spent petroleum catalyst via cooperative smelting-vitrification process with coal fly ash

Spent petroleum catalyst (SPC) is a highly toxic material since it contains heavy metals and hazardous substances. A novel recycling technology based on the cooperative smelting-vitrification process by using coal fly ash (CFA) as a fluxing material was proposed. The benefits of employing CFA in this cooperative smelting-vitrification process of SPC have been demonstrated via the results of lab-scale and scale-up experiments. The experimental results indicated that with a collector iron (Fe) addition of 26 wt%, a C/O molar ration of 1.4, and an H3BO3 addition of 14 wt%, the maximum nickel (Ni) recovery was ∼98% by controlling the CFA addition of 40-50 wt%, basicity of 0.4-0.5, smelting temperature of 1550°C, and smelting time of 60 min, respectively. In this process, a ferronickel (Ni-Fe) alloy with a high Ni grade of 10 wt% was successfully obtained, which could be directly further produced stainless steel. Meanwhile, a glass slag with a low Ni content (below 0.12 wt%) was also obtained, and its leaching characteristics further confirmed it is a non-hazardous slag because heavy metals were successfully encapsulated in glass slag, and thereby, this proposed method achieved the transformation from hazardous solid waste to general solid waste. The results of the 10 kg scale-up experiment indicated the possibility of industrialization of this new technology. Therefore, the process proposed in this study is a practical and promising process for Ni recovery from SPC and reutilization of CFA.

Recovery of lead and chlorine via thermal co-treatment of municipal solid waste incineration fly ash and lead-rich waste cathode-ray tubes: Analysis of chlorination volatilization mechanism

In this study, a new lead (Pb) and chlorine (Cl) recovery process via the thermal co-treatment of Municipal solid waste (MSW) incineration fly ash (FA) and waste cathode-ray tubes (CRT) was developed and the synergistic effects under different CRT ratios, temperatures, and residence times were comprehensively investigated. Thermogravimetric experiments revealed that the co-processing of FA and CRT exhibited a remarkable synergistic effect as evidenced by the considerable increase in mass loss and mass-loss rate when compared with the theoretical values. When the mixtures with 50% CRT addition was treated at 1200 °C for 60 min, Pb removal rate reached the maximum value of 98.67%, and the Cl removal rate considerably increased by 37.32% compared to that with FA treatment alone. Additionally, the Cl content in the residue was < 2%. It was mainly attributed to the volatilization of chlorides, such as PbCl2, NaCl, and KCl. CaCl2 generated from the decomposition of CaClOH in FA was conducive to improve Pb removal in CRT through indirect chlorination and destroying the glass structure in CRT. Co-processing of FA and CRT demonstrates promising potential for several benefits, including the reduction in melting temperature, recovery of Pb and Cl from secondary fly ash, and the reutilization of calcium-rich slag.

The lead removal evolution from hazardous waste cathode ray tube funnel glass under enhancement of red mud melting and synthesizing value-added glass-ceramics via reutilization of silicate resources

Waste CRT funnel glass (FG) is a typical hazardous waste produced by the electronics industry that contains toxic lead oxide, red mud (RM) is the first waste produced during alumina production. Both of these are extremely difficult to reuse. Here, we report a method to control FG waste, in which RM was used to enhance the removal of Pb from FG via a vacuum thermal process. The removed residual glass was utilized to create glass-ceramics. The results showed that RM can enhance the lead removal from waste CRT funnel glass by the vacuum thermal process. When 30% RM was added, the removal rate reached 98.54%. A significant mechanism of enhancing delead is investigated by a Fourier transform infrared (FTIR) spectrometer and X-ray photoelectron spectroscopy (XPS). The results showed that the -Pb-O-Si-O- network structure was broken by the free calcium ions of RM. Afterward, valuable glass-ceramics with tetragonal-KAlSi₂O₆ and triclinic-CaSiO₃ crystals were synthesized using the residual glass. The Pb, Ba, Cr, and Cu leaching concentrations of the glass-ceramics were well below the regulatory limit (5 mg/L) of the CA-EPA, as measured by the toxicity characteristic leaching procedure (TCLP) test. Overall, the results indicated that RM enhanced the removal of lead during the vacuum thermal process. The synthesis of value-added glass-ceramics reutilized silicate resources from waste cathode ray tube (CRT) funnel glass and RM.

An Integrated Capture of Red Mud and One-Step Heat-Treatment Process to Recover Platinum Group Metals and Prepare Glass-Ceramics from Spent Auto-Catalysts

Co-treatment for two kinds of hazardous solid waste is an effective method to reduce cost and increase recycle efficiency of value resource. This work developed an integrated process based on capture of red mud (RM) and a one-step heat-treatment process to efficiently recover PGMs from spent auto-catalysts (SAC) and reuse RM simultaneously. Firstly, the iron oxide in RM was reduced to metallic iron to capture PGMs by the reduction process, without the addition of an extra reducing agent, since SAC contained abundant organic volatiles. Then, the mixed waste of SAC and RM was melted under high temperature with additives of CaO and H3BO3. More than 99% of PGMs can be extracted under the optimal conditions of 40–50 wt% of RM addition, 14 wt% of H3BO3 addition, 0.7–0.8 of basicity, 1500 °C of temperature, and 40 min of holding time. In addition, PGM content in obtained glassy slag was less than 1 g/t. The mechanism of iron trapping PGMs was also discussed in detailed, which mainly contained two stages: migration of PGMs and separation of PGM-bearing alloy and slag phases. Besides, the obtained glassy slag was further prepared into glass-ceramic by a one-step heat-treatment process. It was found that the prepared glass-ceramic has good thermostability and an excellent stabilizing effect on heavy metals. Overall, the results indicated that the developed integrated smelting–collection process is an efficient and promising method for the reutilization of SAC and RM.

E-waste management and its effects on the environment and human health

Challenges in managing electronic waste (E-waste) arise from a lack of technical skills, poor infrastructure, inadequate financial support, and inactive community engagement. This study provides a systematic review of efforts to overcome these challenges in the context of inappropriate recycling protocols of E-waste and their toxic effects on human health and the environment. An inventory of end-of-life electronic products, which can be established through the creation of an environment friendly regulatory regime for recycling, is essential for the proper control of E-waste. An approach has been articulated to help implement effective management of E-waste in both developed and developing countries. Enforcement of systematic management measures for E-waste in developing countries coupled with best practices is expected to minimize adverse impacts while helping maintain a sustainable and resilient environment.

Energy efficient production of glass-ceramics using photovoltaic (P/V) glass and lignite fly ash

This study investigates an innovative approach for the valorization of specific wastes generated from the energy sector and the production of glass-ceramics. The wastes used were photovoltaic (P/V) glass, produced from the renewable energy sector, and lignite fly ash, produced from the conventional energy sector. The process first involved the production of glass after melting specific mixtures of wastes, namely (i) 70% P/V glass and 30% lignite fly ash, and (ii) 80% P/V glass and 20% lignite fly ash, at 1200 °C for 1 h as revealed by the use of a heating microscope. The results indicated that the P/V glass, as a sodium-potassium-rich inorganic waste, reduces energy requirements of the melting process. The produced glass was then used for the production of glass-ceramics. Dense and homogeneous glass-ceramics, exhibiting high chemical stability and no toxicity, were produced after controlled thermal treatment of glass at 800 °C. The mechanical (compressive strength, Vickers hardness) and physical (open porosity, bulk density and water absorption) properties of the produced glass-ceramics were evaluated. X-ray diffraction (XRD) and Energy Dispersive X-ray fluorescence (ED-XRF) were used for the characterization of the raw materials and the produced glass-ceramics. Scanning electron microscopy (SEM) provided further insights on the microstructure of the final products. The properties of the produced glass-ceramics, namely water absorption and compressive strength, render them suitable for applications in the construction industry. The waste valorization approach followed in this study is in line with the principles of circular economy.