Ravindra Rajarao

Concentration of precious metals during their recovery from electronic waste.

The rapid growth of electronic devices, their subsequent obsolescence and disposal has resulted in electronic waste (e-waste) being one of the fastest increasing waste streams worldwide. The main component of e-waste is printed circuit boards (PCBs), which contain substantial quantities of precious metals in concentrations significantly higher than those typically found in corresponding ores. The high value and limited reserves of minerals containing these metals makes urban mining of precious metals very attractive. This article is focused on the concentration and recovery of precious metals during pyro-metallurgical recycling of waste PCBs. High temperature pyrolysis was carried out for ten minutes in a horizontal tube furnace in the temperature range 800-1350°C under Argon gas flowing at 1L/min. These temperatures were chosen to lie below and above the melting point (1084.87°C) of copper, the main metal in PCBs, to study the influence of its physical state on the recovery of precious metals. The heat treatment of waste PCBs resulted in two different types of solid products, namely a carbonaceous non-metallic fraction (NMFs) and metallic products, composed of copper rich foils and/or droplets and tin-lead rich droplets and some wires. Significant proportions of Ag, Au, Pd and Pt were found concentrated within two types of metallic phases, with very limited quantities retained by the NMFs. This process was successful in concentrating several precious metals such as Ag, Au, Pd and Pt in a small volume fraction, and reduced volumes for further processing/refinement by up to 75%. The amounts of secondary wastes produced were also minimised to a great extent. The generation of precious metals rich metallic phases demonstrates high temperature pyrolysis as a viable approach towards the recovery of precious metals from e-waste.

Generation of copper rich metallic phases from waste printed circuit boards

The rapid consumption and obsolescence of electronics have resulted in e-waste being one of the fastest growing waste streams worldwide. Printed circuit boards (PCBs) are among the most complex e-waste, containing significant quantities of hazardous and toxic materials leading to high levels of pollution if landfilled or processed inappropriately. However, PCBs are also an important resource of metals including copper, tin, lead and precious metals; their recycling is appealing especially as the concentration of these metals in PCBs is considerably higher than in their ores. This article is focused on a novel approach to recover copper rich phases from waste PCBs. Crushed PCBs were heat treated at 1150°C under argon gas flowing at 1L/min into a horizontal tube furnace. Samples were placed into an alumina crucible and positioned in the cold zone of the furnace for 5 min to avoid thermal shock, and then pushed into the hot zone, with specimens exposed to high temperatures for 10 and 20 min. After treatment, residues were pulled back to the cold zone and kept there for 5 min to avoid thermal cracking and re-oxidation. This process resulted in the generation of a metallic phase in the form of droplets and a carbonaceous residue. The metallic phase was formed of copper-rich red droplets and tin-rich white droplets along with the presence of several precious metals. The carbonaceous residue was found to consist of slag and ∼30% carbon. The process conditions led to the segregation of hazardous lead and tin clusters in the metallic phase. The heat treatment temperature was chosen to be above the melting point of copper; molten copper helped to concentrate metallic constituents and their separation from the carbonaceous residue and the slag. Inert atmosphere prevented the re-oxidation of metals and the loss of carbon in the gaseous fraction. Recycling e-waste is expected to lead to enhanced metal recovery, conserving natural resources and providing an environmentally sustainable solution to the management of waste products.

Plant root nodule like nickel-oxide–multi-walled carbon nanotube composites for non-enzymatic glucose sensors

Herein, in this work we synthesized plant root nodule like NiO–MWCNT nanocomposites by a simple, rapid and solvent-free method using nickel formate as a precursor. Using a first-principle simulation study the interactions and charge transfer behaviour of the NiO and MWCNT composite is investigated. The as-prepared NiO–MWCNT composite is employed to fabricate a modified non-enzymatic carbon paste electrode (CPE) for glucose sensing. From the electrochemical investigation, the fabricated sensor shows an excellent sensitivity of 6527 μA mM−1 cm−2 with a detection limit of 19 μM and a linear response over a range from 0.001 mM to 14 mM of glucose concentrations, at an applied potential of 0.5 V. Importantly the sensor also exhibits greater stability, selectivity and reproducibility. A first principle simulation study shows the differences in charge density and charge transfer behaviour from nanotubes to NiO nanoparticles, which in turn enhances the electro catalytic property of the NiO–MWCNT composite. Hence, these results indicate that the NiO–MWCNT composite is a potential material for non-enzymatic electrochemical glucose sensors.

High temperature transformations of waste printed circuit boards from computer monitor and CPU: Characterisation of residues and kinetic studies.

This paper investigates the high temperature transformation, specifically the kinetic behaviour of the waste printed circuit board (WPCB) derived from computer monitor (single-sided/SSWPCB) and computer processing boards - CPU (multi-layered/MLWPCB) using Thermo-Gravimetric Analyser (TGA) and Vertical Thermo-Gravimetric Analyser (VTGA) techniques under nitrogen atmosphere. Furthermore, the resulting WPCB residues were subjected to characterisation using X-ray Fluorescence spectrometry (XRF), Carbon Analyser, X-ray Photoelectron Spectrometer (XPS) and Scanning Electron Microscopy (SEM). In order to analyse the material degradation of WPCB, TGA from 40°C to 700°C at the rates of 10°C, 20°C and 30°C and VTGA at 700°C, 900°C and 1100°C were performed respectively. The data obtained was analysed on the basis of first order reaction kinetics. Through experiments it is observed that there exists a substantial difference between SSWPCB and MLWPCB in their decomposition levels, kinetic behaviour and structural properties. The calculated activation energy (EA) of SSWPCB is found to be lower than that of MLWPCB. Elemental analysis of SSWPCB determines to have high carbon content in contrast to MLWPCB and differences in materials properties have significant influence on kinetics, which is ceramic rich, proving to have differences in the physicochemical properties. These high temperature transformation studies and associated analytical investigations provide fundamental understanding of different WPCB and its major variations.

Characteristics of waste automotive glasses as silica resource in ferrosilicon synthesis.

This fundamental research on end-of-life automotive glasses, which are difficult to recycle, is aimed at understanding the chemical and physical characteristics of waste glasses as a resource of silica to produce ferrosilicon. Laboratory experiments at 1550°C were carried out using different automotive glasses and the results compared with those obtained with pure silica. In situ images of slag–metal separation showed similar behaviour for waste glasses and silica-bearing pellets. Though X-ray diffraction (XRD) showed different slag compositions for glass and silica-bearing pellets, formation of ferrosilicon was confirmed. Synthesized ferrosilicon alloy from waste glasses and silica were compared by Raman, X-ray photoelectron spectroscopy and scanning electron microscopy (SEM) analysis. Silicon concentration in the synthesized alloys showed almost 92% silicon recovery from the silica-bearing pellet and 74–92% silicon recoveries from various waste glass pellets. The polyvinyl butyral (PVB) plastic layer in the windshield glass decomposed at low temperature and did not show any detrimental effect on ferrosilicon synthesis. This innovative approach of using waste automotive glasses as a silica source for ferrosilicon production has the potential to create sustainable pathways, which will reduce specialty glass waste in landfill.

Environmental Impact of Processing Electronic Waste – Key Issues and Challenges

Extensive utilization of electric and electronic equipment in a wide range of applications has resulted in the generation of huge volumes of electronic waste (e-waste) globally. Highly complex e-waste can contain metals, polymers and ceramics along with several hazardous and toxic constituents. There are presently no standard approaches for han‐ dling, dismantling, and the processing of e-waste to recover valuable resources. Inappro‐ priate and unsafe practices produce additional hazardous compounds and highly toxic emissions as well. This chapter presents an overview of the environmental impact of proc‐ essing e-waste with specific focus on toxic elements present initially in a variety of e-waste as well as hazardous compounds generated during e-waste processing. Hazardous constit‐ uents/ and contaminants were classified in three categories: primary contaminants, secon‐ dary contaminants, and tertiary contaminants. Primary contaminants represent hazardous substances present initially within various types of e-waste; these include heavy metals such as lead, mercury, nickel and cadmium, flame retardants presents in polymers etc. Sec‐ ondary contaminants such as spent acids, volatile/toxic compounds, PAHs are the byproducts or waste residues produced after inappropriate processing of e-waste and the tertiary contaminants include leftover reagents or compounds used during processing. A detailed report is presented on the environmental impact of processing e-waste and the detrimental impact on soil contamination, vegetation degradation, water and air quality along with implications for human health. Challenges and opportunities associated with appropriate e-waste management are also discussed.

Green Manufacturing: A Key to Innovation Economy

This thematic section focuses on different aspects of transformations of ‘e-waste’ into value-added materials and the associated developments. The papers selected demonstrate how innovative scientific research and development is delivering economically viable, real-world solutions for industry by reimagining waste as a resource for the future. These three papers cover analysing above ground resources, simple technique for measuring the elements inside the waste and high temperature transformation of waste.

Zinc Oxide Nanoparticles from Waste Zn-C Battery via Thermal Route: Characterization and Properties

Disposable batteries are becoming the primary sources of powering day-to-day gadgets and consequently contributing to e-waste generation. The emerging e-waste worldwide is creating concern regarding environmental and health issues. Therefore, a sustainable recycling approach of spent batteries has become a critical focus. This study reports the detail characterization and properties of ZnO nanoparticles recovered from spent Zn-C batteries via a facile thermal synthesis route. ZnO nanoparticles are used in many applications including energy storage, gas sensors, optoelectronics, etc. due to the exceptional physical and optical properties. A thermal treatment at 900 °C under an inert atmosphere of argon was applied to synthesize ZnO nanoparticles from a spent Zn-C battery using a horizontal quartz tube furnace. X-ray diffraction (XRD), selected area electron diffraction (SAED) and X-ray photoelectron spectroscopy (XPS) results confirmed the formation of crystalline ZnO nanoparticles. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analysis confirmed that the size of synthesised ZnO particles were less than 50 nm and mainly composed of sphere shaped nanoparticles. Synthesized ZnO exhibited BET surface area of 9.2629 m2/g and showed absorption of light in the UV region. Excitation of ZnO by UV light showed photoluminescence in the visible range. This study will create an opportunity for potential applications of ZnO nanoparticles from spent batteries and will benefit the environment by reducing the volume of e-waste in landfills.

Formation of carbyne-like materials during low temperature pyrolysis of lignocellulosic biomass: A natural resource of linear sp carbons

The exploration, understanding and potential applications of ‘Carbyne’, the one-dimensional sp allotrope of carbon, have been severely limited due to its extreme reactivity and a tendency for highly exothermic cross-linking. Due to ill-defined materials, limited characterization and a lack of compelling definitive evidence, even the existence of linear carbons has been questioned. We report a first-ever investigation on the formation of carbyne-like materials during low temperature pyrolysis of biobased lignin, a natural bioresource. The presence of carbyne was confirmed by detecting acetylenic –C≡C– bonds in lignin chars using NMR, Raman and FTIR spectroscopies. The crystallographic structure of this phase was determined as hexagonal: a = 6.052 Å, c = 6.96 Å from x-ray diffraction results. HRSEM images on lignin chars showed that the carbyne phase was present as nanoscale flakes/fibers (~10 nm thick) dispersed in an organic matrix and showed no sign of overlapping or physical contact. These nanostructures did not show any tendency towards cross-linking, but preferred to branch out instead. Overcoming key issues/challenges associated with their formation and stability, this study presents a novel approach for producing a stable condensed phase of sp-bonded linear carbons from a low-cost, naturally abundant, and renewable bioresource.

High voltage pulses to recover copper from waste printed circuit boards

Electronic waste (e-waste) is one of the rapidly growing solid waste streams around the world. Advancement in technology, increase in usage of electronic products and rise in population during the last decade is causing the rapid obsolescence of e-waste. E-waste generation is around 40 million tonnes each year and increasing at the rate of 3–5% per annum. E-waste is heterogeneous in nature and contains both valuable and hazardous materials. Printed circuit boards (PCBs), a key component is used in most of the electronics and contributes 3% by weight to the total e-waste. PCBs contain copper and gold 20 times more than their respective ores hence various physical, chemical, electrostatic, pyrolysis and metallurgical techniques are investigated to recover copper. But due to disadvantages such as (a) release of toxic gases during crushing (b) non-selective fragmentation between metals and non-metals (c) use of chemicals or acids (d) high energy utilization demands the environmental friendly and sustainable technique to recover copper from waste PCBs. In this study, we have used high voltage pulse technology to recover copper from waste PCBs. To achieve high recovery, operating conditions such as voltage and number of pulses were optimised. The results signify that applied electric voltage and number of high energy pulse were the important factors to segregate copper from waste PCBs. Reduction of noxious gases, high recovery of copper and negligible mechanical damage were the advantages of using high voltage pulse technology to recover copper from waste.