An innovative route for valorising iron and aluminium oxide rich industrial wastes: Recovery of multiple metals.

Several industrial wastes including biomass, fly ashes, red mud, mill scales, water treatment residues, have significant concentrations of metal oxides: Fe2O3, Al2O3, TiO2, SiO2 etc. Several efforts have been made towards recovering metals within these wastes. Rather than recovering one metal at a time, we report a novel approach for simultaneously extracting multiple metals from mixed oxides in a single process step. Using three distinct furnaces/heating regimes, the carbothermic reduction of Fe2O3/Al2O3/SiO2 system was investigated at 1450-1700 °C for up to 2 h over a wide composition range. Complete reduction was achieved for both Fe2O3 and SiO2 in all cases leading to the formation of Fe and Fe-Si alloys. The reduction of alumina at moderate temperatures was the key challenge. No alumina reduction was observed during reductions at 1450 °C. A partial reduction of alumina and the formation of Fe-Al alloys was detected in the Al2O3/Fe2O3/C system at 1550 °C. The formation of Fe-Si-Al alloys was also observed in the Fe2O3/SiO2/Al2O3/C system at 1550 °C. Complete reduction of alumina was observed at 1600-1700 °C, even for up to 50 wt% alumina in the system. Optimal operating conditions and reference standards were established for the simultaneous recovery of multiple metals from waste oxides. While conserving natural resources, this novel route will lower the burden on waste storage facilities with significant contributions to the economic and environmental sustainability of industrial waste management.

Factors influencing the release of potentially toxic elements (PTEs) during thermal processing of electronic waste.

The release of potentially toxic elements as airborne fine particulates is a significant environmental risk associated with recycling e-waste. Some of these may redeposit near emission sites or be transported over long distances causing wide-spread pollution. With an aim to identify key factors affecting particulate emissions, we report novel investigations on the adsorptive capture of particulate matter (PM) released during low temperature pyrolysis (600 °C; 15 min) of waste printed circuit boards (PCBs). A significant proportion of the released particulates (5.3 to 37%) were captured by adsorbents located downstream and in close proximity to the emitting source. Data was collected for four different PCBs and three adsorbents: alumina, silica-gel and activated carbon. With sizes ranging from nanoparticles to over 10 µm, adsorbed particulates were present as fines, spheres, oblongs, clusters and larger particles with no specific shape. Of the 24 elements identified initially in waste PCBs, only 14 were detected in released particulates: major PTEs- Zn, Sn, Pb and Cu (up to 400 ppm); minor PTEs- Ni, Mn, Cd, Cr and Ba (up to 10 ppm); trace PTEs- Co, In, Bi, Be and Sb (up to 1 ppm). Key factors influencing the release of PTEs during thermal processing were identified as basic elemental characteristics, densities, melting points, vapor pressures, initial concentrations, local bonding and mechanical strength. These results show that the presence of low melting point/high vapour pressure elements (Zn, Pb, Sn) should be minimised for a significant reduction in PTE emissions during e-waste processing.

High temperature investigations on optimising the recovery of copper from waste printed circuit boards.

High temperature pyrolysis investigations were carried out on waste printed circuit boards (PCBs) in the temperature range 800-1000°C under inert conditions, with an aim to determine optimal operating conditions for the recovery of copper. Pyrolysis residues were characterized using ICP-OES analysis, SEM/EDS and XRD investigations. Copper foils were successfully recovered after pyrolysis at 800°C for 10-20 min; the levels of Pb and Sn present were found to be quite low and these were generally present near the foil edges. The relative proportions of Pb and Sn became progressively higher at longer heating times due to enhanced diffusion of these molten metals in solid copper. While a similar behaviour was observed at 900°C, the pyrolysis at 1000°C resulted in copper forming Cu-Sn-Pb alloys; copper foils could no longer be recovered. Optimal conditions were identified for the direct recovery of copper from waste PCBs with minimal processing. This approach is expected to make significant contributions towards enhancing material recovery, process efficiency and the environmental sustainability of recycling e-waste. Pyrolysis at lower temperatures, short heating times, coupled with reductions in process steps are expected to significantly reduce energy consumption and pollution associated with the handling and processing of waste PCBs.

Concentration of rare earth elements during high temperature pyrolysis of waste printed circuit boards.

An in-depth investigation was carried out on the recovery of rare earth elements (REEs) from a variety of waste printed circuit boards (PCBs). High temperature pyrolysis was carried out at 850 °C for 15 min using horizontal resistance and thermal plasma furnaces with different levels of turbulence. The concentration of REEs in key pyrolysis residues, namely, copper rich red metallic fraction, lead/tin rich white metallic fraction and slag rich carbonaceous residues, were determined using ICP analysis. Most of the REEs were found concentrated in the carbonaceous residue with negligible levels of REEs recovered in the two metallic fractions. Most of the recovered REEs showed a high affinity towards to refractory oxides silica and alumina, and little affinity towards metals Cu, Pb and Sn. The yield of REEs was significantly higher from the plasma furnace indicating the important role of turbulence in the dissociation & subsequent diffusion of REEs during pyrolysis. While La, Pr, Sm and Y required turbulent conditions for their recovery, Nd, Gd, Ce and Dy were relatively easy to dissociate and extract from the waste. Significant amounts of REEs could thus be recovered from waste PCBs as concentrated recyclates for further processing and extraction of individual rare earths. This study has shown that PCBs could prove to be a valuable urban mining resource of REEs. The recovery of REEs, in addition to precious and other metals, could play an important role towards enhancing the economic and environmental sustainability of e-waste recycling.

A novel approach for reducing toxic emissions during high temperature processing of electronic waste.

A novel approach is presented to capture some of the potentially toxic elements (PTEs), other particulates and emissions during the heat treatment of e-waste using alumina adsorbents. Waste PCBs from mobile phones were mechanically crushed to sizes less than 1mm; their thermal degradation was investigated using thermo-gravimetric analysis. Observed weight loss was attributed to the degradation of polymers and the vaporization of organic constituents and volatile metals. The sample assembly containing PCB powder and adsorbent was heat treated at 600°C for times ranging between 10 and 30min with air, nitrogen and argon as carrier gases. Weight gains up to ∼17% were recorded in the adsorbent thereby indicating the capture of significant amounts of particulates. The highest level of adsorption was observed in N2 atmosphere for small particle sizes of alumina. SEM/EDS results on the adsorbent indicated the presence of Cu, Pb, Si, Mg and C. These studies were supplemented with ICP-OES analysis to determine the extent of various species captured as a function of operating parameters. This innovative, low-cost approach has the potential for utilization in the informal sector and/or developing countries, and could play a significant role in reducing toxic emissions from e-waste processing towards environmentally safe limits.

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.

Treatment of electronic waste to recover metal values using thermal plasma coupled with acid leaching--a response surface modeling approach.

The global crisis of the hazardous electronic waste (E-waste) is on the rise due to increasing usage and disposal of electronic devices. A process was developed to treat E-waste in an environmentally benign process. The process consisted of thermal plasma treatment followed by recovery of metal values through mineral acid leaching. In the thermal process, the E-waste was melted to recover the metal values as a metallic mixture. The metallic mixture was subjected to acid leaching in presence of depolarizer. The leached liquor mainly contained copper as the other elements like Al and Fe were mostly in alloy form as per the XRD and phase diagram studies. Response surface model was used to optimize the conditions for leaching. More than 90% leaching efficiency at room temperature was observed for Cu, Ni and Co with HCl as the solvent, whereas Fe and Al showed less than 40% efficiency.

Validity of Queen's College step test for use with young Indian men.

OBJECTIVES: To assess the suitability of the Queen's College step test (QCT) to predict maximum oxygen uptake in Indian men. METHODS: Thirty sedentary male university students from West Bengal, India, with the same socioeconomic background and mean (SD) age, height, and weight of 22.6 (0.2) years, 166.4 (0.5) cm, and 53.8 (0.2) kg, respectively, were randomly sampled from University of Calcutta. VO2max of each participant was determined by direct procedure involving incremental bicycle exercise and also by applying indirect QCT method with a gap of 4 days between the tests. RESULTS: The difference between the mean (SD) VO2max values directly measured (VO2max = 39.8 (1.03) ml/min/kg body mass) and indirectly predicted (PVO2max = 39.3 (1.07) ml/min/kg body mass) was statistically insignificant (p>0.10). PVO2max and VO2max values expressed as ml/min/kg body mass corroborated with previous studies in the same laboratory involving the same population, and also exhibited significant statistical correlation (r = 0.95, p<0.001) between them. CONCLUSION: The results suggest that QCT can be applied in the studied population to produce a good estimation of maximum oxygen uptake, especially in the field where large numbers of participants are to be evaluated without a well equipped laboratory.

Morphohistobiochemical characteristics of embryogenic and nonembryogenic callus cultures of sweet potato (Ipomoea batatas L.).

Ipomoea batatas callus culture raised in a medium supplemented with 2,4-D (2,4-dichlorophenoxy acetic acid) alone or 2,4-D in combination with benzyl adenine, were found to be embryogenic. Supplementation of exogenous chemicals, such as 5 g/l NaCI or 0.7 g/l proline together with a mild dose of 0.2 mg/l 2,4-D, enhanced somatic embryogenesis significantly in all the genotypes tested. Morphological, growth, physiological, histological, and biochemical characteristics of the embryogenic callus were different from the nonembryogenic callus. The former was compact, slow growing, and nodular compared with the fast growing, fragile, nonembryogenic callus. The embryogenic callus tissue had more dry matter, protein and reducing sugar contents compared with the less embryogenic callus. The somatic embryogenic response remained steady in the cultures for up to 96 weeks.

Determination of amphetamine in dog plasma by gas chromatography with mass selective detection.

This paper describes the validation of an analytical method for the determination of amphetamine in beagle dog plasma by gas chromatography coupled to mass spectrometry (GC-MS). d-Amphetamine-d(6) was used as the internal standard. The method consisted of a rapid single-step liquid-liquid extraction and derivatization of amphetamine with 2,2,2-trichloroethyl chloroformate, followed by sensitive GC-MS detection. This is the first report utilizing the combination of trichloroethyl chloroformate as a derivatization reagent and a deuterated amphetamine analog as an IS for the quantification of amphetamine in plasma. The method was validated in terms of specificity, curve fit, precision, accuracy, recovery and stability, and was acceptable according to FDA draft guidelines for validation of bioanalytical methods. The limit of detection was 0.65 ng/mL. The calibration range was 5-150 ng/mL. The validated method was successfully employed for the quantitation of amphetamine in dog plasma samples for pharmacokinetic profiling.

Ultraviolet and fluorescence derivatization reagents for carboxylic acids suitable for high performance liquid chromatography: a review.

Pre- and postcolumn derivatization with a suitable chromophore or fluorophore have often been utilized to enhance the sensitivity and selectivity of detection for analytes possessing a carboxyl group. The major classes of UV and fluorescent derivatization reagents include the coumarin analogues, alkyl halides, diazoalkanes, and amines. The derivatization reaction conditions, HPLC systems for separation of the conjugates and detection limits of various analytes are presented in this review. High mass sensitivity for various carboxylic acids have been achieved with the hydrazides, anthracenes, and diazoalkanes.

Analysis of gamma-(cholesteryloxy)butyric acid in biologic samples by derivatization with 5-(bromomethyl)fluorescein followed by high-performance liquid chromatography with laser-induced fluorescence detection.

This report describes the first application of 5-(bromo-methyl)fluorescein (5-BMF) for the quantitation of a pharmaceutically relevant carboxyl-containing analyte in a biological matrix. An analytical method for quantitation of gamma-(cholesteryloxy)butyric acid (CBA), a relatively new antitumor agent, in different tissues of Sprague-Dawley rats was developed. 5-BMF was employed to form a stable and spectrally well-characterized conjugate of CBA. The derivatization yield was maximized by optimizing several reaction variables. The conjugate was separated by high-performance liquid chromatography and quantitated by a laboratory-constructed argon ion laser fluorometer. The detection limits for CBA were 4.6 x 10(-9) and 6.34 x 10(-11) M by conventional and laser-induced fluorescence (LIF), respectively. A derivatization limit of detection of 1.85 x 10(-9) M was achieved by LIF for the conjugate The analytical method was useful for quantitation of CBA in various tissues in the picogram per milliliter range.

5-Bromomethyl fluorescein (5-BMF) for derivatization of carboxyl containing analytes for use with laser-induced fluorescence detection.

PURPOSE: 5-Bromomethyl fluorescein (5-BMF) was evaluated in this work as a pre-column, off-line derivatizing reagent for analytes containing a free carboxyl group. The reagent possessed high molar absorptivity and quantum yield and it's excitation maximum matched the intense 488.0 nm emission line of an argon ion laser. The thermal and photo-stability of the reagent were also suitable for our work. METHODS: A mixture of 5-BMF, palmitic acid, 18-crown-6 and potassium carbonate was reacted at 76 degrees C for one hour. The reaction yield was maximized by a sequential single-factor optimization of the reaction variables. Spectral characterizations were accomplished using conventional instrumentation and detection limits were evaluated using a laboratory constructed laser-induced fluorescence (LIF) detector which was optimized for concentration detection. RESULTS: Two apparent conjugates of palmitic acid were formed under the reaction conditions employed. The conjugate chosen for quantitative purposes was stable at room temperature over 24 hours and possessed high molar absorptivity (128,832 M-1cm-1) and quantum yield (0.82) under basic conditions. The excitation and emission maxima of the conjugate were 500 nm and 523 nm respectively which maintains suitability for argon-ion laser excitation. An argon-ion LIF detector suitable for use with conventional liquid chromatography was constructed. A detection limit of 7.56 x 10(-10)M of palmitic acid was achieved at a signal to noise ratio of three, using the strong 488.0 nm laser emission line and a commercially available flow cell component. This corresponds to 38 femtomoles of palmitic acid on-column. CONCLUSION: The concentration detection limit was superior to literature reports for detection of fatty acids. The mass detection limit provided approximately an order of magnitude improvement over conventional fluorescence. The reagent is potentially useful for analysis of carboxyl containing analytes at low concentrations.