Non-metallic Fraction Research Articles

Characterizing the environmental implications of the recycling of non-metallic fractions from waste printed circuit boards

Non-metallic fractions (NMFs), which make up almost three fourths (by weight) of waste printed circuit boards, have become a matter of great concern for e-waste recyclers, because most of them contain hazardous substances with low utilization value. This study used an advanced Sales Obsolescence Model approach to quantify the generation and flows of non-metallic fractions in China, and to examine the potential environmental impacts associated with both the fractions themselves, and their end-of-life processing activities: disposal into landfills or incineration, and recycling via physical or chemical methods. The results show that approximately 201,000 tons (one time standard deviation: 67,000) of scrap non-metallic fractions were expected to be generated in 2015, and that this amount could increase to 279,000 tons by 2020. Both our own analysis and a systematic review of existing studies on the hazardous characterization of printed circuit boards waste, non-metallic fractions, and their recycling and disposal activities, indicate the threat of environmental pollution, from heavy metals, brominated flame retardants and secondary persistent organic pollutants, particularly dioxins.

Recycling oriented vertical vibratory separation of copper and polypropylene particles

Vibration has been employed in various engineering processes for material handling. The famous Brazil nut effect, large particles tend to rise to the top under vibration, initiates various research about vibration induced particle segregation. Particle size and density are two determining factors for their behavior under vibration. Previous research in University of Nottingham proves vertical vibratory separation to be a promising environmental friendly mechanical separation method for recycling metallic fraction from shredded Waste Electric and Electronic Equipment (WEEE) stream. A pilot scale thin cell vibratory separator has been developed to investigate the potential for WEEE recycling applications. Shredded copper and polypropylene particles have been chosen to mimic metallic and non-metallic fractions in WEEE. Vibratory separation experiment with controlled environment and addition of solid lubricant are presented in this paper. The result demonstrates the effect of relative humidity and solid lubricant on improving flowability of granular system hence successful vibratory separation. The proposed mechanisms for the presence of moisture and solid lubricant are lubricant effect and elimination of static electricity.

Preparation of hierarchical porous carbon from waste printed circuit boards for high performance electric double-layer capacitors

Renewable clean energy and resources recycling have become inevitable choices to solve worldwide energy shortages and environmental pollution problems. It is a great challenge to recycle tons of waste printed circuit boards (PCB) produced every year for clean environment while creating values. In this work, low cost, high quality activated carbons (ACs) were synthesized from non-metallic fractions (NMF) of waste PCB to offer a great potential for applications of electrochemical double-layer capacitors (EDLCs). After recovering metal from waste PCB, hierarchical porous carbons were produced from NMF by carbonization and activation processes. The experimental results exhibit that some pores were formed after carbonization due to the escape of impurity atoms introduced by additives in NMF. Then the pore structure was further tailored by adjusting the activation parameters. Roles of micropores and non-micropores in charge storage were investigated when the hierarchical porous carbons were applied as electrode of EDLCs. The highest specific capacitance of 210 F g−1 (at 50 mA g−1) and excellent rate capability were achieved when the ACs possessing a proper micropores/non-micropores ratio. This work not only provides a promising method to recycle PCB, but also investigates the structure tailoring arts for a rational hierarchical porous structure in energy storage/conversion.

Study on the effect of alumina nano-fluid on sharp-edge orifice flow characteristics in both cavitations and non-cavitations turbulent flow regimes

In the present study, the effects of alumina nano-fluid concentration on sharp-edge orifice flow characteristics in both cavitations and non-cavitations turbulent flow regimes are numerically investigated. At different concentration of AL2O3 nonmetallic particles (2%, 4%, 6%, 8%, and 10%) volume fractions in pure liquid water as a base fluid. A single-hole orifice pipe is with a small diameter ratio 0.297 and the orifice plate thickness 14mm. The effects of alumina nano-fluid concentration on sharp-edge orifice flow characteristics have been investigated based on the turbulent kinetic energy, turbulent intensity, turbulent viscosity, and volume fraction of vapor. The results show that for increasing the nonmetallic particle volume fraction from 0.0 to 10%, the turbulent kinetic energy decreases by 20.87% in average downstream the orifice in the whole region, the turbulent intensity decreases by 11.11% in average downstream the orifice in the whole region, the turbulent intensity decreases by 11% in average in the whole region, and the volume fraction of vapor increases by 16.9%. Also, in the separation region downstream the orifice the turbulent kinetic energy increases by 160% in average and the turbulent intensity increases by 74% in average for increasing the nano-fluid concentration from 0.0% to 2%. These are mainly because for using the alumina nano-fluid the separation phenomena decrease due to the increase of the viscosity of the nano-fluid, the total losses in the sharp-edge orifice increase for the increase of the viscosity of the nano-fluid and this causes the increase of the rate of vaporization. In the orifice pipe the total-stress criterion predicts larger cavitating regions in the flow field. However using the nano-fluid with high concentration accelerates the cavitations at the orifice pipe.

Mathematical analysis of the gas–solid fluidized bed separation of metals and nonmetals from waste PCB powders

Modern society is generating increasing quantities of waste printed circuit boards (PCBs). Together with the complicated components of high values, the treatment of waste PCBs has been a heavily researched and difficult topic in the disposal of waste electrical and electronic equipment (WEEE). The application of an air separation technology to produce comminuted PCB particles can achieve efficient separation of metal and nonmetallic fractions for further treatment and purification. With the advantages of a simple operation, environmental-soundness, and avoidance of secondary pollution, this technology is of great significance in the recycling of waste PCBs. In this paper, the air separation principles of waste PCB particles in a fluidized bed were mathematically analyzed. The shape factor of metal and non-metallic particles and the uneven airflow velocity distribution in the radial dimension were considered, and the formula for metal grade and yield were deduced. Experiments were designed and performed to obtain metal grade and yield data, which were compared with the calculation results. The calculated grade is in good agreement with the experimental results. The presented mathematical analysis can act as a guide for the engineering design and operating configuration of air separation for waste PCB particles in determining the terminal velocity and for selecting the particle size, feed volume, and discharging height.

Separation of the metallic and non-metallic fraction from printed circuit boards employing green technology

The generation of electrical and electronic waste is increasing day by day; recycling is attractive because of the metallic fraction containing these. Nevertheless, conventional techniques are highly polluting. The comminution of the printed circuit boards followed by an inverse flotation process is a clean technique that allows one to separate the metallic fraction from the non-metallic fraction. It was found that particle size and superficial air velocity are the main variables in the separation of the different fractions. In this way an efficient separation is achieved by avoiding the environmental contamination coupled with the possible utilization of the different fractions obtained.

Structural, thermal, morphological and dynamic mechanical characteristics of waste‐reinforced polypropylene composites: A novel approach for recycling electronic waste

ABSTRACTAn in‐depth investigation has been carried toward utilizing polymer‐rich nonmetallic fraction of printed circuit boards (PCBs) as reinforcing fillers in polypropylene (PP) composites. The influence of waste additions (up to 25 wt %) on structural, thermal, morphological, and dynamic mechanical behavior of PP composites was investigated using a range of analytical techniques. The incorporation of PCB waste was found to affect the crystalline morphology resulting in the formation of smaller spherulites. The presence of glass fibers in PCB waste promoted the formation of β‐crystal enhancing the mechanical properties of composites. Thermal analysis showed a maximum increase of ∼15 °C in the crystallization onset temperature (Tco) suggesting the nucleating effect of the filler, a feature also supported by structural investigations. Polarized microscopy revealed a reduction in the spherulite size after 5 wt % PCB waste loading owing to the presence of large number of nucleation sites. The incorporation of waste also increased the thermal stability of composites increasing the final degradation temperature by up to 14 °C. Dynamic mechanical properties of PP/PCB waste composites were determined in the temperature range −20 to 155 °C; a significant increase in the storage modulus further confirmed the reinforcing effect of waste additives. This investigation has shown that the nonmetallic fraction of PCB waste could be used as a cost‐effective reinforcing filler for PP, providing an environmental friendly route to utilize electronic waste in value‐added products. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43389.

Removing inorganics from nonmetal fraction of waste printed circuit boards by triboelectric separation

Metals recycling from WPCBs has been studied for a long time, which results in the appearance of many proven techniques. However, the nonmetal fraction in WPCBs has not been fully recycled due to hybridpropertiesof inorganic and organic composition. In order to improve the usability of the nonmetal fraction from WPCBs, nonmetal materials separation by using a laboratory triboelectric separation system was carried out to improve the reuse efficiency of WPCBs nonmetal fraction. The optimum tribocharger material was investigated by using the charge–mass ratio measurement system, and PMMA is the optimum tribocharger material compared with PVC, PPFT, PPR, SS. The effects of airflow, voltage and feed rate on triboelectric separation were investigated. The product LOI of positive plate is up to 77.26% with recovery rate of 25.49%, while the product LOI of negative plate is down to 47.35% with recovery rate of 35.37%, and the remove rate of inorganics is up to 43.02% by triboelectric separation. The analysis results of X-ray diffraction indicate that the main inorganic materials mixed in nonmetal fraction are SiO2, Al2O3, CaO, Cu, Fe, Sn. The X-ray fluorescence analysis shows that the triboelectric separation can effectively remove the content of SiO2 and Al2O3. The scanning electron microscope images show that inorganics tribocharge positively and distribute in product collection grooves that close to negative plate.

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.

Evaluation of the economic feasibility of a processing plant for steelmaking slag.

The utilisation of steelmaking slag as recycled aggregate for concretes is a widely investigated solution for mitigating the expenditure and environmental impacts of its storage. The Brazilian steel industry is investing in research and slag reprocessing practices, aiming to reuse most of its metallic fraction and properly allocate the non-metallic fraction, saving energy and reducing mining impacts. Research results demonstrate the technical and environmental feasibility of steel slag aggregates for civil construction. However, it is essential to evaluate whether the processing of the slag is economically feasible for this purpose. Economic analysis of the processing of steel slag was conducted through simulation - Monte Carlo method - in which it is possible to determine the risks and uncertainties inherent to the project. The costs that comprise the proposed project, from design through construction and operation itself, were estimated at US$2.8 million. The result of the simulation indicates economic feasibility of the project with 98% certainty, and an estimated profit of around 42%.

Recovery of metals from pyrolysed PCBs by hydrometallurgical techniques

Present paper is a part of developed novel process to recover various metals (Cu, Fe, Ni and Pb) environmentally from waste printed circuit boards (WPCBs). The process consists of pyrolysis-physical beneficiation-leaching-solvent extraction-electrowinning-cementation. The PCBs were pyrolysed at a temperature of 300°C and the obtained poly-cracker ash of PCBs was subjected to comminution for the separation of metallic from non-metallic fractions using scutter crusher and grinding mills. Further, the ground poly-cracker ash of PCBs was scrubbed/washed with water without using any additives to enrich the metallic concentrate up to 98%. The scrubbed sample was further screened to separate low and high metal concentrates. Further, the high metal concentrate (+10 mesh i.e. >2mm size) was leached in 4M HNO3 at 90°C for 60min maintaining pulp density 30g/L and stirring speed 250rpm. Result showed the complete dissolution of the metals viz. Cu, Fe, Pb and 57.5% Ni etc. present in the concentrate. Systematic scientific studies were also carried out to recover acid and metal from leach liquor of the poly-cracker ash of PCBs. To recover nitric acid from the leach liquor, the experiments were carried out using 60% TBP diluted in kerosene, which resulted in the extraction of 98% HNO3 in three stages at O/A ratio 3/1 in 12min. Subsequently, air sparging was performed to separate and recover Fe as precipitate. After the recovery of acid and iron, the leach liquor was further processed to recover Cu using 25% LIX 84IC diluted in kerosene. The copper was found to be extracted 99.99% in two stages at pH2.5, O/A ratio 1/1 in 20min, leaving Ni and Pb in the raffinate. Cu solution was stripped from loaded organic using 10% H2SO4. Cu metal sheet was obtained from the strip solution by electrowinning process in 4h at temperature 30°C using a cathode current density of 200A/m2. Further, the raffinate was processed for the recovery of Ni and Pb. Based on the experimental results a process flow-sheet is proposed for the extraction of all major metals (Cu, Fe, Ni and Pb) from the waste PCBs. The process has the potential to be commercialized after scale-up studies.

Overall heat transfer coefficient and pressure drop in a typical tubular exchanger employing alumina nano-fluid as the tube side hot fluid

Nano-fluids are used to improve the heat transfer rates in heat exchangers, especially; the shell-and-tube heat exchanger that is considered one of the most important types of heat exchangers. In the present study, an experimental loop is constructed to study the thermal characteristics of the shell-and-tube heat exchanger; at different concentrations of Al2O3 nonmetallic particles (0.0, 2, 4, and 6 %). This material concentrations is by volume concentrations in pure water as a base fluid. The effects of nano-fluid concentrations on the performance of shell and tube heat exchanger have been conducted based on the overall heat transfer coefficient, the friction factor, the pressure drop in tube side, and the entropy generation rate. The experimental results show that; the highest heat transfer coefficient is obtained at a nano-fluid concentration of 4 % of the shell side. In shell side the maximum percentage increase in the overall heat transfer coefficient has reached 29.8 % for a nano-fluid concentration of 4 %, relative to the case of the base fluid (water) at the same tube side Reynolds number. However; in the tube side the maximum relative increase in pressure drop has recorded the values of 12, 28 and 48 % for a nano-material concentration of 2, 4 and 6 %, respectively, relative to the case without nano-fluid, at an approximate value of 56,000 for Reynolds number. The entropy generation reduces with increasing the nonmetallic particle volume fraction of the same flow rates. For increase the nonmetallic particle volume fraction from 0.0 to 6 % the rate of entropy generation decrease by 10 %.

Recycling of black dross containing rare earths originating from melting and recycling of magnesium alloys

The process of melting and recycling magnesium alloys using fluxes produces a residue termed black dross. The black dross investigated contained metal and non-metallic phases with a considerable content of rare earth metals (REEs). The black dross was separated by crushing and screening into metal and non-metallic fractions. The non-metallic fraction was further processed by water and acid leaching. In the water leach, NaCl, KCl and CaCl2 were separated for crystallisation. In the acid leach the residue was treated with hydrochloric acid in order to dissolve the rare earth elements Ce, La, Nd and Pr. Selective precipitation by oxalic acid and solvent extraction using D2EHPA or PC88A enables a recovery of up to 92.6% of the REEs from the oxide-salt-fraction. The equilibrium isotherms of the solvent extraction operation indicate the potential for further separating the rare earth elements. A flow sheet of the whole processes was developed in order to guide industrial application.

Mechanical strength evaluation of composites made from waste printed circuit boards (PCBs)

ABSTRACTSustainable resource recovery and recycling forms an integral part of a developed and developing economy. In line with this universally acceptable sustainable practice, the feasibility of utilizing the nonmetallic fraction (NMF) from waste printed circuit boards (PCBs) as a reinforcing additive in the waste polyvinyl chloride (PVC) from the piping industry to form a usable composite material was investigated. Mechanical strength evaluation of PCB–PVC composites was investigated in terms of morphological NMF powder properties and fracture analysis at surfaces of PCB–PVC composites. The acquired results showed that the NMF addition to a certain limit can significantly improve the mechanical strength properties of waste PVC such as the tensile strength, bending strength, and modulus. An optimum NMF ratio value of 20% for improved mechanical strength properties was identified. Adding 500 µm NMF with optimum weight ratio increased the tensile strength (40%), tensile modulus (38.8%), bending strength (12.7%), and bending modulus (31%) of composites in comparison with nonadditive recycled PVC. Further it was observed that changing the NMF particle size from 500 to 150 µm decreased the tensile strength (7.14%), modulus (16%) and increased bending strength (7.74%) and modulus (5.7%). This investigation suggests that the waste NMF of PCBs in the identified optimum weight ratio can form an effective addition to the waste (PVC) to improve its mechanical strength properties. The effective use in this manner will lead to a promising new way of recycling the waste NMF of PCBs resulting in potential new uses by simultaneous sustainable waste reduction and reuse of otherwise a hazardous waste.

Preparation of epoxy resin-based activated carbons from waste printed circuit boards by steam activation

Epoxy resin-based activated carbons were prepared from waste printed circuit boards by physical activation with steam in a two-step approach, firstly carbonized and then activated with steam. The important parameters, which affect the characteristics of epoxy resin-based activated carbon greatly, such as the carbonization temperature, carbonization time, activation temperature and activation time, were investigated in this study. Compared with the carbonized chars, the activated carbon through steam activation has obvious improvements in the BET surface area and pore volume. The results indicated that the best quality epoxy resin-based activated carbon was obtained at carbonization temperature of 600°C, carbonization time of 2h, activation temperature of 800°C and activation time of 90min. The non-metallic fraction of WPCBs could be a promising material for preparing epoxy resin-based activated carbon with developed microporous and small mesoporous structures.

Recovery and utilisation of non-metallic fraction from waste printed circuit boards in polypropylene composites

Extreme complexity in the range of polymer composition in waste printed circuit boards (WPCBs) will leave us to follow a series of steps to formulate an efficient recycling system. The current study deals with the recovery and utilisation of non-metallic fractions from WPCBs through dismantling, size reduction and sieve analysis. Density based techniques have been adopted in the current studies to separate the non-metallic fractions from metallic one due to its simplicity and cost effectiveness. The non-metallic fractions are quantified through sieve analysis and are utilised as reinforcing filler material in polypropylene matrix. Composite material with WPCBs has been prepared via melt blending techniques and is subjected to mechanical, thermal and morphological analysis to investigate its feasibility for automobile application.

The application of pneumatic jigging in the recovery of metallic fraction from shredded printed wiring boards.

Waste electrical and electronic equipment (WEEE) is one of the fastest growing waste streams worldwide with volumes increasing by 40% each year. WEEE has attracted increasing concern worldwide due to its high metal content and the potential environmental threat which results from uncontrolled recycling practices. Innovative physical separation techniques for WEEE recycling are preferential compared with chemical methods because of the reduction of energy and chemical consumption as well as potential environmental threats. Pneumatic jigging is a dry separation process capable of achieving good separation of coarse material within a very narrow density range, which makes it suitable as a pretreatment process for WEEE recycling. The work presented in this paper investigates the potential application of pneumatic jigging in metal recovery from WEEE. A pilot scale pneumatic jig has been developed by University of Nottingham Ningbo to separate shredded printed wiring boards into two streams: a light fraction (mainly non-metallic fraction consisting of glass fiber, fluffs, and plastic pieces) and dense fraction (metallic fraction). The novelty of work presented in this paper is the application of a dry separation technique in WEEE recycling for metal recovery. Compared with conventional wet separation processes involved in WEEE recycling industry, dry separation has the advantage of zero secondary pollution. The results of this experimental program show pneumatic jigging to be an effective and environmental friendly technique as a pretreatment process for the recovery of the metallic fraction from shredded WEEE.

Novel carbon micro fibers and foams from waste printed circuit boards

We report the generation of novel carbon micro fibers and foam structures during the pyrolysis of polymer rich waste printed circuit boards (PCBs) in the temperature range of 750°C to 1550°C under argon atmosphere. Following initial polymer degradation and the separation of most of the metallic phase, the carbonaceous residue was seen to evolve into a variety of structures. Carbon fibers started to nucleate ~1150°C, had a thickness ranging between 2 and 10 microns, contained up to 95% C with morphologies ranging between tubular, foamy network and fibrous. The chemical compositions of these carbon structures was determined through X-ray microanalysis; the carbon content was close to 90% along with 5–7% oxygen, traces of phosphorus, antimony, tin and copper.The transformation of carbon fibers to a well-defined foam structure was observed at 1250°C; these structures were found to be stable even at higher temperatures. The formation of carbon foams/fibers was found to be not very sensitive to the relative concentration of oxide impurities present. This study shows that a potentially vast source of carbon could be recovered from the non-metallic fraction of e-waste for applications such as reduction reactions, carburization, metal–carbon composites or as a source of fuel and energy.

Conventional flotation techniques to separate metallic and nonmetallic fractions from waste printed circuit boards with particles nonconventional size

This paper shows the results obtained by using a conventional Denver D12 flotation cell to separate the metal and a non-metallic material obtained from printed circuit boards (PCB). The bubble superficial surface rate (SB) and percentage of solids in feed was changed to evaluate the recovery of nonmetallic material in overflow product (concentrate) and the metal material in underflow (tailings). The solids content in feed is most influential parameter in nonmetallic material recovery. Finally, a flotation circuit is proposed as well as a flotation mechanism for this unconventional mix.

Encapsulation of nonmetallic fractions recovered from printed circuit boards waste with thermoplastic

The present work includes a process for encapsulation by combining substantially simultaneously dry nonmetallic printed circuit boards (PCBs) powder and recycled high-density polyethylene (rHDPE) in an extruder to form a homogenous matrix. The extruded materials were then molded into standard tensile, flexural, and impact properties testing specimens. Nonmetallic PCB mainly consists of large amount of glass fiber–reinforced epoxy resin materials. Incorporation of 50 wt% nonmetallic PCB in rHDPE matrix had increased the flexural strength and modulus by 35% and 130%, respectively. Tensile strength reported to be constant without much improvement. However, the Young’s modulus has increased by 180%, with incorporation of 50 wt% nonmetallic PCB. The addition of 6 phr (parts per hundred) maleated polyethylene (MAPE) resulted in 2-fold increase in tensile and flexural strength. Regarding the leaching properties, Cu was identified as the metal that leached at the highest level from the raw nonmetallic PCB, at 59.09 mg/L. However, after the nonmetallic PCB was filled in rHDPE/PCB composites, the concentration of Cu was reduced far below the regulatory limit, to only 3 mg/L. Thermal properties of composites were studied, and it was found out that incorporation of nonmetallic PCB fillers in rHDPE resulted in low thermal conductivity, whereas mechanical strength of the composites showed maximum improvements at 220 °C. Overall, the encapsulation technique using nonmetallic PCB waste has formed a monolithic waste form that provides a barrier to the dispersion of wastes into the environment.ImplicationsNonmetallic materials reclaimed from waste PCBs were used to analyze the chemical composition, and it was found that nonmetalllic PCBs mainly consist of glass fiber–reinforced epoxy resin materials. With such millions of glass fibers in nonmetallic PCBs, there are mass-excellent supporting bodies that enhance the mechanical properties of composites. In fact, utilization of nonmetallic PCB waste as filler in composites can dramatically restrain the solubility of heavy metals in leachate solution, thus making it safe to be used in practical products.