Enhancement of the recycling of waste Ni-Cd and Ni-MH batteries by mechanical treatment

A serious environmental problem was presented by waste batteries resulting from lack of relevant regulations and effective recycling technologies in China. The present work considered the enhancement of waste Ni-Cd and Ni-MH batteries recycling by mechanical treatment. In the process of characterization, two types of waste batteries (Ni-Cd and Ni-MH batteries) were selected and their components were characterized in relation to their elemental chemical compositions. In the process of mechanical separation and recycling, waste Ni-Cd and Ni-MH batteries were processed by a recycling technology without a negative impact on the environment. The technology contained mechanical crushing, size classification, gravity separation, and magnetic separation. The results obtained demonstrated that: (1) Mechanical crushing was an effective process to strip the metallic parts from separators and pastes. High liberation efficiency of the metallic parts from separators and pastes was attained in the crushing process until the fractions reached particle sizes smaller than 2 mm. (2) The classified materials mainly consisted of the fractions with the size of particles between 0.5 and 2 mm after size classification. (3) The metallic concentrates of the samples were improved from around 75% to 90% by gravity separation. More than 90% of the metallic materials were separated into heavy fractions when the particle sizes were larger than 0.5 mm. (4) The size of particles between 0.5 and 2 mm and the rotational speed of the separator between 30 and 60 rpm were suitable for magnetic separation during industrial application, with the recycling efficiency exceeding 95%.     

New characterisation method of electrical and electronic equipment wastes (WEEE)

Innovative separation and beneficiation techniques of various materials encountered in electrical and electronic equipment wastes (WEEE) is a major improvement for its recycling. Mechanical separation-oriented characterisation of WEEE was conducted in an attempt to evaluate the amenability of mechanical separation processes. Properties such as liberation degree of fractions (plastics, metals ferrous and non-ferrous), which are essential for mechanical separation, are analysed by means of a grain counting approach. Two different samples from different recycling industries were characterised in this work. The first sample is a heterogeneous material containing different types of plastics, metals (ferrous and non-ferrous), printed circuit board (PCB), rubber and wood. The second sample contains a mixture of mainly plastics. It is found for the first sample that all aluminium particles are free (100%) in all investigated size fractions. Between 92% and 95% of plastics are present as free particles; however, 67% in average of ferromagnetic particles are liberated. It can be observed that only 42% of ferromagnetic particles are free in the size fraction larger than 20 mm. Particle shapes were also quantified manually particle by particle. The results show that the particle shapes as a result of shredding, turn out to be heterogeneous, thereby complicating mechanical separation processes. In addition, the separability of various materials was ascertained by a sink–float analysis and eddy current separation. The second sample was separated by automatic sensor sorting in four different products: ABS, PC–ABS, PS and rest product. The fractions were characterised by using the methodology described in this paper. The results show that the grade and liberation degree of the plastic products ABS, PC–ABS and PS are close to 100%. Sink–float separation and infrared plastic identification equipment confirms the high plastic quality. On the basis of these findings, a global separation flow sheet is proposed to improve the plastic separation of WEEE.     

Electrostatic separators of particles: Application to plastic/metal, metal/metal and plastic/plastic mixtures

Electrostatic separation is a generic term given to a significant class of technologies of industrial waste processing, widely used for the sorting of granular mixtures due to electric forces acting on particles whose average size is approximately 5mm. The focus of this paper is on three electrostatic processes of separation used for processing of different types of mixtures: (i) role-type electrostatic separator, used to sort mixtures containing metal/plastic particles (copper/PVC for example); (ii) plate-type electrostatic separator, used to sort mixtures containing metal/metal particles (copper/lead for example) and (iii) free-fall electrostatic separator, used to sort mixtures of plastic/plastic particles (PVC/PE for example). Experiments carried out on industrial samples using laboratory electrostatic separators confirm the efficiency of these processes and show that the processes can improve the recovery and purity of products resulting from industrial wastes.     

Enrichment of the metallic components from waste printed circuit boards by a mechanical separation process using a stamp mill

Printed circuit boards incorporated in most electrical and electronic equipment contain valuable metals such as Cu, Ni, Au, Ag, Pd, Fe, Sn, and Pb. In order to employ a hydrometallurgical route for the recycling of valuable metals from printed circuit boards, a mechanical pre-treatment step is needed. In this study, the metallic components from waste printed circuit boards have been enriched using a mechanical separation process. Waste printed circuit boards shredded to <10mm were milled using a stamp mill to liberate the various metallic components, and then the milled printed circuit boards were classified into fractions of <0.6, 0.6-1.2, 1.2-2.5, 2.5-5.0, and >5.0mm. The fractions of milled printed circuit boards of size <5.0mm were separated into a light fraction of mostly non-metallic components and a heavy fraction of the metallic components by gravity separation using a zig-zag classifier. The >5.0mm fraction and the heavy fraction were subjected to two-step magnetic separation. Through the first magnetic separation at 700 Gauss, 83% of the nickel and iron, based on the whole printed circuit boards, was recovered in the magnetic fraction, and 92% of the copper was recovered in the non-magnetic fraction. The cumulative recovery of nickel-iron concentrate was increased by a second magnetic separation at 3000 Gauss, but the grade of the concentrate decreased remarkably from 76% to 56%. The cumulative recovery of copper concentrate decreased, but the grade increased slightly from 71.6% to 75.4%. This study has demonstrated the feasibility of the mechanical separation process consisting of milling/size classification/gravity separation/two-step magnetic separation for enriching metallic components such as Cu, Ni, Al, and Fe from waste printed circuit boards.     

Utilization of magnetic and electrostatic separation in the recycling of printed circuit boards scrap

The progress of the technology is directly related to the growth of production and consumption of electrical/electronics equipment, especially of personal computers. This type of equipment has a relatively short average lifetime, 2-3 years. The amount of defective or obsolete equipment has been increasing substantially; consequently its disposition and/or recycling should be studied. In this work, printed circuit boards, which are used in personal computers, were studied in order to recover the metals in the circuit boards through mechanical processing, such as crushing, screening, as well as magnetic and electrostatic separation. The results obtained demonstrate the feasibility of using these processes to separate metal fractions from polymers and ceramics, and that it is possible to obtain a fraction concentrated in metals containing more than 50% on average of copper, 24% of tin and 8% of lead.     

Precious Metals in Municipal Solid Waste Incineration Bottom Ash

Municipal solid waste incineration (MSWI) bottom ash contains economically significant levels of silver and gold. Bottom ashes from incinerators at Amsterdam and Ludwigshafen were sampled, processed, and analyzed to determine the composition, size, and mass distribution of the precious metals. In order to establish accurate statistics of the gold particles, a sample of heavy non-ferrous metals produced from 15 tons of wet processed Amsterdam ash was analyzed by a new technology called magnetic density separation (MDS). Amsterdam’s bottom ash contains approximately 10 ppm of silver and 0.4 ppm of gold, which was found in particulate form in all size fractions below 20 mm. The sample from Ludwigshafen was too small to give accurate values on the gold content, but the silver content was found to be identical to the value measured for the Amsterdam ash. Precious metal value in particles smaller than 2 mm seems to derive mainly from waste of electrical and electronic equipment (WEEE), whereas larger precious metal particles are from jewelry and constitute the major part of the economic value. Economical analysis shows that separation of precious metals from the ash may be viable with the presently high prices of non-ferrous metals. In order to recover the precious metals, bottom ash must first be classified into different size fractions. Then, the heavy non-ferrous (HNF) metals should be concentrated by physical separation (eddy current separation, density separation, etc.). Finally, MDS can separate gold from the other HNF metals (copper, zinc). Gold-enriched concentrates can be sold to the precious metal smelter and the copper-zinc fraction to a brass or copper smelter.     

Evaluation of entanglement properties of crushed automobile shredded residue and detachment of entrapped particles

Automobile shredded residue is a potential solid fuel when its metal and chlorine-containing parts have been removed. The authors have investigated physical separation of automobile shredded residue to obtain the components that may be used in solid fuel and found that agglomerates of entangling fiber-like components are formed during crushing, making removal of metals and chlorine-containing parts difficult. In this paper, a reattachment ratio, entrapment ratio, and disentanglement ratio are proposed to evaluate the entanglement properties of crushed automobile shredded residue. It is found that products smaller than 16 mm were not reattached easily in the sieving process, and an index based on entanglement properties proposed here is useful to predict suitable crushing conditions. Wet detachment of entrapped particles from agglomerates of entangling materials was also applied to separate particulate matter from crushed ASR.     

Hybrid sensor for metal grade measurement of a falling stream of solid waste particles

A hybrid sensor system for accurate detection of the metal grade of a stream of falling solid waste particles is investigated and experimentally verified. The system holds an infrared and an electromagnetic unit around a central tube and counts all the particles and only the metal particles, respectively. The count ratio together with the measured average particle mass ratio (k) of non-metal and metal particles is sufficient for calculation of grade. The performance of the system is accurately verified using synthetic mixtures of sand and metal particles. Towards an application a case study is performed using municipal solid waste incineration bottom ash in size fractions 1-6mm, which presents a major challenge for nonferrous metal recovery. The particle count ratio was inherently accurate for particle feed rates up to 13 per second. The average value and spread of k for bottom ash was determined as 0.49 ± 0.07 and used to calculate grade within 2.4% from the manually analysed grade. At higher feed rates the sensors start missing particles which fall simultaneously through the central tube, but the hybrid system still counted highly repeatable. This allowed for implementation of a count correction ratio to eliminate the stationary error. In combination with averaging in measurement intervals for suppression of stochastic variations the hybrid system regained its accuracy for particle feed rates up to 143 per second. This performance and its special design, intended to render it insensitive to external interference and noise when applied in an eddy current separator, make the hybrid sensor suitable for applications such as quality control and sensor controlled separation.     

The cause and influence of self-cementing properties of fine recycled concrete aggregates on the properties of unbound sub-base

The use of coarse recycled concrete aggregates (CRCA) in conjunction with fine recycled concrete aggregates (FRCA) as sub-base materials has been widely studied. Although research results indicate that it is feasible to employ both CRCA and FRCA as granular sub-base, the influence of the unhydrated cement in the adhered mortar of the RCA on the properties of the sub-base materials has not been thoroughly studied. Generally, it is known that the strength of the sub-base materials prepared with RCA increases over time. However, this mechanism, known as the self-cementing properties, is not well understood and is believed to be governed by the properties of the fine portion of the RCA (<5mm). This paper presents an investigation on the cause of the self-cementing properties by measuring X-ray diffraction patterns, pH values, compressive strength and permeability of various size fractions of the FRCA obtained from a commercially operated construction and demolition waste recycling plant. Their influence on the overall sub-base materials was determined. The results indicate that the size fractions of <0.15 and 0.3-0.6mm (active fractions) were most likely to be the principal cause of the self-cementing properties of the FRCA. However, the effects on the properties of the overall RCA sub-base materials were minimal if the total quantity of the active fractions was limited to a threshold by weight of the total fine aggregate.     

Recycling of construction and demolition waste materials: a chemical-mineralogical appraisal

Building activity is currently demanding remarkable amounts of inert materials (such as gravel and sand) that are usually provided by alluvial sediments. The EU directives and Italian Legislation are encouraging the re-use of construction and demolition waste provided by continuous urban redevelopment. The re-utilisation of building waste is a relatively new issue for Italy: unfortunately the employment of recycled inert materials is still limited to general bulk and drainage fills, while a more complete re-evaluation is generally hampered by the lack of suitable recycling plants. In this paper, chemical-mineralogical characterization of recycled inert materials was carried out after preliminary crushing and grain-size sorting. XRF and XRD analysis of the different grain-size classes allowed us to recognise particular granulometric classes that can be re-utilised as first-order material in the building activity. Specifically, the presented chemical-mineralogical appraisal indicates that the recycled grain-size fraction 0.6-0.125 mm could be directly re-employed in the preparation of new mortar and concrete, while finer fractions could be considered as components for industrial processing in the preparation of cements and bricks/tiles.     

Electronic scraps--recovering of valuable materials from parallel wire cables

Every year, the number of discarded electro-electronic products is increasing. For this reason recycling is needed, to avoid wasting non-renewable natural resources. The objective of this work is to study the recycling of materials from parallel wire cable through unit operations of mineral processing. Parallel wire cables are basically composed of polymer and copper. The following unit operations were tested: grinding, size classification, dense medium separation, electrostatic separation, scrubbing, panning, and elutriation. It was observed that the operations used obtained copper and PVC concentrates with a low degree of cross contamination. It was concluded that total liberation of the materials was accomplished after grinding to less than 3 mm, using a cage mill. Separation using panning and elutriation presented the best results in terms of recovery and cross contamination.     

Jig separation of crushed automobile shredded residue and its evaluation by float and sink analysis

Automobile shredded residue is a potential solid fuel when its metal and chloride-containing components have been removed. The authors have investigated physical separation of automobile shredded residue to isolate components that may be used as solid fuel and reported that agglomerates of entangling fiber-like material are formed during crushing. These agglomerates make removal of metals and chloride-containing components difficult, and the paper proposes a treatment flowchart consisting of separate treatments of the coarse size fraction containing entangling fiber-like components and the smaller size fraction containing particulate matter. This paper reports the treatment of the smaller size fraction treated with jigging to obtain a low-ash and low-chloride-content product. A new washability curve was developed based on float and sink analysis test results, and it was applied to estimate the gravity separation performance of treatments such as jigging and dense medium separation. The estimated results show good agreement with the experimental results of jig separation.     

Transmission electron microscopy (TEM) investigations of Mn-oxide rich cathodic material from spent disposable alkaline batteries

Transmission electron microscopy (TEM) techniques were used to investigate the spent cathodic material of a single common brand of disposable alkaline batteries. Mn-oxide particles are anhedral and irregular in shape and compose an estimated 99-95% of the <10mum size fraction of sample material. Diameters of particles vary widely and typically are between 50nm and 3mum; however, most particles are approximately 200-400nm in diameter. Chemical composition varies for Mn-oxide particles with concentrations being SiO(2) (0.00-1.52wt%), TiO(2) (0.49-4.58wt%), MnO (65.85-92.06wt%), ZnO (1.00-7.53wt%), K(2)O (4.97-20.48wt%) and SO(3) (0.43-2.21wt%). Discrete prismatic zinc crystals occur and vary from a maximum of approximately 0.8mum longx0.15mum wide, to 100nm longx20nm wide. Titanium metal was also observed in samples and composes approximately 0.25-1.0% of the <10mum size fraction of sample material. Results of this study suggest that battery components may be recycled in some special applications. Examples are low energy-low material requirement products such as paint pigments and Zn nanoparticles. This investigation provides detailed constraints on the nature of spent cathodic materials to improve existing recycling methods and develop new technologies.     

Evaluation of a recycling process for printed circuit board by physical separation and heat treatment

Printed circuit boards (PCBs) from discarded personal computer (PC) and hard disk drive were crushed by explosion in water or mechanical comminution in order to disintegrate the attached parts. More parts were stripped from PCB of PC, composed of epoxy resin; than from PCB of household appliance, composed of phenol resin.In an attempt to raise the copper grade of PCB by removing other components, a carbonization treatment was investigated. The crushed PCB without surface-mounted parts was carbonized under a nitrogen atmosphere at 873–1073 K. After screening, the char was classified by size into oversized pieces, undersized pieces and powder. The copper foil and glass fiber pieces were liberated and collected in undersized fraction. The copper foil was liberated easily from glass fiber by stamping treatment.As one of the mounted parts, the multi-layered ceramic capacitors (MLCCs), which contain nickel, were carbonized at 873 K. The magnetic separation is carried out at a lower magnetic field strength of 0.1 T and then at 0.8 T. In the +0.5 mm size fraction the nickel grade in magnetic product was increased from 0.16% to 6.7% and the nickel recovery is 74%.The other useful mounted parts are tantalum capacitors. The tantalum capacitors were collected from mounted parts. The tantalum-sintered bodies were separated from molded resins by heat treatment at 723–773 K in air atmosphere and screening of 0.5 mm. Silica was removed and 70% of tantalum grade was obtained after more than 823 K heating and separation.Next, the evaluation of Cu recycling in PCB is estimated. Energy consumption of new process increased and the treatment cost becomes 3 times higher comparing the conventional process, while the environmental burden of new process decreased comparing conventional process.The nickel recovery process in fine ground particles increased energy and energy cost comparing those of the conventional process. However, the environmental burden decreased than the conventional one.The process for recovering tantalum used more heat for the treatment and therefore the energy consumption increased by 50%, when comparing with conventional process. However, the market price for tantalum is very large; the profit for tantalum recovery is added. Also the environmental burden decreased by the recycling of tantalum recovery. Therefore, the tantalum recovery is very important step in the PCB recycling. If there is no tantalum, the consumed energy and treatment cost increase in the new process, though the environmental burden decreases.     

Trace chemical partitioning in construction and demolition debris fines: process and market implications

Construction and demolition debris (CDD) fines, a residue generated from mechanized CDD recycling, can often be beneficially reused. Concentrations of chemicals of potential concern in CDD fines should be evaluated prior to being reintroduced into the environment to assess risk and make informed decisions about appropriate reuse opportunities. The distribution of trace chemicals in CDD fines as a function of particle size was measured to evaluate if concentrations in the bulk material can be reduced by removing certain particle size ranges through screening. Chemicals of potential concern, including arsenic, lead, sulfate and polycyclic aromatic hydrocarbons (PAH), were characterized in four different size fractions (19–4.8 mm, 4.8–0.84 mm, 0.84–0.3 mm, < 0.3 mm) of CDD fine samples collected from 12 US CDD recycling facilities throughout the US. Results revealed that aluminum, arsenic and chromium concentrations were distributed evenly throughout all four size fractions. As for the remaining chemicals, most samples had lower concentrations in the 19–4.8 mm size range. In some samples and for certain chemicals, removal of the finer size fractions reduced overall concentrations in CDD fines, suggesting that additional processing may be worth further investigation.     

Chemical and process mineralogical characterizations of spent lithium-ion batteries: An approach by multi-analytical techniques

Mineral processing operation is a critical step in any recycling process to realize liberation, separation and concentration of the target parts. Developing effective recycling methods to recover all the valuable parts from spent lithium-ion batteries is in great necessity. The aim of this study is to carefully undertake chemical and process mineralogical characterizations of spent lithium-ion batteries by coupling several analytical techniques to provide basic information for the researches on effective mechanical crushing and separation methods in recycling process. The results show that the grade of Co, Cu and Al is fairly high in spent lithium ion batteries and up to 17.62 wt.%, 7.17 wt.% and 21.60 wt.%. Spent lithium-ion batteries have good selective crushing property, the crushed products could be divided into three parts, they are Al-enriched fraction (+2 mm), Cu and Al-enriched fraction (?2 + 0.25 mm) and Co and graphite-enriched fraction (?0.25 mm). The mineral phase and chemical state analysis reveal the electrode materials recovered from ?0.25 mm size fraction keep the original crystal forms and chemical states in lithium-ion batteries, but the surface of the powders has been coated by a certain kind of hydrocarbon. Based on these results a flowsheet to recycle spent LiBs is proposed.     

Application of a gas-solid fluidized bed separator for shredded municipal bulky solid waste separation

A laboratory-scale gas-solid fluidized bed separator able to separate fractions of 5.6-50mm was used for separation of shredded municipal bulky waste (SBW) into combustibles and incombustibles. In batch-scale tests, it was found that accumulation of SBW in the bottom of the bed significantly reduced the separation efficiency. In this study, stirring was shown to be effective in preventing this accumulation. Flexible sheet materials such as paper and film plastics also significantly decreased the separation efficiency. In batch-scale tests, an overall efficiency of 90% was obtained when flexible materials such as film plastics and paper were excluded from the feed SBW. In continuous feeding tests, purities of the float and sink fractions attained 95% and 86% efficiencies, respectively, with an overall efficiency of 79%. The effect of feedstock shape on separation efficiency was also investigated. This study revealed that large particles can be properly separated on the basis of density, while the shape of the material significantly influenced behavior in the fluidizing bed.     

Physical separation,mechanical enrichment and recycling-oriented characterization of spent NiMH batteries

Nickel–metal hydride (NiMH) batteries contain high amount of industrial metals, especially iron, nickel, cobalt and rare earth elements. Although the battery waste is a considerable secondary source for metal and chemical industries, a recycling process requires a suitable pretreatment method before proceeding with recovery step to reclaim all valuable elements. In this study, AA- and AAA-type spent NiMH batteries were ground and then sieved for size measurement and classification. Chemical composition of the ground battery black mass and sorted six different size fractions were determined by an analytical technique. Crystal structures of the samples were analyzed by X-ray diffraction. Results show that after mechanical treatment, almost 87 wt% of the spent NiMH batteries are suitable for further recycling steps. Size classification by sieving enriched the iron content of the samples in the coarse fraction which is bigger than 0.25 mm. On the other hand, the amounts of nickel and rare earth elements increased by decreasing sample size, and concentrated in the finer fractions. Anode and cathode active materials that are hydrogen storage alloy and nickel hydroxide were mainly collected in finer size fraction of the battery black mass.     

Recovering metallic fractions from waste electrical and electronic equipment by a novel vibration system

The need to recover and recycle valuable resources from Waste Electrical and Electronic Equipment (WEEE) is of growing importance as increasing amounts are generated due to shorter product life cycles, market expansions, new product developments and, higher consumption and production rates. The European Commission (EC) directive, 2002/96/EC, on WEEE became law in UK in January 2007 setting targets to recover up to 80% of all WEEE generated.Printed Wire Board (PWB) and/or Printed Circuit Board (PCB) is an important component of WEEE with an ever increasing tonnage being generated. However, the lack of an accurate estimate for PCB production, future supply and uncertain demands of its recycled materials in international markets has provided the motivation to explore different approaches to recycle PCBs.The work contained in this paper focuses on a novel, dry separation methodology in which vertical vibration is used to separate the metallic and non-metallic fractions of PCBs. When PCBs were comminuted to less than 1 mm in size, metallic grades as high as 95% (measured by heavy liquid analysis) could be achieved in the recovered products.     

Characterization of shredded television scrap and implications for materials recovery

Characterization of TV scrap was carried out by using a variety of methods, such as chemical analysis, particle size and shape analysis, liberation degree analysis, thermogravimetric analysis, sink-float test, and IR spectrometry. A comparison of TV scrap, personal computer scrap, and printed circuit board scrap shows that the content of non-ferrous metals and precious metals in TV scrap is much lower than that in personal computer scrap or printed circuit board scrap. It is expected that recycling of TV scrap will not be cost-effective by utilizing conventional manual disassembly. The result of particle shape analysis indicates that the non-ferrous metal particles in TV scrap formed as a variety of shapes; it is much more heterogeneous than that of plastics and printed circuit boards. Furthermore, the separability of TV scrap using density-based techniques was evaluated by the sink-float test. The result demonstrates that a high recovery of copper could be obtained by using an effective gravity separation process. Identification of plastics shows that the major plastic in TV scrap is high impact polystyrene. Gravity separation of plastics may encounter some challenges in separation of plastics from TV scrap because of specific density variations.