Experimental study on thermal treatment of used printed wiring boards (PWBS)

The availability of cheaper and better electronic products as a result of the rapid innovation in technology in past decades has driven the production of e-waste forward. Printed wiring board (PWB) is a component made of one or more layers of insulating material with electrical conductors. The existing processes of recycling PWBs use pyrometallurgical or hydrometallurgical methods, which generate atmospheric pollution. Green recycling has obvious benefits to decrease the amount of PWBs. Green recycling includes two features, 1) little or zero pollution of toxic gases and heavy metals, and 2) efficient (quick and economical) recycling. The aim of this work is to investigate green thermal treatment of PWB wastes in laboratory scales. For small scale experiments, PWB powders were combusted and pyrolyzed using TG/DTA, and the emitted gases were measured using MS. The suitable combustion conditions: 15 °C/min heating rate, \u3e125 ml/min gas flow rate, above 600 °C top temperature, and the holding time is not important for combustion process; The suitable pyrolysis conditions: 15-20 °C/min, \u3e100 ml/min gas flow rate, above 900 °C top temperature, and longer holding time. In combustion experiments, CaCO₃, NaOH, NaHCO₃ and Na₂CO₃ were mixed with PWB powders with a mass ratio of 1:1 to control toxic gas emission like HBr. In pyrolysis experiments, additives such as CaCO₃, CaO, Fe₂O₃, ZSM-5, Y-Zeolite were mixed with PWB powders with mass ratio of 5:1 to control toxic gas emission and enhance the pyrolysis reaction. CaCO₃ was the best additive to efficiently control toxic emitted gas during the combustion process, and Fe₂O₃ was the best choice to control toxic emitted gas and enhance the reaction speed during pyrolysis experiment. For large scale experiments, PWB samples were pyrolyzed to solid, liquid and gas products in a tube furnace. Liquid products were analyzed by FTIR. For pyrolysis of PWB without additives, averagely there were 47% solid products, 20% liquid products and 33% gas products. The yield (47%) of solid products in the tube furnace was far more than the yield (36%) in TG/DTA experiments. The results also showed that pyrolyzing smaller PWB powders produced more solid products--Abstract, pages iii-iv

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Mechanical and Pyrometallurgical Recycling of Electronic Wastes

In this paper, the mechanical milling of the electronic wastes was carried out. The metal parts and plastic parts were roughly separated. The final plastic powder size could be as small as ∼100 μm. Then the pyrometallurgical recycling Printed Circuit Boards (PCB) was executed. The mechanisms of thermal degradation and combustion are investigated using TG/DTA and MS. Some chemical powders, such as Na2CO3, NaHCO3, NaOH and CaCO3 are used to control the exhausted toxic gas such as Br2

Recycling of Electronic Wastes: Degradation and Combustion

In this paper, firstly recycling methods of Printed Circuit Boards (PCBs) were briefly reviewed. Then PCB materials from a waste printer and waste TV were heated in TG/DTA and MS machines with the aim of separating and recovering the organic and metallic materials. The effects of top temperature, holding time, gas flow rate, heating rate were investigated. Synthetic air and argon were used as working gases respectively. The mass loss, conversion fraction with the temperature, reaction temperature and activation energy were summarized

Green Pyrolysis of Used Printed Wiring Board Powders

Rapid technological innovation has propelled the use of electronic equipment leading to the generation of more and more waste electrical and electronic equipments (WEEE). Printed wiring board (PWB) is a component made of one or more layers of insulating material with electrical conductors. to investigate an environmentally friendly process to recycle PWBs, PWB samples with and without additives were pyrolyzed. Liquid, gas and solid products were achieved with different conversion fraction. Analysis of the exhaust gases from the experiments using GC-MS and MS showed that without CaCO3 additives poisonous gases such as C6H6 and HBr were produced which were adequately controlled if CaCO3 was added

Tribological Properties of Brake Disc Material for a High-Speed Train and the Evolution of Debris

The stability and reliability of braking system are essential factors for the safe operation of high-speed trains. In the proposed work, tribological properties of a newly developed brake disc material namely BD-1 were studied considering the thermal-mechanical effects, as well as the evolutions of wear debris, were particularly examined. The tribological properties were also compared with an existing commercial brake disc material namely BD-2 in text. Friction and wear tests were carried out on BD-1 and BD-2 against a commercial brake pad material (BP) to simulate the real emergence braking conditions of a 350 km/h high-speed railway. The thermal-mechanical coupling effects of the friction velocity, wear mass, temperatures and the friction coefficient were investigated. Local wear track and wear debris were analyzed by using SEM and EDS. Results show that the shape and size of wear debris evolve as the dominant wear mechanism varies during braking tests. As the sliding speed increases from 250 to 1250 rpm, the debris may become fine particles, then into a mixture of lamellar shape and flake shape, and finally becomes fine particles again at high speed. The maximum size of wear debris is first from 20 μm to 65 μm, and then down to 10 μm. As the local area temperature increased by more than 400 °C, debris adhere to the surface forming an adhesive layer that may act as a lubricant. Debris may help to form an adhesive lubrication layer and undertake plastics defor-mation at the speed range of 500–1000 rpm. The local area temperatures prompted the wear debris adhesion and oxidation. After reaching a certain speed limit, a uniform third body appears to protect the material surface from high speed and high temperature. Results suggested that the BD-1 could be a good candidate braking material for high-speed railway applications

Characterization of Disintegrator Milled Electronic Waste Powders for Materials Recovery

In this paper, the mechanical milling of the Printed Circuit Boards (PCB) was carried out. the new air classification stand was developed for testing the separation of lightweight particles like tinfoil stripes and plastics. the test results for separation of heavier fractions like non-ferrous metals (Al, Cu) are presented. For milled materials characterization the sieve analysis, laser diffraction analysis and a scanning electron microscope were used. the chemical composition of the PCB powders was studied by means of the energy dispersive X-ray microanalysis. Then, the pyrometallurgical recycling PCB was executed. the mechanisms of thermal degradation and combustion are investigated using TG/DTA and MS machines with the aim of separating and recovering the organic and metallic materials. the mass loss, conversion fraction with the temperature, activation energy etc. are investigated. Some alkalis, such as Na2CO3, NaHCO3, NaOH and CaCO3 were used to control the exhausted toxic gas such as HBr and benzene

Distribution Law of In Situ Stress and Its Engineering Application in Rock Burst Control in Juye Mining Area

This paper presents an integrated approach for mathematical statistics, theoretical analysis, and a field test to investigate the distribution law of in-situ stress and its engineering practice of rock burst control. The test site is located in the Juye mining area, Shandong Province, China. The main conclusions included: (1) There are two types of in-situ stress states in the Juye mining area, σH > σV > σh (42.42%) and σH > σh > σV (57.57%), which are mainly caused by the tectonic stress of the Heze and Fushan faults (The σH, σV, and σh is the maximum principal stress, vertical principal stress or intermediate principal stress and minimum principal stress respectively). (2) The lateral pressure coefficients KH, Kh, and Kav show a non-linear distribution with increased depth, approaching 1.32, 0.96, and 1.41, respectively. The variation range of the horizontal difference stress μd is 0.09–0.58. (3) The average value of the stress gradient is 3.05 MPa/100 m, and the main directions of the maximum horizontal principal stress are northeast–southwest, and northwest–southeast. (4) A new combined supporting strategy, incorporating optimization of roadway layout, anti-impact support system design, and local reasonable pressure relief, was proposed for the rock burst control, and its validity was verified via field monitoring. All these design principles and support strategies for the rock burst control presented in this study can potentially be applied to other similar projects

Distribution Law of In Situ Stress and Its Engineering Application in Rock Burst Control in Juye Mining Area

This paper presents an integrated approach for mathematical statistics, theoretical analysis, and a field test to investigate the distribution law of in-situ stress and its engineering practice of rock burst control. The test site is located in the Juye mining area, Shandong Province, China. The main conclusions included: (1) There are two types of in-situ stress states in the Juye mining area, σH > σV > σh (42.42%) and σH > σh > σV (57.57%), which are mainly caused by the tectonic stress of the Heze and Fushan faults (The σH, σV, and σh is the maximum principal stress, vertical principal stress or intermediate principal stress and minimum principal stress respectively). (2) The lateral pressure coefficients KH, Kh, and Kav show a non-linear distribution with increased depth, approaching 1.32, 0.96, and 1.41, respectively. The variation range of the horizontal difference stress μd is 0.09–0.58. (3) The average value of the stress gradient is 3.05 MPa/100 m, and the main directions of the maximum horizontal principal stress are northeast–southwest, and northwest–southeast. (4) A new combined supporting strategy, incorporating optimization of roadway layout, anti-impact support system design, and local reasonable pressure relief, was proposed for the rock burst control, and its validity was verified via field monitoring. All these design principles and support strategies for the rock burst control presented in this study can potentially be applied to other similar projects