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1

Waste solder and printed circuit board: the emerging secondary sources for recovery of metals

Jadhav U. U., Hocheng H.

Archives of Materials Science and Engineering

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2015

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Vol. 72, nr 1

5--15

EN

Purpose: Purpose: The goal of the paper is to focus on waste solder and printed circuit board: the emerging secondary sources for recovery of metals. Design/methodology/approach: The worldwide reserves of high-grade ores are diminishing. At the same time the demand for heavy metals is ever increasing with the progress of the industrialized world. The rapid progress of electronic packaging technology is resulting in huge amounts of electronic waste (E-Waste) particularly in the form of solders and printed circuit boards (PCBs). Such E-waste contains various metals. The waste solders and PCB can act as large stockpiles of metals. Hence, they can be important secondary sources of valuable metals. Thus recycling of waste solders and PCB is not only useful for resource recovery from waste materials, but also for the protection of the environment. Findings: Comparing with the pyrometallurgical processing, hydrometallurgical method is more exact, more predictable, and more easily controlled. Bio-hydrometallurgical processes are emerging as potential environmentally friendly approaches. Research limitations/implications: Several promising metal recovery processes were developed to recover the precious metals from E-waste. There is a need to fill the gap areas in achieving a cleaner and economical recycling process. Also more studies are needed in the area of metal separation and recovery from PCB leach liquor. Orginality/Value: This review article will provide a concise overview of current disposal and recycling operations. Keywords: Electronic waste; Solder; Printed circuit board; Metal recovery; Pyrometallurgy, Hydrometallurgy; Bio-hydrometallurgy.

2

A review of recovery of metals from industrial waste

Jadhav U U, Hocheng H.

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 54, nr 2

159--167

EN

Due to rapid industrialization the demand for heavy metals is ever increasing, but the reserves of high-grade ores are diminishing. Therefore there is a need to explore alternative sources of heavy metals. The rapid industrialization generates a variety of industrial wastes. These industrial wastes possess toxic elements such as heavy metals. Improper disposal of these wastes becomes a key factor in metal contamination and thus when leached into atmosphere cause serious environmental problem. These metals exert wide variety of adverse effects on human being. Some of the metals have extremely long biological half-life that essentially makes it a cumulative toxin. Also some metals are carcinogenic in nature. Among the wastes, electronic scraps, medical waste, metal finishing industry waste, spent petroleum catalysts, battery wastes, fly ash etc., are some of the major industrially produced wastes. These solid wastes mostly contain Au, Ag, Ni, Mo, Co, Cu, Zn, and Cr like heavy metals in it. Hence these waste materials which are causing serious environmental problems, can act as potential source for heavy metals. In this sense these industrial wastes can act as artifitial ores. The valuable metals can be recovered from these industrial wastes. There are varieties of methods in use for recovery of heavy metals. These include pyrometallurgical, hydrometallurgical and bio-hydrometallurgical methods. Pyrometallurgical recovery consists of the thermal treatment of ores and metal containing wastes to bring about physical and chemical transformations. This enables recovery of valuable metals. Calcining, roasting, smelting and refining are the pyrometallurgical processes used for metal recovery. The hydrometallurgical recovery uses mainly the leaching process. It involves the use of aqueous solutions containing a lixiviant which is brought into contact with a material containing a valuable metal. Further the metals are concentrated and purified by using precipitation, cementation, solvent extraction and ion exchange. The metals are finally recovered in pure form by using electrolysis and precipitation methods. Biohydrometallurgy is one of the most promising and revolutionary biotechnologies. This technique exploits microbiological processes for recovery of heavy metal ions. In last few decades the concept of microbiological leaching have played a grate role to recover valuable metals from various sulfide minerals or low grade ores. Now the microbiological leaching process has been shifted for its application to recover valuable metals from the different industrial wastes. There are many microrganisms which play important role in recovery of heavy metals from industrial wastes. Among the bacteria Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans, and Sulfolobus sp., are well known for the bioleaching activity while Penicillium, and Aspergillus niger are some fungi those help in metal leaching process. The process of recovery makes sense only if the cost of recovery is much less than the value of the precious metal. The restrictions imposed on waste disposal and stringent environmental regulations demand eco-friendly technologies for metal recovery. This paper reports a review of number of industrial processes that generate metal containing waste and the various methods in use for recovery of metals from these wastes. This will help in selection of a proper method for recovery of heavy metals from industrial wastes.

3

A brighter place: overview of microstructured sunlight guide

Hocheng H., Huang T. Y., Chou T. H., Yang W. H.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 43, nr 1

409--417

EN

Purpose: This article provides an overview of the daylighting system using existing and advanced submicron technology for buildings. The approaches of movable and fixed sunlight guiding system for saving the energy of artificial lighting will be reviewed. The major part is devoted to the sunlight guide panel / film based on a formed prismatic microstructure on transparent substrate by UV-imprint and roll-to-roll process. Design/methodology/approach: To achieve the prismatic microstructure sunlight guide panel / film, the wide aspects including the suitable materials, optical design of the microstructure and tuning the imprint processes are covered. In addition, to estimate the effectiveness of sunlight guide panel / film, a series of experiments were performed and compared with the prediction. Findings: The analysis reveals the outgoing light above the horizontal level of the transom in a major portion. It indeed provides the adequate indoor daylighting by the proposed sunlight guide panel / film. Research limitations/implications:The use of micro-polygonal-structured sunlight guide panel/film to deliver the daylight into the core area of a building is recommended as future research to enhance the indoor illumination by daylighting system. The portion of outgoing light below 90° causes the glare. Practical implications: The authors conclude the proposed prismatic sunlight guide panel/film is a promising approach for guiding daylight into a room. Originality/value: The reviewed daylighting system with submicron-patterned prismatic sunlight guide panel/film made of inorganic-organic materials is based on the authors’ original work of daylighting techniques. It significantly elevates the use of sunlight and saves energy consumption in a building.

4

Exploring laser-guided metal deposition through a microbe metabolite

Hocheng H., Chang K. E., Chang J. H., Wang J. C.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 37, nr 2

639-643

EN

Purpose: The purpose of the paper is to describe exploring laser-guided metal deposition through a microbe metabolite. Design/methodology/approach: A maskless micro-fabrication of laser-guided deposition process through the metabolite of Acidophilic bacteria Thiobacillus ferrooxidans (T.f.) is explored. Findings: The authors have conducted an analysis of the metal deposition process using the point thermal-source of the Nd:YAG laser through the metabolite of Acidophilic bacteria Thiobacillus. An analytical model adopting the moving point heat source on the substrate and heat transfer conditions is presented. The thermal field generated by the laser input energy is investigated. Practical implications: Though the mechanism of the laser-assisted deposition process is not fully revealed by biologist yet, the current model provides a means of control of the line deposition of metals. Originality/value: Based on the fundamental knowledge of how the line width varies with laser power and scanning speed, more investigation of the mini-scale heat convection and the threshold temperature of chemical reaction is expected in the future for further understanding of this novel metal deposition method triggered and written by laser.

5

Innovative approach to uniform imprint of micron and submicron features

Hocheng H., Wen T. T.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 28, nr 1

79-82

EN

Purpose: To develop methods for uniform imprint of micron and submicron-scale features. Design/methodology/approach: The first is gas-assisted imprint technique. In use of gas to exert isotropic pressure in hot embossing, uniform embossing throughout the area is achieved. Another approach is the electromagnetic force-assisted imprinting technology, which employs the electromagnetic force to pull the magnetic stamp with submicron-scale structures into a UV-curable resist on the substrate. The liquid photopolymer is then cured by UV-irradiation at room temperature. Furthermore, the ferromagnetic UV-curable material is made of nano-Fe powder and UV-curable polymer. The micron and submicron-scale magnetic features can be fabricated. Findings: Uniform embossing throughout the area is achieved. Under the condition of 180°C, 40kgf/cm² and 90 seconds, high quality and uniformity of micro-optical components can be fabricated. For electromagnetic force-assisted imprinting technology, a large area of sub-micron pattern with a line width of 502nm and a pitch of 1µm can be successfully fabricated under the condition of pressure of 1.6kgf/cm² for 30 seconds and UV curing for 0.5 minute. Using ferromagnetic UV-curable resist, the structures can be successfully fabricated under the pressure of 0.92kgf/cm² with the same UV-curable time. These results indicate good uniformity and controllability on both the gas-assisted hot embossing and electromagnetic force-assisted imprinting for efficient fabrication of micron- or submicron-scale structures. Practical implications: The facilities have been designed, constructed and tested. The effects of processing parameters including the processing temperature, pressure, and time on the replication quality were investigated. Originality/value: There are advantages of high uniformity, low pressure and low temperature for various applications in micron and sub-micron features and other micro-optical components such as gratings and waveguides etc.

6

A review of monitoring for nanoimprinting

Hocheng H., Nien C. C.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 24, nr 1

382-389

EN

Purpose: This article provides an overview of the monitoring technique for nanoimprint. Optical and electrical monitoring approaches that have the potential for detecting and monitoring mold deformation and cavity filling in nanoimprint will be reviewed. The major part is devoted to the review of an in-situ mold filling monitoring system based on capacitance measurement for nanoimprinting operations. Design/methodology/approach: In carrying out the capacitive monitoring method, a broad range of areas including tuning the imprint process, designing a reliable capacitive sensor, finding out the right materials and a suitable surface micromachining process for sensing electrodes, and data analysis have seen covered. In addition, to measure the continuous variations in capacitance, a series of imprinting experiments have been performed isothermally, and the capacitance values have also been measured at various imprinting stages. Findings: The final stage of mold filling near the end, which is of particular interest, can be monitored and the experimental results have demonstrated that the capacitance measurements indeed provide the in-situ information that can tell the mold filling status during nanoimprinting. Research limitations/implications: The use of neural networks to model the functional relationship between the capacitance value and the rising height of mold filling is recommended as another potential area for future research to realize the ultimate objective of providing online real-time mold filling information for imprinting process control. Practical implications: Throughout the study, the authors conclude the proposed capacitance measurement technique is a promising approach for monitoring mold filling in nanoimprinting process, and the practical application of the conducted research is feassible with certain improvement of the robustness of the monitoring technique in harsh environment of higher imprinting temperature. Originality/value: The reviewed monitoring methods are based on the authors' approved and pending patents. They are considered pioneering works for the research community of nanoimprint techniques and as the basis of making nanoimprint process automated.