A critical review on the recycling of copper and precious metals from waste printed circuit boards using hydrometallurgy

Currently, increasing amounts of end-of-life （EoL） electronic products are being generated due to their reduced life spans and the unavailability of suitable recycling technologies. In particular, waste printed circuit boards （PCBs） have become of global concern with regard to environmental issues because of their high metal and toxic material contents, which are pollutants. There are many environmental threats owed to the disposal of electronic waste; off-gasses, such as dioxins, furans, polybrominated organic pollutants, and polycyclic aromatic hydrocarbons, can be generated during thermal treatments. which can cause serious health problems if effective off=gas cleaning systems are not developed and improved. Moreover, heavy metals will dissolve, and release into the ground water from the landfill sites. Such waste PCBs contain precious metals which are of monetary value. Therefore, it is beneficial to recover the metal content and protect the environment from pollution. Hydrometallurgy is a successful technique used worldwide for the recovery of precious metals （especially gold and silver） from ores, concentrates, and waste materials. It is generally preferred over other methods because it can offer high recovery rates at a relatively low cost. This article reviews the recent trends and developments with regard to the recycling of precious metals from waste PCBs through hydrometallurgical techniques, such as leaching and recovery.

Failure Mechanisms and Structural Optimization of Shredder Hammer for Metal Scraps

Recycling retired cars can relieve the environmental pollution and resource waste efficiently.However,a few publications can be found on the failure mechanisms and optimization method of recycling equipment,shredders.Thus,the failure mechanisms and structural optimization of shredder hammers for retired cars are studied aiming improving shredding efficiency and reducing cost.Failure types of shredder hammer are studied theoretically,and it is found that wear failure and fatigue failure are the two main failure types of shredder hammer.The shredding process of metal scraps is analyzed by finite element method,and it can be divided into four stages based on the stress states：initial stage,collision stage,grinding stage and separation stage.It is proved that the shredding efficiency can be improved by increasing cutouts on the hammer head.Finally,it is determined that the hammer with two cutouts is the optimal structure for metal scraps,which can improve the shredding efficiency by 20% and lengthen the hammer life by 15%.This study provides scientific basis for the industry application and theoretical foundation for further research.

Metal recycling from waste memory modules efficiently and environmentally friendly by low-temperature alkali melts

Recycling of waste electrical and electronic equipment has become an urgent global issue in recent years from the prospectives of resources recycling and environmental protection.In the present work,the recycling of waste memory modules(WMMs)through low-temperature alkali melts was investigated,based on the thermodynamic analysis of the nonmetallic reactions of brominated epoxy resin,glass fiber and memory chip with the molten mixed alkali.The effects of the reaction temperature and the ratio of alkali mixture on the removal rate of nonmetallic parts in WMMs were discussed under the condition of air atmosphere.The optimum process parameters were further confirmed by in-situ monitoring of the temperature during the whole reaction process.The mixtures with Cu,Fe and Ni as the main components were obtained after the treatment of WMMs in the molten alkali.These mixed metals were further separated into copper-rich and ferronickel-rich metals by physical magnetic separation.Moreover,the precious metals Au and Ag were enriched in Cu-rich alloys.This work provided an efficient and environment-friendly method for metal recycling from WMMs.

Recovery of rare and precious metals from urban mines —— A review

Urban mining is essential for continued natural resource extraction. The recovery of rare and precious metals （RPMs） from urban mines has attracted increasing attention from both academic and industrial sectors, because of the broad application and high price of RPMs, and their low content in natural ores. This study summarizes the distribution characteristics of various RPMs in urban mines, and the advantages and shortcomings of various technologies for RPM recovery from urban mines, including both conventional （pyrometallurgical, hydrometallurgical, and biometallurgical processing）, and emerging （electrochemical, supereritieal fluid, mechanochemical, and ionic liquids processing） technologies. Mechanical/physical technologies are commonly employed to separate RPMs from nonmetallic components in a pre-treatment process. A pyrometallurgical process is often used tbr RPM recovery, although the expensive equipment required has limited its use in small and medium-sized enterprises. Hydrometallurgical processing is effective and easy to operate, with high selectivity of target metals and high recovery efficiency of RPMs, compared to pyrometallurgy. Biometallurgy, though, has shown the most promise for leaching RPMs from urban mines, because of its low cost and environmental friendliness. Newly developed technologies electrochemical, supercritical fluid, ionic liquid, and mechanochemical have offered new choices and achieved some success in laboratory experiments, especially as efficient and environmentally friendly methods of recycling RPMs. With continuing advances in science and technology, more technologies will no doubt be developed in this field, and be able to contribute to the sustainability of RPM mining.

Certification Criteria in Type I Ecolabelling Related to Metals for Sustainable Materials Management

A sustainable materials management for metals should be achieved to conserve resources of metal minerals.For the sustainable materials management,material flows through the whole life cycle of materials have been recognized by material flow analysis(MFA) studies.Former MFA studies pointed out that cyclic use of metals could be enhanced not only by increasing quantity of recovered scrap but also by upgrading quality of the scrap.In general,the quality is degraded by contaminants which commingle at disassembling processes.The mixture of contaminants depends on usage of materials in products.Here,Type I ecolabelling has a potential to convey messages for avoiding mixture of contaminants to the producers of finished products.In this study,on the basis of a survey on existing certification criteria related to metals in the world,a general concept of certification criteria on sustainable materials management for metals in Type I ecolabelling system is proposed.Finally,we propose six criteria in the form of certification criteria in Type I ecolabelling system.