This Review looks at case studies drawn from Japan, Belgium and USA, so as to provide an economic analysis of what is known as urban mines. The term 'urban mine' has been coined to specify designated urban plants where discarded manufactured products can be stored and the extraction of metals from the products carried out (Nanjyo, 1988) . It focuses in particular on the issue of electronic wastes, types of wastes that constitute a complex mixture of still valuable yet extremely hazardous materials. Such materials are the residue of products that have themselves always been important factors in controlling the demand for the primary metals used in their production and have thus contributed to an increase in their price, while the uneven distribution of these often rare metals and the various changing conditions responsible for their price increase have, at the same time, become global issues. Although the potential for recycling electronics products is significant, many products are discarded without due care, and, consequently, are improperly treated. Meanwhile, the latest global financial crisis has caused the price of precious metals to plummet, the market is as a result in turmoil, and the recycling market is also in disarray; all this in its turn has influenced the issue of urban mines. (1) The proper treatment of waste is the premise for the non-ferrous metal industry because the industrial waste, byproducts and scrap are the major materials for them. Also the setup of collection system for WEEE is an important condition for the recycling them. (2) For the effective usage of resources, the enterprises including producers and recyclers, play the decisive role in developing recycling technology. (3) For the low-carbon society, the CO2 reduction by collection and recycling must become the target and the indicator. (4) As the public policy the support for the domestic recycling non- ferrous metal refinery as the important infrastructure for the recycling waste management.
This paper analyzes relations between China's export restrictions and rare earth prices in recent years. China has decreased the rates of Value Added Tax (VAT) rebates on rare earths raw materals (ores, metals and compounds) since 2004. It has also increased the rates of export duties on the same items since 2006. It appears that China has taken such measures to restrict outflows of rare earth raw materials, and these measures have been taken several times in recent years. Rare earth prices generally soared for the last several years. For example, price of dysprosium, one of the rare earth elements, has increased by about six times between June 2003 and June 2008. We analyzed relations between China's measures for export restrictions and prices of ten rare earth metals between June 2003 and June 2008 by using regression models. The findings of this analysis are as follows. (1) There is a strong tendency in which rare earth metal prices increase significantly soon after enforcement of an export restriction by China. (2) As China repeats measures for export restrictions, length of time between enforcement of such a measure and occurance of price increase has become shorter. This paper also mentions the possibility that demand for rare earths will be less price elastic in the near future. It is highly probable that growing needs to tackle global warming will require people to buy a greater number of eco-frindly products including hybrid vehicles. In such a situation, demand for rare earths, which are raw materials for essential parts of such products, would increase substantially. In addition, manufacturers of such products would have no choice other than procuring certain amount of rare earths regardless of their prices, since there is few alternative raw materials for these products. Under such circumstances, demand for rare earths would be less price elastic, and thus, rare earth prices in the future are likely to be more volatile.
The purpose of this study is to clarify the differences in leaching behavior among various kinds of secondary copper sulfide ores. Leaching experiments were carried out in a sulphuric acid solution at different pH values, temperatures and concentrations of ferric ion using three kinds of ores. The grain size of the copper minerals in these ores was measured by QEMSCAN. Although copper minerals in these ores consisted mainly of chalcocite, copper leaching rates varied greatly depending on each ore. In particular, the difference of leaching rates was more than 4 times in the early leaching stage. In the case of the slower leaching rate, the copper extraction could be increased from 15% to 58% after 0.5 days at 40°C and initial pH of 1.0 with 250mg/l of additional ferric ion. In the case of the faster leaching rate, the leaching rate could be increased by increasing the temperature and/or decreasing pH. However, the increase of the leaching rate was almost independent of additional ferric ion throughout the leaching stage. Furthermore, it was found that the grain size of copper minerals in the case of the slower leaching rate was about 1.5 to two times as coarse as that in the case of the faster leaching rate. It is concluded that, from the standpoint of reaction efficiency, the copper leaching behavior in the early leaching stage would be very sensitive to the grain size of copper minerals more than other leaching factors.
Precipitates of zinc oxalates prepared from aqueous ammine solutions were investigated by SEM, FT-IR, chemical analysis and TG-DTA to elucidate their morphology and identification. Thermal decomposition routes of zinc oxalate precipitates forming zinc oxide were also studied. The principal findings are as follows: Precipitates obtained from aqueous solutions of ZnCl2 and H2C2O4, Na2C2O4 or (NH4)2C2O4 were identified as ZnC2O4·2H2O. By aging at 298 K for 24 hrs, those precipitates take the forms of a pyramid about 10μm, tablet and stick type, respectively. However, precipitates prepared from aqueous H2C2O4 and NH3-ZnCl2 or NH3-NH4Cl-ZnCl2 solutions were identified as Zn(NH3)C2O4. By aging the precipitates at 333K for 24hrs, stick or needle like particles with a large aspect ratio were formed. Thermal decomposition reaction occurred above 660K to form ZnO keeping the original morphology of Zn(NH3)C2O4.