This article makes an attempt to answer the three questions of why China is devoting its full effort to promoting a circular economy, what a circular economy is, and how to implement a circular economy in China. The evolutionary process of a circular economy in China, from introduction of the concept and the relevant actions of national decision making to demonstration of the system nationwide, has taken only around 6 years, with strong encouragement from politicians and the urgent need to cope with environmental pollution and a severe shortage of natural resources. The circular economy in China is now being actively implemented at three levels: enterprises, eco-industrial parks, and regions. The consolidated theoretical bases of ecology and economics have helped the circular economy to defi ne its position as a new economic model to effectively resolve the problems of resources and the environment. In this regard, material fl ow management is naturally a unique planning and management method for implementation of a circular economy, and eco-effi ciency is a good indicator to measure circular economic activities. Of particular signifi cance has been initiation of the legislative process for the Circular Economy Law, which is among a number of initiatives developing core policies for a circular economy in China. Stringent enforcement of a set of policies for energy saving and pollution abatement nowadays in China will certainly create an enabling environment for the development of a circular economy.

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Based on (i) the low liquidus temperature of Si–Cu systems, (ii) low solubility of Cu in solid Si, and (iii) a strong affinity of Zr to B for the enhanced boride formation, a novel method to remove B from Si using Zr as a trapping agent via a Si–Cu solvent was developed in this study. B-bearing polygonal ZrB x precipitations found at the bottom of test samples were confirmed as ZrB2 by electron probe microanalysis. Thermodynamic analysis revealed that the solubility products of ZrB2 in a Si–Cu melt were 2.50 × 10–12 (1258 K, Si-57.0 atom % Cu) and 4.11 × 10–12 (1345 K, Si-50.0 atom % Cu). Finally, the compositions of Si–Cu alloys that can form stable ZrB2 particles were estimated by calculating the solubility products of ZrB2 and the equilibrium contents between B and Zr at different corresponding liquidus temperatures. The proposed method provides the potential for B removal via Si–Cu solvent refinement to realize the large-scale production of solar-grade silicon, thereby overcoming the key limitation to the sustainable utilization of solar energy.

Abstract:In this study, eight fly ash samples and three bottom ash samples from different areas are collected for analysis of their physicochemical properties and emission content of dioxin precursors and metals. Their surface characteristics, their effects on dioxin precursors, and important aspects of the compositions of residual ash (fly ash and bottom ash) are investigated. Poly-chlorobenzenes (PCBzs) in the fly ash of a fluidized bed incinerator (FBI) are 7.35 to 357.94 µg/kg, and in that of a fire grate incinerator (FGI) are 6.74 to 96.52 µg/kg. The concentrations in bottom ash are the same (i.e., 2.23 to 2.99 µg/kg) regardless of the furnace type. The concentrations of polycyclic aromatic hydrocarbons (PAHs) in FGI fly ash samples (0.293 to 1.783 mg/kg) are less than these in samples from FBIs (1.820 to 38.012 mg/kg). Low boiling point PAHs (mainly 2-and 3-ringed PAHs) and high boiling point PCBzs (mainly H x CB and P e CBz) are the major constituents of residual ash. Different distributions of PCBzs and PAHs are mainly dictated by the incineration characteristics of FBI and FGI. Al and Fe, as non-toxic "light metals" are the major constituents of the residual ash, and Ni and Zn as non-toxic heavy metals play important roles in the total heavy metal. Cu, Pb, and Cr are the three major toxic heavy metals. The correlation of the metals and the dioxin precursors is discussed and distinguished.

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