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Large amount of coal ash is produced as industrial waste during the electricity generation through the combustion of lignite. Toxic elements arsenic exists in the coal ash, which hinders the subsequent recycling processes. Moreover, coal ash could be recycled further to retrieve scattered metals germanium and tungsten. It is believed that traditional recycling methods present barriers to scaled application, especially serious secondary pollution, such as toxic residue and waste liquid. In this work, a novel sequential vacuum distillation with disulphide method is proposed to separate arsenic, germanium and tungsten from coal ash. First, arsenic can be volatilized completely out of the reaction system at temperatures below 550 °C. Subsequently, Ge and W volatilized in the form of sulfide in the presence of Na 2 S 2 O 3. The optimal condition was 1050 °C, the mass ratio of 0.6 with reaction a pressure of 1 Pa and a time duration of 120 min demonstrated the best evaporation ratio. For coal fly ash, chemical species As 2 S 3 , GeS, and WO x (x < 3)/WS 2 were the main condensed products. For coal bottom ash, As 2 S 3 , GeS, and WO 3 /WS 2 were dominant chemical components. Mechanisms for the process of release and evaporation of As, Ge, and W from coal ash, vacuum reaction, evaporation, and condensation were analyzed. In summary, the vacuum distillation method deserves to be further developed as it provides an eco-friendly method to recycle coal ash. [Display omitted] • An environment-friendly sequential vacuum distillation method is proposed. • Mixed sulfide reagents are used to remove As and recycle Ge, and W step by step. • As 2 S 3 , GeS, and WO x (x < 3)/WS 2 are the main condensed products in ash. • Mechanisms of release and evaporation processes of As, Ge, and W are analyzed. • Residues are not a hazardous material and can be further recycled. [ABSTRACT FROM AUTHOR]

Germanium, as strategic reserve metal, plays critical role in high-tech industry. However, a contradiction of increasing consumption and scarcity of germanium resource is becoming more and more prominent. This paper proposed an integrated process to recycle germanium from coal fly ash. This technological process mainly consisted of two procedures: vacuum reduction with the purposes of enriching germanium and chlorinated distillation with the purposes of purifying germanium. Several highlights are summarized as follows: (i) Separation principle and reaction mechanism were discussed to understand this integrated process. (ii) Optimum designs and product analysis were developed to guide industrial recycling. The appropriate parameters for vacuum reduction process on the basis of response surface methodology (RSM) were 920.53 °C and 259.63 Pa, with 16.64 wt.% reductant, and for the chlorinated distillation process, adding 8 mol/l HCl and L/S 7, 8 wt.% MnO 2 . The global recovery rate of germanium was 83.48 ± 0.36% for the integrated process. (iii) This process overcomes the shortages of traditional process and shows its efficiency and environmental performance. It is significant in accordance with the “Reduce, Reuse and Recycle Principle” for solid waste and further provides a new opportunity for germanium recovery from waste by environment-friendly way. [ABSTRACT FROM AUTHOR]

The demand for germanium in the field of semiconductor, electronics, and optical devices is growing rapidly; however, the resources of germanium are scarce worldwide. As a secondary material, coal fly ash could be further recycled to retrieve germanium. Up to now, the conventional processes to recover germanium have two problems as follows: on the one hand, it is difficult to be satisfactory for its economic and environmental effect; on the other hand, the recovery ratio of germanium is not all that could be desired. In this paper, an environmentally-friendly vacuum reduction metallurgical process (VRMP) was proposed to recover germanium from coal fly ash. The results of the laboratory scale experiments indicated that the appropriate parameters were 1173 K and 10 Pa with 10 wt% coke addition for 40 min, and recovery ratio germanium was 93.96%. On the basis of above condition, the pilot scale experiments were utilized to assess the actual effect of VRMP for recovery of germanium with parameter of 1473 K, 1–10 Pa and heating time 40 min, the recovery ratio of germanium reached 94.64%. This process considerably enhances germanium recovery, meanwhile, eliminates much of the water usage and residue secondary pollution compared with other conventional processes. [ABSTRACT FROM AUTHOR]

• Rule of element distribution of fine particles ashes was clarified to guide recycling. • Morphology of fine particles from fly ash are different from that of bottom ash. • Heavy metals are concentrated in fly ash but not in bottom ash from lignite. • Chemical species of elements show a different distribution for bottom and fly ash. • Formation and release mechanism of fine and ultrafine particles ashes was proposed. With the rapid decrease of high-quality coal reserves, utilization of lignite is already a trend in worldwide. Unlike anthracite, lignite often contains special elements Ge, W, As. When these incineration ashes are reused, some resuspended fine particles will inevitably escape into the air, thereby affecting the surrounding environment. The study aims to understand the rule of element distribution of fine particles incineration ash from lignite to avoid the potential risks in future recycling and reuse process of ashes. Hence, we systematically investigated the morphology, element distribution, and chemical species of heavy metals in fine and ultrafine particles. For bottom ash, the large spherical and blocky particles with D p 10–4.7 were observed in fine particles. The morphology of particles changed to irregular agglomerate particles with D p 4.7–0.4. The average relative percentage of C, O, Si, and Al in bulk was significantly higher than fine particles, but the heavy metals did not present the rule of enrichment. The residue fraction (F4) of heavy metals were the predominant fraction. For fly ash, some spherical particles of D p 1.1–0.7 and D p 0.7–0.4 were agglomerated with irregular ultrafine particles. The concentrations of Na, Ge, W, As, Cr, Cd, Pb increased with the decrease of particle sizes. Ca, Al, Mg etc. were acid extractable fraction (F1), and Fe, Pb, As, W, Ni had more proportion of reducible fraction (F2) and oxidizable fraction (F3). A formation of fine particles ashes and release mechanism of heavy metals in incineration process was proposed. Consequently, this study is quite significant for understand rule of element distribution from lignite and future risk prevention from of fine particles. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Low-temperature thermal degradation of PCDD/Fs for incineration fly ash (IFA), as a novel and emerging technology approach, offers promising features of high degradation efficiency and low energy consumption, presenting enormous potential for application in IFA resource utilization processes. This review summarizes the concentrations, congener distributions, and heterogeneity characteristics of PCDD/Fs in IFA from municipal, medical, and hazardous waste incineration. A comparative analysis of five PCDD/Fs degradation technologies is conducted regarding their characteristics, industrial potential, and applicability. From the perspective of low-temperature degradation mechanisms, pathways to enhance PCDD/Fs degradation efficiency and inhibit their regeneration reactions are discussed in detail. Finally, the challenges to achieve low-temperature degradation of PCDD/Fs for IFA with high-efficiency are prospected. This review seeks to explore new opportunities for the detoxification and resource utilization of IFA by implementing more efficient and viable low-temperature degradation technologies. [Display omitted] • Comparison of PCDD/Fs degradation technologies with industrial potential. • Dynamic game between degradation and regeneration of PCDD/Fs at low temperature. • Specific detoxification methods for low-temperature thermal degradation. • Prospects for the development direction of low-temperature thermal degradation. [ABSTRACT FROM AUTHOR]

During the process of treating and recycling Municipal Solid Waste Incinerators (MSWIs) fly ash, polychlorinated dibenzo-p-dioxins (PCDD/Fs) and polychlorinated dibenzofurans (dl-PCBs) in fly ash may potentially mobilize in the atmosphere and be widely distributed in the environment because of the inevitable re-suspension. Thus, this work presents the distributions of PCDD/Fs and dl-PCBs in inhalable coarse particles (Dp10–2.5 (particle diameter in μm)), fine particles (Dp < 2.5) of fly ash and original fly ash from four MSWI plants in China. The results show that PCDD/Fs and dl-PCBs preferentially concentrated in Dp10–2.5 and Dp < 2.5. Their mass concentrations and TEQ were significantly higher than those in the original fly ash, but the distribution of PCDD/Fs congeners in Dp10–2.5 and Dp < 2.5 was close to that in the original fly ash. The main TEQ contribution included 1,2,3,7,8-PeCDD, 2,3,7,8-TeCDD in PCDDs and 2,3,4,7,8-PeCDF in PCDFs for Dp10–2.5, Dp < 2.5 fractions and the original fly ash. Furthermore, the mass and TEQ contribution of dl-PCBs was relatively low. In addition, compared with the fluidized bed, the samples from the grate-type furnaces had significantly lower dioxin concentrations. In terms of potential health risk, the non-carcinogenic risk of PCDD/Fs in Dp10–2.5 and Dp < 2.5 were estimated at 9.87 × 10 −1 to 4.81 and 1.19–7.95. For the carcinogenic risk of PCDD/Fs, both accumulation of Hazard Quotients (HQ) in Dp10–2.5 and Dp < 2.5 exceeded the threshold limit and should be considered as unacceptable risk for onsite workers. The above findings could provide data to support the risk management of MSWI fly ash during the process of recycle and disposal. [ABSTRACT FROM AUTHOR]