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The presence of organic impurities hinders the resource utilization of industrial waste salt (IWS). In this study, pyrolysis treatment was chosen to remove these organic impurities. The optimal process parameters for the pyrolysis of organic impurities were as follows: a temperature of 500 °C and a holding time of 20 min. Under these optimal conditions, the total organic carbon (TOC) removal rate was 96.32%, inducing a decrease in the TOC mass fraction from 1.88 to 0.08%. Fourier transform infrared spectroscopy (FTIR) results obtained during this process showed that prolonging the pyrolysis time (10-70 min) for IWS resulted in a gradual decrease in the relative content of characteristic functional group, such as C-O in ether groups, and the disappearance of functional group, such as benzophenone carbonyl group and ester carbonyl. Organic impurities can release gas-containing compounds that destroy the initially smooth IWS surface, and the resulting particles with rough and irregular shapes fuse into large or lumpy particles during the pyrolysis process. GC‒MS results clearly showed that the number of different semivolatile organic compounds in the IWS was reduced from 35 to 19 as a result of the pyrolysis process. Correspondingly, organic impurities with molecular formulas containing 5-10 carbon atoms converted into compounds containing 6-20 carbon atoms. These findings provide theoretical support for IWS resource utilization.

The smelting technology and flue dust treatment have an influence on the physical and chemical characteristics of flue dusts collected in copper smelting. We characterized flue dusts from a Bottom-Blowing Bath Smelting (BBS) process and from a Flash Smelting (FS) process by determining their comprehensive physical, chemical, and mineralogical characteristics. Annual flue dust generation data showed that the rate of the BBS process (2 to 3 pct) was clearly lower than that of FS process (5 to 6 pct). The results revealed that copper smelting flue dusts from the FS exhibited a larger entrainment of solids and a smaller particle size than the BBS. The crystallographic and chemical compositions of the samples indicated that the FS flue dusts have a higher degree of crystallinity than those of the BBS. Fe3O4, CuSO4 and PbSO4, Fe3O4, CuFe5O8 were the predominant crystalline phases in the FS and BBS flue dusts, respectively. In the FS and BBS flue dusts, amorphous multicomponent Cu-Zn-FeOx and Cu-Zn-S phases were formed, respectively. Mineralogical examinations and a stepwise chemical extraction confirmed that the majority of arsenic existed in amorphous form and mostly as pentavalent As5+ arsenate or As2O5 except that in BBS-ESPD.

Fayalite is widely used in various fields based on its structural characteristics and only exists in weak reducing environments. Excess ZVI (zero-valent iron) is used to regulate oxygen fugacity when synthesizing fayalite. This paper investigates the function of ZVI during the formation of fayalite. The results indicate that ZVI plays two main roles: it is used as an oxygen scavenger to keep the atmosphere in a weakly reduced state and it is used as a reducing agent to reduce Fe3+ to Fe2+, which produces an Fe1−αO intermediate. The formation of Fe1−αO is a critical step in Si-O-Fe formation. The XPS and XRD results not only provide proof of this process but also indicate that fayalite formation is actually an exchange process between Fe(II) and Si(IV). These data provide theoretical support for basic research on copper slag and other research related to fayalite.

The safe disposal of nuclear waste is a key factor restricting the sustainable use of nuclear energy. Exploring safe and reliable disposal methods for nuclear waste has become a research hotspot. In this paper, cullet-based glass (CBG) was chosen as a new immobilization agent to host the plutonium (Pu). The immobilization mechanism of Pu in the CBG was investigated by using cerium (Ce) as a surrogate for Pu, and the interaction was characterized by using XRD, XPS, FTIR and SEM-EDS analyses. The results indicate that there are two synergistic immobilization mechanisms by which Ce is hosted in the vitrified products. One mechanism is doping of the Ce into the crystal lattice of the glassy matrix to form Ce O Si bonds, which increases the proportions of non-bridging oxygen (NBO) bonds in the glass structure. The other mechanism is Ce co-existing in the glass structure gaps as individual crystals of CeO2. The synergistic immobilization makes Ce hard to release. The PCT results show that the normalized leach rate of Ce decreases with the Ce partitioning ratio in the CeO2 crystalline phase. These data show that CBG can be used as a good immobilization agent to vitrify the Pu presented in high-level radioactive wastes.

The dissolution of Cu2O in fayalite is one of the chief processes that cause copper loss in metallurgical processes. In this paper, the interaction between fayalite and Cu2O is systematically studied to verify the main mechanism of copper loss as well as the variation in the fayalite microstructure. The results indicate the simultaneous occurrence of melting and dissolution of copper in fayalite. The redox reaction of $$ {\text{Cu}}^{ + } + {\text{Fe}}^{2 + } = {\text{Cu}} + {\text{Fe}}^{3 + } $$ occurs in the melt phase, resulting in the generation of metallic copper and amorphous iron. The copper dissolution impacts the fayalite microscopically. With the increase of Cu2O, the obvious phase separation is seen in the fayalite melt, and large metal particles are dispersed in the melt. In addition, the dissolution mechanism of copper and the change in the fayalite microstructure are analyzed by x-ray photoelectron spectroscopy and Raman spectroscopy. The results show that amorphous iron trapping Cu(I) and the formation of fayalite-combined copper are the most probable mechanisms for copper dissolution and the fayalite microstructure changes. These findings provide theoretical support for the secondary extraction of copper resources from copper slag.

The interactions between Fe2SiO4 and ZnO play an essential role in the recovery of zinc from copper slag. The dissolution and substitution mechanism of ZnO in fayalite were investigated by using TG-DSC, XRD, PPMS DynaCool, XPS, Mossbauer and SEM-EDS analyses and compared with MS calculation results. The results indicate that the dissolution and substitution are actually processes of the penetrating dissolution of Zn(II) ions that can be divided into three steps: 1) ZnO dissociates into Zn1-yO and Zn(II) ions; 2) Zn(II) penetrates the gap of the octahedron outer layer to substitute Fe(II) sites in the internal structure of SiOFe(II) (M2) to form (Fe2-x, Znx)SiO4; 3) Fe(II) is forced to migrate to the surface of (Fe2-x, Znx)SiO4 to form (Zn1-y, Fe(II)y)O. These findings can be derived the occurrence state and distribution of zinc in copper slag theoretically.

The safe treatment of heavy metals in wastewater is directly related to human health and social development. In this paper, a new type of recyclable adsorbent is synthesized through the oxidation of enhancer and modification with magnetic nanoparticles. The new adsorbent not only inherits the advantages of multiwall carbon nanotubes (6O-MWCNTs), but also exhibits a new magnetic property and further improved adsorption capacity, which is conducive to the magnetic separation and recovery of heavy metals. The adsorption results indicate that multiwall magnetic carbon nanotubes (6O-MWCNTs@Fe3O4) have a good performance for Pb(II) selective adsorption, with a maximum adsorption capacity of 215.05 mg/g, much higher than the existing adsorption capacity of the same type of adsorbents. Under the action of an external magnetic field, 6O-MWCNTs@Fe3O4 that adsorbed metal ions can quickly achieve good separation from the solution. The joint characterization results of FTIR and XPS show that under the action of both coordination and electrostatic attraction, the C=O bond in the –COOH group is induced to open by the metal ions and transforms into an ionic bond, and the metal ions are stably adsorbed on the surface of 6O-MWCNTs@Fe3O4. Pb(II) has a stronger attraction than Cu(II) and Cd(II) to the lone pair of electrons in oxygen atoms to form complexes, due to the covalent index of Pb (6.41) is more larger than that of Cu (2.98) and Cd (2.71).These data provide a new type of recyclable adsorbent for the efficient treatment of heavy metal ions in wastewater and enrich relevant theoretical knowledge.

Industrial waste salt is classified as hazardous waste to the environment. The organic impurity and its occurrence in industrial waste salt affect the salt resource utilization. In this paper, composition quantitative analysis, XRD, TG-DSC, SEM/FIB-SEM coupled with EDS, FTIR, XPS and GC-Ms were chosen to investigate the organic impurity and its occurrence in industrial waste salt. The organic impurities owe small proportion (1.77%) in the specimen and exhibit weak thermal stability within the temperature of 600°C. A clear definition of organic impurity, including 11 kinds of organic compounds, including aldehyde, benzene and its derivatives etc., were detected in the industrial waste salt. These organic impurities, owing (C-O/C-O-C, C-OH/C = O, C–C/CHx/C = C etc.)-containing function group substance, are mainly distributed both on the surface and inside of the salt particles. Meanwhile, the organic substance may combine with metal cations (Ni2+, Mg2+, Cu2+ etc.) through functional groups, such as hydroxide, carbonyl etc., which increases its stability in the industrial waste salt. These findings provide comprehensive information for the resource utilization of industrial waste salt from chemical industry etc.

Arsenic contamination has been a major problem in copper slag utilization. Arsenic is easily incorporated into the silicate-based matrix, making the arsenic difficult to volatilize. In this study, pyrite was selected to depolymerize the matrix structure and volatilize the glassy arsenic by sulfide-reduction-volatilization reaction. The optimum technological parameters and mechanism of glassy arsenic volatilization by pyrite were further studied. The optimum operating parameters for glassy arsenic volatilization by pyrite were determined to be a temperature of 1200 °C, a holding time of 60 min, a heating rate of 5 °C/min, a basicity of 0.3, and a pyrite addition content of 15%. The arsenic volatilization ratio reached 80.9% under these experimental conditions. Besides, the mechanism of glassy arsenic volatilization was elucidated by XRD, XPS, FTIR, and SEM analyses. These results indicate that, with the increase in temperature, the pyrite decomposes to generate a variety of sulfur-based reducing substances (FeS, FeS1-x, S2(g)). Through “oxygen capture reaction”, these sulfur-based reducing substances depolymerize the bridging oxygen structure from the glass former ([AsO4], [FeO4], and [SiO4]) by the conversion of (Q2 +Q3)→(Q0 +Q1) and result in the precipitation of glass former ([AsO4], [FeO4] and [SiO4]) combining with the nearby cation. In this process, the glassy arsenic is released by the glass network and participates in reductive volatilization reaction with sulfur-based reducing substances, converting the glassy arsenic with high thermal stability to volatile arsenic oxide and arsenic sulfide. These findings provide a theoretical support for the in situ volatilization of arsenic in copper smelting and centralized control of arsenic contamination.

The sintering behaviors among SiO2, FeS and Fe3O4 were detected to reveal the formation mechanism of Fe2SiO4. The results indicated that the formation mechanism is divided into five steps: (1) migration of O2− induced by S2− under a reducing atmosphere; (2) formation of Fe3O4−β ; (3) migration of Fe(II) into a ferrite cluster structure to gain oxygen and form Fe3−x O4; (4) Fe(II) invaded the silicon atomic position and released Si(IV); and (5) formation of the stable structure of Fe2SiO4 through chemical diffusion between cations of Fe(II) and Si(IV). These findings can provide theoretical support for controlling the process of the recovery of valuable metals in copper slag through the combined roasting modification–magnetic separation process.

Arsenic is the most important hazardous trace element in copper concentrates. In order to separate arsenic from the smelting processes, a pyrometallurgical treatment with additives was developed to deal with high-arsenic copper smelter flue dust high in copper sulfate. Under the optimized conditions of mixing 30 wt% pyrite and roasting at 550 °C under an inert atmosphere for 30 min, more than 92% arsenic was volatilized as a high purity arsenic trioxide by-product while most copper was retained in the calcine to be returned to smelting as a high-copper feed. The high separation of arsenic is due to the transformation from the limited vaporization of arsenate to volatile arsenic trioxide by pyrite at above 460 °C. Two reaction paths of pyrite were identified as follows: one followed the pattern FeS2 → Fe2O3 → FeAsO4 → Fe3O4/Fe2O3 and the other was FeS2 → FeS + S2 (g) → Fe3O4/Fe2O3.

Arsenic residue is of great concern due to its environmental hazard. In this study, we first propose to use cullet as the host to immobilize sodium arsenate. All samples have successfully formed glasses in 1200 °C detected by X-ray diffraction spectra (XRD). High arsenic immobilization ratio has been achieved in the experiment. Fourier transform infrared spectrometer (FTIR) and X-ray photoelectron spectroscopy (XPS) have been used to explore the process of arsenic immobilized into the cullet. It can be concluded that the arsenic exists in the form of AsO 4 tetrahedron and forms chemical bonds with SiO 4 tetrahedron via bridging oxygen, resulting in strengthening the Q n structure and new formation of Si-O(BO)-As, which makes arsenic stable in the glass.

The sulfidation roasting behavior was analyzed in detail to reveal the reaction mechanism. Information about the sulfidation reaction, including phase transformation, ionic migration behavior and morphological change, were obtained by XRD, 57Fe Mossbauer spectroscopy, XPS and SEM analysis. The results showed that the sulfidation of zinc ferrite is a process of sulfur inducing and sulfur-oxygen interface exchange. This process can be divided into six stages: decomposition of FeS2, formation of the oxygen-deficient environment, migration of O2− induced by S2(g), formation of ZnFe2O4-δ, migration of Fe2+ accompanied by the precipitation of ZnO, and the sulfur-oxygen interface exchange reaction. The sulfidation products were zinc blende, wurtzite, magnetite and a fraction of zinc-bearing magnetite. These findings can provide theoretical support for controlling the process during which the recovery of Zn and Fe is achieved through the combined flotation-magnetic separation process.

Copper smelters are the main anthropogenic source of arsenic. In this study, the formation pathway of arsenic-lead particulate matter in a heat recovery steam generator (HRSG) of a copper smelting facility were investigated. Lead monoxide and arsenic trioxide reacted easily with each other to form particulate matter with a high arsenic content, while the relative content of lead arsenate and lead arsenite in the particulate matter varied with the fluctuation of the smelting flue gas. The dissociation mechanism by pyrite of particulate matter containing arsenic and lead were also studied for the first time. The structures and components of the resultant composites were characterized by ion chromatography plasma optical emission spectrometry, X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. Pyrite promoted the dissociation of lead arsenate and lead arsenite due to the formation of more lead sulfate, and then further inhibited the formation of lead arsenate and lead arsenite. This study is of great significance for the control of arsenic in flues.

The interactions between Fe

The structural properties of 20CaO–8B2O3–24Fe2O3–48P2O5 + xAs2O3 (x = 0, 1, 5, 10, 15 mol%) glasses have been investigated by X-ray diffraction (XRD), transmission electron microscope (TEM), Raman and Fourier transform infrared spectrum (FTIR), differential thermal analysis (DTA). The XRD and TEM analysis indicates great solubility of arsenic in the modified iron phosphate melts. The Raman and FTIR spectra show that with increasing As2O3 content in glass compositions, the phosphate chains get less depolymerised, resulting in conversion of Q1 to Q2. As takes part network-forming positions and results in the PO2 units interacting with As2O3 and forming P−O−As linkages/bridges. The higher (Tr–Tg) suggests the thermal stability is improved with the addition of As2O3.