In November 2016, the total metal concentrations in nine representative locations in lead (Pb)-zinc (Zn) mining areas, located in Guangdong Province, South China, were determined experimentally by flame atomic absorption spectrometer. The results indicated that the paddy soils were heavily contaminated with Cd (20.25 mg kg−1), Pb (1093.03 mg kg−1), and Zn (867.0 mg kg−1), exceeding their corresponding soil quality standard values and background values. According to the results, the mean enrichment factor levels of the studied metals decreased in the following order: Cd > Zn > Pb > Cu > Ni > Mn > Cr. Among these metals, Cd, Pb, and Zn were predominantly influenced by widespread anthropogenic activities. The highest concentrations of the studied metal pollutants were distributed in the areas surrounding the mining activity district. Multivariate statistical analysis indicated that the major contributing sources of the studied metals were metal ore mining, smelting, and processing activities. However, the composition of soil background was another potential source. Moreover, the assessment results of environment risks showed that the potential ecological risks, in decreasing order, were Cd > Pb > Zn > Cu > Ni > Cr > Mn. Additionally, the non-carcinogenic risk represented the trend of HIPb > HIMn > HIZn > HICu, and the carcinogenic risk ranked as CRCr > CRCd > CRNi. Among the environmental risk substances, Cd and Pb were the main contributors that pose ecological harm and health hazards through their serious pollution. Consequently, greater attention should be paid to this situation.

•The iron in lead-zinc tailings was recycled.•Ag, Ga, Pb, Mn were enriched in the magnetic tailings.•Iron content in magnetic concentrate was 62.14% and iron recovery was 82.16%.•Iron recovery and enrichment of Ag, Ga, Pb and Mn are achieved in a same process.•The recovery of metals is conducive to sustainable development of lead-zinc mine.To comprehensively reuse lead-zinc tailings and avoid environmental pollution, the enrichment of valuable metals and the recovery of iron from the roasted lead-zinc tailings (RM), the cinder after the oxidation roasting of lead-zinc tailings, were performed using magnetizing roasting followed by magnetic separation. The transformation of iron in the RM during the magnetizing roasting was investigated by studying the effects of roasting temperature and ratio of coal to RM on the iron recovery. The results showed that most of iron in the RM was transformed from Fe2O3 to Fe3O4 at the roasting temperature of 720 °C and the ratio of coal to RM of 7:100. The iron recovery rate reached 82.16%, and the iron content in the magnetic concentrate reached 62.14%. The investigation of the enrichment characteristics of the metals in the magnetizing showed that Ag, Ga, Pb and Mn could be enriched in the magnetic tailing, with enrichment ratios of 1.64, 1.39, 1.35 and 1.24, respectively, under the conditions of a roasting temperature of 720 °C and a ratio of coal to RM of 7:100. Furthermore, the transformation of metals during magnetizing roasting was investigated by analyzing the microstructure and mineralogical changes during the magnetizing roasting process. With this method, the processes of iron recovery and other metals enrichment from RM using magnetizing roasting followed by magnetic separation was proposed for the comprehensive utilization of lead-zinc tailings.Download high-res image (137KB)Download full-size image

•Asphaltene was converted to gas, maltene and coke in SCW (supercritical water).•NaOH in SCW increased the asphaltene conversion and its product yields.•Lower coke selectivity and higher maltene selectivity were achieved in SCW + NaOH.•High temperature favored the asphaltene transformation and the formation of gas.•Asphaltene transformation in SCW + NaOH fit the first-order kinetic model better.Asphaltene transformation in SCW (Supercritical Water) and SCW + NaOH experiments were conducted in autoclaves with sealed gold tube reactors to investigate the effect of NaOH, reaction time (0–120 min) and temperature (400–450 °C) on asphaltene transformation. The results showed that asphaltene transformation in SCW + NaOH gave higher asphaltene conversion, maltene yield and coke yield but less gas yield compared with those in SCW at 400 °C during 120 min. Moreover, a longer reaction time and higher temperature could enhance asphaltene reactivity but led to secondary decomposition of maltene and the formation of more gas and coke in SCW + NaOH. Kinetic analysis indicated that asphaltene transformation in SCW and SCW + NaOH both fit first-order kinetics adequately. Furthermore, a three-lump kinetic model considering parallel reactions from asphaltene to maltene + gas to coke and the consecutive reaction from maltene + gas to coke was proposed to explain the effect of NaOH and temperature on asphaltene transformation. Selectivity analysis of the products implied that asphaltene transformation in SCW + NaOH at 425 °C was better than transformation in SCW + NaOH at higher temperatures or in SCW in minimizing coke formation.

DFT calculations have been performed to study the reaction mechanism of N–N bond formation from aryl azide catalyzed by the copper(I) iodide complex. We studied various activation modes for the azide group, and found that the azide group is activated by the Cu(μ-I)2Cu(TMEDA) dimer coordinating to the N-atom of phenyl imine and the internal N-atom of azide.

A systematic DFT study was performed to examine the isomerization of 2-aryl-2H-azirines to 2,3-disubstituted indoles by FeCl2 and Rh2(O2CCF3)4. The results indicate that the isomerization of 2-aryl-2H-azirines mainly proceeds through a stepwise mechanism and the Rh2(O2CCF3)4 exhibits higher catalytic performance than FeCl2. Investigation of the magnetic properties suggests that the C–N bond formation step is pseudoelectrocyclization for the FeCl2-catalyzed system. The calculations show that a water-catalyzed 1,2-H shift for the FeCl2-catalyzed system adopts a proton-transport catalysis strategy, in which chlorine atom coordination to the iron center is critical because it acts as a proton acceptor. When a molecule of water is involved in the Rh2(O2CCF3)4-catalyzed reaction, the 1,2-H shift is significantly promoted, so that the rate-determining step becomes the ring opening of 2-aryl-2H-azirine. In addition, we studied the catalytic activity of Fe(OAc)2 and CuCl.

Density functional theory calculations have been carried out to study the reaction mechanism of the [FeIII(F20TPP)Cl] catalyzed C–H amination reaction. The calculations show that the classical three-step mechanism for other metals (Ru, Rh, Ir and Zn), including N2 liberation, C–N bond formation and 1,2-hydrogen shift, does not fit the iron(III)-catalyzed system. After N2 liberation, the favorable reaction pathway for the iron(III)-catalyzed system is a 1,2-hydrogen shift preceding C–N bond formation, i.e., a H-abstraction/radical rebound mechanism.

Fixation of heavy metals in the slag produced during incineration of sewage sludge will reduce emission of the metals to the atmosphere and make the incineration process more environmentally friendly. The effects of incineration conditions (incineration temperature 500–1100 °C, furnace residence time 0–60 min, mass fraction of water in the sludge 0–75%) on the fixation rates and species partitioning of Cd, Pb, Cr, Cu, Zn, Mn and Ni in slag were investigated. When the incineration temperature was increased from 500 to 1100 °C, the fixation rate of Cd decreased from 87% to 49%, while the fixation rates of Cu and Mn were stable. The maximum fixation rates for Pb and Zn and for Ni and Cr were reached at 900 and 1100 °C, respectively. The fixation rates of Cu, Ni, Cd, Cr and Zn decreased as the residence time increased. With a 20 min residence time, the fixation rates of Pb and Mn were low. The maximum fixation rates of Ni, Mn, Zn, Cu and Cr were achieved when the mass fraction of water in the sludge was 55%. The fixation rate of Cd decreased as the water mass fraction increased, while the fixation rate of Pb increased. Partitioning analysis of the metals contained in the slag showed that increasing the incineration temperature and residence time promoted complete oxidation of the metals. This reduced the non-residual fractions of the metals, which would lower the bioavailability of the metals. The mass fraction of water in the sludge had little effect on the partitioning of the metals. Correlation analysis indicated that the fixation rates of heavy metals in the sludge and the forms of heavy metals in the incinerator slag could be controlled by optimization of the incineration conditions. These results show how the bioavailability of the metals can be reduced for environmentally friendly disposal of the incinerator slag.Highlights► The contents and partitioning of HMs in slag of sludge incineration were examined. ► The fixation rate decreases with residential time and finally keeps a constant. ► Water mass fraction of 55% is optimal for the sediment for Ni, Mn, Zn, Cu and Cr. ► Water mass fraction of 75% is optimal for the sediment for Pb. ► We found higher temperature versus lower non-residual fraction except that of Pb.

A solidification and stabilization method, thermal treatment, was used to investigate the effects of incineration temperature and incineration time on heavy metal fixation rates and leaching behaviors in soils from an e-waste processing site. High concentrations of heavy metals (Ni 153 mg/kg, Cu 448 mg/kg, Zn 227 mg/kg, Cd 0.80 mg/kg, Sn 838 mg/kg, Sb 658 mg/kg and Pb 114 mg/kg) were detected in these soils. In addition, the Mn (67.2%), Co (62.7%), Ni (84.8%), Cu (88.3%), Zn (56.5%), Cd (79.9%) and Pb (67.4%) in these soils mainly occurred in the non-residual fractions. Thermal treatment experiments indicated that better (>80%) Be, V, Cr, Mn, Co, Ni, Cu, Zn, Cd, Sn and Sb fixation rates could be obtained in these soils at an incineration temperature of 700 °C and at an incineration time of 45 min. under these conditions, the concentrations of Be, Cr, Co, Ni, Zn and Cd in the Toxicity Characteristic Leaching Procedure (TCLP) leachates obviously decreased to concentrations that were lower than the corresponding background concentrations of groundwater in Dutch standard, and the Cu concentration in the TCLP leachates decreased from 461 μg/L (before incineration) to 66.4 μg/L. Therefore, thermal treatment technology could be serve as an appropriate measure for Be, Cr, Co, Ni, Cu, Zn and Cd remediation in the soils from the e-waste processing site.

•The lead–zinc tailings mainly consist of pyrite and are potentially acid forming.•The lead–zinc tailings induce acid mine drainage and heavy metals pollution.•The sulfur in the lead–zinc tailings can be removed during roasting.•The SO2 in the flue satisfies the requirement of producing sulfuric acid.•The cinder is non-acid forming and can be processed for further recovery.According to the pollution characteristics and current situation of sulfur resources in lead–zinc tailings, the mineral composition, risk assessment and oxidation reaction characteristics of lead–zinc tailings were investigated. The results showed that the main mineral in the lead–zinc tailings was pyrite and the contents of Fe and S were 23.4% and 24.9%, respectively. The heavy metals Pb, Zn, Cu, Cr and Cd were mainly present in the residual fraction, but the Pb, Zn and Cd in the non-residual fraction were 28.21%, 37.49% and 42.92%, respectively. Additionally, the lead–zinc tailings potentially form acid, which poses a potential heavy metals pollution risk to the environment. The reaction characteristics of tailings, including the roasting temperature, filling rate and air–solid ratio, were investigated in a rotary furnace under different conditions. The results showed that the desulfurization rate was 99.0% and the concentration of SO2 was 5.58–5.07% when the roasting temperature was 400 °C, the filling rate was 4.29%, the air–solid ratio was 1.7 L/g and the residence time was 20 min. After roasting in the rotary furnace, the cinder became non-acid forming and the SO2 in the flue gas can be recovered by producing sulfuric acid. Meanwhile, the roasting procedure concentrates metals such as Fe, Ag and Ga, which assists further recovering the resources in the cinder. All of these results provide a new approach for eliminating the pollution of acid mine drainage and recovering the sulfur from lead–zinc tailings.Download high-res image (99KB)Download full-size image

Toluene exhaust gas is a nuisance to the environment and human beings. In this study, 1-dodecyl-3-methylimidazolium chloride (DDMIM Cl) was selected as the absorbent solution and was combined with photocatalytic oxidation (PCO) for the treatment of toluene gas. The effects of toluene concentration, UV lamp power, catalyst dosage, coexisting ions and pH on the toluene removal ratio by PCO were investigated. Changes to the absorbent structure after four reuses were compared according to the UV–vis absorption spectrum, and the anti-oxidation ability of the absorbent was evaluated. The results showed that the absorbent concentration was an important factor in the absorption of toluene. At the absorbent concentration of 5%, the initial absorptivity reached 96.79%, and the saturated absorption capacity was 43.8 mg/L. With a toluene concentration of 13.1 mg/L, an 18-W UV lamp, a photo catalyst dosage of 400 mg/L, and a reaction time of 80 min, the removal ratio of toluene reached 91.3%. The PCO of toluene followed pseudo-first-order kinetics. The main intermediates of toluene oxidation were benzoic acid and benzaldehyde, while traces of cresol and benzyl alcohol were also found. After four reuses, the absorption capacity of the absorbent was not weakened, and the molecular structure of DDMIM Cl remained stable, reflecting its oxidation resistance. Therefore, the use of an ionic liquid as an absorption solution combined with PCO for the treatment of toluene waste gas is theoretically feasible.

n-Hexane is widely used in industrial production as an organic solvent. As an industrial exhaust gas, the contribution of n-hexane to air pollution and damage to human health are attracting increasing attention. In the present study, aqueous solutions of two fluorocarbon surfactants (FSN100 and FSO100) were investigated for their properties of solubilization and dynamic absorption of n-hexane, as well as their capacity for regeneration and n-hexane recovery by thermal distillation. The results show that the two fluorocarbon surfactants enhance dissolution and absorption of n-hexane, and their effectiveness is closely related to their concentrations in solution. For low concentration solutions (0.01%–0.30%), the partition coefficient decreases dramatically and the saturation capacity increases significantly with increasing concentration, but the changes for both are more modest when the concentration is over 0.30%. The FSO100 solution presents a smaller partition coefficient and a greater saturation capacity than the FSN100 solution at the same concentration, indicating a stronger solubilization for n-hexane. Thermal distillation is a feasible method to recover n-hexane from these absorption solutions, and to regenerate them. With 90 sec heating at 80–85°C, the recovery of n-hexane ranges between 81% and 85%, and the regenerated absorption solution maintains its original performance during reuse. This study provides basic information on two fluorocarbon surfactants for application in the treatment of industrial n-hexane waste gases.Aqueous solutions of two fluorocarbon surfactants (FSN100 and FSO100) were investigated for their properties of solubilization and dynamic absorption of n-hexane. The relationship between the n-hexane absorption saturation concentration and partition coefficient for the FSO100 and FSN100 solutions is not a linear correlation. For low concentration solutions (0.01%–0.1%), a small decrease of the partition coefficient corresponds to a large increase in the saturation concentration. However, with a further decrease of the partition coefficient (0.1%–1.0% of the absorbent concentration), the increase of the saturated absorption concentration becomes slower. This shows that the dynamic absorption process of n-hexane cannot be fully explained by the partition coefficient and is also influenced significantly by operating conditions.Download full-size image

Density functional theory calculations have been carried out to study the reaction mechanism of the [FeIII(F20TPP)Cl] catalyzed C–H amination reaction. The calculations show that the classical three-step mechanism for other metals (Ru, Rh, Ir and Zn), including N2 liberation, C–N bond formation and 1,2-hydrogen shift, does not fit the iron(III)-catalyzed system. After N2 liberation, the favorable reaction pathway for the iron(III)-catalyzed system is a 1,2-hydrogen shift preceding C–N bond formation, i.e., a H-abstraction/radical rebound mechanism.

A systematic DFT study was performed to examine the isomerization of 2-aryl-2H-azirines to 2,3-disubstituted indoles by FeCl2 and Rh2(O2CCF3)4. The results indicate that the isomerization of 2-aryl-2H-azirines mainly proceeds through a stepwise mechanism and the Rh2(O2CCF3)4 exhibits higher catalytic performance than FeCl2. Investigation of the magnetic properties suggests that the C–N bond formation step is pseudoelectrocyclization for the FeCl2-catalyzed system. The calculations show that a water-catalyzed 1,2-H shift for the FeCl2-catalyzed system adopts a proton-transport catalysis strategy, in which chlorine atom coordination to the iron center is critical because it acts as a proton acceptor. When a molecule of water is involved in the Rh2(O2CCF3)4-catalyzed reaction, the 1,2-H shift is significantly promoted, so that the rate-determining step becomes the ring opening of 2-aryl-2H-azirine. In addition, we studied the catalytic activity of Fe(OAc)2 and CuCl.

DFT calculations have been performed to study the reaction mechanism of N–N bond formation from aryl azide catalyzed by the copper(I) iodide complex. We studied various activation modes for the azide group, and found that the azide group is activated by the Cu(μ-I)2Cu(TMEDA) dimer coordinating to the N-atom of phenyl imine and the internal N-atom of azide.