Non-ferrous Smelting Industry Research Articles

Associations of multiple hydroxy-polycyclic aromatic hydrocarbons with serum levels of lipids in the workers from coking and non-ferrous smelting industries

Epidemiological evidence indicates that exposure to polycyclic aromatic hydrocarbons (PAHs) is associated with certain metabolic diseases. However, the relationship between PAHs and serum lipid profiles in exposed subjects remain unknown. Herein, the associations of multiple (8) urinary hydroxylated PAHs (OH-PAHs) in workers of coking (n = 655) and non-ferrous smelting (n = 614) industries with serum lipid levels (marking lipid metabolism) were examined. Multivariable linear regression, Bayesian kernel machine regression, and quantile g-computation were used. Most urinary OH-PAHs were significantly higher (p < 0.001) in coking workers than in non-ferrous smelting workers. In workers of both industries, OH-PAH exposure was associated with elevated levels of serum total cholesterol, total triglyceride, and low-density lipoprotein, as well as reduced high-density lipoprotein levels. Specifically, urinary 4-hydroxyphenanthrene was significantly positively associated with serum total cholesterol, total triglyceride, and low-density lipoprotein levels in non-ferrous smelting workers; however, the completely opposite association of 4-hydroxyphenanthrene with these lipid levels was observed in coking workers. The results of this pioneering examination suggest that exposure to OH-PAHs may contribute to dyslipidemia in coking and non-ferrous smelting workers, and distinct patterns of change were observed. Further prospective studies involving larger sample sizes are needed to further validate the findings.

Application Study on the Activated Coke for Mercury Adsorption in the Nonferrous Smelting Industry

The massive release of mercury undermines environmental sustainability, and with the official entry into force of the Minamata Convention, it is urgent to strengthen the control of mercury pollution. The effectiveness of activated coke (AC) in removing elemental mercury (Hg0) from high temperatures and sulfur nonferrous smelting flue gas before acid production was studied. Experimental results indicated that the optimal temperature for Hg0 adsorption by AC was 150 °C. And the adsorption of Hg0 by AC was predominantly attributed to physical adsorption. Flue gas components (SO2 and O2) impact studies indicated that O2 did not significantly affect Hg0 adsorption compared to pure N2. Conversely, SO2 suppressed the adsorption capacity, while the simultaneous presence of SO2 and O2 exhibited a synergistic effect in facilitating the removal of Hg0. The characterization results of X-ray photoelectron spectroscopy (XPS) indicated that the SO2 molecule favored to anchor at the Oα site, leading to the formation of SO3. This subsequently oxidized the mercury to HgSO4 instead of HgO. The study demonstrates that cheap and easily accessible AC applications in the adsorption of mercury technology may help improve the sustainability of the circular economy and positively impact various environmental aspects.

Characteristics of solid waste from common generation source in nonferrous smelting industry reveal a new classification method

Solid waste produced by the nonferrous smelting industry has a significant number of notable differences. The lack of recognition of solid waste characteristics is the main factor restricting its disposal and utilization. In this study, we analyzed the main production processes of the nonferrous smelting industry; identified the key production nodes of solid waste; and clarified the characteristics, including the physical, chemical, and pollution characteristics of solid wastes, through a large sample statistical analysis. We found similarities among solid wastes from a common generation source as well as notable differences among the different generation sources: slags and sludges from waste acid treatment and wastewater treatment units had a water content of 27.43–52.71% and 51.14–68.27%, respectively, which were significantly higher than those of other metallurgy and dust collection units; the pH of slags from an electrorefining unit was strongly alkaline; the mineral phase of sludges from wastewater treatment was only calcite; slags from a waste acid treatment unit were mainly in phase of gypsum, claudetite, and anglesite; the chemical composition of slags from pyrometallurgy and hydrometallurgy units was mainly SiO2 and Fe2O3. In this paper, we discuss a new classification method based on a common generation source for the first time. These results are beneficial to guide the disposal, utilization, and management of solid waste.

Investigation of heavy metal flows in a copper pyrometallurgical process of a typical smelter

The non-ferrous smelting industry is a major polluter of heavy metals, and investigations on the flow of heavy metals in the metallurgical process are important references and the basis for optimization of the smelting process and control of heavy metal pollution. In this work, using a typical copper smelter as the research object, we examined and analyzed the content and status of the heavy metals lead, arsenic, cadmium, mercury, and chromium in the slag, ash, solid waste, and products of the copper pyrometallurgical process and explored the flow and enrichment of heavy metals in each stage of smelting, converting, and refining. The results showed that lead and arsenic were the most abundant heavy metals in copper concentrate, of which about 66.21% of lead and about 65.02% of arsenic escaped with the flue gas during the pyrometallurgical process and were trapped in the white ash. During the entire copper purification process, about 75.17% of heavy metals were removed in the smelting process, about 21.88% in the converting process, and about 2.92% in the refining process. The final heavy metals discharged into the atmosphere were only lead, arsenic, and mercury, accounting for about 0.03% of the total heavy metal content. It is worth noting that 50% of the mercury in the raw material was discharged into the atmosphere. Since mercury is persistent, easily transportable, highly bio-concentrated, and toxic, mercury pollution requires increased attention.

Establishing a self-supporting system of H2S production from SO2 with induced catalytic reduction process for mercury capture with super-large enrichment

Various sulfur (S) species in the environment possess different functions or adverse impacts, which highly depend on their existing states and forms. In a typical nonferrous smelting industry, the high concentration of SO2 is excrescent and needs further field upcycling, while such industry encounters a desperate shortage of sulfidation reagents (e.g., H2S or CuS) that are used for Hg0 capture in flue gas. Therefore, on-site reduction of SO2 to H2S or CuS for Hg0 capture is a feasible method to realize simultaneous SO2 upcycling and Hg0 immobilization. However, the low activity and rapid deactivation in direct reduction of SO2 with CO (DCRP) restrict actual application. To resolve the problems, an induced catalytic reduction process (ICRP) is established by refluxed partial COS to form nascent sulfurs (Sx*, x < 8), then Sx* is reduced to COS with CO. Subsequently, the obtained COS can be readily hydrolyzed to H2S. Results indicated that COS reduced SO2 showed five times higher rate than CO, which can significantly decrease the ramp from 400 to 375 °C. Moreover, it also can alleviate sulfation poison by COS induced effect because of preferential reaction sequence of SO2 with COS. Thus, the mechanism in ICRP was reasonablely transformed to mixed Mvk and E-R mechanism while DCRP was Mvk mechanism. Then, COS was readily hydrolyzed to H2S at 300 °C. Finally, the yielded H2S in-situ activated CuS exhibit a superior Hg0 capture performance with an adsorption capacity about 32.4 mg/g(CuS), which is 80 times higher than primitive CuS because of generated Sn2- in the presence of SO2 and H2O. This ICRP proved to be helpful in establishing a self-supporting system of H2S for SO2 reuse and Hg0 immobilization with super-large enrichment in nonferrous smelting industries.

Insight into H2S production from CS2 hydrolysis for heavy metals treatment: In-situ FT-IR and DFT studies over crystalline phase-dependent ZrO2

H2S is an efficient vulcanizing reagent for heavy metals treatment in nonferrous smelting industries, yet these industries lack of H2S source is a well known problem. In this study, CS2 was hydrolyzed to a high concentration of H2S (>20 vol%) with different crystalline phase zirconium oxide catalysts. The metastable tetragonal ZrO2 (t-ZrO2) exhibited a sunk octahedron structure was successfully synthesized by calcination of MOF-808. Compared to monoclinic ZrO2 (m-ZrO2), it obtained excellent H2S production performance, which can reach near-perfect 100 % at 450 °C. Furthermore, experimental results shown that KOH modified t-ZrO2 could increase CS2 hydrolysis activity due to it is a base catalytic reaction. The in-situ FT-IR demonstrated that reaction sequences followed the order of CS2 → COS → H2S, in which CS2/H2O adsorption and CO2 desorption would influence the hydrolysis efficiency. t-ZrO2 obtained better CS2 adsorption, hydrophobicity, and CO2 desorption than m-ZrO2, which were attributed to intrinsic structure and abundant surface defects. Subsequently, DFT results profiled that cleave of the first CS bond in CS2 was rate-determining step with the activation energy about 63 kJ/mol over t-ZrO2.

Engineering unsaturated sulfur site in three-dimension MoS2@rGO nanohybrids with expanded interlayer spacing and disordered structure for gaseous elemental mercury trap

Rapid and effective capture of gaseous elemental mercury (Hg0) over a wide operating temperature range is significant for the green and sustainable development of nonferrous smelting industry. High mercury affinity and strong sulfur resistance of two-dimensional layered MoS2 render it an outstanding adsorbent for Hg0 trap. However, the relative lack of serviceable active sites greatly suppresses its extensive application. Herein, a feasible strategy to expand interlayer spacing, build disordered structure and engineer unsaturated sulfur adsorption sites was provided through the construction of three-dimension MoS2@rGO nanohybrids. As expected, compared with bulk and ordered MoS2, the prepared MoS2@rGO hybrid exhibits a remarkable performance improvement for Hg0 adsorption. The average Hg0 adsorption rate of MoS2@rGO is 2.28 μg/g/min and its saturated adsorption capacity reaches 20.91 mg/g. The typical components in nonferrous flue gas have almost no effect on Hg0 adsorption performance. X-ray photoelectron spectroscopy confirms that the formation of abundant unsaturated coordination sulfurs sites with high thermostability is critical for Hg0 adsorption performance improvement. Moreover, the density functional theory calculation results further demonstrate the high adsorption activity of unsaturated coordination sulfur sites for Hg0 capture. Among these sulfur sites, edge sulfur vacancy site plays a dominant role for Hg0 adsorption because of the lowest Hg0 adsorption energy. The final adsorption production is HgS which has negligible environmental toxicity due to its extreme stability. This work not only provides a promising adsorbent for Hg0 removal in industrial application, but also opens up an avenue to engineer unsaturated sulfur for other layered transition metal dichalcogenides.

Looping upcycling SO2 into value-added H2S by fast-induced reduction process for heavy metals treatment in nonferrous smelting industry

Reversing the pollution to a value-added product can simultaneously alleviate environmental problems and achieve a circular economy. In nonferrous smelting industries, SO2 is hazardous pollution that should be disposed, but H2S is usually required for heavy metals (HMs) treatment. Herein, we developed a field SO2 looping upcycling technology for value-added H2S production to meet the HMs treatment. Results demonstrated that the H2 could accelerate the kinetic rate and decrease the energy barriers of the SO2 and CH4 reaction by a fast-induced reduction process (fast-IRP). Thus, the H2S production rate in fast-IRP was three times higher than the direct reaction between SO2 and CH4. Meanwhile, the T90 temperature (690 °C) was significantly lower than SO2 and CH4 reaction about 90 °C. Fast-IRP also can resist the SO2 poison effect and prevent sulfation, enhancing the activity, long-term stability (no visible efficiency loss in 50 h), and selectivity (nearly 100 %). Integrated the characterizations and DFT results, we found that the H2 would firstly attack the uncoordinated sulfur species with a hydrodesulfurization process to form the HS-/H2S intermediate species with a lower energy barrier (1.57 eV) than the CH4 (2.83 eV), which can facilely protect the Mo-terminated to avoid sulfation poison. Subsequently, the HS-/H2S* species would react with the adsorbed SO2 to Sx* to support the deep-reduction reaction for H2S production. This work proposes an actual SO2 field utilization route and also will enlighten an induced redox cycle in the sulfur reduction over the pre-sulfurized catalysts.

Novel process for nitrite removal driven by S(IV): NOx absorption and reductive denitrification in smelting industry

The absorption products of NOx by SO32−-contained solution are mainly NO2− or NO3− which may cause secondary pollution and increase difficulty for further disposal in wastewater. Conversion of NO2− into N2 using S(IV) (HSO3−/SO32−) reduction is a promising method for denitrification, yet it is difficult to be realized under SO2-rich conditions. Here, a self-removal method was put forward for N element conversion driven by S(IV) ions. The first step was the reduction of NO2− into trisulfonic acid (NTS) or amine disulfonic acid (ADS). Followed that the NTS/ADS was hydrolyzed into NH2SO3H. Then the NO2− was reduced to N2 by NH2SO3H. The experimental results indicated that such method guarantee a higher NOx absorption efficiency and the higher than 95% absorption products were NO2−. When S(IV)/NO2− was higher than 4.2, 95% of NO2− was reduced to NTS or ADS, then further hydrolyzed into NH2SO3H with higher than 90% efficiencies. Moreover, the gas chromatograph-mass spectrometer (GC–MS) and ion chromatography (IC) results confirmed that the main products of the reactions between NO2− and self-generated NH2SO3H were N2 and SO42−. This study provides a new route for the safety disposal of NO2− in non-ferrous smelting industry.

Fabrication of Cu2S hollow nanocages with enhanced high-temperature adsorption activity and recyclability for elemental mercury capture

Transition metal sulfides have attracted great interest in nonferrous smelting industries for elemental mercury (Hg0) capture owing to their high activity, low cost and resistance to SO2. However, the major obstacle was the deactivation of active sites in adsorbents after the use or at high temperature. Herein, we fabricated rhombic dodecahedral Cu2S hollow nanocages by using high-quality Cu2O crystals as sacrificial templates. Benefiting from the unique structure and composition, such Cu2S hollow nanocages exhibited not only the enhanced high-temperature adsorption activity for Hg0 (120 °C, removal efficiency > 95%), but also had outstanding recyclability (five cycle, removal efficiency > 85%) without additional reactivation treatment. And the saturation adsorption capacity was about 26.6 mg∙g−1. Further study of the structure-performance correlation indicated that the environmental features of interior architecture might offer inner active S1- sites with the shelter of nanocage shell at high temperature, combining with Hg0 to form HgS. Besides, the recovered adsorption activity was ascribe to the thermal migration of active Cu2+ ions. Thus, this work provides a promising adsorbent for Hg0 capture at high temperature, while opening a new field to design hollow-structured materials for environmental applications.

Profiles, spatial distributions and inventory of brominated dioxin and furan emissions from secondary nonferrous smelting industries in China

Nonferrous metallurgical processes are important sources of carcinogenic polybrominated dibenzo-p-dioxin and dibenzofuran (PBDD/Fs) that transport globally. Studies on the profiles, spatial distributions and inventory of PBDD/F emissions into the atmosphere from nonferrous metallurgical plants are needed for better source control. In this study, field investigations on PBDD/F emissions from typical nonferrous metallurgical plants were conducted to characterize the PBDD/F profiles and derive their emission factors. Based on the PBDD/F profiles, diagnostic ratios of PBDD/Fs for secondary copper, zinc and lead smelting were proposed for identifying the potential sources of PBDD/Fs in environment. The PBDD/F emission factors for the secondary copper, lead, and zinc smelting plants were 0.71, 1.65, and 1.54 μg toxic equivalents/t, respectively. The estimated annual input of PBDD/Fs into atmosphere by secondary nonferrous metallurgical plants in China was 212.4 g by mass and 3511.3 mg by toxic equivalents, which is of significance for further evolving a global inventory. The spatial distribution of PBDD/F emissions from nonferrous metallurgical plants in China was mapped. Larger amounts of PBDD/Fs were emitted in the southeastern coastal region and northern China than elsewhere in China.

Separation and stabilization of arsenic in copper smelting wastewater by zinc slag

Copper smelting wastewater shows strong acidity, has a high arsenic concentration and has many types of heavy metals, which not only restricts the sustainable development of copper smelting enterprises but also poses a danger to the ecological environment. Here, we propose a new process for treating copper smelting wastewater with zinc slag. We studied both the solid-liquid chemical reaction process as well as the mechanism by which zinc slag removes arsenic in copper smelting wastewater in a water bath at 85 °C under atmospheric pressure. Specifically, 5 g of zinc slag reacted with copper smelting wastewater with an initial arsenic concentration of 6000 mg/L for 4 h resulted in an arsenic removal rate of 99.65%, and the leaching concentration of arsenic in the toxicity characteristic leaching procedure experiment was only 0.52 mg/L. Zinc slag is dissolved in Copper smelting wastewater to release iron ions and silicate. The solid-liquid reaction of the two is accompanied by coprecipitation of iron arsenate and the in-situ covering of silica gel, resulting in a core-shell precipitate with iron arsenate as the core and silica gel as the shell. The colloidal chemistry of silica gel and cations and its chemical stability can effectively prevent the dissolution of arsenic ions and significantly improve the stability of iron arsenate. Zinc slag, a dual functional material for removing arsenic and fixing arsenic, shows extraordinary potential for the removal and fixation of arsenic in copper smelting wastewater. This approach could further improve wastewater treatment in the non-ferrous smelting industry.

Current situation and prospect of Denitration technology in nonferrous smelting industry

Air pollution control of the non-ferrous industry is mainly concentrated on the dust and SO2 in the flue gas. NOx control has just started. The relevant standards and specifications are still constantly updated and improved, control technology is also learning from other industries on the basis of continuous exploration and innovation. Through analyzing the NOx emission characteristics and emission standard requirements of non-ferrous smelting industry, this paper points out the current situation and development trend of the non-ferrous smelting industry.

Transformation behavior of the morphology, structure and toxicity of amorphous As2S3 during hydrothermal process

Arsenic sulfide sludge (ASS) is a typical hazardous waste in the non-ferrous smelting industry. In our previous study, ASS was effectively stabilized by hydrothermal treatment. However, the mechanism of hydrothermal stabilization is still unclear. Amorphous As2S3 is the main component of ASS. Therefore, in this work, the hydrothermal transformation behavior of amorphous As2S3 precipitated with NaAsO2 and Na2S·9H2O under acidic aqueous was investigated for a better understanding of hydrothermal stabilization process of ASS. It was found that under the conditions of 210 °C, initial pH 2 and solid-to-liquid (S/L) ratio 1:5, amorphous As2S3 floc gradually transformed to spherulitic particles and showed aggregation behavior with the extension of hydrothermal duration. The spherulitic particles were identified as orpiment, which was the crystalline arsenic mineral in the nature. Moreover, the As leaching concentration of hydrothermal products decreased remarkably with the transformation from amorphous As2S3 to orpiment. Under certain hydrothermal conditions, the As leaching concentration of amorphous As2S3 can be reduced from 139.4 mg/L to less than 5 mg/L. Hence, the mineralization from amorphous As2S3 to orpiment was the significant reason for the stabilization of arsenic sulfide during hydrothermal treatment. This paper provided a theoretical support for the hydrothermal stabilization of ASS.

Pollution Characteristics and Health Risk Assessment of Heavy Metals in Road Dust from Non-ferrous Smelting Parks

In order to explore the pollution characteristics and health risks of heavy metals in dust from roads around non-ferrous smelting activities in different regions, dust samples from urban roads, non-ferrous smelting industry park roads, and tunnel roads were collected from the Mengzi area of Yunnan Province. The dust samples were suspended on Teflon filters by re-suspension equipment to obtain PM2.5 and PM10 samples. Eight heavy metals (Cr, Mn, Ni, Cu, Zn, As, Cd, and Pb) were analyzed by ICP-MS. The results showed that the average content of the total heavy metals in PM2.5 was higher than that in PM10. The average contents of Pb, Cd, As, and Zn were highest in all three types of road dust, and the difference in the total average content in different types of road dust was ranked as:tunnel roads > non-ferrous smelting industrial park roads > urban roads. The average contents of Pb and As in PM2.5 from the tunnel road dust were higher than other heavy metals, and reached up to 92338.3 mg·kg-1 and 12457.7 mg·kg-1, respectively. The average contents of Pb and Zn in PM2.5 from the industrial park road dust were the highest of all heavy metals (4381.7 mg·kg-1 and 4685.0 mg·kg-1, respectively). The average content of Zn and Pb in PM2.5 were the highest of all the heavy metals in the urban road dust (1952.6 mg·kg-1 and 1944.8 mg·kg-1, respectively). The average contents of Cu, Zn, As, Cd, and Pb in the different types of road dust were all higher than their background values in Yunnan Province. The results of the enrichment factor analysis and principal component analysis indicated that Cu, Zn, As, Cd, and Pb were obviously enriched in all three types of road dust, which were significantly affected by the non-ferrous smelting industry and traffic sources. In contrast, Cr, Mn, and Ni were not obviously enriched in the three types of road dust and were less affected by anthropogenic sources. The results of the health risk assessment testified that ingestion was the main exposure route, and that the children's non-carcinogenic risk was higher than that of adults. In PM2.5, As, Cd, and Pb in all types of road dust were associated with non-carcinogenic risks for adults and children. In PM10, As, Cd, and Pb in dust from the non-ferrous smelting industry park roads and tunnel roads had non-carcinogenic risks for humans. As in PM10 from the urban road dust was associated with a non-carcinogenic risk for children, whereas As in dust from the tunnel roads had carcinogenic risks.

Zinc concentrate internal circulation technology for elemental mercury recovery from zinc smelting flue gas

As most of the purposed synthesized mercury sorbents are expensive and insufficient for capturing mercury from the flue gas with ultrahigh concentration of Hg0 and SO2 in smelting processes, the application of sorbent injection for mercury removal in zinc smelting was extremely restricted. In this work, Zinc concentrate (ZC) ore, one of the raw materials for smelting, was developed to capture gaseous Hg0 from zinc smelting flue gas. The average Hg0 adsorption capacity of ZC was greater than 2 mg·g−1, even better than some synthetic binary sulfide sorbents. Meanwhile, ZC presented a good resistance to H2O and SO2 at 60–100 °C. Higher ratio of Cu element in ZC ores can result in better Hg0 adsorption performance due to the increase of active site Sn2− derived from the oxidation of S2− by Cu2+. After capture Hg0, spent ZC can be reused as raw material for zinc production, eliminating the generation of waste sorbent. This technology can as a co-benefit of condensation device to deeply purify mercury pollutants, and the excessive gaseous Hg0 will be removed from the system by condensing into liquid mercury. Moreover, such ZC cycles offers a specific strategy for gaseous Hg0 recovery in other nonferrous smelting industries.

Removal of Cl(−I) from strongly acidic wastewater using NaBiO3: A process of simultaneous oxidation and precipitation

It was proposed to recycle strongly acidic wastewater generated from nonferrous smelting industries as diluted sulfuric acid after the contaminants being removed, however, Cl(−I) removal from strongly acidic wastewater remains a difficulty. In this work, a process of simultaneous oxidation and precipitation using NaBiO3 for Cl(−I) removal from strongly acidic wastewater was proposed, and 98.1% of Cl(−I) was efficiently removed at the stoichiometric NaBiO3 dosage under 30 °C. The mechanism exploration indicated that Cl(−I) was removed in two ways. In the first way, Cl(−I) was oxidized to generate Cl2: (1) NaBiO3 was dissolved, and the produced BiO3− oxidized Cl(−I) and OH− to Cl and OH, respectively; (2) OH oxidized Cl(−I) to generate Cl−; and (3) Cl combined to produce Cl2. In the second way, Bi3+, the reduced product of BiO3−, reacted with H2O and Cl(−I) to produce BiOCl precipitates. Additionally, through treatment by the NaOH absorption solution for Cl2, almost all of BiOCl product was transformed to the regenerated NaBiO3, which was further employed in Cl(−I) removal. Finally, Cl(−I) was transferred from wastewater to the NaOH/NaCl concentrate. This study offered a theoretical foundation for the development of the method to remove Cl(−I) through oxidation.

Efficient removal of arsenic from copper smelting wastewater in form of scorodite using copper slag

Copper smelting wastewater, one of the typical high arsenic-containing acidic wastewater in the metallurgical extraction process of arsenic-associated minerals, greatly threatens human health and ecological safety due to the possible leakage and diffusion from its secondary pollution. However, the state-of-the-art technologies suffer from the great challenge that the disposal of wastewater emits an enormous amount of arsenic-containing hazardous wastes with the poor long-term stability and the high arsenic leachability. Herein, a novel strategy is proposed to remove and stabilize arsenic from copper smelting wastewater in the form of environmental friendly scorodite using copper slag as a neutralizer and an in situ iron donator. The thermodynamic analysis and the bath experiments were investigated to explore the reaction behavior between wastewater and copper slag. The result shows that 97.86% of arsenic was successfully removed from wastewater with an initial arsenic concentration of 10230 g/L at by using copper slag at an Fe/As molar ratio of 2.0 and 80 °C for 12 h, resulting in a scorodite-SiO2-sulfate composite with an arsenic leached concentration of 3 mg/L in the leaching test. The main phases of Fe2SiO4 and Fe3O4 from copper slag dissolve in wastewater and release abundant Fe ions to synthesize scorodite and secondary minerals (silica gel and sulfate complexes). The initial precipitates from the second minerals are likely to serve as nucleation sites for the formation and growth of scorodite. We demonstrate an inherent arsenic disposal process for the copper smelting industries, and the process allows the removal and stabilization of arsenic from wastewater using solid waste. It might provide an efficient and low-cost solution for the disposal of arsenic-containing wastewater in the nonferrous smelting industry.

Removal and immobilization of arsenic from copper smelting wastewater using copper slag by in situ encapsulation with silica gel

Ferric arsenate is an important arsenic-containing compound in the mining-impacted environment and hydrometallurgical tailings, especially in the disposal of smelting wastewater in nonferrous smelting industries. It acts as an intermediate for arsenic removal and immobilization in the disposal of arsenic-containing wastewater. However, amorphous ferric arsenate suffers from poor stability with a high arsenic leachability in the aqueous environment. In this study, we develop a new strategy to remove and immobilize arsenic from copper smelting wastewater using copper slag through an in situ encapsulation of ferric arsenate with silica gel. The strategy provides an inherent arsenic disposal solution for copper smelting processes, allowing the removal of arsenic in the form of environmentally friendly precipitates. The results show copper slag mainly composed of Fe2SiO4 and Fe3O4 can be dissolved in copper smelting wastewater containing high sulfuric acid and arsenic, providing abundant Fe3+ ions and silicates for the following arsenic precipitation. In the room-temperature solid-liquid reaction between copper slag and wastewater, the Fe-As co-precipitation and the in situ encapsulation results in an environmentally stable and core-shell structured precipitate consisting of an amorphous ferric arsenate core and a silica gel shell. Copper slag achieves an arsenic removal efficiency of 98.85% and an arsenic removal capacity of 66.86 mg/g in the disposal of smelting wastewater with an initial arsenic concentration of 8458 mg/L. The findings and proposed strategy demonstrates the potential for the efficient and affordable disposal of arsenic-containing wastewater.

Surface nano-traps of Fe0/COFs for arsenic(III) depth removal from wastewater in non-ferrous smelting industry

The chemical valence state of arsenic changed with the redox state which influenced by the aquatic environmental factors. One challenge for arsenic control is the depth removal of trivalent arsenic (As(III)) from wastewater from non-ferrous industries. Immobilization of As(III) could be realized through an enhanced adsorption method. In this study, zero-valent iron (Fe0) nanoparticles assembled on porous covalent organic frameworks (COFs) were selected as “nanotraps” for arsenic ions capture and surface stabilization. Fe0/TAPB-PDA COFs composites were synthesized through an in-situ growth method. The porous surface of COFs offered efficient spaces for Fe0 loading as well as the reaction sites. The results showed that Fe0/COFs exhibited a better performance in As(III) adsorption than pure nZVI (nanoscale zero-valent iron), and the maximum adsorption capacity reached to 135.78 mg/g. In addition, the effects of co-existed anions and metal ions were also investigated. Such a novel composite exhibited a huge potential for heavy metals purification in future study.