leaching toxicity
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Molecules ◽  
2022 ◽  
Vol 27 (2) ◽  
pp. 462
Author(s):  
Fenghui Wu ◽  
Can Yang ◽  
Guangfei Qu ◽  
Liangliang Liu ◽  
Bangjin Chen ◽  
...  

Phosphogypsum (PG) treatment is one of the research hotspots in the field of environmental protection. Many researchers both at home and abroad have devoted themselves to studies on harmless resource treatment of PG, but the treatment technology is unable to meet the demand of PG consumption due to the huge production and storage demands. In order to solve the problem of PG pollution, this study explored the different solidified effects of various modification formulations on the hazardous components in PG, using industrial solid waste calcium carbide slag (CCS) as an alkaline regulator; Portland cement (PC), polyaluminum chloride (PAC) and CaCl2 as the main raw materials of the solidification and stabilization formula and the water content in PG as the reaction medium. The results showed that CCS (0.5%), PC (0.4%) and PAC (0.3%) had a more significant solidified effect on phosphorus (P) and fluoride (F). PAC was added in two steps and reacted under normal temperature and pressure, and its leaching toxicity meets the requirements of relevant standards, which laid an excellent foundation for PG-based ecological restoration materials and filling materials, with low economic cost, simple process and strong feasibility. This will provide great convenience for the later mining and metallurgy.


Processes ◽  
2022 ◽  
Vol 10 (1) ◽  
pp. 142
Author(s):  
Jiacong Sun ◽  
Yating Luo ◽  
Jien Ye ◽  
Chunhui Li ◽  
Jiyan Shi

Hexavalent chromium (Cr(VI)) waste produced by chrome plating activities pollutes the surrounding environment and harms human health. However, information about the chromium (Cr) pollution characteristics of actual electroplating sites is still lacking. In this study, the concentration, leachability and speciation of Cr in soils from a typical chrome plating site were analyzed. Our results showed that this site was severely contaminated by Cr (7.2 to 7735.2 mg/kg) and Cr(VI) reached the mean concentration of 138.7 mg/kg. The spatial distribution of Cr(VI) was related to the plating processes. Chrome plating and sewage treatment areas could be considered as the hot spots of contaminated sites. The vertical distribution of Cr(VI) was mainly affected by soil properties, where the loam layer retained and reduced a large amount of Cr(VI) due to its high content of iron minerals and finer particle fractions. Additionally, the chemical extraction results showed that Cr was mainly in non-residual fractions and the existence of Cr(VI) led to a high leaching toxicity based on the toxicity characteristic leaching procedure (TCLP) results. Moreover, X-ray photoelectron spectroscopy (XPS) results revealed the speciation of Cr in the long-term contaminated soils. A large amount of Cr(VI) was reduced into Cr(III) and mainly existed as Cr(OH)3 and Cr2O3. Furthermore, Cr(VI) tended to precipitate as CaCrO4 and persisted in soils. Therefore, it is necessary to find appropriate strategies to remediate these contaminated soils. Overall, these findings strengthen our understanding of Cr(VI) behaviors and lay a foundation for the future pollution investigation, ecological remediation and risk assessment of sites contaminated by electroplating.


2021 ◽  
Author(s):  
Chao-Qiang Wang ◽  
De-Ming Xiong ◽  
Yu Chen ◽  
Kai Wu ◽  
Pei-Xin Wang ◽  
...  

Abstract The waste product Phosphogypsum (PG) produces in phosphoric acid production processes. Its storage requires large amounts of land resources and exist serious environmental risks. In this work detailed experimental research was carried out to investigate the potential reuse of PG after calcination modification as a novel building material for cast-in-place concrete products. The calcination modification mechanism was studied and the environmental risk assessment of modified PG is presented. The calcination modification includes crystal phase transformation, removal of impurities and modifying the pH value. The calcination was carried out at 280℃ for 3-4 hours, where the resulting product is a pH value of 7.3, and the soluble fluorine and phosphorus removal rates reach up to 72.7% and 82.4% respectively. These removal rates meet the requirements of the national Phosphogypsum standard (GB/T 23456-2009). To ensure the environmental safety, ecological risk assessment methods for determining the leaching toxicity of the modified PG were employed. The toxicity of Ba and P elements in the modified PG products was assessed, as well as the leaching toxicity concentrations of all particular heavy metals, which were found well below the limits set by the national standards. All the results presented strongly suggest that the 280℃ modified PG presented here has excellent application potential as a raw component in building materials.


Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5855
Author(s):  
Shaoyan Hu ◽  
Deyong Wang ◽  
Dong Hou ◽  
Wei Zhao ◽  
Xianglong Li ◽  
...  

Secondary aluminum dross is a byproduct of the electrolytic aluminum industry, whose main components are Al2O3, AlN and Na3AlF6. Secondary aluminum dross is a type of hazardous waste, with a tremendous yield every year. Realizing the harmless treatment or resource utilization of secondary aluminum dross has important economic and social benefits. In the present research, the process of preparing premelted calcium aluminate slag used for molten steel refining from secondary aluminum dross was studied in detail. Firstly, the chemical composition and phase component of secondary aluminum dross were analyzed systematically. Then, according to phase diagram analysis and melting point measurement, the appropriate mixing ratio of CaO and secondary aluminum dross and the appropriate calcination temperature were determined. On this basis, an experiment of premelted calcium aluminate slag preparation was carried out in a tubular resistance furnace. The phase component and micromorphology of the premelted slag were analyzed by XRD and SEM. The results show that the main component of the premelted calcium aluminate slag is 11CaO·7Al2O3·CaF2 phase with a low melting point. The original Na3AlF6 phase, which is the cause of leachable fluoride in secondary aluminum dross, disappears totally, and there is no water-soluble fluoride detected in the leaching toxicity detection. The research indicates that the process of preparing premelted calcium slag from secondary aluminum dross is feasible, which provides a helpful reference for the resource utilization of secondary aluminum dross.


2021 ◽  
Author(s):  
Bing Wang ◽  
Qingtong Cao ◽  
Guomin Li ◽  
Jian Zhang

Abstract Given that the biological treatment of antibiotic wastewater can easily induce resistant bacteria, the photocatalytic degradation of antibiotics is considered a better method for treating antibiotic wastewater. Therefore, the ability to remove Tylosin (TYL) and Tetracycline (TC) in aqueous solution using rare earth element Tb-doped g-C3N4 under simulated natural solar radiation was investigated. A series of rare earth Tb3+ doped mesoporous g-C3N4 were successfully prepared by nitric acid treatment and Tb(NO3)3·5H2O samples showed significantly higher degradation efficiency for TYL and TC than pure g-C3N4. Leaching toxicity experiments were carried out on the catalyst using chard seeds and demonstrated negligible toxicity of the leachate from the catalyst. The structure, elemental state, optical properties, morphology and photogenerated carrier separation of the prepared xTCN catalysts were characterized by XRD, XPS, UV-Vis DRS, TEM and PL. The results showed that Tb doping enhanced the photocatalytic activity of the g-C3N4 catalyst by narrowing the band gap while improving the light-trapping ability; The separation and transport rate of photogenerated carriers were significantly increased after Tb doping. Finally, a simple, efficient and non-polluting Tb-doped carbon nitride photocatalyst is successfully developed in this paper.


2021 ◽  
Author(s):  
Yonghao Zhu ◽  
Yanjun Hu ◽  
Qianqian Guo ◽  
Lingqin Zhao ◽  
Bin Xu

Abstract Wet-treatment is usually employed to recover metals from bottom ash (BA). However, its effectiveness on regulating the leaching behavior of BA and minimizing environmental impact is still unquantified when BA is used as engineering materials. This study investigated the leaching behavior of targeted pollutants including Cu, Zn, Ni, SO42- and Cl- in fresh bottom ash (FBA) and treated bottom ash (TBA) using batch, standard column up-flow leaching and simulated rainfall down-flow leaching tests. It was firstly noted by the batch leaching that the potential ecological risk of MSWI bottom ash could not be ignore during its reutilization, and wet treatment enabled reduce the leaching concentration of Cu, Zn, Cl- and SO42- by 7.1%, 33.8%, 46.3% and 18.9%, respectively. The leaching concentrations of the targeted ions in FBA are generally higher than those of TBA. Furthermore, when BA was applied in water dynamic system such as rainfall environment, its toxicity leaching should be paid more attention onto the early leaching stage with a very high water dissolved salts release, such as Cl- and SO42-. The leaching concentration of Cu particularly exceeded the limit value before L/S=1. Meanwhile, it was also found that the leaching of SO42-, Ni, Cu and Zn in water dynamic system were directly proportionate to the liquid-to-solid (L/S) ratio. The leaching concentration of the pollutants obtained from the simulate rainfall down-flow tests was usually 4-6 times higher than those from the standard up-flow column when at the same ratio of liquid and solid.


2021 ◽  
Vol 6 (2) ◽  
Author(s):  
Hu T ◽  
◽  
Zhao K ◽  
Chen D ◽  
Hu Y ◽  
...  

The application of Municipal Solid Waste Incineration (MSWI) fly ash in asphalt mixtures is an efficient way to utilize fly ash. The feasibility of applying various kinds of dechlorinated fly ash in asphalt mixtures was comprehensively discussed in the study. The effects of types and amounts of dechlorinated fly ash on the performances of prepared asphalt mixtures were explored. Additionally, their environmental risks and economic values were further evaluated. The water absorption coefficient and porosity of fly ash-asphalt mixtures were respectively in the ranges of 0.15-0.5% and 3-4%, which met the application requirements of asphalt. The replacement of Raw Fly Ash (RFA) and Dechlorinated Fly Ash (DFA) improved Marshall stability, split strength, and Tensile Strength Ratio (TSR) of asphalt mixtures. DFA realized the more significant improvements. The leaching concentrations of heavy metals in all the prepared asphalt mixtures were lower than the detection limit, indicating that there was no risk of leaching toxicity.


2021 ◽  
Author(s):  
XueHong Du ◽  
Xiangdong Li ◽  
Qiyan Feng ◽  
Lei Meng ◽  
Yue Sun

Abstract This paper conducts sequential batch extraction experiments on phosphorus gypsum, titanium gypsum and desulfurized gypsum to explore their leaching characteristics and evaluate the hazards of the three types of gypsum. In addition, COMSOL Multiphysics is used to numerically solve the filling models of the three gypsum materials and the patterns of migration of metal elements in gypsum are observed. The result show that the leaching concentration of metal elements of the three gypsums is much lower than the leaching toxicity identification standard, so none of the three have the characteristics of leaching toxicity, and they are not classified as hazardous solid wastes; phosphorus gypsum and FGD gypsum are easier to release metal elements under low pH conditions, while the release of metal elements in titanium gypsum is not obvious under acidic conditions; the simulation results show that the diffusion concentration of metal elements increases with the passage of time, and its migration ability decreases with the increase of depth. The three gypsums can be considered as filling material for abandoned mines. During the filling process, the diffusion rate, diffusion distance and final concentration of metallic elements in gypsum are all affected by the initial concentration.


2021 ◽  
Vol 13 (12) ◽  
pp. 6532
Author(s):  
Hang Zhao ◽  
Yang Tian ◽  
Rong Wang ◽  
Rui Wang ◽  
Xiangfei Zeng ◽  
...  

Metal mobility and toxicity of the municipal solid waste incineration (MSWI) fly ash from different seasons in Beijing were studied using leaching toxicity procedures, sequential extraction procedures, and bioavailability procedures. The X-ray diffraction results showed that MSWI fly ash contained CaSO4, CaCO3, and KCl. The Pb, Zn, and Cd contents of MSWI fly ash were high, especially during autumn, being 42, 77, and 1260 times higher than that of their soil backgrounds, respectively. Leaching toxicity experiments showed that MSWI fly ash is hazardous, since Pb exceeded the maximum threshold (5 mg/L). The main alkali metal ions and anions, heavy metals total content, leaching concentration, chemical speciation, and bioavailability varied seasonally. The Pb and Zn leaching concentrations in summer and autumn were higher than that of the other two seasons. Sequential extraction procedures indicated that Pb, Zn, and Cd showed extremely high metal mobility, i.e., the residual states of Pb and Cd in spring were 5.83% and 1.21%, respectively, and that of Zn in autumn was 10.68%. These results will help industries, governments, and the public better understand the risk of MSWI fly ash and will urge them to pay more attention to preventing harm to the ecosystem and human beings.


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