Effects of acid and phosphate on arsenic solidification in a phosphogypsum-based cement backfill process

Jia

et al. 2022

Front. Environ. Sci.

Phosphogypsum is a solid waste produced in the production of wet-process phosphoric acid. The main component is calcium sulfate dihydrate, and its constant calcium activity is very low. It is a very difficult waste to handle. The slag produced in the ironmaking processes of the Jiuquan Iron and Steel Company has high activity and can be mixed with phosphogypsum to prepare backfilling cementitious materials for the backfilling of goaf (see Introduction below) to prevent its subsidence and cracking and subsequent subsidence of the land surface above the goaf. In this paper, an orthogonal test of material strength under different ratios and finenesses was carried out, and the optimal formula of phosphogypsum-based cementitious material was obtained. On this basis, SEM (Scanning Electron Microscope) and XRD (X-ray Diffraction) were used to observe the internal structure of phosphogypsum-based cementitious materials. The results show that: when the content of quicklime is 5.5%–6.0%, the content of phosphogypsum is 30%–33%, the content of NaOH is 1.5%–2.0%, the content of Glauber’s salt is 2.5%–3%, the average particle size is 15.88 μm, and grinding aids and an early strengthening agent were added, and in the case of the strengthening agent, the 3-days and 7-days strengths of the filling reached the highest values of 1.58 MPa (mean flexural strength) and 4.1 MPa, respectively. The formation of calcium silicate hydrates gel (C-S-H) and ettringite (AFt) gradually increased with age, and the structure became denser. The ettringite plays the role of interspersed support in the filling body, thereby improving the overall strength. This research provides a theoretical basis and practical reference for the treatment of goaf.

Section: Introductionmentioning

confidence: 99%

Research on formulation optimization and hydration mechanism of phosphogypsum-based filling cementitious materials

Jia

et al. 2022

Front. Environ. Sci.

“…Although the treatment of a PG backfill involves, essentially, the dumping of PG into the underground goaf [ 12 ], the impact of toxic and hazardous substances precipitated from the backfilling body on the underground environment limits the application of phosphogypsum backfilling (PGB) technology. Yin et al [ 13 ] found that the PG generated during phosphoric acid production contains high levels of arsenic (As), resulting in adverse effects on the surrounding environment, as well as on human health when PG is stacked or handled. Chen et al [ 14 , 15 , 16 , 17 , 18 ] conducted toxic leaching tests on PGB specimens and observed precipitations of small amounts of phosphorus, fluorine, and other elements from PG even under the action of cement curing.…”

Section: Introductionmentioning

confidence: 99%

The Phosphorus Transport in Groundwater from Phosphogypsum-Based Cemented Paste Backfill in a Phosphate Mine: A Numerical Study

Chen

Zhou

Liu

et al. 2022

IJERPH

Stacked phosphogypsum (PG) can not only cause a waste of resources but also has a serious negative impact on the surface environment. Phosphogypsum backfilling (PGB) in the underground goaf is a useful approach to effectively address the PG environmental problems. However, the effects of this approach on the groundwater environment have not been studied. Therefore, the present study aims to assess the spatiotemporal evolution mechanism of total phosphorus (TP) in groundwater to solve the diffusion regular pattern of TP in PGB bodies, as well as to manage and mitigate the impacts of TP on the groundwater system. In this study, leaching toxicity experiments and a numerical groundwater simulation software (GMS10.4) were combined to develop a three-dimensional conceptual model for predicting the groundwater flow and contaminant transport under steady-state conditions in a phosphorus mine in Anhui. The results showed a lower TP concentration than the TP standard concentration (0.2 mg/L) at a source concentration of 0.59 mg/L. However, groundwater TP source concentrations of 1.88 and 2.46 mg/L in the study area were found to exceed the standard concentration for a certain time and areas. In addition, the transport and dispersion of TP are influenced not only by the groundwater flow field, drainage ditches, rivers, and wells but also by the adsorption and attenuation effects of the soil that occur during the transport process, affecting the dispersion distance and distribution of groundwater TP concentrations. The results of the present study can promote the development of groundwater-friendly PGB technology, providing a great significance to the construction of green mines and the promotion of ecological civilization.

“…In order to reduce the toxicity of arsenic, solidi cation/stabilization (S/S) technology is always applied to dispose arsenic-bearing waste by restricting the mobility of As atoms. Several methods have been proposed to reduce arsenic contamination, such as cement solidi cation (Kundu and Gupta 2008;Yin et al 2019;Yoon et al 2010), geopolymer solidi cation (Shi et al 2017;Xu et al 2006) and vitri cation solidi cation (Shi et al 2015; Zhao et al 2015;Zhao et al 2016). As for the cement solidi cation method, arsenic atoms can be immobilized by three ways: Firstly, arsenic-bearing wastes can be enwrapped by cement (Liu et al 2018); Secondly, arsenic can react with cement and form insoluble calcium-arsenic compounds (Vandecasteele et al 2002), such as Ca 3 (AsO 4 ) 2 and CaHAsO 3 ; Thirdly, arsenic can be absorbed onto the surface of calcium silicate hydrate (C-S-H) (Li et al 2018).…”

Section: Introductionmentioning

confidence: 99%

Effect of Oxygen Content and Temperature On Stabilization of Arsenic in Copper Smelting System

Zhang

et al. 2021

Preprint

Arsenic-bearing wastes from copper smelting system are usually disposed by trapping them in slag tailing. However, arsenic in slag tailing is not that stable, which can infiltrate into the groundwater, threatening the environment and human health. The solidification/stabilization (S/S) of arsenic is the only way to deal with arsenic contamination. The flash smelting method shows relatively high S/S ability of arsenic, but the process and mechanism remain unclear. In this paper, we aim at revealing the effect of atmosphere on the S/S process of arsenic owing to the different content of oxygen in reaction shaft and sedimentation tank in copper smelting system. Calcium arsenate, SiO2, Fe2O3 and iron powders were sintered at different temperature in air and argon to simulate the S/S reaction. The results show that the sintering product is Fe-Si oxide in air and fayalite in argon, and the fayalite possesses better capacity to solidify arsenic than that of Fe-Si oxide. The toxicity characteristic leaching procedure (TCLP) results reveal that the leached concentration of arsenic from fayalite fabricated at 1200 ℃ is only 2.916 mg L-1, which satisfies the identification standard for hazardous substances in China. Furthermore, the theoretical calculation reveals that AsO4 and SiO4 tetrahedrons can be connected by O atoms when sintered in argon, and the Si-O-As covalent bond can evidently inhibit the release of As atom from fayalite. This work can not only clarify the S/S mechanism of arsenic in flash smelting process, but also provide theoretical guidances to dispose arsenic-bearing waste harmlessly.