Experimental Study on Solidification of Pb2+ in Fly Ash-Based Geopolymers

Fly ash from the incineration of domestic waste contains heavy metals, which is harmful to the environment. To reduce and prevent their contamination, heavy metal ions need to be sequestered. In this study, the geopolymer prepared by fly ash, a kind of power plant waste, is used to cure the heavy metal Pb2+, and to investigate the effect of different concentrations of Pb2+ on the compressive strength of the solidified body at different ages; the curing effect is judged by the toxic leaching concentration of heavy metals; the resistance of the solidified body to immersion is evaluated by comparing the change in strength before and after leaching; the fly ash-based geopolymer solidified body is compared with the cement solidified body in terms of curing effectiveness; the properties of the geopolymer and its mechanism of curing heavy metals are explored by microscopic tests. The results show that the fly ash-based geopolymer solidified body has good resistance to immersion; the optimum curing concentration of Pb2+ in fly ash-based geopolymers is 2.0%; compared to pure geopolymers, the strength of the solidified body at 28 d decreases by only 13.0%, and the leaching concentration of Pb2+ is 4.73 mg·L−1, which meets the specification requirements; the curing effect of the fly ash-based geopolymer is better than the cement solidified body; the microscopic test results indicate that the curing of Pb2+ by the fly ash-based geopolymer is a combination of both chemical bonding and physical fixation.

Modification of Low-Density Slag Cementing Slurry with SiC Whiskers at High Temperature

The aim of this study was to improve the mechanical properties of a slag solidified body at high temperatures. Composite materials with different contents of SiC whiskers were prepared and characterized using techniques such as mechanical testing, scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FT-IR). When the SiC whisker addition is 1% mass percentage, the compressive and tensile strength of the slag solidified body after hydration for 7 days increased by 10.2% and 39.3%, respectively, and Young’s modulus decreased by 16.8%. The results show that the addition of SiC whiskers can enhance the mechanical properties of solidified slag bodies at high temperatures. According to the test results, the hydration products of the slag solidified body mainly consist of honeycomb tobermorite (C-S-H) gel at high temperatures in addition to a small number of spherical products. The spheres are connected to form a dense structure; however, noticeable cracks were present. The addition of SiC whiskers effectively inhibited the initiation and further development of microcracks and improved the bearing capacity of the slag solidified body.

Study on the Mechanical Properties and Heavy Metal Ions Immobilization Capability of Solidified Body for MSWI Fly Ash with Geopolymer

In this study, municipal solid waste incineration fly ash (hereinafter called MSWI fly ash) was used as a main raw material, and it was prepared into a solidified body for MSWI fly ash with geopolymer by a single-component chemical alkali excitation method. The results were shown that when the content of MSWI fly ash was 50%, SiO2/Al2O3 was between 3.51-4.04, and Na2O/Al2O3 was between 0.24-0.30, with the increasing of SiO2/Al2O3 and Na2O/Al2O3, the 28d compressive strength of the solidified body showed a trend of increasing first and then decreasing, the maximum 28d compressive strength was 17.7MPa. When SiO2/Al2O3 was 4.04 and Na2O/Al2O3 was 0.30, the minimum leaching concentrations of Pb2+ and Cd2+ were 0.018mg/L and 0.027 mg/L. When the content of MSWI fly ash was increasing, the 28d compressive strength of the solidified body gradually decreased, and the heavy metal ions leaching concentration gradually increased. The result of XRD and FTIR indicated that the MSWI fly ash was involved in the polymerization reaction, and the heavy metal ions in MSWI fly ash were also chemically solidified into the geopolymer structure.

Kinetics of Copper Ion Leaching from Cement-Solidified Body of Blast Furnace Slag Adsorbing Copper Ion

Blast furnace slag has good adsorption performance and can be used to adsorb heavy metal ions in waste liquid. It’s worth studying whether the blast furnace slag absorbing heavy metal ions will pose a potential threat to the environment during the process when used in cement-based materials.This paper has studied the leaching amount of copper ions in the blast furnace slag-cement system was analyzed, and analyzed the leaching kinetics of copper ions. The results showed that the leaching amount of copper ions in the blast furnace slag-cement system that adsorbed copper ions basically met the national standard, and the solidified body age was 28 days,blast furnace slag content 30% is the smallest condition for the amount of copper ion leaching.The leaching model of copper ions in the blast furnace slag-cement system is the Elovich equation, which is a heterogeneous diffusion process. The longer the curing age is the slower the leaching process is completed and do not cause environmental pollution during long-term use.

Study on Solidification of Chromium-Containing Sludge With Alkali Slag Combined With Attapulgite

In order to solve the harm of hazardous waste chromium-containing sludge to humans and the environment, this paper uses attapulgite to strengthen alkali slag to prepare cementitious materials to solidify/stabilize chromium-containing sludge. Single-factor and orthogonal experiments were used to optimize the preparation parameters of alkali slag cementitious materials. The compressive strength, heavy metal leaching toxicity, and microscopic characterization of chromium-containing sludge solidified body were tested to investigate the solidification effect and mechanism of chromium-containing sludge. The results show that: The best content of attapulgite is 4%. The compressive strength of the solidified body decreased with the increase of chromium sludge content, and the leaching concentration of Cr and Cu increased with the rise of chromium-sludge content. The addition of attapulgite enhanced the compressive strength. Compared with the original chromium-containing sludge, the leaching concentration of heavy metals in the solidified body is significantly reduced. The XRD and FTIR analysis showed that the solidified body might solidify/stabilize heavy metals by physical encapsulation of amorphous form and chemical immobilization. This research realizes the use of waste to treat waste and provides the possibility for the application of solidified products in construction.

Monitoring of pollution factor of solidified body leachate in drilling well site and its influence on surface water environment

Aiming at the pollution of the leaching solution of the solidified body in the wellbore, a water eutrophication level evaluation algorithm based on the optimized analytic hierarchy process is proposed from the current situation of many factors affecting the eutrophication of the water body and the difficulty of evaluation. Based on this, the user-oriented PC software monitoring system was developed, which mainly includes three major modules: surface water environment monitoring, water eutrophication evaluation, water bloom prediction and warning, and system assistance. The surface water environment monitoring module can receive and display the surface water environment parameter information in real time, and has the functions of data comparison analysis and historical data search, and the eutrophication assessment and water bloom prediction and warning module can analyze the eutrophication status of water bodies in real time and provide short-term and medium-term warnings for water blooms. The research can promote the control of the leachate pollution of the wellbore in the wellbore and the optimization of the surface water environment.

Analysis of the Sealing Mechanism of Cement-Sodium Silicate Grout in Rock Fractures with Flowing Water

The diffusion and sealing mechanisms of cement-sodium silicate grout (C-S grout), which is widely used in flowing water sealing projects, are complicated. Based on a large-scale quasi-three-dimensional simulation test platform of fracture dynamic water grouting, an orthogonal experiment of flowing-water sealing of C-S grout was performed. The grout was shown to diffuse in the form of an asymmetric ellipse. The flowing-water sealing process consists of three stages: (1) the grout diffuses to the fracture boundary in an asymmetrical ellipse; (2) the solidified body of grout develops; (3) the stable solidified body forms. The sealing efficiency was evaluated and graded by the reduction of water drainage through the fracture after grouting. Based on the test data, the factors that affect sealing efficiency can be listed in the following order from strong to weak: grout gel time, flowing water velocity, grout take, fracture plane width, and fracture aperture. Finally, a fitting equation was acquired to provide a reference for practical engineering applications.

Study of Surface Layer Hardening after Treatment Complex Tool

The results of experimental studies of the thin surface layer of samples made of steel 45 after treatment with surface plastic deformation (SPD) multiradius roller (MR-roller) are presented. On the basis of the apparatus of the mechanics of technological inheritance, taking into account the effect of the solidified body, a model of the process according to the scheme of multiple loading-unloading of metal, taking into account the phenomenology of the SPD process and the properties of the material, is created. Distributions of parameters of the stress-strain state in the deformation centre are obtained, the parameters of roughness and microhardness of the surface layer are investigated.

Mechanical Properties and Microstructure of Slag Solidified Body

The mechanical properties of slag solidified bodies tend to be degraded when the temperature of slag solidified bodies is high. It is easy to crack under the action of perforated fracturing to lose the effect of sealing and interlayer sealing, and affect the cementing quality. Therefore, the mechanical properties of the solidified slag at several bottom-hole cyclic temperatures (30 °C, 50 °C, 70 °C, 90 °C) were studied in the present investigation. The results showed that the early strength of the slag solidified body cured at 90 °C was stronger than the early strength of the slag solidified body at 30 °C and 50 °C but lower than 70 °C. However, when the curing time reaches 28 days, the compressive strength of the slag solidified body at 90 °C droped sharply lower than the strength of the slag solidified body at 30°C. SEM and XRD indicated that the hydration products of slag at 90 °C were primarily network-like C-S-H gels. Compared with low temperature conditions, slag solidified bodies at high temperatures (>90 °C) were prone to micro-cracks and the structure easily damaged.

Natural magmatic granite as matrix for immobilizing simulated An4+ waste

In nature, many rocks contain radionuclides, and returning radioactive waste to nature is an environmentally friendly way. In this work, a natural magmatic granite rock has been studied as a host matrix for simulated An4+ waste disposal. The blank granite, in the form of powder, was firstly treated by muffle furnace heating in the temperature range of 800 °C to 1400 °C. It was found that the lowest crystallinity of the samples was obtained at 1300 °C. Moreover, 8 wt.% of simulated tetravalent actinides (CeO2) could be successfully immobilized in the natural granite at 1300 °C for 60 min. Raman results show the structure disordering in samples tends to increase with the increased amount of CeO2. SEM-EDS observation shows that the distribution of Ce was relatively uniform in the matrix. Moreover, the hardness of solidified body is comparable to traditional glasses and it decreases with the increase of CeO2 content.