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Lead is a toxic heavy metal and is non-biodegradable, often causes soil pollution, and how to fix the soil is a major environmental issue currently facing. The porous material used as lead adsorption materials is one way to solve this problem. In this study, porous adsorption materials were prepared using magnesium phosphate cement (MPC) as a matrix. Their adsorption properties concerning lead ions were studied to understand its fixation ability of lead ions better. The obtained porous materials were characterized by the Brunauer–Emmett–Teller method (BET), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and thermogravimetry (TG) techniques. Batch experiments were conducted to evaluate the effects of leaching time, initial concentration of lead ion solution, and temperature on the prepared materials' performance. The results showed that the pore size distribution of the porous materials based on magnesium phosphate cement (PMMPC) was mainly constituted of mesopores of 4–10 nm. At the same time, the specific surface area was 16.841 m2/g. The PMMPC exhibited an excellent adsorption performance for lead ions at 298 K, with a maximum adsorption capacity of 208.233 mg/g. The fitting results of the kinetic and isothermal adsorption equations demonstrated that the adsorption of lead ions by PMMPC followed a pseudo-second-order kinetic and Langmuir model, indicating the occurrence of chemisorption. Within the experimental temperature (298–318 K) and initial concentration (100–250 mg/L) range, the adsorption of Pb2+ on PMMPC was spontaneous owing to the negative values of ΔG. Therefore, PMMPC is a highly effective adsorbent for removing lead ions from aqueous solutions and has vast application potential in wastewater treatment.

Chemically bonded phosphate ceramics (CBPC) are prepared by the acid-base neutralization reaction of MgO and KH2PO4, which has a wide application prospect in the field of solidifying high-level liquid wastes and heavy metals. Herein, the effect of Cs+ on the solidifying process of the CBPC matrix with different M/Ps is studied through the change in pH values of the hydration process, the microstructure, and the phase composition of hydration products, as well as the compressive strength and leaching rate of the solidified form. The results show that with the increase in the Cs+ content, although the initial compressive strength of the solidified form with the M/P ratio in the range of 6:1 to 10:1 decreases, the compressive strength of the specimens reached 7 MPa after curing for 6 h, which was suitable for the rapid emergency treatment of Cs-containing wastes. Cs+ participates in the hydration reaction of the CBPC matrix but does not change the type of hydration products. With the addition of Cs+, the microstructure of hydration products changes from dense prismatic crystals to loose and porous cluster-like materials. The existing forms of Cs+ in the CBPC matrix are MgCsxK1-xPO4·6H2O and Cs3PO4. Generally, CBPC solidified form has an excellent solidification performance on Cs+; the normalized leaching rate of Cs+ in CBPC solidified form is in the range of 1.3127·10−6 ~ 9.1362·10−6 g/(m2·d), and the effective solidification rate is more than 99.136%.

The pore structure and permeability of cement-based materials have great influence on the durability of application of this materials. The effects of bentonite on the pore structure and permeability of cement mortar were investigated in this paper. Bentonite, as a swelling potential clay, was added to mortar at content 0, 4 and 8% by weight of cement. The compressive strength, flexural strength, and impermeability pressure were determined for cement mortar with bentonite and compared with plain cement mortar specimens. Test results showed that the addition of 8% bentonite could cause a significant increase of 61.48%, 42.09% and 76.47% for compressive strength, flexural strength, and impermeability pressure, respectively. The enhancement of impermeability is mainly due to the pore structure refinement by the bentonite, which is validated by test results of the Mercury intrusion porosimetry (MIP). Moreover, needle-like and amorphous hydration products grow on the surface or edge of bentonite resulting in more tortuous penetration path to improve the barrier performance of cement mortar.

Waste glass is a bulk solid waste, and its utilization is of great consequence for environmental protection, the application of waste glass to magnesium phosphate cement can also play a prominent role in its recycling. The purpose of this study is to evaluate the effect of glass powder (GP) on the mechanical and working properties of magnesium potassium phosphate cement (MKPC). Moreover, a 40 mm × 40 mm × 40 mm mold was used in this experiment, the workability, setting time, strength, hydration heat release, porosity, and microstructure of the specimens were evaluated. The results indicated that the addition of glass powder prolonged the setting time of MKPC, reduced the workability of the matrix, and effectively lowered the hydration heat of the MKPC. Compared to an M/P ratio (MgO/KH2PO4 mass ratio) of 1:1, the workability of the MKPC with M/P ratios of 2:1 and 3:1 was reduced by 1% and 2.1%, respectively, and the peak hydration temperatures were reduced by 0.5% and 14.6%, respectively. The compressive strength of MKPC increased with an increase in the glass powder content at the M/P ratio of 1:1, and the addition of glass powder reduced the porosity of the matrix, effectively increased the yield of struvite-K, and affected the morphology of the hydration products. With an increase in the M/P ratio, the struvite-K content decreased, many tiny pores were more prevalent on the surface of the matrix, and the bonding integrity between the MKPC was weakened, thereby reducing the compressive strength of the matrix. At less than 40 wt.% glass powder content, the performance of MKPC improved at an M/P ratio of 1:1. In general, the addition of glass powders improved the mechanical properties of MKPC and reduced the heat of hydration.

Ceramic solidification offers higher waste loading and a more stable state than can be provided by the glass solidification method because of the stable crystalline structure of its forms, but the process of fabricating large bulk solidified ceramic forms is complicated and therefore limited in application. In this paper, particulate ceramic solidification forms were first prepared by using high-temperature sintering; particulate ceramic solidification forms were then added into a paste of magnesium phosphate cement (MPC), which form composite solidified forms after curing. The mechanical and durability properties of the samples were investigated, and the phases, microstructure, high-temperature stability, and leaching properties of samples were measured by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and inductively coupled plasma mass spectrometry. The results show that the solidified forms prepared have excellent mechanical properties, high-temperature stability, soaking resistance, and freeze–thaw resistance. The compressive strength of samples decreased with increasing ceramic content, with the strength reaching 27.8 MPa with a 50 wt% load content of ceramic. With adsorption of the simulated nuclides by the hydration products of cement and the retardation effect of MPC, the leaching rate of the simulated nucleus was found to be 1.86 × 10−7 cm/day, which is less than that of the ceramic solidified form. A protective layer on the surface of the solidified ceramic form with MPC can further improve the performance of the solidified form.

Rapid solidification of radioactive wastes is one of the most effective methods to prevent the spreading of radioactive contamination after a nuclear emergency. In this study, magnesium phosphate cement (MPC) was used as matrix to rapidly solidify denitrated high-level liquid wastes (HLLW). The compressive strengths and leaching rates of the samples were studied to evaluate the performance of the solidification forms. Further, XRD, SEM, and EDS were used to measure phase compositions, microstructures, and microscopic chemical compositions, respectively, of the as-prepared samples. Moreover, the solidification mechanism of simulated radioactive ions in phosphate cement is discussed in this paper. According to the results, the compressive strength of the solidified forms was affected by the actual mass ratio of dead-burned magnesia (MgO) powders to potassium dihydrogen phosphate (KH2PO4) (M/P) and unreacted KH2PO4; with up to 50 wt% HLLW content, 4.2 MPa and 13.2 MPa can be achieved for an M/P ratio of 1 after 3 h and one day, respectively. The leaching rates of Sr2+ and Cs+ for the solidified forms were below 10−7 g/m2/d and 10−4 g/m2/d, respectively. The immobilization of radioactive ions via an MPC paste is not only due to chemical immobilization, but also due to the physical encapsulation offered by the dense structure of the MPC. The cement offers sufficient strength in a short time for the temporary storage and transportation of the solidified forms.

High permeability and strength magnesium phosphate cement (MPC) with porosity, average pore size, and compressive strength varied from 63.2% to 74%, 138.7 μm to 284.7 μm and 2.3 MPa to 4.7 MPa, respectively, were successfully prepared by combining the physical foaming method and chemically entrained gas method at room temperature. The effects of borax content, chemical foaming agent content, zinc powder content and W/S ratio on the porosity, pore size distribution, compressive strength, and permeability of the MPC were investigated. The results indicate that the chemical foaming agent content tends to have little impact on the porosity and compressive strength, and the zinc powder content has the most significant influence on the average pore size of MPC. The air pores distribution and connectivity of MPC were mainly controlled by the borax content, W/S ratio, and chemical foaming agent content. Zinc powder played a destructive role in the pores formed by the early physical foaming and led to an increase in pore size and a large number of through pores, which increased the permeability of the materials.