Recent advances in immobilization of radioactive cesium and strontium-bearing wastes in alkali activated materials A review.

This review discusses recent advances in the use of alkali-activated materials (AAMs) to host high heat and radiation-emitting cesium (Cs) and strontium (Sr) wastes. It examines the evolution of geopolymerization, mechanical properties, mineralogy, microstructure, and leaching behavior of Cs-and/or Sr-bearing AAMs, considering their chemical interaction with Cs and Sr nuclides and exposure to temperature and gamma radiation induced by Cs and Sr. The literature indicates that Cs and Sr slightly degrade the mechanical properties of AAMs, with Sr having a more pronounced effect. For AAMs with a low SiO2/Al2O3 ratio, decay heat from Cs and Sr can crystallize zeolitic phases, which are beneficial in the short term but detrimental in the long term because of their low stability against gamma radiation. Cs was immobilized via ion exchange within the aluminosilicate phase and Sr mainly by precipitation, but the immobilization of their respective daughter nuclides Ba and Zr was not demonstrated. Gamma radiation exposure does not significantly alter AAM properties, and nitrates in Cs and Sr-bearing wastes reduce gamma-induced water radiolysis. AAMs are promising hosts for Cs and Sr-bearing wastes, but further studies are needed using realistic Cs and Sr waste loading to evaluate the synergistic effects of Cs and Sr chemical behavior, decay heat, and gamma irradiation on the evolution of properties of waste forms, and the ability of AAMs to accommodate daughter nuclides Ba and Zr.

Preparation of non-sintered permeable bricks using electrolytic manganese residue: Environmental and NH3-N recovery benefits.

The present study aims to prepare non-sintered permeable bricks using significant amount of electrolytic manganese residue (EMR), discharged by electrolytic metal manganese industry. Mechanical and environmental properties were investigated. The microstructure was analyzed by means of XRD, FTIR, TG-DSC and SEM-EDS. It was observed that the splitting tensile strength and permeability coefficient of the optimum proportion were 3.53 MPa and 3.2 × 10-2 cm/s respectively. The main hydration products were found to be ettringite, C-S-H, aluminosilicates and C-A-S-H. The leaching test showed that Mn, Pb, Cd, total Cr and NH3-N in the non-sintered permeable bricks were solidified up to concentrations lower than groundwater standard. In addition to that, the NH3-N produced during the process was transformed into ammonia water which was in turn recycled and reused in manganese electrolysis. Besides, non-sintered permeable bricks have been produced at large scale and applied successfully as pavement materials in Songtao, China. Therefore, the use of EMR to produce non-sintered permeable bricks possesses important environmental and economic significance because the process not only utilizes large quantities of EMR and saves EMR disposal cost, but also saves a lot of natural resources and improves the urban environment.