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• Solid industrial wastes were the selected precursors for alkali activated material. • Physico-chemical properties and natural radioactivity of materials were evaluated. • Dosimetric indexes of the precursors, paste and mortars were determined. • It was found that geopolymers (in paste and mortar form) comply to Euratom Directive. Alkali-activated materials were prepared from four typical precursors (coal fly ash, granulated blast furnace slag, metakaolin, and brick waste powder) characterized for granulometry, elemental composition, and microstructure. High-resolution gamma-ray spectrometry was used to determine the activity concentration of Naturally Occurring Radioactive Materials (NORM) in all the materials to assess their radiological impact. All the investigated materials have been found to comply with the European dosimetric index (I) according to Directive 2013/59/Euratom. The results suggest the need for an accurate check of radioactivity throughout the mixing phases to prevent I exceedances. The productive chains were also evaluated by principal component analysis. [ABSTRACT FROM AUTHOR]

• LCGGM with a large content of CG was prepared by composite activation. • The comprehensive advantages of CG, BFS and FA can be utilized. • The RSM was utilized to obtain the quantitative trend of each response and each factor. • The main reaction products of LCGGM are C-(N)-A-S-H and C-S-H gels. To prepare a low-cost geopolymer grouting material (LCGGM), the industrial solid wastes coal gangue (CG), blast furnace slag (BFS) and fly ash (FA) were used as silica-alumina materials; desulfurized gypsum and an alkaline activator were used as ligands; and small amounts of additives were supplemented. The response surface methodology (RSM) was used to design macroscopic tests of the fluidity, setting time, compressive strength and impermeability of LCGGM, and XRD, FTIR, TG-DSC and SEM-EDS were used to analyse the mechanism of action. The results showed the following: (1) Optimized formulation could be achieved at coal gangue powder: slag: fly ash ratio of 5:4:1, 1.64 M sodium silicate modulus, 6.7% sodium silicate and 5% Na 2 O. The LCGGM possesses clean production, high fluidity, fast setting, low bleeding rate, high compressive strength and seepage pressure, providing appealing properties as grouting materials for reinforcement. The establish regression model and response surface well reflect the impacts of various factors on the properties of the LCGGM. (2) Microscopic analysis showed that the three materials with different fineness improved the density of the stone body and participated in the hydrolytic polymerization reactions of the multiple systems at different times, which ensured the strength of the stone body in the early and late stages. [ABSTRACT FROM AUTHOR]

• Geopolymer adsorbents was prepared from the precursor mixed fly ash and metakaolin. • The geopolymer can effectively remove Pb2+ and Cd2+ from solution. • There are some differences in the adsorption mechanism of geopolymers for Pb2+ and Cd2+. • Synthesize geopolymer adsorbent by industrial waste is a promising approach. In this study, geopolymers were prepared using a mixed precursor of coal fly ash (35 wt%) and metakaolin (65 wt%) in order to investigate the adsorption capacity for Pb2+and Cd2+ in solution. The specific surface area of the geopolymer was up to 82.8 mg/m2. The results show that the maximum adsorption capacity of the geopolymer for Pb2+ and Cd2+ removal were 164.1 and 78.2 mg/g, respectively. Mixing fly ash and metakaolin as raw materials for geopolymer synthesis not only yields an adsorbent material with excellent performance, but is also an effective way to utilize industrial waste resources. [ABSTRACT FROM AUTHOR]