Surleva A.Ilieva D.Angelova L.2026-01-202026-01-202026-01-202026-01-202025-01-011733-349010.24425/amm.2025.155490SCOPUS_ID:105024307406https://rlib.uctm.edu/handle/123456789/1937Alkaline reactivity characterizes the dissolution and reactive capacity of a solid material in alkaline media. The results are of significance in the development of technology for geopolymers obtaining based on the studied raw materials. However, no validated analytical procedure for estimation of alkaline reactivity of coal combustion by-products and mine tailing exists. It imposed the development of specific procedure for analysis and its verification. This report presents a procedure based on ICP-OES measurement of the concentration of Al, Si and Ca in alkali solution. Some problems of the analysis were successfully addressed, as a high salt content of leachates, and the procedure was verified applying a reference laboratory approach. The alkaline reactivity was studied as a function of time at 6.5 M NaOH during 48 h. Additionally, to reactive silica determination, the study was extended to reactive alumina and calcium, as these components contribute to the development of geopolymer matrix. To estimate the percentage of dissolved Al, Si and Ca detailed precise data about chemical composition of raw materials were required. To achieve it, samples components were determined by ICP-OES after digestion in acid oxidizing medium, combined with alkali fusion for silica determination, as well as loss of ignition and humidity determination. In contrast to the approach, usually reported in the literature, presenting the alkaline reactivity as a concentration of dissolved ions in the alkaline solution, in this study we proposed a new procedure. Alkaline reactivity was estimated: by a percentage of dissolved component in mg per kg dry sample. This approach allowed comparability of the data between various laboratories, procedures or raw materials. Moreover, the approach allowed the relative ratio between reactive components to be calculated.enArticle