Based on a review of the existing literature on the use of diatomite and the functioning of phase-change heat accumulators, in this study, we conducted empirical research on the creation of a phase-change composite based on Carpathian diatomite. As part of our mineralogical research, we determined the phase composition of the Carpathian diatomites in this work. Their internal nanostructure was identified. Nanopores create regular systems that, depending on the variety of diatoms, may have sieve, tubular, or "honeycomb" shapes. Diatomites' internal structure benefits the absorption capacity of phase-change materials (PCM). The obtained calorimetric thermograms of the organic phase-change material and the diatomite compound highlighted an extension of the temperature range in which phase transformation occurs from 4-5 °C (for pure PCM RT28HC) to 15-17 °C for the composites tested with weight proportions of 1:1 and 4:6. In the case of water-rich varieties, the presence of mixed-package minerals, i.e., montmorillonite, with its small size and specific 2:1 package structure, can hinder the penetration and accumulation of PCM. The ability to bind and accumulate heat will be influenced by the size of the diatomite particles or the relative size of the PCM and pores, i.e., structural and textural features.
Keywords: circular economy; heat accumulators; minerals; phase-change materials; rock raw materials.