Abstract
Re-using ash-slag waste from coal-fired power plants for thermal-insulation products offers a viable route to waste valorisation and energy saving. In this work, natural diatomite and ash-slag waste were jointly mechanochemically activated for 20 min in a «NXQM-2A» centrifugal planetary mill (powder-to-ball mass ratio 1:4) and simultaneously modified with graphite. High-energy milling destroyed residual crystalline phases, increased the amorphous aluminosilicate fraction and preserved an intrinsic pore network, which lowered the thermal conductivity of the composites to 0.10-0.12 W/m·K while raising bulk density and compressive strength (diatomite: 5.6-23.2 MPa; fly ash: 10.5-37.6 MPa). Addition of 10 wt % graphite further enhanced the hydrophobicity of diatomite – reducing water uptake by about 50% produced the minimum λ-value (0.11 W/m·K) for the ash-slag system. Conversely, 20 wt% graphite generated excessive macroporosity, lowering strength to 4-2 MPa and diminishing moisture resistance. Thus, mechanochemical activation combined with moderate graphite dosing markedly improves the thermal (lower λ) and mechanical (higher strength) performance of diatomite- and ash-based composites while simultaneously decreasing water absorption. The results confirm the feasibility of upcycling ash-slag waste into high-efficiency insulation materials suitable for building envelopes and other thermal-barrier applications.