Effects of particle size and moisture on respirable coal dust generation in pakistan's informal bituminous mines.

Respirable coal dust remains a major occupational hazard in informal mining operations in Pakistan, where high-ash, low-moisture bituminous coals are handled without engineered dust-control systems. This study evaluates how particle size distribution (PSD), moisture content, and surface wettability influence dust-generation potential in coal from the Darra Adam Khel coalfield. Laboratory analyses were conducted on three particle-size fractions (> 75 μm, 45–75 μm, and < 45 μm) to measure moisture retention, slurry pH, and contact-angle–based wettability under ambient conditions. Results show a size-dependent response, with ultrafine particles (< 45 μm) retaining the highest moisture (up to 6.60%) and exhibiting near-neutral pH (6.7), indicating increased carbonate dissolution. Contact angles ranged from 72° to 109°, confirming moderate–strong hydrophobicity that intensified upon compaction. Because dust-generation chamber tests were not available, respirable dust-suppression efficiency (35–58%) was estimated from established Pakistani benchmarks rather than measured directly. The study also acknowledges that the hypothesized 8% moisture threshold for optimal suppression could not be experimentally validated, as the maximum achievable sample moisture was 6.60%. High-pressure gas-atmosphere wettability trends (He, N₂, CO₂) referenced in the discussion represent conceptual mechanisms from published literature, not in-house experimental data. Overall, the findings indicate that Darra Adam Khel coal exhibits limited natural wettability and low moisture-holding capacity, providing a physicochemical basis for enhanced dust-control strategies such as pH conditioning and nonionic surfactants to address hydrophobic surface behavior in semi-arid mining environments.