Radiation absorption by disperse solid particles in a turbulent square duct flow was studied experimentally for different particle loadings. The fully-developed flow of air at a Reynolds number of ReH = 20 · 103 was loaded with 12 μm diameter Nickel particles and exposed to monochromatic near-infrared radiation. Optical measurements confirmed the existence of significant preferential concentration at the low loadings. Total radiation transmission through the particle laden flow and mean gas temperature rise, were analyzed for mass loading ratios ranging from 0.1 to 0.4. Transmission measurements are in good agreement with the exponential decay predicted by the Beer-Lambert law. Estimates of the gas temperature rise from a one-dimensional model making use of the optically thin approximation are found to over predict the gas temperature at the highest loading when compared with the experimental data.