Pore, surface and fillet moisture in centrifuged beds of coarse coal

The moisture content of the coarse coking coal product from the centrifuges of preparation plants was investigated to evaluate the contribution of three types of water: that held internally in pores, that in fillets at points of contacts between the particles, and the moisture covering the surface. A standardised laboratory centrifuge test was used to measure the total non-centrifugable moisture (NCM) content and also the quantity held in internal pores, called NCMi. The fillet moisture NCMf was estimated by means of a formulation which relies on experimentally measured holdup volumes, supplemented by a physical model. The surface moisture NCMs could then be derived by difference. The NCMf, which depends on the body force, the particle size and the surface tension and contact angle of the liquid, ranges from effectively zero for large particles to 10% for fines. The surface moisture NCMs is of the order of 0.5% for high rank coals and increases to 4.5% for lower rank coals. (C) 2002 Elsevier Science Ltd. All rights reserved.

Sorption and desorption behaviour of acetochlor in surface, subsurface and size-fractionated soil

Pesticides leaching through a soil profile will be exposed to changing environmental sorption and desorption conditions as different horizons with distinct physical and chemical properties are encountered. Soil cores were taken from a clay soil profile and samples taken from 0.0 to 0.3 m (surface), 1.0-1.3 m (mid) and 2.7-3.0 m (deep) and treated with the chloroacetanilide herbicide, acetochlor. Freundlich isotherms revealed that sorption and desorption behaviour varied with each depth sampled. As soil depth increased, the extent and strength of sorption decreased, indicating that the potential for leaching was increased in the subsoils compared with the surface soil. Hysteresis was evident at each of the three depths sampled, although no significant correlations between soil properties and the hysteresis coefficients were evident. Desorption studies using soil fractions with diameters of > 2000, 250-2000, 53-250, 20-53, 2-20, 0-2 and 0-1 mum separated from each of the three soil depths showed that differential desorption kinetics occurred and that the retention of acetochlor significantly correlated (R-2 = 0.998) with organic matter content. A greater understanding of the influence of soil components on the overall sorption and desorption potential of surface and subsurface soils is required to allow accurate prediction of acetochlor retention in the soil. In addition, it is likely that the proportion of each size fraction in a soil horizon would influence acetochlor bioavailability and movement to groundwater.