The use of tracer gases to determine dust dispersion patterns and ventilation parameters in a mineral processing plant.

A study was conducted in a fluorspar milling plant to assess the effectiveness of tracer gases as a reliable supplement to conventional air-monitoring and ventilation measurements. In the course of this study, a tracer gas was used as a surrogate substance to analyze the direction and the rate of spread of contaminants from various potential dust production points in the plant. Time-weighted average and continuous mineral dust concentrations were measured in several areas of the plant; these results were compared and correlated with steady-state tracer gas concentrations in the mill. Time-weighted average dust concentrations varied between 0.18 and 0.57 mg/m3 for total dust and 0.04 and 0.20 mg/m3 for quartz respirable dust, depending on the location. Correlation of these values with steady-state tracer gas concentrations yielded linear relationships with correlation coefficients (R2) of 0.95 and 0.87, respectively, for total and quartz dust. Results from this study, therefore, indicate that tracer gases may help model the spread of airborne respirable dust from point sources. These tracer gas releases also allowed the simultaneous quantitative determination of air residence times and contaminant clearance times from the building. Hence, tracer gases will help industrial hygienists obtain useful data with respect to building ventilation.

Reduction of airborne radioactive dust by means of a charged water spray.

An electrostatic precipitator based on charged water spray technology has been used in an underground uranium mine to control long-lived radioactive dust and short-lived aerosol concentration in a mine gallery where dust from a rock breaking/ore transportation operation was discharged. Two main sampling stations were established: one upstream of the dust precipitator and one downstream. In addition, dust samplers were placed at different locations between the dust discharge and the end of the mine gallery. Long-lived radioactive dust was measured using cascade impactors and nylon cyclone dust samplers, and measurement of the radioactivity on the samples was carried out by conventional methods. Radon and thoron progeny were estimated using standard techniques. Experiments were conducted under a variety of airflow conditions. A maximum radioactive dust reduction of about 40% (approximately 20% caused by gravitational settling) at a ventilation rate of 0.61 m3/sec was obtained as a result of the combined action of water scrubbing and electrostatic precipitation by the charged water spray electrostatic precipitator. This represents the optimum efficiency attained within the range of ventilation rates investigated. The dust reduction efficiency of the charged water spray decreased with increasing ventilation rate, i.e., decreasing air residence time, and hence, reduced dust cloud/charged water droplets mixing time.