Determination of flow patterns in industrial gold leaching tank by radiotracer residence time distribution measurement

The carbon-in-leach (CIL) process is one the most efficient methods of gold recovery from gold bearing ores. The efficiency of the leaching process greatly depends on the flow structure created by mechanical agitation (in some cases air agitation) in the leaching tanks. Residence time distribution (RTD) measurement was conducted in the CIL section of a gold processing plant in order to determine the flow structure in the first tank using the 131I radioactive tracer. The shape of the experimental data revealed that the flow behaviour in the tank was close to an ideal mixer. Modelling of the experimental data, however, revealed that the tank was not behaving as a single perfect mixer, but consisted of two mixing zones. The flow structure in the tank was best described by the “perfect mixers with exchange” model consisting of two mixing zones. The model allowed the determination of flow parameters including the mean residence time, flow rate and volumes of the mixing zones.