Designing and testing the representative samplers for sampling a milling circuit at Nkana copper/cobalt concentrator

The primary objective in any ore processing method, is to prepare the ore for economical and effective extraction the valuable minerals. Milling circuits are extremely energy intensive, making them very expensive operations and it is very pertinent to optimise their operation to be economically viable. Therefore, their design is very critical and this can only be achieve by adopting new control strategies to improve energy utilisation. Nkana Mine concentrator of the Zambia Consolidated Copper Mines Limited (ZCCM) has been experiencing problems in establishing the optimum mesh of grind for the various ores, to achieve effective separation of the cobalt minerals from those of copper. This prompted the designing and testing of representative samplers for sampling the milling circuit at Nkana Concentrator. In the design of the samplers, use was made of the Gy’s formula to determine the minimum weight of the sample to be extracted from various process streams. The particle size distribution of the streams was conducted to determine the size of the largest particle in each stream. Samplers were designed on the basis of theoretical and practical applications and a factor of three was built in the normal sampler width opening. This enabled that the entire stream had equal chance of entering the sampler.The milling circuit on which a sampling campaign was conducted consisted of a 2.7m by 3.6m (9ft, 12ft) Rod Mill in open circuit with a 760mm (30inch) hydrocyclone which was in closed circuit with a Ball Mill of the same dimension as the Rod Mill. Samples were taken from the feed to the Rod Mill, Rod Mill discharge, Cyclone underflow( feed to the Ball Mill), Ball Mill discharge and the cyclone overflow using appropriate sampling techniques for a complete shift at equally spaced intervals. Sampling was only started when it was established that steady state operation of the plant was attained. Important operating parameters were established which included the throughput of the material to the Rod Mill, the pulp densities of the streams in the milling circuit, the particle size distribution of the streams, volumetric flow rates of the streams and the rate at which dilution water was added. These parameters were then used to carry out Mass balancing using a mineral processing simulation software called JKSimMet which has been developed by the Julius Kruttschnitt Mineral Research Centre at the University of Queensland in Australia. The simulator can be used to predict the possible alternatives to optimising the circuit performance and physical modifications which can be made to the plant with confidence. The correlation between the measured and the calculated parameters was found to be fairly satisfactorily. This showed that the designed samplers and the sampling techniques used were suitable for obtaining representative samples from the milling circuit. This paper describes the method used in designing the samplers, the sampling techniques used and the results obtained from the JKSimMet software.