Closed Circuit Simulation of SAG Mill and Hydrocyclone Units at Aghdarreh Gold Plant

The run-of-mine ore of Aghdarreh gold mine is comminuted through crushing and grinding stages to achieve the required degree of liberation of gold particles. The comminution circuit consists of a SAG mill equipped with a discharge trommel and a hydrocyclone package which is operated in closed circuit with the SAG mill. The hydrocyclone package, is used to classify the particles ground by the SAG mill. The overflow of hydrocyclone package is fed to the gold recovery circuit at downstream. Gold extraction is carried out by leaching process and cyanidation within the stirred tanks.
In this research, optimization study of the grinding circuit of Aghdarreh gold processing plant was done by modeling and simulation using MODSIM software to reduce P₈₀ of the closed SAG circuit to less than 70 microns in order to increase the degree of liberation of gold particles at the same current circuit capacity. Plant sampling campaigns were scheduled to determine the required parameters of SAG mill model, i.e., breakage distribution function, selection function, calibrating Plitt's model and validation of models. Breakage distribution function was defined by the MODSIM software based on t₁₀ vs. E_CS model parameters (A and b) and abrasion parameter (t_a) provided by the user. Selection function was also defined by the simulation software based on the given Austin model parameters (a, α, μ and Λ). Two plant surveys were done to collect the samples from various grinding circuit streams. In both sampling surveys, incremental sampling from all circuit streams including trommel undersize and oversize (ore scats), hydrocyclone feed, underflow and overflow were done at steady state for a time period of two hours. The SAG mill fresh feed was also sampled by temporarily stopping the conveyor belt and collecting enough ore material from a cut with two meters length. Operating conditions during the sampling were recorded based on the control room readings. The final sample for each stream was prepared by combining the incremental samples taken every ten minutes.
Particles size distribution and solid percent of all samples, except SAG mill feed, were determined in the laboratory and then balanced by NorBal data reconciliation software. The balanced particle size distributions and flow rates were used in the MODSIM software for models’ calibration and subsequent simulations. After validating the calibrated Plitt's model based on the second sampling survey, circuit simulations were done for internal overflow and underflow diameters equal to 82 and 70 mm, respectively, six hydrocyclones in operation, increasing the charge volume from 21 to 35 % and increasing the ball charge volume from 10 to 12 %. Based on the mentioned input data, the prediction showed that P₈₀ of the circuit product can be reduced to approximately 51 microns.
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