The above nine tests were conducted at 36% solids for the grinding circuit product• However, as seen in the first optimisation step, the percentage of solids modifies the plant performance. It was then decided to change the % solids and to simulate, for the new operating conditions, the same tests as above. The results are presented in Figure 12. Clearly at constant % solids and feed rate F, the efficiency El is directly a function of the particle fineness, expressed here as the % 74 bun. The efficiency is monotonously increasing with the % -74 ~tm, without exhibiting a maximum value. This is due to the fact that the average flotation rate continuously increases up to 10 gm and is still high for the 10btm particles. Undoubtedly, the rate of flotation decreases for fine particles, and extended PSD in the fine size range would have shown a decrease of the flotation efficiency. The effect of the % solids is caused here neither by the behaviour of the hydrocyclone, since the classifier efficiency is not related to the dilution, nor by the behaviour of the mill, since the slurry rheology is not taken into account in the breakage model. Its effect is related to the change of the MRTs in the grinding mill and the flotation circuit. As a matter of fact, the latter explains almost all the observed phenomenon.