Grinding circuit modeling and simulation of particle size control at Siilinjärvi concentrator

Concentrator throughput can depend highly on the operation of a grinding circuit. The mill feed rate adjustments and resulting slurry particle size distribution has a great impact on performance of the following separation stage. At the Yara Siilinjärvi phosphate concentrator the aim is to avoid over coarse apatite grain size, since it declines flotation recovery, while the fresh ore feed rate should be maximized. Here, most of the recovery disturbances originate from frequent ore type changeovers. At Siilinjärvi, outlet slurry of the grinding circuit is measured with a high precision on-line laser diffraction based slurry particle size analyzer. In this study, process experiments for modeling of the grinding circuit were carried out. Then multivariable-PI, fuzzy, and model predictive controls were evaluated with the simulated process. The assessment indicated increase of around 1.8% in the ore feed rate, while variation in the particle size distribution was reduced, as a result of the formulated fuzzy-MPC control scheme.