Yara has operated the Siilinjärvi mine in Finland since 1979. Each year, the mine produces around 1 M t of apatite concentrate from 11 M t ore, and it is Western Europe’s only phosphate mine. The concentrate is processed into phosphoric acid in Siilinjärvi and then further into fertilisers and feed phosphates in Yara’s plants in Finland and Norway. The tailings have to be deposited at the Siilinjärvi plant, and the existing tailings storage facility (TSF) was reaching full capacity. Yara did an extensive study for future storage of tailings and decided to adopt a thickened tailings solution. The tailings would be thickened to 68–72% by weight in order to build a +2° sloped deposit, thereby sufficiently increasing the storage capacity.
Weir Minerals supported Yara from the pilot plant operation, continuing in the sizing of the full plant pumping system until execution and commissioning of the paste pumping plant. After evaluation of the pilot plant results, it was concluded that additional loop testing was required in order to determine the pressure gradients for the full plant pumping system. During project execution, Weir Minerals supplied a complete pumping solution to Yara, comprising of three GEHO® TZPM 2000 pumps and Warman® AH® 10/8F centrifugal pumps. In addition, Weir Minerals supplied the required Isogate® hydraulic-actuated slurry valves, suction strainers, slurry instrumentation and developed the functional description for Yara’s distributed control system (DCS). The system is operated remotely from the plant DCS without any programmable local control (PLC) devices to enable future unmanned, automated operation of the complete pump station. Local control can be established through tablets which are connected to the DCS, providing diagnostic performance reviews of the pump and plant operation. The system was successfully commissioned in February 2017, with slurry solids concentrations reaching planned targets, resulting in a slope at the TSF of approximately 3°. This paper describes the development of the project from the feasibility to the commissioning stage, highlights the main challenges and reflects Yara’s future expectations for plant development and operations at the Siilinjärvi mine.
Keywords: thickened tailings disposal, piston diaphragm pumps
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