The Southwest is home to several large producers of copper cathode from leaching and subsequent electro-plating, a process known as solution extraction and electro winning (SX/EW). The first step – leaching, begins by sprinkling a low concentration of sulphuric acid and water solution on a stockpile of ore. The liquid percolates through the stockpile, dissolving copper minerals and producing a copper-laden liquid called 'pregnant leach solution' (PLS). The PLS flows to a collection reservoir, and then to a solvent extraction plant where it is mixed with a diluent designed to extract the copper. The leach solution minus its copper, called 'raffinate,' is replenished and returned to the leach pile for reuse, completing the solution stream cycle.
One of this client's raffinate booster pump stations needed to deliver 50,000 gpm of raffinate to the next 20 lifts of the stockpile, with a total increase in elevation of 600 feet. The pumps operate 24 hours per day year-round and must cover 20 design points (each 30-foot lift). HDR designed a total of three large raffinate pump stations for this client. Prior to commencing with the design, the client requested a maintenance-friendly pump station layout that included:
Flexible operating conditions to meet increasing stockpile elevations.
Ability to handle harsh operating conditions.
Designing a layout that could serve as a template for future pump stations.
The result was a pump station layout that minimized buried piping; allowed motors to be removed without disconnecting cables; provided access to valves and instruments without climbing over pipes or stairs; and allowed maintenance vehicles close access to all pumps and electrical gear. The use of vertical turbine pumps provided the ability to change impeller sizes and add stages as the discharge pressure increased to meet higher stockpile elevations. HDR performed detailed hydraulic modeling for each stockpile lift to ensure all hydraulic conditions could be met, and identified operating scenarios with the lowest energy consumption and the least number of shut-downs required to add stages and change impeller sizes. Through close coordination with the client while designing the first pump station, HDR saved time and budget on two additional raffinate pump stations. HDR also prepared technical specifications and procurement specifications for the major equipment.
Raffinate Booster Pump Station case study