Mud Cat Custom Dredge for SQM, Chile

Sociedad Quimica Minera de Chile SA (SQM) purchased a customized auger dredge to extract potassium nitrate from the Mud Cat Division of Mud Cat International.

The dredge was used to extract potassium nitrate from solar evaporation ponds at Coya Sur, 1,200 meters above sea level in northern Chile. The dredge is actually Mud Cat’s™ smallest, the SP-810, fitted with auger wheels to allow the dredge to excavate without damaging the pond liners. Powered by a single Detroit Diesel model 4-53T diesel engine rated at 160HP at 2,100rpm, the dredge has a draft of 22 inches (560cm) and a total weight 12,200lbs (5,534kg). It excavates a 2.44 meter wide trench on each pass, and a submerged 6 inch (152mm) dredge pump propels 280m3 of potassium nitrate mixture per hour 1.5km to the processing plant.

The ponds are only one stage in a long production process. SQM uses mechanical shovels to extract caliche from its Maria Elena and Pedro de Valdivia sites. It is then trucked 30km to be milled to 3-4cm in size and prepared for vat leaching. This leaching process results in a nitrate solution which produces sodium salt crystals upon cooling. The rest of the solution is processed in the final stage of the Pedro de Valdivia plant and at the Maria Elena facility to extract iodine.

Once this process is completed, light solutions are produced which are sent to the Coya Sur evaporation plant for concentration. At the plant the solution is placed in 10 cement ponds and 4 PVC lined ponds, each which is approximately 220m x 220m x 1.4 meters deep. After potassium is added to the concentrated nitrate solution, crystals of potassium nitrate form in the pond.

This is where SQM’s problems arose, as normal dry land excavators, draglines and dredges could not work in the ponds since they would damage the concrete or PVC liners. Also, the 1,200 meter altitude, -500C temperatures, and highly corrosive brines meant that equipment would have to be capable of resisting extremely hostile environmental conditions. Therefore, the customized auger dredge from Mud Cat provided the solution. SQM’s potassium nitrate capacity amounts to 850,000 tpa, while production of iodine and sodium sulfate are 40,000 tpa and 70,000 tpa respectively.

Reprinted from Industrial Minerals