The settling-washing system is one of the important systems in an Alumina production plant. The function of the settling-washing system is that, with the assistance of a settling aid, the aluminate solution (NaAl(OH)₄) is separated from the slurry after digestion to proceed to fine filtration before crystallizing the Al(OH)₃ product. After separating the aluminate solution, red mud will be counter-currently washed to recover caustic soda (NaOH) and alumina (Al₂O₃) before discharging the red mud to the tailings pond.

To optimize and stabilize the technology during operation, save settling aid, and recover more caustic soda and alumina, monitoring and controlling the stability of the material layers in the settling and washing equipment is very important.

Currently, controlling the height of the slurry layers in the settling and washing equipment of the Lam Dong and Nhan Co Alumina plants is entirely done manually, so the accuracy is not high and not continuous, making it very difficult to adjust the technology in time to ensure the technological objectives of the aforementioned area. In addition, all equipment for pumping settling aid, pumping underflow slurry of the settling and washing equipment are manually controlled, so stability is low, consuming settling aid and making it difficult to adjust in time when the process parameters in the system change.

To address the technological requirements for the red mud settling-washing area, the National Research Institute of Mechanical Engineering researched the application of equipment for measuring the height of slurry layers in settling-washing equipment using advanced technology, integrated a control system, and has installed and tested for the Lam Dong Alumina plant 02 monitoring and control systems for mud layers in the settling-washing equipment, serving the operation and production process.

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