Abstract: The medium preparation and addition processes are currently carried out in a manual mode in coal preparation plants. The troubles with the manual operation include uneven height of medium pile in medium tank, inaccurate control of liquid level in correct medium tank, deposition of medium solids caused by delay in operation, high labor intensity and harsh working environment. To deal with this situation, an intelligent unattended medium adding system based on 3D laser-scanning technologies is developed. Besides, a similar system of the closed-circuit type is specifically developed for a plant which uses two-stage two-product heavy medium cyclone as primary washing equipment, and has difficulties in making civil work and erecting steel structures because of space limitations. The former system consists of the medium preparation and thick medium adding and control subsystems, which can perform automatic medium preparation and accurate adding function through 3D LiDAR recognition, automatic control of flushing of water and intelligent addition of medium. The intelligent closed-circuit system mentioned above can carry out recognition of liquid level in thick medium tank, automatic replenishment of medium and accurate addition of thick medium. Through the system, high-density medium suspension can be automatically led into thick medium tank to cater to the needs of the primary washing process for addition of medium. Application of the 3D LiDAR system at Bulianta Plant has led to a cut of medium consumption by 0.51 kg/t on average, a save of 7 140 tons of medium a year, and realization of automatic preparation and addition of medium. With the use of the intelligent closed-circuit system at Shaqu Plant, the medium is added at the time when deviation of medium density is greater than or equal to 0.02 g/cm³, with a duration of only 150 s. Other attractions include less requirements for civil work and erection of steel structures, reduced maintenance work, and rapid increase of medium suspension density to required level. Field application of the two systems has made it possible to improve coal washing efficiency and quality of product, reduce energy consumption and operating costs. The development of the two intelligent medium adding system provides a technical support for intelligent transformation of coal preparation plants.