The core of the slag environmental protection treatment system is to separate the shield slag into coarse aggregate, medium and fine sand, dried mud cake and water according to the difference in particle size between the components. However, the mud and water in the original shield slag stick the sand and gravel into clumps, so it is difficult to separate them, so it is necessary to convert the slag into a fluid state by adding water before carrying out the separation, and the fluid system principle of the slag environmental protection treatment system is shown in Figure 2.
First of all, in the vibration sieving module, through the combination of high-pressure water spray and vibration, on the one hand, can shake loose, flush the clumped soil, on the other hand, the soil dilution. After the vibrating screen, the sludge can be divided into sand and gravel with a particle size of not less than 2mm, and a fluid mixture of sand and gravel and slurry with a particle size of less than 2mm. Then the sand and gravel with particle size less than 2mm are separated from the fluid mixture by the sand washing machine and cyclone. After the fluid mixture enters the sand washer, it tumbles under the impeller, and the sand and gravel grind each other to remove the impurities covering the surface of the sand and gravel, while adding the sand washer spray water to take away the sludge.
The clean sand and gravel is taken away by the blade and poured into the next level of sand washer for the second cleaning, and finally poured into the dewatering screen for dewatering, and the mud enters the cyclone supply tank from the overflow port. The mud in the cyclone liquid supply tank still contains a small amount of sand and gravel, so the mud is sent into the cyclone through the slurry pump for further separation, and the cyclone separates the fine sand from the mud according to the principle that the solid and liquid phases are subject to different centrifugal forces. The discharged mud enters the flocculation tank, and under the action of PAM (polyacrylamide) agent, the mud in the mud flocculates into a mass and settles in the tank [13], which is finally separated into mud cake and water by the filter press [14,15].
The water overflowing from the flocculation tank and the water pressed out by the filter press both enter the three-stage sedimentation tank for sedimentation, and the clear water is supplied by pumps to each module as vibration spray, sand washing spray, shaft seal water, cooling water, etc., which are recycled in the system.
