Experimental Study Of Slime Water Sedimentation Assisted In External Electric Field

Coal washing and processing is the source of clean coal technology, about3m3slime water will be produced after washing1ton raw coal, so the slime water treatment is very important to coal washing and environmental protection. Because with the increase of coal mining mechanization, coal gangue content increases. Chemical coagulation is most common technology of industrial coal slurry water treatment, not every time the effect is ideal. So the new technology of slime water sedimentation assisted in external electric field is used to deal with difficult settling slime water, the principle of which is that the charged coal slime including clay mineral can get faster sedimentation under the influence of electric field force. The following are the specific experimental studies based on the technology.By use of X-ray diffraction, laser particle size analyzer and zetaprobe, the size composition, mineral composition and electrokinetic potential features of coal slime are measured and analysed from A thermal coal preparation plant and A coking coal preparation plant. It is found that coal slime in both plants contain a lot of kaolinite and quartz, also a small amount of montmorillonite, chlorite and calcite mineral.The coal slime in both plant is mainly focused on the size fraction of-0.045mm, wich is70%～80%of total amount. For the size fraction of-0.045mm the average particle size is4.15um and3.029um, ash content was71.57%and65%, respectively for A thermal coal and A coking coal, both of the coal ash content of-0.045mm is very high. Zeta potential of the coal slime water is26.2mv and32.3mv respectively for A thermal coal and A coking coal, both of the Zeta potential are relatively modest. The total ash content of coal slime are38.12and57.70, the concentrations of slime water are17g/L and35g/L, respectively for A thermal coal and A coking coal, both of the total ash content are very high.By changing the applied electric field conditions (charging voltage, charging time, distance between two electrodes, settling cup cross-sectional area).Change the slime water features (pH, concentration, particle size of slime water). Change the dosing dose (flocculating agent, agglomeration agent, coagulation agent). some conclusions have been gotten from the experimental researchs about external electric field assisting slime water sedimentation. It is found that with the increase of charging voltage and charging time or the decrease of distance between the two electrode plates and the area of settling cup cross-sectional, the initial sedimentation velocity of slime water from both coal preparation plants get smaller, supernatant transmittance get bigger. For the A thermal coal’s slime water when the charging time is10min, the initial sedimentation velocity is0.81m/h, supernatant transmittance is61.2%which is minimal. when the charging voltage is1.4kv, the initial settlement velocity is0.70m/h, but the supernatant transmittance is40.1%. For the slime water of both coal preparation plants, with the increase of pH of slime water, the initial sedimentation velocity increase, the supernatant transmittance decreases. with the increase of slime water concentration, the initial sedimentation velocity and supernatant transmittance both decreased, and there is not obvious regularity for different particle sizes. Under the combination of external electric field and flocculating agent, or agglomeration agent, or coagulation agent there are all better effect of slime water sedimentation effect than under external electric field, except that the initial sedimentation under the combination of external electric field and coagulation agent is smaller than under the only external electric field. Above test data and regularity can give a certain reference value for the application of new slime water treatment, which helps to solve the problem of the clarification of difficult sedimentation slime water.