Study On Fractal Characteristics Of Flocs And Coagulation Mechanism Under Slime Water With High Concentration

Slime water is a typical water with high concentration, which is produced in theindustrial process of washing coal. It has some characteristics, such as large flow,suspended fine particles with high concentrations, and it’s hard to sedimentatenaturally. In actual treatment of slime water, coagulation process is used to achieveclosed-circuit circulation utilization of slime water. But because of the complexstructure of flocs which are formed in process of coagulation and the insufficientknowledge in coagulation mechanism of high concentration slime water, leading tolarge coagulant dosage, poor water quality, slow settling velocity of flocs, difficultfilter pressing and so on, in the treatment process of coal slime water. While, with thequantity of washing coal increasing in actual production process, in order to processslime water on the basis of primary craft, there should be achieved the goal of rapidclarification and efficient concentration. Therefore, it needs to study the structure offlocs deeply in the process of coagulation, and to understand the coagu-flocculationmechanism of high concentration slime water further.60g/L coal slime water is regarded as raw water, and polyacrylamide (PAM) isused as coagulant in the paper, determining the optimal control conditions in thecoagulation process of high concentration slime water by changing single factor intest and orthogonal test at first; Second, morphological structure of flocs, whichformed in coagulation process of high concentration slime water under differenthydraulic conditions, are descripted quantificationally with the help of fractaldimension, and coagu-flocculation mechanism of different types of coagulantcombination is explored. Coagulation sedimentation physical model of highconcentration slime water is proposed on the basis of fractal theory and generalcoagulation sedimentation physical model. Finally, the theoretical equation of flocsedimentation characteristics is deduced and experimental data is fitted, lookingforward to guiding practical control process of coagulation. The specific conclusionsare as followed:(1) The best dosage of PAM is1.8mg/L and primary and secondary order offour factors which affect the process of coagulation is: the velocity gradient of mixedphase (G1)> time of coagu-flocculation stage (T2)> the velocity gradient ofcoagu-flocculation stage (G2)> time of mixed phase (T1), and the optimum hydrauliccondition combination is:382(s-1)+50(s)+57(s-1)+180(s) are determined in60 g/L of high concentration Slime Water.(2) Structures of flocs which formed in process of coagulation under different values of G1, T1, G2, T2are different. When the best hydraulic conditions, The flocs obtained during process of coagulation sedimentation are the biggest and most compact, and the largest fractal dimension value is up to1.8847. And the optimum energy consumption value needed in mixing phase is:G1T1=19100and the best energy consumption value needed in coagu-flocculation stage is:G2T2=10260are obtained.(3) Coagu-flocculation mechanism of different types of coagulant are different. The main coagulation mechanism of inorganic coagulant (PAC) with macromolecule in high concentration slime water is compressure double electric layer and electrical neutralization; When using PAM, the main coagulation mechanism is adsorption bridging; Without considering the net capture and sweep coagulation mechanism, it can be concluded that when using PAC and PAM together, the main coagu-flocculation mechanism is shown that compressure double electric layer and electrical neutralization work firstly, and then adsorption bridging and filling and package coagulation mechanism.(4) The suitable physical model of coagulation in high concentration slime water is put forward based on results of coagulation sedimentation test and coagulation mechanism exploration, while combining physical model of general coagulation process with physical model of evaluation coagulation process by fractal dimension.(5) The suitable equation of mathematical relationship between fractal dimension of floes and settling rate of floes is obtained as followed:U(mm/s)=1.1×42/3df; While the experimental datas are matched and the theoretical equation is amended, and the mathematical model of relationship between fractal dimension of flocs and settling rate of flocs which accords with actual coagulation process better can be concluded as U(mm/s)=1.14×42/3df.