Abstract:To investigate the influence of hydraulic shear conditions on the floc size evolution during the two-step flocculation process，this study employed focused beam reflectance measurement （FBRM） to monitor， in real time，the dynamic changes in floc size of kaolinite particles. A systematic evaluation was conducted on the regulatory effects of primary shear rate and duration （G₁，T₁），as well as secondary shear rate and duration （G₂， T₂），on floc formation，breakage and restructuring. The results showed that the primary shear stage was critical for floc nucleation and the formation of primary structures. Moderate shear intensity （G₁=400 r/min） and duration （T₁=90 s） promoted the generation of large，structurally stable flocs，whereas excessive shear strength or prolonged duration led to premature breakage，exhibiting a distinct “growth-breakage” threshold behavior. The secondary shear stage predominantly governed the reorganization and stabilization of higher-order floc structures. Appropriate shear conditions （G₂=200 r/min，T₂=180 s） effectively enhanced reflocculation and improved floc integrity，while excessive shear intensity or prolonged exposure caused edge peeling or framework disintegration，resulting in size reduction and a nonlinear “reflocculation-deconstruction” evolution pattern. This study delineates the functional boundaries and synergistic interplay of shear rate and duration at different stages，providing a theoretical foundation and technical support for efficient flocculation control and structural regulation under complex conditions such as tailings water treatment.