Applied clay Science
Jiang Tao;Wu Yongkang;Liu Chunlong;Whittle Andrew J.;Guo Dongdong;Zhang Guoping
An experimental investigation is presented of the kinetics of particle size distributions (PSDs) of flocculated illite suspensions subject to varying ionic strength, pH, and hydrodynamic shearing. A total of 21 PSD measurements were conducted by analyzing the high-resolution optical images of particle flocs extracted from illite suspensions with a concentration of 0.4 g/L prepared at four ionic strengths (i.e., 0, 0.09, 0.17, 0.60 M NaCl solution), three pHs (i.e., 8.61, 4.51, 2.25), and three vibrational shaking speeds (i.e., 150, 225, 300 oscillation/min) at four shaking durations (i.e., 10, 30, 60, 1440 min). Experimental PSD histograms were constructed using a new bin size index (BSI) data binning method involving the conversion of original multimodal lognormal distributions into regular Gaussian distributions, followed by the probability density function (PDF)-based deconvolution to extract the number, mean, standard deviation, and fraction of different characteristic particle size groups: primary particles, flocculi, microflocs, and macroflocs. Results show that flocculation is enhanced by the high ionic strength and low pH, and more microflocs and macroflocs form at higher ionic strengths (i.e., 0.60 M) and more acidic pHs (i.e., 2.25, 4.51). Moreover, higher hydrodynamic shearing causes more breakdown of weaker flocs, but promotes stronger and smaller ones. The new BSI data binning method can better reveal the smaller-sized particle groups due to the logarithmic conversion. The PSD kinetics of illite suspensions is chiefly controlled by the face-to-face and edge-to-face interparticle interactions, caused by the suppression of the electrical double layer and generation of positive edge charges, respectively. Finally, the implications and significance of PSD kinetics of clay suspensions for engineering practices and environmental processes are discussed.
