Unidirectional consolidation of clay soils and flocculated suspensions

A model of the unidirectional consolidation of a clay soil or flocculated suspension between a series of parallel drains is developed. A convective-diffusion equation for the pore pressure is derived, and an equal-strain approximation leads to an expression for the average effective stress profile between the drains. The solution depends on a Peclet number quantifying the ratio of the bulk soil flow rate to the rate of consolidation. By adjusting the number, height and spacing of the drains, very high rates of dewatering can be achieved. A potential application of the method to the rapid dewatering of mine tailings is described.

INFLUENCE OF FLOCCULANT TYPE ON STRENGTH CHARACTERISTICS OF FLOCS IN CLAY-SALT SUSPENSIONS

The results of studies on the effect of the flocculant type on the strength characteristics of floccules in clay-salt suspensions, obtained using a laser analyzer of particle size Lasentec D600L FBRM systems were presented in the article. The coefficients of strength and reduction of aggregates formed by polyacrylamide and its anionic and cationic copolymers were determined. Increasing the speed of mixing by using of polymers various types leads to the destruction of the formed aggregates in the flocculated suspension. The size of flocs induced by a cationic flocculant is reduced from 250 to 110 mm, for anionic and non-ionic flocculants - from 500 to 250 mm. The dependence of floc strength on the macromolecules adsorption mechanism on a solid surface was established. The decrease in hydrodynamic effects entails the partial restoration of floccules. It was shown that the recovery of flocs for all studied polymers was limited, which indicates a significant irreversibility of the aggregates destruction process. When using cationic flocculant, the ability to restore the aggregates is 2.5 times lower compared to anionic and non-ionic polymers. For nonionic and anionic polymers, the dependence of flocs coefficients of strength and recovery on the flocculant dosage was established. Dosage of cationic polymer does not affect these indicators. The dynamics of flocculation, destruction and reflocculation processes using various flocculants was considered. The influence of the charge type and polymer consumption on the mechanism of particles interaction was established. The potential possibility of using the obtained results to improve the technology of potassium chloride production at the stages of thickening and dehydrating clay-salt sludge was shown.

Theoretical and Experimental Analyses of Colloidal Processing of Nanoparticles

The stability of dispersed and flocculated colloidal particles under 1 atm and applied pressure was discussed thermodynamically with the activity and chemical potential defined by Henry’s law and Raoult’s law. The calculated result under 1 atm is represented by a colloidal phase diagram as functions of surface potential and solid content of particles. Application of pressure accelerates the phase transition from dispersed to flocculated suspension. The phase transition pressure, which is observed in the applied pressure-suspension height relation during pressure filtration at a constant crosshead speed of piston, is affected by (1) particle concentration, (2) particle size, (3) surface potential, (4) degree of dissociation of polyelectrolyte dispersant and (5) applied electric field (DC and AC). The influence of above factors was discussed theoretically and experimentally.

Evaluation of floc strength by morphological analysis and PDA online monitoring

This paper established a method for the evaluation of floc strength by morphological analysis and PDA online monitoring. Theoretically, the binding force of a floc can be expressed as B=k1d2Df/3, where k1 is a coefficient, d is floc size and Df is the fractal dimension of the floc. In order to calculate the binding force under a given flocculation condition, a jar test was conducted and d and Df were measured by image analysis. A shear force was exerted on the grown flocs by introducing the flocculated suspension through a transparent tube where the velocity gradient value of the flow could be accurately controlled. As the tube was connected with a particle dispersion analyzer (PDA), the condition of floc breakage was online monitored and the critical condition was identified by analyzing the PDA outputs (FI curves). The binding force coefficient k1 could thus be determined, and the binding force B which represented the floc strength was evaluated. The validity of this method was proved by a series of experiments using aluminium sulphate as coagulant for the flocculation of humic substances.