Describing Mining Tailing Flocculation in Seawater by Population Balance Models: Effect of Mixing Intensity

Abstract

A population balance model (PBM) is used to describe flocculation of particle tailings in seawater at pH 8 for a range of mixing intensities. The size of the aggregates is represented by the mean chord length, determined by the focused beam reflectance measurement (FBRM) technique. The PBM follows the dynamics of aggregation and breakage processes underlying flocculation and provides a good approximation to the temporal evolution of aggregate size. The structure of the aggregates during flocculation is described by a constant or time-dependent fractal dimension. The results revealed that the compensations between the aggregation and breakage rates lead to a correct representation of the flocculation kinetics of the tailings of particles in seawater and, in addition, that the representation of the flocculation kinetics in optimal conditions is equally good with a constant or variable fractal dimension. The aggregation and breakage functions and their corresponding parameters are sensitive to the choice of the fractal dimension of the aggregates, whether constant or time dependent, however, under optimal conditions, a constant fractal dimension is sufficient. The model is robust and predictive with a few parameters and can be used to find the optimal flocculation conditions at different mixing intensities, and the optimal flocculation time can be used for a cost-effective evaluation of the quality of the flocculant used.Metals 2020, 10, 240 2 of 15 the operational priorities is to close the water cycle, a process that can be successful with proper management of the thickening stages. Generally, the concentration stages are carried out at alkaline pH, which means that both particles and flocculant molecules (such as hydrolyzed polyacrylamide) carry anionic charges. Although reagents may have a low affinity with the particles, it is sufficient to form porous aggregates with low density, which facilitate the transport of the thick pulp from the bottom of the thickener to the tailing dams. The fact that industrial water has some ionic charge can be beneficial. There is evidence in the literature that the presence of ions in the liquor is necessary for adequate flocculation, because ions allow the adsorption of polymeric molecules on the charged surfaces [1][2][3]. There is also evidence that flocculants may exhibit different behaviors when interacting in saline media. For example, studies have indicated that flocculated kaolinite shows decreasing sedimentation rates in environments with high salinity [4,5], while other studies show the opposite [6]. We recently demonstrated that the increase in salinity promotes the adsorption of polyelectrolytes on mineral surfaces but decreases the size of the polymer in solution, resulting in a competitive effect that can benefit or impair particle agglomeration. Thus, varied behaviors are expected [7,8].There is great interest in studying flocculation from a microscopic level because the mechanisms involved during the aggregation of colloidal particles determine the efficiency of t...

Lime/Sodium Carbonate Treated Seawater to Improve Flocculation and Sedimentation of Clay-Based Tailings

“…Regarding the dose of the flocculant, Figure 10 c shows that the higher the dose, the greater the fractal dimension, although the increase is slight, from 2.2 to 8 g/t to 2.4 to 21 g/t. This result is consistent with the results of a previous study by Jeldres et al [ 36 ]. In contrast, the density of the aggregates remained relatively constant at 1450 g/cm3 in the dose range used.…”

“…For example, the fractal dimension starts with a value of 2.36 at 20 s of flocculation and ends at 2.21 after 80 s of flocculation. The density begins at a value of at 1480 g/cm 3 at 20 s and ends at 1410 g/cm 3 at 80 s. These results are in agreement with those of Quezada et al [ 36 ], who observed that aggregates from mine tailings flocculated with anionic polyacrylamides maintain their structure when the shear rate is less than 200 s −1 . The effect of the magnesium content is different when seawater is treated with varying proportions of lime and sodium carbonate.…”

Clay Tailings Flocculated in Seawater and Industrial Water: Analysis of Aggregates, Sedimentation, and Supernatant Quality

“…Studies have confirmed that the use of FBRM technology is a valuable tool for understanding flocculation phenomena in mine tailings [36][37][38][39][40][41]. This phenomenon allows determining: (i) the optimal dose of flocculant, (ii) the size distribution of the flocculated aggregates over time, (iii) population balance studies, (iv) estimation of the resistance of aggregates in shear conditions, and (v) research on floc restructuring.…”

Modelling of Red-Mud Particle-Solid Distribution in the Feeder Cup of a Thickener Using the Combined CFD-DPM Approach

“…The population balance equation (PBE) is the method most widely used to model particle aggregation, coagulation, and flocculation. Both foreign and Russian researchers use PBE to model particle coagulation in order to further optimize flocculation [18][19][20].…”