Investigating the settling behaviour of saline tailing suspensions using kaolinite, bentonite, and illite clay minerals

Abstract

This study aimed to understand the dewatering behaviour of three types of clay minerals (i.e. kaolinite, bentonite, and illite) in saline water, and in particular the effect of factors including clay mineralogy, clay suspended solid concentration, water salinity, and polymer flocculant dosage on dewatering behaviour. It was demonstrated that the addition of polymer flocculants helped all three clay types to settle due to the polymer bridging effect. In saline water, this bridging effect worked best above a certain threshold level for illite but tailed off for the other two clay types. As well, high-salinity water was observed to assist bentonite and illite to settle faster but to hinder the settling rate of kaolinite. In addition to inter-particle forces, the clay aggregate structures formed through the addition of the flocculants were identified to play an important role in determining the dewatering behaviour of clay minerals in saline water. Cryo-scanning electron microscopy (SEM) identified that, depending on the clay type, the floc structures in saline water were either dense (water-excluding) or loose (watertrapping). Dense flocs were observed to settle more quickly than loose flocs. This study has practical applications in providing guidance for the processing of complex tailings containing clay minerals in saline water. Highlights Several factors affect the dewatering behaviour of clay minerals in saline water.  High-salinity water assists bentonite and illite to settle but hinders kaolinite.  Polymer works best above a threshold dose for illite but tails off for other clays.  Clay aggregate structures can either be dense or loose and vary by clay type.  Both inter-particle forces and aggregate structures influence the dewatering rate.

Copper Tailing Flocculation in Seawater: Relating the Yield Stress with Fractal Aggregates at Varied Mixing Conditions

“…Ultimately, the thickened tailings are transported through pipes to a disposal area for subsequent dehydration and consolidation [4].Tailings produced in the copper mining operations generally have clays contents like kaolinite, where their colloidal size and amorphous structure cause varied challenges in thickening. Usually, the settling rate of the flocculated slurries drop [5][6][7], and the rheological parameters can rise to acquire non-Newtonian behaviours [8,9]. Several studies have examined the adsorption of polyacrylamides on the surface of kaolinite, standing out as the main flocculants and most common clay that appear in the copper industry.…”

Influence of polymer structure on the gelation kinetics and gel strength of acrylamide‐based copolymers, bentonite and polyethylenimine systems for conformance control of oil reservoirs

“…On the other hand, under alkaline pH values, polymer chains with anionically charged functional groups, such as carboxylates (COO − ) and sulfonates (SO 3 − ), strongly repel negatively charged clay particles, leading to weaker adsorption of polymer onto clay surface through hydrogen bonds . Moreover, the introduction of AMPS moieties into the polymer backbone promotes stronger steric hindrance than that of acrylate moieties, further reducing the hydrogen bonding of nonionic groups to the clay particles, and thereby improving the clay dispersion within the hydrogel network …”

“…These positive cations of the brine effectively outweigh the electrical repulsions between the anionic segments of the polymer chains and/or the negatively charged surfaces of the clay (screening effect), promoting the adsorption of the polymer onto the clay particles, which may induce clay mineral aggregation, thus affecting the homogeneity of the clay dispersion within the hydrogel network …”

“…60 Moreover, the introduction of AMPS moieties into the polymer backbone promotes stronger steric hindrance than that of acrylate moieties, further reducing the hydrogen bonding of nonionic groups to the clay particles, and thereby improving the clay dispersion within the hydrogel network. 25,41,43,44,55,61,62 Besides the polymer structure and the pH value, the clay-polymer interaction is also influenced by the molecular weight and the charge density of the polymer, as well as by the salinity/hardness of the water.…”

“…These positive cations of the brine effectively outweigh the electrical repulsions between the anionic segments of the polymer chains and/or the negatively charged surfaces of the clay (screening effect), promoting the adsorption of the polymer onto the clay particles, which may induce clay mineral aggregation, thus affecting the homogeneity of the clay dispersion within the hydrogel network. 62 This phenomenon of salt-assisted clay aggregation was observed for nonionic PAM with low molecular weight (e.g., PAM 0 LM), anionic acrylate-acrylamide copolymers with low-high charge densities (e.g., PHPA 5 LM, PHPA 10 LM, and PHPA 30 HM), and AMPS-NVP-acrylamide copolymers with sulfonation degree lower than 10% (e.g., PAM-AMPS-NVP 1 LM and PAM-AMPS-NVP 7 LM). These samples formed homogeneous composite hydrogels in distilled water, and heterogeneous composite hydrogels in oilfield brines.…”