Structural investigation of tailings flocculation and consolidation via quantitative 3D dual fluorescence/reflectance confocal microscopy

Study on strength characteristics and thickening characteristics of classified-fine cemented backfill in gold mine

For some new mines, the utilization rate of tailings is not satisfactory when using unclassified tailings as backfill aggregate for cemented backfill. At the same time, with the progress of mineral processing technology, the tailings discharged by the concentrator gradually become finer. Therefore, cemented filling with fine-grained tailings as aggregate will become the development direction of filling technology in the future. In this paper, the feasibility of fine particle tailings backfill is studied by taking the particle tailings of-200 mesh as aggregate in Shaling gold mine. The calculation shows that the utilization rate of tailings is increased from 45.1% to 90.3% by using-200 mesh tailings as filling aggregate. The response surface central composite design method (RSM-CCD) was used to study the strength of backfill with alkali-activated cementitious material as binder by taking the mass concentration of backfill slurry and sand-binder ratio as input factors. The results show that the 28-day strength of the backfill with graded fine-grained tailings as filling aggregate can reach 5.41 MPa when the sand-binder ratio is 4, which can fully meet the needs of the mine for the strength of the backfill. The thickening test of-200 mesh fine particle tailings was carried out by static limit concentration test and dynamic thickening test. In the case of adding 35 g/t BASF 6920 non-ionic flocculant, the concentration of 64.74% tail mortar can reach 67.71% after 2 h of static thickening, and the concentration can reach 69.62% after 2 h of static thickening. The feeding speed of thickener should be controlled between 0.4 and 0.59 t/(m² h). In this case, the underflow concentration of thickener is relatively high, which is 64.92-65.78%, and the solid content of overflow water is less than 164 ppm. The conventional full tailings thickening process was improved by using the design of high-efficiency deep cone thickener and vertical sand silo. The feasibility of fine-grained tailings as filling aggregate was demonstrated by combining the filling ratio test of fine-grained tailings, the data of thickening test and the improved thickening process. The research results can provide reference for other mines to use fine-grained tailings as filling aggregate to design filling system.

Enhanced rheological and tribological properties of nanoenhanced greases by tuning interparticle contacts

HYPOTHESIS

Despite the wide spectrum of available nanoparticles, their utilization in lubricant and grease formulations remains challenging. To enhance their performance, an improved link between the interparticle contacts, brittleness of the resulting particle network, time-dependent rheology and tribology is required.

EXPERIMENTS

We systematically changed interparticle contacts and examined their effect on the colloidal stability, microstructure, rheological and tribological behavior of model greases by investigating four types of nanoclays: montmorillonite (Cloisite Na⁺), oleic-acid functionalized Cloisite Na⁺ (OA-Cloisite Na⁺), organomodified montmorillonite (C20A) and oleic-acid functionalized C20A (C20A-OA).

FINDINGS

We observed a range of behaviors, starting from the lack of colloidal stability in greases derived with Cloisite Na⁺ and OA-Cloisite Na⁺ to semi-solid type systems with C20A and C20A-OA. Consistent with previous studies, the rheological and tribological properties of C20A systems scale with nanoclay loadings. Surprisingly, the functionalized C20A-OA system exhibited a delayed transition towards hydrodynamic lubrication, and enhanced lubrication properties, both of which were largely independent of nanoclay loadings. Coupled microstructural investigation and time-dependent rheology reveal that this behavior is governed by increasing repulsive forces, decreasing inter-particle friction between C20A-OA nanoparticles, and faster reorganization of the C20A-OA nanoparticle network under shear. Increased interparticle repulsion enables C20A-OA nanoclays to pass each other under shear and align in direction of shear, which reduces the overall viscosity, while the presence of OA on nanoclays decreases inter-particle friction and particle-steel surface friction.

Effects of Polymer Molecular Weight on Structure and Dynamics of Colloid-Polymer Bridging Systems

We investigate the effects of polymer molecular weight on the structure and dynamics of a model colloid-polymer bridging system using confocal microscopy. Polymer-induced bridging interactions between trifluoroethyl methacrylate-co-tert-butyl methacrylate (TtMA) copolymer particles and poly(acrylic acid) (PAA) polymers of molecular weight M_w of 130, 450, 3000, or 4000 kDa and normalized concentrations c/c* ranging from 0.05 to 2 are driven by hydrogen bonding of PAA to one of the particle stabilizers. At a constant particle volume fraction ϕ = 0.05, the particles form clusters or networks of maximal size at an intermediate polymer concentration and become more dispersed upon further addition of polymer. Increasing the polymer M_w at a fixed normalized concentration c/c* increases the cluster size: suspensions with 130 kDa polymer contain small clusters that remain diffusive, and those with 4000 kDa polymer form larger, dynamically arrested clusters. Biphasic suspensions with distinct populations of disperse and arrested particles form at low c/c*, where there is insufficient polymer to bridge all particles, or high c/c*, where some particles are sterically stabilized by the added polymer. Thus, the microstructure and dynamics in these mixtures can be tuned through the size and concentration of the bridging polymer.

Flocculation Efficiency and Spatial Distribution of Water in Oil Sands Tailings Flocculated with a Partially Hydrophobic Graft Copolymer

This work investigates the effect of partially hydrophobic grafted polymers on flocculation and dewatering of oil sands mature fine tailings. Here, we combine confocal microscopy and rheology to investigate how the graft density of ethylene-propylene-diene grafted with hydrolyzed poly(methyl acrylate) (EPDM-g-HPMA) affects its dispersion in water and flocculation efficiency in terms of sediment solids content and long-term dewatering of oil sands tailings. Increasing the graft density from 30 to 50% makes the flocculant easier to disperse, increases the rate of initial dewatering, and also enhances the viscoelastic response of the flocculated sediments. Conversely, the long-term rheological properties of the flocculated sediments were similar for all flocculants. Tri-dimensional microscopic details of the spatial distribution of water within the flocculated sludge provide novel insights into the performance of the flocculants. Increasing the graft density in EPDM-g-HPMA traps more water within the individual flocs and, consequently, decreases the post-flocculation dewatering rate. Our systematic approach confirms the importance of the spatial distribution of water in the flocculated sediment, which depends on how the flocculant is dispersed and how it retains water in the flocs.

Electrical impedance spectroscopy as a potential tool to investigate the structure and size of aggregates during water and wastewater treatment

Microscopic structure and size are important metrics for estimating aggregates environmental behaviors during water and wastewater treatment. However, in-situ determination of these characteristics is still a challenge. Here, we drew inspiration from a block disassembly process to propose an electrical impedance spectroscopy (EIS) method and constructed a generalized framework to associate macroscale electrical properties with microscopic structure and size-related characteristics of aggregates of different hierarchies. Extracted via EIS, the proposed models were verified to be capable of describing the self-similarity of aggregates and capturing the fractal and size information. Further, the proposed models exhibited a wide range of applications, which agrees well with the data gathered from various activated sludges, other colloids, and microgels in water and wastewater treatment. Finally, the EIS method was achieved online monitoring of fractal dimension and floc size during a sludge pre-oxidation conditioning process, which was elected as an example to illustrate the potential online applications of this EIS method in real water and wastewater environment. The obtained on-line data were used to indicate the potential suitable oxidation time during sludge pre-oxidation conditioning. These observations may inspire new methods of quantifying the aggregate structure and promote intelligent and dynamic decision-making during water and wastewater treatment.