Floc Structure Research Articles

Comparative evaluation of pilot-scale reactors based on pulsating floc blanket clarification and conventional clariflocculation technologies in simultaneous treatment of natural organic matter and turbidity

Abstract Simultaneous treatment of synthetic raw water containing natural organic matter (6 mg L−1) and clayey turbidity (0–20 NTU) was carried out with PACl on continuous upflow type pilot-scale models of pulsating floc blanket clarifier (PFBC) and conventional clariflocculator (CC) each designed for a capacity to treat about 8,000 liters per day, to understand mechanistic differences in their functioning. Fluidized bed of pre-flocculated particles prompted contact flocculation and enmeshment which lowered the residual turbidity for PFBC (0.07 ± 0.09 NTU) compared to CC (2.48 ± 1.71 NTU). Fine particles suspended in water clarified from PFBC and CC were hetero-disperse with Zavg as 2,341 nm and 5,693 nm respectively. On average, total residual aluminum was found to be 147 ± 33 ppb and 141 ± 51 ppb, while dissolved residual aluminum was found to be 31 ppb and 59 ppb for PFBC and CC respectively. Average total organic carbon reduction by PFBC and CC was 70.4% and 67.7% respectively. Size, structure and fractal dimensions of flocs were studied and average settling velocity of PFBC flocs was calculated to be 37% higher than CC flocs. Distinctness in characteristics of sludge formed in the two reactors has been highlighted by means of SEM micrographs and FT-IR spectra.

A metabolomic view of how the anaerobic side-stream reactors achieves in-situ sludge reduction

Anaerobic side-stream reactors (ASR), which were inserted in the sludge recirculation line of activated sludge process, can achieve in-situ sludge reduction. The lysis-cryptic growth occurred in ASR was accompanied with the release and reuse of dissolved organic matter (DOM), resulting in changes in DOM characteristics and affecting the microbial metabolic strategies, ultimately causing lower sludge yield in ASR. However, the variations in metabolic strategies of microorganisms in response to DOM changes in ASR systems remained unclear. Here, the sludge morphological feature, molecular properties of DOM and microbial metabolomics were analyzed to investigate the phenotype discrepancies and intrinsic causes of low biomass yield. Results showed that ASR systems achieved 22.9% sludge reduction efficiency. In the ASR system, the decreased microbial activity (adenosine triphosphate decreased by 10.3%) and unstable flocs structure implied the sludge destruction, causing the accumulation of proteins in extracellular polymeric substances (increased by 58.3%). The microorganisms in stressed ASR tended to utilize some tough aromatic carbon sources in DOM, finally affecting biomass growth. At the metabolite level, decreased lipid and purine/pyrimidine metabolism pathways activities provided less nucleic acids for synthesis of cellular structure and bacterial proliferation in the mainstream aerobic tank of ASR system, respectively. Microbes facilitate the metabolism of cheaper amino acids rather than costly ones due to the weaker cell activity. Notably, this change of amino acid utilization strategy would lead to the low level of nucleic metabolism, thus restraining the biomass yield. This study unraveled the low biomass yield mechanisms on sludge-reduction bacteria in response to the change of DOM molecular characteristics, which will help provide a deep theoretical foundation for promoting its full-scale applications.

Effects of potassium ferrate-walnut shell pretreatment on dehydration performance of residual sludge.

Sludge dehydration is not only the first process of sludge reduction but also difficult for sludge treatment and disposal, while the high moisture content of sludge would also limit its resource utilization. In this paper, the residual sludge was treated by the strong oxidizing property of potassium ferrate (PF), and walnut shells were used as a skeleton builder to obtain the recycling dehydrated sludge. It also provides a new solution for the poor stability of PF in the treatment of sludge and waste walnut shells. The experiment results showed that the optimum dosage of PF and walnut shell was 60mg/gDS and 0.8g/gDS, respectively, and the water content of the combined PF and walnut shell treatment decreased by 5.2% and 3.7% compared to that of PF conditioning alone and walnut shell conditioning alone, respectively. In addition, scanning electron microscopy and three-dimensional fluorescence spectroscopy revealed a large number of cracks on the sludge surface after the combined treatment, and the sludge floc structure became more loose and dispersed, and the hydrophobic substances humic acid and fulvic acid increased, indicating that the dewatering performance of the sludge was effectively improved, further confirming that the combined PF and walnut shells treatment provides a new idea and method for sludge dewatering.

A novel application of dissolved ozone flotation on sewage sludge thickening: Performance and mechanism investigation

Sludge thickening in sewage treatment plants is an essential step to reduce the sewage sludge volume and provide space for collaborative anaerobic digestion of sludge and other urban organic wastes. Dissolved ozone flotation (DOF) is a novel choice worthy of application in the field of sludge thickening. In order to investigate the effect of DOF thickening, the total solid content (TS %) was used to characterize the thickening performance under different O3 dosage. The optimal condition was determined to be polyacrylamide (PAM) dosage = 3 ‰ TS, air floatation time = 2 h and O3 dosage = 12 mg/g TS, under which the TS % of raw-sewage sludge (RS) increased from 0.33 ± 0.01 % to 8.03 ± 0.06 %. In this study, the relationship between the sludge thickening performance, physicochemical properties, and the changes of organic matter (content, structure and molecular weight) in extracellular polymers (EPS) was systematically clarified. The results indicated that the DOF couple with PAM could change the sludge surface properties, destroy the sludge floc structure, release intracellular organic matter, and increase moisture fluidity. The surface hydrophilicity/hydrophobicity, protein (PN) secondary structure and moisture distribution were mainly responsible for sludge thickening performance. Moreover, the change of TS % during the DOF thickening process was mainly caused by the variations of the organic matter content in EMPS layer. The identification of key influencing factors was conducive to the further regulation and upgrading of the novel application for enhanced sludge thickening in sewage treatment plants.

A potential online quantifier of sludge dewaterability developed from the similitude of water and electricity: Understanding the water release resistances as the medium

Chemical conditioning is a common but chemicals consuming procedure for improving sludge dewatering performance. However, real-time monitoring of dewaterability for accurate regulation of conditioner dosage is still tricky. One of the pending questions causing this challenge is that the key mechanisms affecting water release are not fully revealed. This study traced the entire process of water release in sludge flocs to investigate and clarify the possible release resistances, including the viscous resistance derived from binding effect of contact interface, and the interfacial resistance originating from morphology of pore wall, as well as the resistance arising from structure of flocs. Key resistances in an individual nanopore were determined using the state-of-art principles in confined water flow. Then the investigation was expanded to the multi-porous flocs scale. Based on the water release behavior and inspired by the similitude of water and electricity, an online quantifier derived from electrical impedance spectroscopy (EIS) analysis was developed to achieve real-time determination of dewaterability in a probe-like type. Our results showed that both viscous resistance of pores and structural resistance of flocs affected the water release, the contribution of flocs structural resistance cannot be neglected. Moreover, strong linear correlations (r ≥ 0.943, p < 0.01) were obtained between the online quantifier, named normalized spectral dimension, and the sludge dewaterability in two typical sludge conditioning processes. The optimal dosages were successfully revealed by normalized spectral dimension in an established semi-automatic conditioning and online dewaterability monitoring system. These observations may promote the development of smart sludge treatment technologies.

Flocculation of quartz by a dual polymer system containing tannic acid and poly(ethylene oxide): Effect of polymer chemistry and hydrodynamic conditions

The flocculation behaviors of quartz using a dual polymer system containing tannic acid (TAN) and poly(ethylene oxide) (PEO) were investigated in this study, with dynamic floc size monitoring by the in-situ focused beam reflectance measurement technique. Variables of concern and their influence on the flocculation process were investigated from both physicochemical and hydrodynamic aspects, including solution pH, TAN/PEO ratio, and shear intensity. Floc structure was characterized using confocal scanning microscopy in suspension as well as freeze-drying-SEM imaging method. It was found that prior addition of TAN significantly increased the flocculation efficiency of quartz by PEO at neutral and alkaline pH, but not in acidic solutions despite that PEO induced the largest floc size at pH 3.1 when used alone. An optimal TAN/PEO ratio of 2 was observed for the best flocculation of quartz under the experimental conditions. Additionally, tannic acid could increase the strength of flocs formed by PEO, and the shear resistance of the flocs increased with increasing TAN/PEO ratio. The dual polymer system also contributed to the re-flocculation of quartz under cycled shear conditions, a phenomenon that was not observed when PEO was used alone. Zeta potential and adsorption density measurements confirmed that the pathway of the dual polymer flocculation was via the initial formation of TAN-PEO associative complexes in solution and then bridging of quartz by the associative complexes. The TAN-PEO associative complexes showed different structures and configurations at different pH, in line with a change in hydrogen bonding, which in turn affected floc structures and properties under turbulent conditions. This study helps to understand the improved flocculation, shear resistance and re-flocculation of fine particles induced by dual polymer system.

On the Variability of Floc Characteristics in a Shallow Estuary

AbstractWe conducted field work in South San Francisco Bay to examine cohesive sediment flocculation dynamics in a shallow, wave‐ and current‐driven estuarine environment. Drawing on data collected using a suite of acoustic and optical instrumentation over three distinct seasons, we found that the factors driving floc size variability differed substantially when comparing locally sourced sediment (i.e., through wave‐driven resuspension) to suspended sediment advected from upstream. Statistical analysis of our extensive field data revealed additional seasonal variability in these trends, with wave stress promoting floc breakup during the summer and winter months, and biological processes encouraging floc growth during the spring productive period. Combining these data with fractal dimension estimates, we found that seasonally varying floc composition can lead to differences in floc settling velocity by a factor of approximately two to five for a given floc size. Finally, by analyzing co‐located turbulence and sediment flux measurements from the bottom boundary layer, we present evidence that the relationship between floc size and the inverse turbulent Schmidt number varies with floc structure. These results can be used to inform sediment transport modeling parameterizations in estuarine environments.

Effects of initial water content on compression behaviour of municipal sewage sludge

To investigate effects of initial water content on compression behaviour of municipal sewage sludge and clarify its intrinsic compression characteristics. Oedometer tests were conducted on sludge with various initial water content of 0·13–1·48 times the liquid limit. It is observed that the sludge is organic high liquid limit silt, whose e–log σ′vcompression curves are inverse ‘S’ shape due to organic floc structure of sludge potentially. When the effective vertical stress σ′v &gt; 100 kPa, a clear gap of compression curves of various initial water content still exists, different from Burland's viewpoint that compression curves tend to be consistent. Burland's concept of intrinsic compression line (ICL) is adopted for correlating compression curves of sludge well, and an ICL of the sludge is derived. The ICL of sludge is below ones reported by Hong and Burland when σ′v &lt; 100 kPa, due to the difference in initial water content. A generalised void index is tentatively proposed by introducing generalised intrinsic parameters e*y1and e*y2, which may be related to the loading history of the soil and the maximum load that the soil may bear in future engineering, respectively.

Pyrite activated peroxymonosulfate combined with as a physical-chemical conditioner modified biochar to improve sludge dewaterability: analysis of sludge floc structure and dewatering mechanism.

In this study, we proposed an advanced oxidation process of pyrite (FeS2) and peroxymonosulfate (PMS) and prepared a modified polyaluminum chloride biochar (P-BC). The motivation is to use the combination of FeS2 + PMS + P-BC to improve waste activated sludge (WAS) dewaterability. The method to improve the sludge dewatering effect with the combination of FeS2 + PMS + P-BC is as follows: in the first step, pour 0.75 g/g TSS FeS2 and 0.6 g/g TSS PMS into the sludge, and stir for 15 min. Then, add P-BC and stir for 5 min; complete the entire WAS processing process. The vacuum filtration test was used to evaluate the dehydration effect. The water content (Wc) and specific resistance to filtration (SRF) of the raw sludge can be reduced from the original values of 92% and 2.36 × 1013 m/kg to 67% and 9.89 × 1011 m/kg, respectively. The results showed that the combination of FeS2 + PMS + P-BC can effectively improve the sludge dewatering effect through oxidation. A laser particle size analyzer is used to observe changes in sludge particle size. The median diameter of sludge particles increased from 55.37 to 64.56 μm. A zeta analyzer to is used observe changes in sludge zeta potential. The zeta potential of sludge particles increased from − 15.8 to 0.4 mV. In the analysis of extracellular polymeric substances (EPS) of sludge, it was found that protein (PN) and polysaccharide (PS) in EPS decreased significantly. To further analyze the phenomenon of PN and PS drop, excitation-emission-matrix spectra (3D-EEM) was used. To observe the changes of sludge functional group, X-ray photoelectron spectroscopy was used. It was found that FeS2 + PMS + P-BC can destroy the functional groups of sludge, such as O–H, C–C, and O═C—NH– related to proteins and polysaccharides.Graphical abstract Supplementary InformationThe online version contains supplementary material available at 10.1007/s11356-022-21074-4.

Temperature Variation Characteristics and Model Optimization of Flocculation Sedimentation of Overflow Ultra-Fine Iron Tailings

In order to study the effect of temperature on the settling characteristics of overflow ultra-fine iron tailings, the settling velocity of overflow ultra-fine iron tailings at eight different temperatures at 10–80 °C was experimentally studied. The results show that, with the increase in slurry temperature, the flocculation settling velocity of overflow ultra-fine iron tailings increases first and then decreases. That is, when the temperature is less than 60 °C, the settling velocity of flocs increases with the increase in temperature. When the temperature is 60 °C, the settling velocity reaches the maximum 5.66 mm/s. When the temperature is more than 60 °C, the settling velocity of tailings flocs gradually decreases. In addition, with the increase in the test temperature, when the temperature is less than 60 °C, the particle size, fractal dimension, and density of tailings flocculant gradually increase, the gap of flocculant structure gradually decreases, and the floc structure becomes denser. When the temperature is higher than 60 °C, the particle size, fractal dimension, and density of flocs gradually decrease, and the gap between flocs is larger than that at 60 °C. On this basis, the temperature model of overflow ultra-fine iron tailings is established according to the analysis of particle settling process, and the settling model was optimized according to different settling areas. The mean absolute error between the optimized settling velocity and the actual velocity is 0.007, the root mean square error is 0.002, and the error is small. The theoretical calculation results are in good agreement with the experimental data, and the optimized flocculation settling model has an important role in promoting the theoretical study of the flocculation settling of such ultra-fine iron mineral particles, and can be used to guide the sedimentation and separation system to achieve good sedimentation treatment effect under the best working conditions as required.

Pyrite catalyzed peroxydisulfate for improving dewaterability of waste activated sludge: Reaction sequence of hydrophobic/hydrophilic structures

Dewatering is an essential step for reduction, harmlessness, and resource utilization of waste activated sludge (WAS). In this study, the WAS dewaterability was investigated using pyrite activated peroxydisulfate (PDS) conditioning and the intrinsic mechanism was explored. The experimental results showed that the specific resistance to filtration (SRF) and the sludge water content (Wc) of sludge cake values decreased from 43.17 ± 1.71 × 1012 m kg−1 and 85.94 ± 0.30% to 2.59 ± 0.07 × 1012 m kg−1 and 74.39 ± 0.25% with optimal pyrite and PDS dosages, respectively. The reactive radicals (∙OH and SO4-∙) generated through the reaction of pyrite/PDS destroying the hydrophilic functional groups in the extracellular polymeric substances (EPS), leading to the release of bound water. Besides, the collapse of sludge floc structure and a decrease in the mean particle size of sludge were found. Meanwhile, the smaller value of α-helix/(β-sheet + random coil) reflected that the protein structure was looser and the hydrophobic sites or groups of the proteins were more likely to appear. Further analysis of hydrophobic and hydrophilic structures in the sludge revealed that the hydrophilic substances were exposed first, followed by the protein structure unfolding, causing the exposure of the unsaturated and hydrophobic structures, and thus posing a positive effect on sludge dewaterability. Collectively, this study offered a new alternative to enhance sludge dewaterability through the application of natural minerals.

Enhanced removal of extracellular microcystin-LR using chitosan coagulation-ultrafiltration: Performance and mechanisms

Although many studies have proposed different drinking water treatment strategies to cope with harmful algal blooms (HABs), the removal of dissolved cyanotoxins remains a technical challenge. In this study, well-controlled laboratory experiments were performed to investigate the performance of chitosan as an alternative to traditional metallic coagulants in a hybrid coagulation-ultrafiltration (UF) process for addressing multiple HABs impacts in drinking water treatment. Compared to aluminum chlorohydrate (ACH), chitosan induced the formation of much larger and compact flocs, resulting in about 50% of M. aeruginosa cells removal after simple straining. While coagulation with ACH slightly reduced the rate and extent of UF permeate flux decline, chitosan coagulation at low doses (up to 0.25 mg/L) significantly reduced membrane fouling by 33%. At optimal dose (0.25 mg/L), chitosan coagulation showed a remarkable enhancement effect on the extracellular microcystin-LR (MC-LR) removal by UF membrane, up to 50% higher than those achieved with ACH (20%) coagulation and control condition (15%). However, excessive chitosan dosing would lead to severe membrane fouling. Molecular dynamic simulation results confirmed that chitosan exhibited affinity towards MC-LR via electrostatic interactions and weaker yet prevalent hydrogen bonding. The binding between chitosan and MC-LR would lead to toxin encapsulation within the flocs structure and thus an increased level of toxin retention by UF membrane based on the mechanism of size exclusion.

Pulse electrocoagulation combined with a coagulant to remove antimony in wastewater

Pulse electrocoagulation (PEC) was used to evaluate the treatment of synthetic solutions containing antimony (Sb). The effects of electrode materials, distance between electrodes, duty ratio, current frequency, and initial pH on the removal efficiency were investigated. The removal of Sb reached 93.5% when the distance between the FeAl electrodes was 20 mm, the duty ratio was 40%, the frequency was 400 Hz, the initial pH was 4, and the operation time was 30 min. The analysis of the floc structure using scanning electron microscopy during the floc formation process revealed that the three periods can be divided into formation, fluctuation, and reaggregation. The removal rate of Sb showed a transient downward trend during formation and fluctuation. Then, polymeric aluminum chloride (PAC) was applied as a coagulant to improve the floc structure. The best strategy for PAC addition was 0.6 mg/L in 5 min and 0.3 mg/L in 18 min, and the removal effect increased to 99.9%. Importantly, this method effectively treats actual dyeing wastewater containing Sb and chemical oxygen demand (COD). These findings demonstrate that a coagulant can effectively elevate floc structure and intensity in the process of pulse electrocoagulation and also provide an innovative method for practical applications of Sb removal from wastewater.

Research on Flocculant Selection for Classified Fine Tailings Based on Micro-Characterization of Floc Structure Characteristics.

The rapid settlement of tailings is an important technical guarantee for the continuous production of downhole filling. The selection of a reasonable flocculant is essential for accelerating the settlement speed of classified fine tailings. The present paper conducts indoor static sedimentation experiments, NMR observation, electron microscope scanning, and other methods to analyze the porosity and pore-size distribution characteristics of floc solution for classified fine tailing under four flocculants, namely, ZYZ, ZYD, JYC-1, and JYC-2. The dimension, spatial distribution characteristics, particle size characteristics, and morphological characteristics of the scanning electron microscope images of floc were studied. Results show that the unit consumption of flocculant at 30 g/t is the critical value for increasing the flocculation and sedimentation effect of the classified fine tailings solution. The highest distribution percentage of small-sized classified fine tailings and the lowest average pore size was observed under the ZYZ-type flocculant. This flocculant also obtained the lowest porosity, largest average floc size, largest area occupied by the floc, lowest pore percentage, and the densest floc structure. Thus, this flocculant showed the best flocculation effect. A negative correlation was observed between the equivalent diameter of floc with varying settlement heights. The dimension of floc increased with the decrease in bed settlement height, and the overall structure of the floc gradually transitioned from loose to dense from top to bottom. The present paper characterizes the microscopic morphology and spatial structure characteristics of floc under different flocculants from a microscopic point of view. The present paper also provides a scientific basis for the selection of the optimal flocculant.

Mechanism of Rake Frame Shear Drainage during Gravity Dewatering of Ultrafine Unclassified Tailings for Paste Preparation

To study the mechanism of reverse percolation and drainage of unclassified tailings, improve the disposal concentration of tailings and solve the bottleneck in the development of filling technology, this study performed semi-industrial flocculation and sedimentation tests using macroscopic continuous thickener tests and a self-developed continuous thickener test platform to observe the evolution pattern and formation mechanism of unclassified tailings flocs. Then, in situ sampling was performed on the compressed thickener zone of tailings at the bottom of the bed with the help of industrial CT scanning tests and 3D images. Avizo software was used to establish the seepage channels and construct an evolutionary model to analyze the effect of tailings dewatering and concentration on tailings concentration from a microscopic perspective. The study shows that the distribution of seepage channels is closely related to the height of the bed. As the bed height increases, the bed concentration increases; shear has a significant effect on the water flow inside the pore space. After shear, the water between the sample pores has been discharged. Therefore, the flow rate is relatively slow. Shear produces pressure and tension effects, breaking the static equilibrium between flocs and water forming seepage channels. Shear can effectively break the floc structure and release the water so that the mutual position between flocs and water constantly changes, The concentration of the tailings bed is increased.

Moringa oleifera-derived coagulants for water treatment: Floc structure, residual organics, and performance trade-offs.

The study explored the suitability of unfractionated extracts from the seeds of the Moringa oleifera tree as a coagulant for water treatment. The coagulant was obtained by soaking crushed and sieved seeds in a low salinity aqueous solution: a simple and inexpensive alternative to conventional coagulants in settings where specialized expertise and equipment are lacking. The performance of M. oleifera-derived coagulants was quantified in terms of turbidity removal, bacteriophage clearance, concentration of residual organics, as well as meta-parameters such as floc size and fractal dimension. Treating high turbidity clay suspensions at the optimal coagulant dosage (14.7mg(DOC)/L) and flocculation mixing conditions ([Formula: see text]= 22.4s-1) removed > 94% of turbidity, similar to that recorded in reference tests with alum. Floc size distribution shifted to larger sizes during the first 10min of flocculation with no change afterwards, while the floc fractal dimension, [Formula: see text], continued to increase, pointing to the gradual formation of denser ([Formula: see text]= 2.1 to 2.2), more settleable flocs. Preliminary tests with MS2 bacteriophage showed that coagulation with M. oleifera decreased the viable MS2 titre by ~ 1.3log, which was significantly above the turbidity removal (~ 1log). The extraction process, however, allowed a large amount of residual organics (> 78% of extracted DOC) into the treated water. Combining the coagulants with downstream filtration and adsorption, employing UV or solar disinfection, or limiting applications to non-potable reuse is suggested for mitigating the concerns related to residual DOC.

Flocculation and Settlement Characteristics of Ultrafine Tailings and Microscopic Characteristics of Flocs

Aiming to solve the problems related to the slow settling speed and the long-term consumption of ultra-fine tailings in mine filling, the effect of flocculant type on the flocculation and settling performance of ultra-fine tailings was studied through static sedimentation experiments on tailings. The microstructure of the flocculation was observed and analyzed using an electron microscope. On this basis, the selection of the optimum flocculant type and dosage parameters was carried out. The results show that the best addition amount of the AZ9020 anionic flocculant was 30 g/t, a solution concentration of 0.3%, and a stirring time of more than 45 min. The floc structure of the full-tailings flocculation solution was formed by the AZ9020 anionic flocculant. Moreover, the size of less than 0.1 μm was still relatively large; thus, the overall size of the structure was small and uniformly dispersed. The floc solution had the smallest porosity, the fractal dimension was the largest, the molecular weight of the floc was the largest, and the floc was the most compact, making it appropriate for the rapid removal of floc structures from water. Sedimentation is also the best flocculant for flocculation and sedimentation. The size of the flocs decreased as the height of the flocculation sediment bed increased during flocculation and sedimentation. The research results provide a microscopic view for the selection of the best flocculant type.

Viscous and filamentous bulking in activated sludge: Rheological and hydrodynamic modelling based on experimental data

Although achieving good activated sludge settleability is a key requirement for meeting effluent quality criteria, wastewater treatment plants often face undesired floc structure changes. Filamentous bulking has widely been studied, however, viscous sludge formation much less investigated so far. Our main goal was to find relationship between sludge floc structure and related rheological properties, moreover, to estimate pressure loss in pipe networks through hydrodynamic modelling of the non-Newtonian flows in case of well settling (ideal-like), viscous and filamentous sludge. Severe viscous and filamentous kinds of bulking were generated separately in continuous-flow lab-scale systems initially seeded with the same reference (ideal-like) biomass and the entire evolution of viscous and filamentous bulking was monitored. The results suggested correlation between the rheological properties and the floc structure transformations, and showed the most appropriate fit for the Herschel-Bulkley model (vs. Power-law and Bingham). Validated computational fluid dynamics studies estimated the pipe pressure loss in a wide Reynolds number range for the initial well settling (reference) and the final viscous and filamentous sludge as well. A practical standard modelling protocol was developed for improving energy efficiency of sludge pumping in different floc structure scenarios.

Flocculation of Clay-Based Tailings: Differences of Kaolin and Sodium Montmorillonite in Salt Medium.

Complex gangues and low-quality waters are a concern for the mining industries, particularly in water shortage areas, where the closure of hydric circuits and reduction in water use are essential to maintain the economic and environmental sustainability of mineral processing. This study analyzes the phenomena involved in the water recovery stage, such as sedimentation of clay-based tailings flocculated with anionic polyelectrolyte in industrial water and seawater. Flocculation–sedimentation batch tests were performed to ascertain the aggregate size distribution, the hindered settling rate, and the structure of flocs expressed through their fractal dimension and density. The aggregates’ properties were characterized by the Focused Beam Reflectance Measurement (FBRM) and Particle Vision Microscope (PVM) techniques. The impact of the type of water depends on the type of clay that constitutes the suspension. For quartz/kaolin, the highest performance was obtained in industrial water, with bigger aggregates and faster settling rates. However, the tailings composed of quartz/Na-montmorillonite reversed this trend. The type of water impacted the efficiency of primary-particle aggregation. The trials in industrial water generated a portion of non-flocculated particles, which was observed through a bimodal distribution in the unweighted chord-length distribution. This behavior was not observed in seawater, where a perceptible fraction of non-flocculated particles was not found. The additional cationic bonds that offer seawater favor finer primary-particle agglomeration for all tailings types.

Enhancement of flocculant-aided filtration performance of coal tailings under alternating low and high shear rates

Although flocculation has been widely applied to improve filtration performance before filtered dry stack tailings storage, it is still a challenge to create flocculated aggregates having desired characteristics which are both conducive to improving the filtration rate and reducing the filter cake moisture content. In this paper, the alternate shear conditions were investigated to enhance flocculant-aided filtration performance of coal tailings. The focused beam reflectance measurement (FBRM) was used as an in-situ monitor to measure the floc size under different shear conditions in the presence of anionic polyacrylamide. Compared with single shear conditions, sequenced flocculation produced stronger flocs. It was also found that the flocs formed under two cycles of high (1192.8 s−1) and low (637.6 s−1) shear rates were the strongest and contained fewer particles and small flocs. The particle vision measurement (PVM) was used to analyze the effects of alternate shear conditions on floc morphological characteristics. It was observed that the floc structure became more compact with the number of cycles. Lastly, the filtration experiments were conducted to determine the filtration performance of coal tailings. The results showed that the coal tailings had the best comprehensive filtration performance under the sequenced flocculation with two cycles of high and low shear rates, the filtration time was 12.17 min, which was very close to the fastest 12.03 min of single low shear rate, and 21.2% of cake moisture content was about the same as the minimum 21.1%. The filtration outcomes were consistent with that given by FBRM and PVM.