Slurry Filtration Research Articles

Effect of cement slurry filtrate on methane hydrate stability during deepwater cementing operations

Whether the hydrate layer is stabilized during deepwater cementing operations has a direct impact on the safety of the cementing process and the quality of the cementing. When the cement slurry enters the annular space and waits for solidification, it will be extruded to produce filtrate under the action of formation temperature and pressure. Moreover, the inorganic ions and organic matter contained in the filtrate may penetrate into the formation. However, whether these processes have an effect on the stability of the hydrate layer is not clear at present.In this paper, we initially developed a methane hydrate generation system, termed the water-quartz sand-methane system. This system efficiently produces methane hydrate within a short time and ensures a uniform distribution of the gas-solid phase, which is highly suitable for further research into methane hydrate stability. Subsequently, the primary constituents of the cement slurry filtrate and the principal functional groups of the cement additive were identified. Furthermore, enhancements were made to the existing formula for quantifying methane gas alteration. Additionally, a hydrate testing experimental system was employed to circulate a solution comprising the primary constituents of the cement slurry filtrate over the methane hydrate surface. Ultimately, utilizing the amount of change in the volume of methane gas in the cyclic process as a criterion to evaluate the impact of various components of the cement slurry filtrate on methane hydrate stability, an investigation into the effect of the cement slurry filtrate on methane hydrate stability was conducted. It was confirmed that Ca2+, Na+, Cl- ions within the cement slurry filtrate, along with the pH value, minimally influence methane hydrate stability. Conversely, the cement additive exhibits a discernible disruptive effect on methane hydrate stability, with the retarder demonstrating the most pronounced impact when mass fractions are equated.This study suggests that the adverse effects of amide and carboxyl groups on hydrate stability must be considered in the selection of additives for deepwater cementing slurries. The findings offer guidance for the research and development of additives for deepwater cementing slurries and establish a theoretical foundation for studying cementing slurry systems in hydrate formations.

Investigation of the Dewatering Process with Geotextile Tubes by Sedimentation, One- and Two-Dimensional Filtration Test Methods

AbstractDewatering applications are carried out with geotextile tubes for the disposal or reuse of industrial wastes with high water content. Class F Seyitomer thermal power plant fly ash, an industrial waste, was selected in this study. Turbidity, sedimentation and filtration experiments were carried out using anionic and cationic polymers and polypropylene synthetic fiber to investigate the effect of polymers and fibers on the dewatering of fly ash. The use of polymers was determined to significantly accelerate filtration and soil sedimentation speed while leading to a slight increase in the volume of the filter cake. When effective polymer and dosage are used, slurry filtration time can be reduced up to one-eighth of the time and dewatering can be achieved much faster. The addition of synthetic fiber accelerated the sedimentation of the slurry and increased the filtration in the vertical direction, while it did not show a significant effect on the total filtration in two-dimensional filtration. In geotextile tube applications, although one-dimensional filtration experiments might give misleading results in terms of estimating the effectiveness of the polymers used in solid–liquid separation and dewatering times, the jar test, sedimentation and two-dimensional filtration experiments were determined to give compatible and more realistic results. In two-dimensional filtration experiments, approximately 75% of the filtration occurred in the radial direction and the dewatering time was approximately 21–55% of the time estimated by one-dimensional filtration experiment. Geotextile tube dewatering design can be made more predictable and cost-effective in the field by performing small-scale laboratory experiments with the two-dimensional filtration test system designed for this study and various dewatering applications.

Study on the Compatibility of Acrylic Acid-acrylamide-diethyldiallyl Ammonium Chloride Copolymer with Cement Slurry in CO2 Environment.

This paper investigates the structure and aggregation stability of acrylic acid-acrylamide-diethyldiallylammonium chloride (FA367), followed by an investigation into the impact of acidic CO2 environments on the interaction between FA367 and cement slurry. The results showed that FA367 formed stable flocculation in cement slurry filtrate, which was not affected by acid gas CO2. With an FA367 concentration of 0.6%, the fluidity of the cement slurry measures 18.1 cm, but this fluidity is lost upon introducing CO2. At 90 °C, the compressive strength after 1, 3, and 7 days is 10.23, 77.48, and 62.97%, respectively, compared to pure cement. However, with the addition of CO2, the compressive strength increases to 27.03, 99.59, and 75.47%, respectively. The interaction between FA367 and cement slurry impedes cement hydration without altering hydration product composition. Instead, it fosters needle-like aggregations between hydration products, affecting the cement stone's compact structure. Upon CO2 introduction, these needle-like structures diminish, resulting in an overall more intact cement stone structure.

Synergistic Leaching of Titanium, Aluminum, and Magnesium Components during Dilute Acid Pressure Treatment of High-Titanium Blast Furnace Slag.

This study focuses on an improved leaching process through the combination of pressurized conditions and direct filtration of acid leaching slurry, which is conductive to improving the filterability of acid leaching systems and the extraction rates of Ti, Al, and Mg components. The effects of sulfuric acid concentration, reaction temperature, particle size of materials, acid-slag ratio, and reaction time on the leaching efficiency were systematically investigated. The results showed that pressurization significantly enhances the filtration efficiency of the reaction slurry. Under the same filtration time, the filtration efficiency increased from 46% under ordinary pressure to 78% under pressurized conditions. Moreover, under the optimal reaction conditions, the extraction rates of Ti, Al, and Mg components were more than 88.21%, 97.8%, and 96.31%, respectively. Additionally, XRD and FTIR showed that titanium oxide sulfate hydrate crystals were produced in the acid-leached residues when the reaction temperature exceeded 190 °C, thereby reducing the extraction rate of Ti component. And the XRD pattern shows that when the reaction temperature is maintained at 190 °C and the reaction time is extended to 150 min, titanium oxide sulfate hydrate crystals will be formed to reduce the extraction rate of the Ti component. In summary, this study not only provides important theoretical support for the resource utilization of high-titanium blast furnace slag but also offers a feasible solution for efficient extraction and convenient filtration, thus holding significant academic and practical implications.

Effects of a new synthetic Fe-PAM flocculants on filtration and consolidation of bentonite slurry

To improve the dewatering performances of the waste slurry, a new Fe-Polyacrylamide (Fe-PAM) flocculant was synthesized. Comparative analysis with various ionic forms of polyacrylamide (PAM) reveals that the Fe-PAM flocculant has the shortest flocculation time, the lowest optimal shear gradient for flocculation, and the best filtration performance. The capillary suction time (CST) of Fe-PAM treated slurry was improved from 262.3 s (raw sample) to 6.0 s. Moreover, sludge treated with Fe-PAM exhibits the lowest porosity under the same consolidation pressure and the highest permeability at the same void ratio. In addition, mercury intrusion porosimetry (MIP) results indicated that the Fe-PAM-treated sample features the highest number of largesized inter-aggregate pores (average value of 184.2 nm and median value of 23.2 nm) and the greatest pore connectivity (60.55 %), contributing to its superior permeability. The effectiveness of Fe-PAM is further elaborated through a synergistic flocculation mechanism, encompassing the electrical neutralization effect of the inorganic metal Fe3+ and the adsorption bridging effect of PAM's long-chains. This study demonstrates the potential of the synthesized Fe-PAM flocculant to enhance the dewatering efficiency of high-water content slurry and offers valuable insights for synthesizing advanced flocculants in slurry treatment engineering.

Understanding and Enhancing Silicon Nanoparticle Distribution during Electrode Processing

Silicon-dominant anodes are of great interest because of their potential to boost the cell-level energy of state-of-the-art Li-ion batteries. While silicon materials have been extensively studied, understanding interactions at the electrode level has recieved little attention, especially the coating process of Si particles, which plays an equally important role in unlocking the full potential of silicon anodes. Herein, the electrode processing of a Si-dominated anode (52.8 wt%, 3.5–4.5 mAh cm−2) is being investigated to understand the relationship of processing on the morphology and properties of Si anodes at the electrode level. It has been found that almost-undetectable Si agglomerates easily form during electrode processing, which grow into largeprotrusions after lithiation and trigger potential internal shorting and self-discharge problems. A facile slurry filtration step is proposed to homogenize the particle distribution within Si-dominant electrodes which improves the electrochemical performance and storage stability of Si-based Li ion batteries.

Scale up validation tests for Buckingham Pi theorem applied to leaf test experiments for iron ore slurry

Bench tests were conducted on ore slurry filtration using the leaf test method, varying scales, pressures, and water/solids ratios. These results were compared with analytical outcomes derived from applying the dimensionless Buckingham pi method to the general equation of slurry filtration with incompressible cakes under constant pressure. The aim was to validate the tests by corroborating experimental findings with calculated parameters for scale-up purposes. Vacuum pressure was employed to facilitate slurry dewatering, forming a cake comprising solids from the slurry. This cake’s thickness evolved over time, introducing specific resistivity that impeded filtering efficiency. Parameters such as cake resistance and filter media resistance were computed. Filtrate volume was measured over time to determine the filtration rate. These values were then adjusted using factors obtained through dimensional analysis. These factors facilitated comparisons to validate the feasibility of employing the Buckingham pi method for predicting slurry filtration results at larger scales. The results indicated lower errors when analyzing the filtrate rate over time with a solids/water ratio of 20/80%. When evaluating cake resistance, the method yielded lower errors at a ratio of 70/30%, while results for medium resistance were inconclusive. It’s important to consider the ratio and associated errors when predicting the behavior of an industrial filter based on bench test results, aiming to achieve theoretical scaled filtration rates and cake resistances. However, it’s not advisable to rely on the Buckingham pi method for scale-up purposes when evaluating medium resistance.

Modified (Spherical and Cylindrical) Permeation Diffusion Model Considering Deep Bed Filtration Effect

The study of the slurry reinforcement mechanism is mainly focused on the interaction between slurry and soil. The seepage effect of the slurry always exists no matter what way the slurry interacts with the soil around the pile. In the process of slurry diffusion, the porosity of the soil, the permeability of the slurry, and the slurry pressure vary due to some cement particles being blocked by the soil particle skeleton. Therefore, the study of the slurry filtration effect is of great significance for predicting the permeation and diffusion law of slurry. In this paper, a macroscopic linear filtration model was introduced and the changes of slurry properties in the permeation diffusion process were considered. Firstly, a spherical (cylindrical) permeation diffusion model, which takes the linear filtration effect and the variation of slurry viscosity into account, was derived based on the conservation of mass. Furthermore, in order to more accurately reflect the influence of the filtration effect on the slurry permeation diffusion model, a polynomial nonlinear filtration model was proposed, and the numerical solution for the permeation diffusion model was derived using finite difference and finite element methods. Finally, the numerically simulated values, the measured values, and the values from the spherical permeation diffusion model that does not consider slurry viscosity variations were compared. The results indicate that the grout pressure is inconsistent with the measured value without considering the effect of the filtration. The initial grouting pressure calculated by the model in this paper is slightly larger, and the required grouting pressure over time is greater than that without considering the filtration effect, regardless of whether the grout diffuses in a spherical or cylindrical manner. The results of this study can contribute to a better understanding of grouting engineering and provide some theoretical guidance for actual grouting.

Clinker Slurry for Cementing Across Salt Formations

Summary Potassium chloride (KCl) is more effective in preventing salt layer dissolution than sodium chloride (NaCl) while cementing across salt formations. This paper studied the effect of KCl on the properties of cement slurry and found that KCl worsened the flowability of cement slurry. Experimental evidence confirmed that an alkaline environment promoted the dissolution of gypsum, leading to its reaction with KCl to produce syngenite. A large amount of needle-shaped syngenite caused the cement slurry to lose flowability. In addition, silica flour slurry was designed to prove the formation of syngenite and the effect of syngenite on the rheological property of the slurry. In a new way, clinker was used to prepare slurry containing KCl to prevent the generation of syngenite. The effect of KCl on the properties of clinker slurry was evaluated. The dissolution experiment of halite in clinker slurry filtrate proved that KCl had a strong ability to inhibit the dissolution of halite.

Research on graphene oxide modified polymer as multifunctional filtration reducer for oil-well cementing

Conventional filtration reducers have limited utility in cementing at deep oil and gas fields because of their poor temperature resistance and single function. As a novel multifunctional filtration reducer, graphene oxide-modified polymer GO-PADI was developed by radically copolymerizing 2-acrylamido-2-methylpropane sulfonic acid (AMPS), N, N-dimethyl acrylamide (DMAM) and itaconic acid (IA) between graphene oxide sheets. The microstructure of GO-PADI was confirmed through the utilization of different methods such as fourier transform infrared spectroscopy (FT-IR). The performance evaluation results showed that GO-PADI had the high thermal stability, and could control filtration of cement slurry as conducted by the American Petroleum Institute (API) less than 50 mL, which is 17 % lower than that of the traditional filtration reducer PADI. GO-PADI could increase compressive strength of cement stone by 30.3 %, and decrease elastic modulus by 10.9 % in three-day curing period. GO-PADI has the multifunctional functions of reducing fluid loss, strengthening and toughening, and can effectively improve the engineering performances for high-temperature cement slurry.

CFD–DEM modelling of the infiltration of non-spherical slurry particles in granular soils

The slurry filtration process at an excavation surface plays an important role in supporting pressure transmission, which is crucial to the stability of a tunnel face during slurry shield tunnelling. In this paper, a series of coupled computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulations were carried out to model the slurry filtration column test. Oblate spheroids of varying aspect ratios were adopted to represent slurry particles. A simplified pitching torque model was implemented to better simulate the motion of slurry particles. The pressure distribution, void fraction, permeability and orientations of the particles were analysed as the aspect ratio was systematically changed. The pressure distribution, void fraction and the permeability within a stratum are highly dependent on the aspect ratio of the particles. Particles with larger aspect ratios tend to effectively seal infiltration channels and transfer slurry pressure to effective pressure, thereby helping to maintain stability at the tunnel face. This research study explores how particle shape impacts the slurry infiltration procedure and the microstructure of the filter cake.

Cake and precoat filtration – Evaluating influences of increased backwash efficiency on cloth lifetime

In beet juice purification the greatest challenge is to evade a frequent blockage of the filter cloth during carbonation slurry filtration. Lenzing Filtration started an investigation on backwash efficiency of tubular pressure candle filters and how this affects the lifetime of filter cloth in carbonation slurry filtration. The patent pending CakeFil filter candle of Lenzing Filtration is made from a continuous casted structure, closed at the lower end with an on-welded plug and at the upper end with a connector to the filtrate chamber. After 85 backwashes under laboratory conditions the CakeFil technology had approx. 77% less residues compared to two different standard candle filters. Pilot-scale testing in a German sugar factory with carbonation slurry 1 confirmed the outstanding lab performance as the filter cloth of LENZING CakeFil endured the entire campaign of 71 days without any filter cloth change, whereas the standard candle filter clothes had to be changed four times and external washing had to be performed three times during the same period. Also the filtrate-quality analysis showed that the results were identical compared to existing candle filters quality.

Effect of main functional groups of cement slurry additives on the stability of methane hydrate: Experiment and molecular dynamics simulation

There are a lot of hydrates in deep-water and shallow layer, which accumulate at relatively shallow depths (<100–120 m). During cementation in the deep-water shallow formation, the free inorganic ions and organic molecules in the cement slurry filtrate enter the formation via percolation, which may affect the stability of the hydrate. The free organic matter in cement slurry acts mainly as retarder, fluid loss additive and dispersant. First, the representative fluid loss additive BXF-200 L, retarder PC-H21L, and dispersant PC-F41L were selected for infrared spectroscopy. Then, the influence of BXF-200 L, which contains all the previously mentioned functional groups, was studied for its impact on hydrate stability using an experimental method. Second, a molecular dynamics simulation method was used to study the adsorption properties of the functional groups on the surface of sI methane hydrate under canonical (NVT) ensemble, which it is the most widely distributed hydrate type in nature. What is more, in order to characterize the influence of functional groups on the decomposition of methane hydrate, the molecular conformation, mean square displacement (MSD), diffusion coefficient (D) and adsorption energy (Eadsorption) were calculated using the dynamics simulation trajectory of sI methane hydrate.The experimental results showed that the main functional groups in cement slurry filtrate additives were carboxyl, sulfonate, and acylamino groups. Further, BXF-200 L can promote hydrate decomposition. Subsequently, the simulation results showed that under the same conditions, the adsorption energy of sulfonate group on the surface of methane hydrate was the largest and the adsorption capacity was the greatest. When the concentration was ≤ 1 mol%, among the three functional groups, acylamino had the most obvious promoting effect on the decomposition of sI methane hydrate, and the hydrate decomposition rate increased by 16.31%. When the concentration was more than 1 mol%, the decomposition rate of hydrate was increased under the interaction of carboxyl, acylamino, and sulfonate groups, by 12.49%, 19.46% and 27.74%, respectively, compared with that under pure water-hydrate system.

Surfactant-enhanced extraction of valuable metals from limonitic laterite: Porous kinetics and mechanism analysis

The efficient extraction of valuable metals from low-grade mineral resources is an important initiative to implement the concept of carbon neutrality and achieve energy conservation and emission reduction. Atmospheric leaching of laterite ores is widely noted for its low cost. However, low extraction and difficulties in slurry filtration have severely restricted its development. Inspired by our previous studies on the porous kinetics, two options for improving the nitric acid atmospheric leaching (NAAL) of limonitic laterite are proposed. 84.85 % of Ni extraction is achieved under the optimal process conditions (Temperature: 98 °C, Time: 3.5 h, Liquid/Solid: 4.7 mL/g, and the initial nitric acid concentration: 487 g/L). After enhanced treatment, the Ni extraction is increased by 3.16 % (bleed air), 4.55 % (SDS: sodium dodecyl sulphate), and 5.67 % (DTAB: dodecyl trimethyl ammonium bromide), respectively. In addition, DTAB not only promotes the leaching of laterite ores but also improves the filtration performance of the slurry. The filtration rate was more than three times higher than in the absence of DTAB. The presence of silicic acid is responsible for the difficult filtration of the slurry and the low extraction of valuable metals. Analysis of the intensification mechanism shows that the bleed air treatment mainly eliminates the obstruction of leaching by air in the pores, thus increasing the effective reaction area. The reinforcing effect of surfactants is mainly due to the improvement of diffusion efficiency, the reduction of adsorption, and the increase in permeability. This paper provided a feasible option for the enhanced leaching of limonitic laterite, and the reinforcement mechanism was explained clearly. It not only responds to the call for energy conservation and emission reduction by achieving efficient extraction of valuable metals from low grade laterite resources, but also avoids the treatment of laterite ores by means of high temperature and pressure.

The filtration of aqueous clay mineral suspension in the presence of bitumen

Typical mine tailings can be dewatered by filter press to filter cakes containing >=85 wt% solids that are ready for reclamation, but Alberta oil sands tailings could only reach about 60 wt% solids using the same technology, even when the dominant particle sizes are similar. In this work, the effects of residual bitumen, one of the distinguishing features of oil sands tailings, were investigated. The residual bitumen in the oil sands tailings exists in the forms of bulk bitumen, emulsified bitumen, and adsorbed bitumen. The roles of the three forms of bitumen were investigated in the filtration of primarily a model mineral kaolinite mineral slurry supplemented by rutile, quartz and montmorillonite slurries. Generally, bulk bitumen was found not to affect filtration significantly, emulsified bitumen facilitated filtration possibly by mopping the ultrafine particles, while bitumen adsorbed on mineral surfaces had more complex effects: a thin bitumen coating improved filtration because of the induced surface hydrophobicity, while a thick bitumen coating impeded filtration due to its mobile and deformable nature. The poor filterability of oil sands tailings may be partly caused by the mobile and deformable bitumen coating on the sands/clay mineral surfaces. This study elucidated the effects of a third deformable organic phase on the filtration of an aqueous mineral slurry, providing insights for solid–liquid separation in the presence of a mobile third phase.

Damage of Green Synthetic Cement Slurry to Clastic Rock Reservoir

Green synthesis and metal oxide composites have attracted much attention from researchers of industry and academia. As a typical application of green synthesis and metal oxide composites, the protection of oil and gas reservoirs is related to various links such as exploration, drilling, completion, and development. It is a complex and systematic project, which directly affects whether the oil and gas fields can be discovered, evaluated, and efficiently developed in time, and it is also related to the development of oil and gas fields recovery rate. As the most critical part of oil and gas well construction, the cementing process mainly pays attention to the safe pumping of the cement slurry and the long-term effective interlayer isolation capability of the cement sheath. Less attention is paid to the reservoir protection during the cementing process. The high-pressure difference between the annulus and the formation, the high fluid loss, and the high solids content of the cementing slurry during the cementing process have also become major challenges. In order to solve this problem, this study takes a typical clastic rock block in an oilfield in western China as the research object and carries out a geological survey of fracture development, pressure deficit, and cement slurry permeability leakage in the reservoir. The reservoir physical properties, clay mineral characteristics, and formation water quality of rock reservoirs are analyzed. The influence of cement slurry filtrate and solid phase particles on reservoir clay expansion rate and permeability was tested by core porosity and permeability tester. XRD and SEM techniques were used to analyze the damage mechanism of cement slurry filtrate and solid phase particles to the reservoir. The research results show that the average porosity of the clastic rock reservoir in the study area is 15%, the permeability is high, the average pore size of the reservoir is between 37 and 56 μm, the microfractures are developed in the reservoir section, and the porosity and permeability conditions are good; high-valent cations and inorganic ions in the filtrate generate inorganic scales such as CaCO3 and Mg(OH)2 and cross-link with dissolved polymers to form flocculation substances, which cause the filtrate to damage the reservoir, and at the same time, the cement particles in the pore throats in the near wellbore zone are lost along with the leakage. Furthermore, hydration, tightly bonding the inert admixture and the clastic rock formation, forms a tight sealing layer, which reduces the permeability of the reservoir sharply; the expansive clay particles in the reservoir absorb the moisture of the cement slurry filtrate and expand. The volume of the particles increases, and the porous formation containing expansive clay minerals absorbs moisture and causes internal expansion, and the volume expansion rate can reach 9%, which eventually causes the porosity and permeability of the reservoir to decrease, resulting in reservoir damage and solid phase in the cement slurry. The damage of particles to the reservoir is mainly due to the blockage of the reservoir pore throats and the hydration and consolidation of cement particles inside the reservoir caused by the external admixtures in the cement slurry that do not participate in the hydration reaction. The solid phase particles form a filter cake on the surface of the reservoir core and cannot enter the reservoir, but under the condition of porous formation leakage, the solid phase particles with a particle size of 1–10 μm in the cement slurry will directly penetrate into the reservoir rock resulting in shallow plugging in the reservoir near the wellbore. The research results provide theoretical data support for the research on low-damage cementing slurry technology in clastic rock reservoirs. The work provides an important application guidance to green synthesis and metal oxide composites.

Understanding the processes of thickening and filtration of yellow cake slurry (ammonium polyuranate) generated by in-situ uranium leaching sites

One of the key stages in the in-situ leaching of uranium includes thickening of yellow cake slurry to obtain washed uranium concentrate. Russian in-situ leaching sites tackle this by using membrane filter presses. In spite of their high performance, filter presses have one major drawback &ndash; the filtration is done periodically. This paper describes the results of a laboratory study suggesting that, together with membrane filter presses, continuous band vacuum filters could also be used in this application. The yellow cake slurry obtained after precipitation of ammonium polyuranate from Dalur JSC&rsquo;s eluates has the density of 1060&ndash;1065 kg/m3. In laboratory conditions, the slurry was thickened by adding 1 g/dm3 of Praestol 2530 slurry. The settling rate was 5.4 m/h, the thickening performance &ndash; 2.8 t/(m2.day). The resultant thickened product with a density of 1600 kg/m3&nbsp;was filtered in a band filter with a three-stage counter-current washing cycle at a fresh water flow rate of 1 m3/t solid and a vacuum of &ndash;49 kPa. The process resulted in an average filtration performance of 8&ndash;9 t/(m2.day) and a 17&ndash;18 mm thick washed precipitate with 41&ndash;43% humidity. The duration of the overall filtration and washing cycle was 110&ndash;140 sec. The maximum concentration of sulphate-ion in the washed and dried yellow cake precipitate did not exceed 2.0%, which is significantly lower than the 4% allowed. It is noted that, if necessary, these indicators can be improved by raising the rinse water flow rate.

Influence of rheology in the filtration of leach slurry generated by alkaline pressure leaching of a limestone ore

The Nuclear Power Plant, which uses uranium as a fuel, is considered as a clean source of energy with low carbon footprint and less environmental damage. In processing the uranium ore, the filtration of alkaline leach slurry generated by oxidative pressure leaching is a challenge due to very fine grind size coupled with high total dissolved solutes (TDS). The present study aimed at improving and understanding the filtration of the leach slurry with the help of slurry rheology. The effect of solid concentration, temperature, particle size, and dosages of dewatering aids on the rheological behavior of the slurry and the filtration performance was investigated. The slurry rheology was delineated by the Herschel–Bulkley model, temperature effects were incorporated using the Arrhenius type model, and particle size distribution (PSD) was represented by the Rosin–Rammler PSD model. The dosages of dewatering aids were compared using rheological parameters. It was found that the filtration rate decreases as solid concentration increases (10 to 75%, w/w) due to an increase in the shear stress (9.93 to 757 Pa at 1400 s−1). The leach slurry showed shear thickening at ≤ 60% solids (w/w) and shear thinning at ≥ 70% solids. The maximum solid packing volume fraction was found to be 0.59 and 0.54 at 1300 and 441 s−1, respectively. Increase in filtration rate was observed at elevated temperatures as the apparent viscosity (at 1300 s−1) decreased from 0.0195 Pa.s at 20 °C to 0.0135 Pa.s at 70 °C. The fluid flow activation energy was determined to be 5.5 and 7.1 kJ/mol at 1110 s−1 for 50 and 73% solid concentration (w/w), respectively. When the particle size (d90) was changed from 66 to 42 µm, a decrease in filtration rate was observed due to an increase in apparent viscosity from 0.0120 to 0.0163 Pa.s at 1400 s−1. The high molecular weight polyacrylamide based non-ionic synthetic flocculant N 100 and non-ionic biodegradable polysaccharide surfactant guar gum formed flocs through the bridging mechanism and gave best flocculation results, and therefore selected. The present work helps the researchers in better understanding and improving the filtration process of ore slurries.

A Mesoscopic Viewpoint on Slurry Penetration and Pressure Transfer Mechanisms for Slurry Shield Tunneling

The penetration characteristics of the slurry and the support pressure transfer mechanisms are critical to the tunnel face stability control during a mechanized excavation. In this paper, numerical calculations coupling computational fluid dynamics (CFD) with the discrete element method (DEM) are carried out to simulate sand column penetration tests considering different particle size ratios. The reasonableness of the numerical model is verified by comparing the variation patterns of the soil permeability coefficients monitored in the numerical tests with the results of existing laboratory tests. The mesoscopic transport characteristics of the slurry particles in the sand soil pores are considered based on numerical tests, while the slurry support effects corresponding to different penetration types are evaluated. Three main basic types of slurry infiltration are observed due to the different ratios of slurry particle size over soil pore size. For the first penetration type, the slurry particles are accumulated and able to form a supporting filter cake. The slurry support is effective because of the significant pressure drop generated on both sides of the filter cake. For the second penetration type, both a filter cake and an infiltration zone are present. A dense filling network is formed between the filter cake and the penetration zone. The third type corresponds to a purely penetration zone. An effective impermeable filling network cannot be formed, and the slurry support effect is not obvious. The development of slurry penetration distance shows an obvious time effect; the farther the penetration distance, the larger the slurry filtration loss, and the worse the transformation effect of slurry support pressure.

Alkali-Resistant and pH-Sensitive Water Absorbent Self-Healing Materials Suitable for Oil Well Cement

Oil well cement microcracks cause formation fluid channeling, compromising oil and gas extraction safety. Superabsorbent polymer (SAP) can absorb water and swell to prevent fluid channeling. In this study, an alkali-resistant and pH-sensitive SAP was prepared based on the properties of oil well cement slurry. The preparation of the SAP was optimized, including monomer ratio, cross-linking agent dosage, and monomer concentration. The pH sensitivity and alkali resistance of the SAP were evaluated. The results revealed that the SAP exhibited good pH sensitivity, with the absorption rate in water being 2.18 times that of cement slurry filtrate (CSF) at 95 °C. Furthermore, the FTIR spectrum showed that the SAP had a stable molecular structure. The secondary absorption rate in water of the SAP after soaking in CSF was not different from the original absorption rate. Styrene–butadiene latex (SBL) can be used to adjust the SAP’s absorption rate. The SAP’s absorption rate had a good exponential functional relationship with SBL dosage. The SBL dosage can be determined by the functional relationships to prepare a SAP with the required properties.