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

The implications of physical conditions of the feedwell on the rheological properties of synthetic copper tailings, flocculated in seawater, were analysed. The mixing intensity of flocculation was related to the structural characteristics of the aggregates, and the outcomes were linked to the yield stress of the pulp sediments. Tailings settling assays were conducted by using a 30 mm turbine type stirrer with an in-situ aggregate size characterisation. The structural characteristics of the aggregates were determined by using the focused beam reflectance measurement (FBRM). After a mixing time between the pulp and the flocculant, the sample was allowed to settle for 2.5 h, where the variation of the sediment height was minimal. The sediment was gently removed and subjected to rheological characterisation. The yield stress was measured on an Anton Paar MCR 102 rheometer (ANAMIN Group, Santiago, Chile), with a vane-in-cup configuration. The mixing intensity was related to the characteristics of the aggregates, and the outcomes were linked to the yield stress of the flocculated pulp sediments. More aggressive hydrodynamics deteriorated the structure of the aggregates, promoting the reduction of both its size and the fractal dimension. This brought direct consequences on the rheological properties of the sediments: at higher mixing level, the yield stress was lower. The explanation lies in the structural changes of the aggregates, where at a fixed mixing rate, the yield stress presented a seemingly exponential increase over the fractal dimension. Additionally, correlations were found between the rheological properties with settling rate and aggregate size.

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Effect of Pre-Shear on Agglomeration and Rheological Parameters of Cement Paste

Materials ◽

10.3390/ma13092173 ◽

2020 ◽

Vol 13 (9) ◽

pp. 2173

Author(s):

Mareike Thiedeitz ◽

Inka Dressler ◽

Thomas Kränkel ◽

Christoph Gehlen ◽

Dirk Lowke

Keyword(s):

Yield Stress ◽

Mixing Time ◽

Length Distribution ◽

Chord Length ◽

Rheological Parameters ◽

Reflectance Measurement ◽

Time Dynamic ◽

Chord Length Distribution ◽

In Situ Investigation

Cementitious pastes are multiphase suspensions that are rheologically characterized by viscosity and yield stress. They tend to flocculate during rest due to attractive interparticle forces, and desagglomerate when shear is induced. The shear history, e.g., mixing energy and time, determines the apparent state of flocculation and accordingly the particle size distribution of the cement in the suspension, which itself affects suspension’s plastic viscosity and yield stress. Thus, it is crucial to understand the effect of the mixing procedure of cementitious suspensions before starting rheological measurements. However, the measurement of the in-situ particle agglomeration status is difficult, due to rapidly changing particle network structuration. The focused beam reflectance measurement (FBRM) technique offers an opportunity for the in-situ investigation of the chord length distribution. This enables to detect the state of flocculation of the particles during shear. Cementitious pastes differing in their solid fraction and superplasticizer content were analyzed after various pre-shear histories, i.e., mixing times. Yield stress and viscosity were measured in a parallel-plate-rheometer and related to in-situ measurements of the chord length distribution with the FBRM-probe to characterize the agglomeration status. With increasing mixing time agglomerates were increasingly broken up in dependence of pre-shear: After 300 s of pre-shear the agglomerate sizes decreased by 10 µm to 15 µm compared to a 30 s pre-shear. At the same time dynamic yield stress and viscosity decreased up to 30% until a state of equilibrium was almost reached. The investigations show a correlation between mean chord length and the corresponding rheological parameters affected by the duration of pre-shear.

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Reducing Magnesium within Seawater Used in Mineral Processing to Improve Water Recovery and Rheological Properties When Dewatering Clay-Based Tailings

Polymers ◽

10.3390/polym14020339 ◽

2022 ◽

Vol 14 (2) ◽

pp. 339

Author(s):

Matías Jeldres ◽

Norman Toro ◽

Sandra Gallegos ◽

Pedro Robles ◽

Iván Salazar ◽

...

Keyword(s):

Yield Stress ◽

Aggregate Size ◽

Complete Removal ◽

Mineral Processing ◽

Water Recovery ◽

Concentrated Suspensions ◽

Reflectance Measurement ◽

Pre Treatment ◽

A Minor ◽

The Impact

In areas where access to water for mineral processing is limited, the direct use of seawater in processing has been considered as an alternative to the expense of its desalination. However, efficient flotation of copper sulfides from non-valuable phases is best achieved at a pH > 10.5, and raising the pH of seawater leads to magnesium precipitates that adversely affect subsequent tailings dewatering. Seawater pre-treatment with lime can precipitate the majority of magnesium present, with these solids then being removed by filtration. To understand how such treatment may aid tailings dewatering, treated seawater (TSw) was mixed with raw seawater (Rsw) at different ratios, analyzing the impact on the flocculated settling rate, aggregate size as measured by focused beam reflectance measurement (FBRM), and vane yield stress for two synthetic clay-based tailings. A higher proportion of Tsw (10 mg/L Mg2+) led to larger aggregates and higher settling rates at a fixed dosage, with FBRM suggesting that higher calcium concentrations in Tsw may also favor fines coagulation. The yield stress of concentrated suspensions formed after flocculation decreased with higher proportions of Tsw, a consequence of lower flocculant demand and the reduced presence of precipitates; while the latter is a minor phase by mass, their high impact on rheology reflects a small particle size. Reducing magnesium concentrations in seawater in advance of use in processing offers advantages in the water return from thickening and subsequent underflow transport. However, this may not require complete removal, with blending Tsw and Rsw an option to obtain acceptable industrial performance.

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

Metals ◽

10.3390/met10020240 ◽

2020 ◽

Vol 10 (2) ◽

pp. 240

Author(s):

Gonzalo R. Quezada ◽

Luís Ayala ◽

Williams H. Leiva ◽

Norman Toro ◽

Pedro G. Toledo ◽

...

Keyword(s):

Fractal Dimension ◽

Aggregate Size ◽

Population Balance ◽

Cost Effective ◽

Time Dependent ◽

Balance Model ◽

Optimal Conditions ◽

Reflectance Measurement ◽

Correct Representation

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.

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Improving the Flocculation Performance of Clay-Based Tailings in Seawater: A Population Balance Modelling Approach

Minerals ◽

10.3390/min10090782 ◽

2020 ◽

Vol 10 (9) ◽

pp. 782

Author(s):

Gonzalo R. Quezada ◽

Matías Jeldres ◽

Pedro Robles ◽

Norman Toro ◽

David Torres ◽

...

Keyword(s):

Fractal Dimension ◽

Goodness Of Fit ◽

Aggregate Size ◽

Population Balance ◽

Magnesium Content ◽

Balance Model ◽

Collision Efficiency ◽

Reflectance Measurement ◽

Vacuum Filtration ◽

The Impact

A population balance model described the flocculation of clay-based mining tailings in treated seawater with reduced magnesium content. For the treatment, 0.06 M of lime was added to the liquor, generating solid magnesium complexes that were subsequently removed by vacuum filtration. Magnesium content varied between 10–1440 ppm when mixing raw seawater with treated seawater. The aggregate size was analysed by the Focused Beam Reflectance Measurement (FBRM) technology. The model follows the dynamics of the aggregation-rupture and it provides a good approximation to the temporal evolution. A decrease in collision efficiency was implemented as an indicator of the polymer depletion, describing the size reduction. Lower magnesium content makes larger aggregates with a higher fractal dimension, but an increase in the concentration of clays reduces both the size of aggregates and the fractal dimension, indicating more open and porous structures, with higher permeability to the passage of fluid. The model efficiently illustrates the experimental data, with R-square (R2) greater than 0.9 and Goodness of Fit (GoF) greater than 95% in most cases, wherein the fitting parameters allowed for analysing the impact of magnesium and clays on the collision efficiency, collision frequency, and fragmentation rate. The model is predictive with few parameters, and it is potentially a powerful tool for water management optimisation.

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Using Coupled Rheometer-FBRM to Study Rheological Properties and Microstructure of Cemented Paste Backfill

Advances in Materials Science and Engineering ◽

10.1155/2019/6813929 ◽

2019 ◽

Vol 2019 ◽

pp. 1-10 ◽

Cited By ~ 2

Author(s):

Hongjiang Wang ◽

Liuhua Yang ◽

Hong Li ◽

Xu Zhou ◽

Xiaotian Wang

Keyword(s):

Shear Rate ◽

Rheological Properties ◽

Yield Stress ◽

Rheological Behavior ◽

Shear Thickening ◽

Threshold Value ◽

Rheological Parameters ◽

Cemented Paste Backfill ◽

Reflectance Measurement ◽

Paste Backfill

Rheological properties, such as the yield stress, viscosity, and thixotropy, are related to the microstructure of cemented paste backfill (CPB). To highlight the relationship, two instruments were combined to measure the changes in the microstructure and the rheological properties of CPB simultaneously. In this way, the particle/agglomerate size distribution characterized by the focused beam reflectance measurement (FBRM) and the rheological factors measured by the rheometers could be directly linked. The results show that when under shearing, the intrinsic network structure of CPB responds to the shear-induced stresses with the interference of interparticle forces, leading to changes in the rheological behavior. Shear thinning can be found in CPB suspensions with a microstructure that is either loose interconnection or random. With an increase in the shear rate, random collisions among particles become organized in the flow, lowering the yield stress and viscosity. However, when the shear rate exceeds a certain threshold value, the rheological parameters change as a result of shear thickening. The results of this study contribute to better understanding of the complex rheological behavior of CPB.

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A Criterion for Estimating the Strength of Flocculated Aggregates in Salt Solutions

Minerals ◽

10.3390/min11070713 ◽

2021 ◽

Vol 11 (7) ◽

pp. 713

Author(s):

Matías Jeldres ◽

Luis Ayala ◽

Pedro Robles ◽

Edelmira Gálvez ◽

Williams H. Leiva ◽

...

Keyword(s):

Shear Rate ◽

Mixing Time ◽

Length Distribution ◽

Aggregate Size ◽

Final Size ◽

Separation Processes ◽

Reflectance Measurement ◽

The Mean ◽

Solid Liquid ◽

Saline Solutions

A simple criterion is proposed to quantitatively estimate the resistance of aggregates based on incremental mechanical shear disturbances. Aggregate strength can be affected by the hydrodynamic conditions under which flocculation occurs; therefore, an experimental method is standardized to determine the resistance of aggregate structures that are formed under defined conditions of salinity (NaCl 0–0.1 M), mixing time (3 min), and mean shear rate (G = 273 s−1). Kaolin particles were flocculated in saline solutions with an anionic flocculant of high molecular weight. The method involves increasing the mean shear rate (G = 0–1516 s−1). Each increment represents a new experiment that starts from the base of 273 s−1. Target aggregates are increasingly fragmented as mechanical disturbance increases. The monotonic relationship between the mean shear rate increments (ΔG) and the final size of the aggregates is used for a quantitative estimate of the resistance of the target aggregates since this resistance underlies this relationship. The evolution of aggregate size is analyzed by the Focused Beam Reflectance Measurement (FBRM) method, which may capture the chord length distribution on concentrated slurries. To estimate and compare the resistance of the target aggregates in solutions with different salinities, a pseudo-first-order model that describes the rupture degree as a function of shear rate increments obtains the characteristic shear rate. The rupture percentage is reached with considerably lower agitation increments at higher salinity than at low salinity. This criterion is expected to help improve the efficiency of solid–liquid separation processes, especially in plants operating with seawater, be it raw or partially desalinated.

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Use of Multi-Anionic Sodium Tripolyphosphate to Enhance Dispersion of Concentrated Kaolin Slurries in Seawater

Metals ◽

10.3390/met11071085 ◽

2021 ◽

Vol 11 (7) ◽

pp. 1085

Author(s):

Williams Leiva ◽

Norman Toro ◽

Pedro Robles ◽

Edelmira Gálvez ◽

Ricardo Ivan Jeldres

Keyword(s):

Rheological Properties ◽

Fine Particles ◽

Sodium Tripolyphosphate ◽

Mining Industry ◽

Chord Length ◽

Water Recovery ◽

Reflectance Measurement ◽

Anionic Charge ◽

Free Environment ◽

The Impact

This research aims to analyze the impact of sodium tripolyphosphate (STPP) as a rheological modifier of concentrated kaolin slurries in seawater at pH 8, which is characteristic of copper sulfide processing operations. The dispersion phenomenon was analyzed through chord length measurements using the focused beam reflectance measurement (FBRM) technique, complementing size distributions in unweighted and square-weighted modes. The reduction of the rheological properties was significant, decreasing from 231 Pa in a reagent-free environment to 80 Pa after the application of STPP. A frequency sweep in a linear viscoelastic regime indicated that by applying a characteristic dosage of 0.53 kg/t of STPP, the pulp before yielding increases its phase angle, which increases its liquid-like character. Measurements of the chord length verified the dispersion of particles, which showed an apparent increase in the proportion of fine particles and a reduction of the coarser aggregates when STPP was applied. Measurements of the zeta potential suggested that the high anionic charge of the reagent (pentavalent) increases the electrostatic repulsions between particles, overcoming the effect of cations in seawater. The results are relevant for the mining industry, especially when the deposits have high contents of complex gangues, such as clays, that increase the rheological properties. This increases the energy costs and water consumption needed for pumping the tailings from thickeners to the tailing storages facilities. The strategies that allow for the improvement of the fluidity and deformation of the tailings generate slack in order to maximize water recovery in the thickening stages.

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Comparison of the Effects of Conching Parameters on the Contents of Three Dominant Flavan3-ols, Rheological Properties and Sensory Quality in Chocolate Milk Mass Based on Liquor from Unroasted Cocoa Beans

Molecules ◽

10.3390/molecules26092502 ◽

2021 ◽

Vol 26 (9) ◽

pp. 2502

Author(s):

Bogumiła Urbańska ◽

Hanna Kowalska ◽

Karolina Szulc ◽

Małgorzata Ziarno ◽

Irina Pochitskaya ◽

...

Keyword(s):

Rheological Properties ◽

Yield Stress ◽

Sensory Quality ◽

Raw Material ◽

Antioxidant Compounds ◽

Chocolate Milk ◽

Cocoa Beans ◽

Variable Parameters ◽

The Relationship ◽

Manufacturing Parameters

The content of polyphenols in chocolate depends on many factors related to the properties of raw material and manufacturing parameters. The trend toward developing chocolates made from unroasted cocoa beans encourages research in this area. In addition, modern customers attach great importance to how the food they consume benefits their bodies. One such benefit that consumers value is the preservation of natural antioxidant compounds in food products (e.g., polyphenols). Therefore, in our study we attempted to determine the relationship between variable parameters at the conching stage (i.e., temperature and time of) and the content of dominant polyphenols (i.e.,catechins, epicatechins, and procyanidin B2) in chocolate milk mass (CMM) obtained from unroasted cocoa beans. Increasing the conching temperature from 50 to 60 °C decreased the content of three basic flavan-3-ols. The highest number of these compounds was determined when the process was carried out at 50 °C. However, the time that caused the least degradation of these compounds differed. For catechin, it was 2 h; for epicatechin it was 1 h; and for procyanidin it was 3 h. The influence of both the temperature and conching time on the rheological properties of chocolate milk mass was demonstrated. At 50 °C, the viscosity and the yield stress of the conched mass showed its highest value.

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Study of Properties of Expanded Graphite – Polymer Porous Composite by Acoustic Emission Method

Archives of Metallurgy and Materials ◽

10.2478/amm-2013-0169 ◽

2013 ◽

Vol 58 (4) ◽

pp. 1331-1336 ◽

Cited By ~ 1

Author(s):

J. Berdowski ◽

S. Berdowska ◽

F. Aubry

Keyword(s):

Acoustic Emission ◽

Structural Changes ◽

Structural Characteristics ◽

Physical And Mechanical Properties ◽

Expanded Graphite ◽

Composite Membranes ◽

Acoustic Emission Method ◽

Emission Method ◽

Graphite Composite ◽

Wide Range

Abstract The purpose of this paper was to investigate the physical and mechanical properties of compressed expanded graphite (CEG) and their porous derivatives after impregnation, polymerization; and carbonization by the use of acoustic emission method (AE). The mechanical and structural characteristics of compressed expanded graphite and their three groups of porous composites after each technological process are presented and discussed. The measurements of acoustic emission parameters in these materials were carried out at wide range of frequency of the waves (0.1÷2.5 MHz). The changes of two of parameters: - AE pulses counts rate and spectrum distribution of AE waves - are presented in this paper. The analysis of the respective parameters AE also gives possibility to determine the micro- and macro structural changes of materials at different levels of technological processes. Applications of these materials as catalysts with high specific surface make them very interesting subject of study. Also compressed expanded graphite composite membranes prepared from furfuryl alcohol polymers are promising for gas separation.

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The structure and changes of China’s land system

China Agricultural Economic Review ◽

10.1108/caer-05-2018-0102 ◽

2019 ◽

Vol 11 (3) ◽

pp. 471-488 ◽

Cited By ~ 3

Author(s):

Liu Shouying

Keyword(s):

Economic Growth ◽

Institutional Change ◽

Structural Changes ◽

Structural Characteristics ◽

Institutional Arrangements ◽

Reform Process ◽

Content Type ◽

The Past ◽

Land System ◽

Rapid Economic Growth

Purpose The purpose of this paper is to analyze the structure and changes of China’s land system. To achieve this aim, the paper is divided into four parts. The first part gives a brief introduction to the structural characteristics of the Chinese land institutional arrangements; the second part analyzes the reform process of the land system in the past 40 years and its path of change; the third part engages the discussion about the historic contribution made by the land institutional change to rapid economic growth and structural changes; and the final part is conclusion and some policy implications. Design/methodology/approach After 40 years of reforms and opening up, China has not only created a growth miracle unparalleled for any major country in human history, but also transformed itself from a rural to an urban society. Behind this great transformation is a systemic reform in land institutions. Rural land institutions went from collectively owned to household responsibility system, thereby protecting farmers’ land rights. This process resulted in long-term sustainable growth in China’s agriculture, a massive rural-urban migration and a historical agricultural transformation. The conversion of agricultural land to non-agricultural uses and the introduction of market mechanisms made land a policy tool in driving high economic growth, industrialization and urbanization. Findings Research shows that the role of land and its relationship with the economy will inevitably change as China’s economy enters a new stage of medium-to-high speed growth. With economic restructuring, low-cost industrial land will be less effective. Urbanization is also shifting from rapid expansion to endogenous growth so that returns on land capitalization will decrease and risks will increase. Therefore, China must abandon land-dependent growth model through deepening land reforms and adapt a new pattern of economic development. Originality/value This paper gives a brief introduction to the structural characteristics of the Chinese land institutional arrangements, analyzes the reform process of the land system in the past 40 years and its path of change, and evaluates the historic contribution made by the land institutional change to rapid economic growth and structural changes.

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