Reversible flocculation and deflocculation of ball clays

One of the main usages of ball clays is in the pottery industry. However, in order to transport the clay suspensions from the mine site, some distance away from the consumer, dewatering of the clay suspension must be performed. The main restriction is that any dewatering treatment must not interfere in obtaining deflocculated, free flowing suspensions required by the pottery manufacturer.Investigations in the flocculation/deflocculation of these clay suspensions, resulted in finding a technique capable of achieving both requirements. The technique employs flocculation by an anionic flocculant in the presence of 10 mM of magnesium sulfate, thus achieving the dewatering step. When the magnesium sulfate was removed from the flocculated suspensions by simply washing the filter cake, good deflocculation of the clay suspension was achieved at alkaline pH. The role of MgSO₄ in the flocculant adsorption/flocculation, and subsequently in the flocculant desorption/deflocculation, was discussed.     

The flocculation and de-watering of kimberlite clay slimes

The crushing of kimberlite at certain diamond mines produces a very persistent “slime” which is exceptionally difficult to filter or de-water. The colloidally stable component has been identified as a swelling clay, saponite, which carries a strong negative charge in alkaline media.Methods of coagulating or flocculating these slimes have been investigated; the most convenient method found was the combined use of magnesium sulphate and an anionic polyacrylamide (A-130 from B.T.I. Chemicals Ltd.). Optimal results were obtained only in a narrow range of conditions but with these it was possible to build flocs of any required size.The permeability and de-watering of coagulated or flocculated kimberlite slimes has been investigated with a hydraulic apparatus and in the capillary suction time (c.s.t.) apparatus. Typically compressible filter-cakes are obtained, their character varying greatly with the flocculation conditions.     

Comparison of controlling mechanisms of flocculation processes in estuaries

During estuarine mixing, dissolved metals come into the particulate phase due to the flocculation processes. Such processes are biologically vital. In the present study, controlling mechanisms of elemental flocculation during estuarine mixing in northern and southern estuaries of Iran in relation to the various physical and chemical parameters of waters have been compared. Except for zinc and lead, for other studied elements in Minab River, water flocculate at higher rates in comparison with the rivers flowing into the Caspian Sea. Redox potential might have negative effect on flocculation process in Minab Estuary. Contrary to rivers flowing into the Caspian Sea, in Minab River elemental flocculation is governed by dissolved organic carbon and it shows a non-liner and conservative behavior during estuarine mixing which implies that dissolved organic carbon originates from terrigenous source. The results also shows that maximum removal of elements occurs in lower salinities (1.5 to 5.8 ‰) for the rivers in North of Iran and 3.3 to 11.4 ‰ for Minab River in South of Iran. Flocculation of studied metal in different rivers results in reduction of overall metal pollution load by various percentages. The initial metal contents on river water and mean discharge of river might lead to higher flocculation rates.     

Selective flocculation of synthetic mineral mixtures using modified polymers

The role of the presence of active groups in polymers and operating variables such as conditioning time in producing flocculation in single and mixed mineral slimes made of hematite, quartz and chalcopyrite is examined at different conditions of pH. Selective flocculation was achieved on the basis of results obtained for single mineral systems as, for example, in the case of hematite—quartz mixtures using sulfonated polymer. Flocculation was found to go through a maximum as the mineral was conditioned with the polymer solution. Interestingly, the times of maximum flocculation for various minerals were sufficiently different from each other so that it could be considered as a potential factor for achieving selectivity. Also, cleaning of the selectively flocculated product by simple redispersion in water improved the separation. Electrokinetic studies conducted to study the mechanisms involved provided indication for the shift of shear plane.     

Selective flocculation applied to Barsuan iron ore tailings

Experiments have shown that it is possible to obtain a concentrate containing 65% iron, 1.8% alumina and 1.4% silica with an iron recovery of 80% from the tailings of Barsuan iron ore plant containing 52.5% iron, 7.4% alumina and 7.8% silica through selective flocculation employing starch. Key to such success lies in the manner in which the flocculant is desired from the parent starch. Barsuan deposit being a limiting case of typical fine-grained high-alumina iron ores, the results open up technical possibilities of better utilization of such deposits.     

紊流对粘性细颗粒泥沙絮凝影响

以分形聚集生长模型为基础,通过三维模拟泥沙颗粒在布朗运动、重力沉降和紊流作用下的碰撞、粘结和破碎过程,探讨了紊流对粘性细颗粒泥沙絮凝速度、絮团平均粒径及分形维数的时空影响。试验结果表明:紊流作用下,泥沙絮凝及絮团平均粒径的变化可分为加速段、等速段和减速段,絮凝等速段的作用时间及粒径等速增长段的速度均随紊动强度呈先增后减的规律,且中部区域的絮凝速度和絮团平均粒径较小;泥沙絮团分形维数随水流紊动强度的增加逐渐增大,最终趋于稳定,随时间呈先减后增的规律。模拟空间下部区域分形维数最大,上部次之,中部最小。     

Removal of surfactant from industrial wastewaters by coagulation flocculation process

Surfactants are among the most widely disseminated xenobiotics that contribute significantly to the pollution profile of sewage and wastewaters of all kinds. Among the currently employed chemical unit processes in the treatment of wastewaters, coagulation-flocculation has received considerable attention for yielding high pollutant removal efficiency. Jar-test experiments are employed in order to determine the optimum conditions for the removal of surfactants, COD and turbidity in terms of effective dosage, and pH control. Treatment with FeCl₃ proved to be effective in a pH range between 7 and 9. The process is very effective in the reduction of surfactants and COD, the removals are 99 and 88 % respectively, and increased BOD⁵/COD index from 0.17 to 0.41. In addition to precipitation coagulation process, adsorptive micellar flocculation mechanism seems contribute to the removal of surfactants and organic matters from this rejection.     

Role of metal species in flocculation rate during estuarine mixing

Flocculation can be considered as an effective mechanism in self-purification of metals during estuarine mixing. In the present investigation, flocculation of metals during mixing of Minab River water with the Strait of Hormuz (The Persian Gulf) water is studied for the first time. Flocculation behavior of metals (except for Pb) is governed by dissolved organic carbon. The source of dissolved organic carbon is terrigenous in the estuarine waters of study area. The general pattern of flocculation of studied metals is manganese (180 μg/L) > zinc (88 μg/L)> nickle (73 μg/L)> copper (30 μg/L)> lead (19 μg/L). The results of present study show that metal species are a very important factor in overall flocculation rate. It is found that solids and oxides have the highest and lowest flocculation levels, respectively. Eh-pH diagram indicated that lead is present as lead oxide in Minab River water and the least flocculation rate is attributed to this element. The results also showed that flocculation rate of metal species could be as solids > free ions ≈ hydroxides > oxides. The amount of metal flocculation is about 30.5, 6.6, 25.3, 10.4 and 62.5 ton/y for zinc, Pb, Ni, Cu and Mn, respectively.     

高岭土颗粒的絮凝沉降试验研究

粘性细颗粒泥沙在盐水中会产生絮凝。影响其絮凝的因素很多,矿物组成是其中的一个重要因素。选取高岭土作为研究对象,通过一系列试验得出所研究的高岭土的中值粒径为0.0084mm,最佳絮凝盐度为13‰,起动流速为8.5 cm/s~10 cm/s,由试验数据分析得出高岭土在不同流速条件下的淤积量以及淤积百分比,既而确定其不淤流速为40 cm/s。     

A theoretical approach to the magnetic flocculation of weakly magnetic minerals

Energy of interaction of a system of mineral paramagnetic and diamagnetic particles of colloidal dimensions is calculated under the influence of external magnetic field according to DLVO theory. Conditions of rapid flocculation into a potential well are derived in terms of threshold magnetic field as a function of particle size and magnetic susceptibility. The effect of surface potential, Debye-Hückel reciprocal length parameter and Hamaker constant is briefly discussed. The values of the flocculating magnetic field correspond more closely to reality than other theoretical models.     

Development of a selective flocculation process for a complex copper ore

Problems encountered in developing a selective flocculation process for a complex copper ore and ways of overcoming these difficulties are reported. To obtain a useful enrichment ratio, multiple stages of flocculation and redispersion were found necessary in order to release entrapped, unwanted particles. Particular attention was given to the dispersion process of the ore suspensions, and the importance of mechanical and chemical factors were established. The effects of solids content and quality of water on the performance of selective flocculation have been investigated. The possibility of developing new, selective or more powerful dispersants was confirmed and one such reagent was tested.     

Enhanced removal of dissolved metal ions in radioactive effluents by flocculation

Decontamination of radioactive effluents of low or intermediate level of radioactivity generated from different nuclear industries is done through the chemical precipitation route. The precipitates thus formed are of very fine sizes thereby requiring flocculation for faster settlement. The presence of polyacrylamide-based polymer not only enhances settling velocity but also increases removal of dissolved non-radioactive as well as radioactive metal ions from the liquid. About 99.5% of Cu²⁺ and Fe³⁺ ions are removed due to the presence of cationic Rishabh 611. Flocculation by either cationic or anionic flocculant has shown improvement in removal of radioactive strontium while turbidity of the liquid is reduced to a very low value (0.8 NTU). Decontamination factors (DF) of the effluents from different plants are improved by 3–5 times.     

Pelleting flocculation—an alternative technique to optimise sludge conditioning

The process of pelleting flocculation, a further development of classical flocculation technology, is defined as a formation of wet pellets directly in a liquid medium. Apart from well described mechanisms of flocculation like perikinetic and orthokinetic flocculation, the mechanism responsible for the formation of dense agglomerates is the mechanical syneresis guaranteed by the appropriate reactor form. Upon the two established models in the literature: the series system and the parallel system, experiments were performed to simulate a layer-by-layer particle deposition on the so-called “mother seeds” conforming to the parallel system.The present paper deals with the results originating from laboratory scale experiments with model sludge, kaolin suspension. The layering process was conducted in the presence of different cationic flocculants and the resulting relationships with respect to their nature and to the applied energy level have been assessed. The achieved agglomerates exhibit an “onion like” structure with densities up to 1.42 g/cm³ and solid matter content up to 48% after gravity dewatering. Thus generated sludge agglomerates reveal the optimisation potential for sludge treatment manifested by improved characteristics achieved during the conditioning.     

Synthesis of PAMG chelating polymers for the selective flocculation of copper minerals

Experimental techniques for preparation and characterization of polyacrylamide-glyoxal-bis-hydroxyanil (PAMG) selective flocculant are reported. The polymer could be prepared either by direct reaction of glyoxal-bis-hydroxyanil with polyacrylamide and formaldehyde, or by condensation of a diaminiphenol with glyoxal and formaldehyde on polyacrylamide.These reactions were confirmed by various techniques, namely, alcohol precipitation, dialysis, UV and IR spectroscopy. Fractionation of the polymer by membrane filtration and gel chromatography was also reported.     

Particulate matter grain-size characteristics and flocculation in a partially mixed estuary

The concentration and grain size of the natural and deflocculated inorganic suspended particulate matter were measured along the length of the Miramichi Estuary and interpreted with respect to flocculation and transport properties. Changes in particulate matter concentration are associated with regular changes in grain-size characteristics. In the turbidity maximum region of the estuary the suspended matter occurs mostly as large flocculated particles whereas, in the waters with lower particle concentrations, a larger proportion of the material occurs as fine material. At higher concentrations natural floc modes and inorganic grain modes vary simultaneously but at low concentrations the two modes vary inversely. This modal relationship and the variation in organic matter within the estuary is proposed to result from variation in inorganic—organic composition of flocs. Increase in settling rates due to flocculation is believed to increase the trapping effect of the estuarine circulation that produces the turbidity maximum.     

Mechanisms of large landslides

SummaryMechanisms of Large Landslides The moving components of many large landslides show a remarkable tendency to remain in more or less undisturbed sequential order. In the present study this lack of laminar or turbulent flow is mathematically analyzed and explained. The high energy concentration thus resulting for the zone near the gliding surfaces points to self-lubrication by transformed (fused or dissociated) rock as a fundamental tribological mechanism. The idea is backed by two important facts: the impossibility to explain the observed economy of locomotion (and especially its increase with size) by any of the mechanisms considered hitherto; and a calculation yielding an unexpectedly low amount of energy susceptible to be dissipated far away from the gliding surfaces. Further analysis demonstrates numerically the plausibility of the self-lubrication concept both for primitive and carbonate rock. The development of useful prediction algorithms is not impossible in the future.

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ZusammenfassungMechanismen groer Bergstürze Die Trümmerströme vieler großer Bergstürze zeigen eine bemerkenswerte Tendenz zum Verbleiben in mehr oder weniger undurchmischtem Verband. In der vorliegenden Arbeit wird dieses Fehlen laminarer oder turbulenter Strömung auf Grund einer mathematischen Untersuchung erklärt. Die dabei resultierende hohe Energiedichte in der Nähe der Gleitflächen deutet auf Selbstschmierung durch transformiertes (geschmolzenes oder dissoziiertes) Gestein als entscheidenden tribologischen Mechanismus. Zwei wesentliche Tatsachen sprechen für diese Idee: das Versagen aller bisher vorgeschlagenen Mechanismen bei der Erklärung der beobachteten Bewegungsökonomie, speziell im Hinblick auf deren Steigerung in Funktion der Größe; und der rechnerisch ermittelte überraschend niedrige Energieanteil, der in größerer Entfernung von den Gleitflächen umgesetzt werden kann. Eine weitere Rechnung demonstriert zahlenmäßig die Plausibilität der Selbstschmierung sowohl für Urgesteine wie für Kalke. Die Entwicklung brauchbarer Vorhersage-Algorithmen rückt damit in den Bereich des Möglichen.

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RésuméLes mécanismes de gros éboulements Les composantes de gros éboulements montrent une tendance remarquable à se déplacer dans un ordre plus ou moins invariable. L'étude explique mathématiquement cette absence d'écoulements laminaire ou turbulant. La haute concentration d'énergie aux environs immédiats des surfaces de glissement implique la possibilité d'une auto-lubrification par le rocher métamorphosé (soit fondu, soit dissocié) en tant que mécanisme tribologique fondamental. Deux faits importants appuient cette hypothèse: d'une part l'impossibilité jusqu'à maintenant d'expliquer l'économie d'énergie observée (et spécialement en corrélation avec la grandeur de l'évènement) par un mécanisme quelconque; d'autre part la fraction d'énergie déterminée par calcul, étonnament basse, susceptible d'être métamorphosée à grande distance des surfaces de glissement. En outre le calcul démontre la possibilité du mécanisme d'auto-lubrification pour les plus importants types de rochers (primitifs et sédimentaires). Le développement futur d'algorithmes de prédiction utilisables entre de ce fait dans le domaine du possible.

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Notation a acceleration (m/s²) - A area (m²) - c specific heat (J/kg °C) - C transformation heat (J/kg) - d distance between two narrow passages (m) - e base of natural logarithms = 2.72 - e thickness of layer (m) - g gravitational acceleration = 9.81 m/s² - h thickness of mass (m) - k resistance coefficient - L global coefficient describing tribological quality (m/s⁴) - m mass (kg) - M lubrication quality factor - p pressure (Pa) - P power (W) - r wave amplitude (m) - s air cushion or gap thickness (m) - t time (s) - v velocity, speed (m/s) - V volume (m³) - W specific energy (J/kg) - x distance travelled (m) - z height (m) - Z height of center of gravity (m) - slope angle - relative portion of volume occupied by voids - dissipation coefficient - difference - relative fraction of A acting as narrow passage - depth (m) - viscosity (kg/ms) - temperature (°C) - adiabatic constant of air = 1.4 - wavelength (m) - µ coefficient of friction (solid state) - average coefficient of friction - Ludolf's number = 3.14 - density (kg/m³) - fidelity coefficient - jet contraction factor Indices a primitive rock - A air cushion - b feldspar - c quartz - d lubricant generated from primitive rock - d dissipation - e sedimentary rock - E air escape gap - f CaO - g CO₂ - h lubricant generated from sedimentary rock - i ordinal number - L lubricant - M total area - R rock - o initial, basic, 30 = after 30 s With 12 Figures     

The flocculation of iron,aluminium and humates from river water by electrolytes

This paper reports on the flocculation of iron, aluminium and humates from Scottish river water by the three major salts in sea water. The molarities of the salts required to precipitate the maximum amounts of Fe, Al and humates decrease in the order: NaCl, MgCl₂, CaCl₂. The maximum amounts of a species precipitated by the salts are shown to increase in the same order. Chemical and electrostatic interactions are both involved in the flocculation process.     

Selective flocculation of cassiterite in mixtures with quartz using a modified polyacrylamide flocculant

Polyacrylamide was modified to give a linear polymer containing 69% amide, 23% carboxylic and 8% hydroxamic acid groups. The modified polymer selectively flocculates cassiterite from mixtures with quartz in aqueous suspensions at a pH between 3.5 and 7.     

三峡库区泥沙絮凝临界条件现场测量

三峡库区絮凝现象是细颗粒泥沙淤积的重要原因,泥沙絮凝临界条件对三峡库区泥沙淤积规律和模拟具有重要意义。在三峡库区忠县和奉节河段开展泥沙絮凝的现场测量,基于声学多普勒流速仪（Acoustic Doppler Velocimeter,ADV）和泥沙采样测得同步的瞬时流速和含沙量,通过泥沙扩散理论反算现场泥沙沉速及絮团粒径,得到了三峡库区泥沙絮凝度及其与粒径、流速和含沙量的关系。结果表明:库区细颗粒泥沙发生絮凝,且多为中轻度絮凝,重度絮凝较少;库区泥沙絮凝的临界粒径约为0.018 mm,临界流速约为0.7 m/s,临界含沙量约为0.8 kg/m3。研究结果可为三峡库区泥沙的运动规律以及泥沙淤积模拟等提供一定的理论支撑。