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By George Gardner

THE application of wet cleaning processes for the beneficiation of bituminous coal has created in some localities a problem in the recovery and disposal of fine solids in the washery water. The maximum allowable concentration of these solids in the washery circuit that is consistent with satisfactory operation of the cleaning units remains a controversial point. It has, however, been generally recognized for a number of years that some degree of control should be exerted over the concentration of such material. Early methods of control involved intermittent or continuous dis-charge of a portion of the plant slurry into near-by streams or settling ponds, and this persisted even after the adoption of settling tanks or cones. The practice is not always economical, for two reasons: first, because of the waste of coal, and, second, because it is sometimes difficult and expensive to obtain an adequate supply of water. The latter condi-tion often is aggravated by chemical treatment of the make-up water that is necessary to prevent excessive corrosion of plant equipment. The modern approach to this problem has been the adoption of continuous thickening devices. However, because such equipment occupies consid-erable plant space and is somewhat expensive to construct, the practice of loading these thickeners beyond their rated capacity is widespread, there-fore often the performance of such units is not altogether satisfactory. In recent years, European washeries have increased the rate of settling of the fine coal from the slurry by the addition of specially pre-pared starch solutions. These reagents cause flocculation of the solid particles and thereby increase the rate of sedimentation.

Jan 1, 1939

By George Gardner

THE application of wet cleaning processes for the beneficiation of bituminous coal has created in some localities a problem in the recovery and disposal of fine solids in the washery water. The maximum allowable concentration of these solids in the washery circuit that is consistent with satisfactory operation of the cleaning units remains a controversial point. It has, however, been generally recognized for a number of years that some degree of control should be exerted over the concentration of such material. Early methods of control involved intermittent or continuous dis-charge of a portion of the plant slurry into near-by streams or settling ponds, and this persisted even after the adoption of settling tanks or cones. The practice is not always economical, for two reasons: first, because of the waste of coal, and, second, because it is sometimes difficult and expensive to obtain an adequate supply of water. The latter condi-tion often is aggravated by chemical treatment of the make-up water that is necessary to prevent excessive corrosion of plant equipment. The modern approach to this problem has been the adoption of continuous thickening devices. However, because such equipment occupies consid-erable plant space and is somewhat expensive to construct, the practice of loading these thickeners beyond their rated capacity is widespread, there-fore often the performance of such units is not altogether satisfactory. In recent years, European washeries have increased the rate of settling of the fine coal from the slurry by the addition of specially pre-pared starch solutions. These reagents cause flocculation of the solid particles and thereby increase the rate of sedimentation.

Jan 1, 1939

By George R. Gardner, Kenneth B. Ray

THE application of wet cleaning processes for the beneficiation of bituminous coal has created in some localities a problem in the recovery and disposal of fine solids in the washery water. The maximum allowable concentration of these solids in the washery circuit that is consistent with satisfactory operation of the cleaning units remains a controversial point. It has, however, been generally recognized for a number of years that some degree of control should be exerted over the concentration of such material. Early methods of control involved intermittent or continuous discharge of a portion of the plant slurry into near-by streams or settling ponds, and this persisted even after the adoption of settling tanks or cones. The practice is not always economical, for two reasons: first, because of the waste of coal, and, second, because it is sometimes difficult and expensive to obtain an adequate supply of water. The latter condition often is aggravated by chemical treatment of the make-up water that is necessary to prevent excessive corrosion of plant equipment. The modern approach to this problem has been the adoption of continuous thickening devices. However, because such equipment occupies considerable plant space and is somewhat expensive to construct, the practice of loading these thickeners beyond their rated capacity is widespread, therefore often the performance of such units is not altogether satisfactory. In recent years, European washeries have increased the rate of settling of the fine coal from the slurry by the addition of specially prepared starch solutions. These reagents cause flocculation of the solid particles and thereby increase the rate of sedimentation. The first important work on the flocculation and clarification of coal slurry was done by Henry, who developed the Henry process and used it successfully in Belgian preparation plants. Soon after the initiation in Belgium, the process was introduced into England, where subsequent investigation developed similar processes, which were successfully used in

Jan 1, 1939

By John Ralston, Jonas Addai-Mensah, Patience Mpofu

The flocculation and dewatering behaviour of kaolinite (non swelling) and smectite (swelling) clay dispersions has been investigated using hydrolysable metal ions Mn(II) and Ca(II) and anionic polyacrylamide-acrylate copolymer (PAM) at pH 7.5 and 10.5. A pH-dependent, specific metal ion adsorption behaviour, accompanied by a marked reduction in particle zeta potential and slurry shear yield stress, was observed to have a profound influence on the colloid stability of both types of clays. Due to the differences in the cation exchange capacity, the smectite clay dispersion required a higher amount of metal ions than kaolinite dispersion to produce similar effects. The adsorption density of the anionic PAM at the negatively charged clay particle surfaces correlated well with metal ion hydrolysis and adsorption behaviour, all of which had a strong effect on slurry settling rate and extent of consolidation. At pH 7.5 where Mn(II) ions hydrolyse, metal ion and flocculant adsorption densities were both greater in the presence of Mn(II) than Ca(II) ions. At pH 10.5, however, where Ca(II) ions begins to hydrolyse, higher adsorption densities were observed for Ca(II) ions in comparison with Mn(II) ions, as the latter hydrolysed completely and precipitated. The metal ion mediated flocculant adsorption led to improved hydrogen bond driven particle bridging and facilitated charge neutralisation flocculation mechanisms which significantly enhanced the dewaterability of both clay dispersions.

Jan 1, 2003

By John Ralston, Jona Addai-Mensah, Patience Mpofu

The flocculation and dewatering behaviour of kaolinite (non swelling) and smectite (swelling) clay dispersions has been investigated using hydrolysable metal ions Mn(II) and Ca(II) and anionic polyacrylamide-acrylate copolymer (PAM) at pH 7.5 and 10.5. A pH-dependent, specific metal ion adsorption behaviour, accompanied by a marked reduction in particle zeta potential and slurry shear yield stress, was observed to have a profound influence on the colloid stability of both types of clays. Due to the differences in the cation exchange capacity, the smectite clay dispersion required a higher amount of metal ions than kaolinite dispersion to produce similar effects. The adsorption density of the anionic PAM at the negatively charged clay particle surfaces correlated well with metal ion hydrolysis and adsorption behaviour, all of which had a strong effect on slurry settling rate and extent of consolidation. At pH 7.5 where Mn(II) ions hydrolyse, metal ion and flocculant adsorption densities were both greater in the presence of Mn(II) than Ca(II) ions. At pH 10.5, however, where Ca(II) ions begins to hydrolyse, higher adsorption densities were observed for Ca(II) ions in comparison with Mn(II) ions, as the latter hydrolysed completely and precipitated. The metal ion mediated flocculant adsorption led to improved hydrogen bond driven particle bridging and facilitated charge neutralisation flocculation mechanisms which significantly enhanced the dewaterability of both clay dispersions.

Jan 1, 2003

By D. M. Deason, R. M. Chhatre, G. Y. Onoda

INTRODUCTION The treatment of colloidal suspensions is a subject of increasing interest in mining and benefication (1). Colloidal suspensions are not readily operated upon by mechanical and physical methods useful with coarse suspensions, such as filtration, thickening, and flotation. This is because colloids are strongly affected by interfacial and interparticle forces that may be large compared with, and resistant to, external forces. The degree and type of interactions between colloids can be modified by small additions of reagents such as coagulants, flocculants, dispersants, and immiscible liquids. These alterations in turn change the properties of the suspension and provide possible opportunities for transforming suspensions to a more favorable condition for a given processing operation. Phosphate slimes are an example of a colloidal system of interest today. In the mining and beneficiation of phosphate rock in Florida, slimes are a waste product. The phosphate ore (called matrix in the industry) is slurrified hydraulically and pumped to a beneficiation plant, where the -150 mesh material is removed by cycloning from the coarser phosphate rock and silica. The resulting -150 mesh slurry, called phosphate slime, is pumped to large impoundments. The solid content of the slime entering the impoundment is around four weight percent, and over 80% of the solids is less than one micron in size. The immediate problems with phosphate slime relate to their disposal (2, 3). The disposal problem is associated with the very large volumes and the poor dewatering characteristics of the slimes. To have sufficient impoundment volume, large earthen dams are built around the mined areas. The volume above ground level approaches and

Jan 1, 1980

By S. K. Kawatra, H. Haselhuhn

"In many mineral processing applications it is necessary to know the isoelectric points of the various minerals in the ore to properly perform flotation and other mineral separations. However, current zeta potential analysis technology used to determine the isoelectric point of a particle suspension cannot deliver the isoelectric point of each individual mineral, just an average of the mineral system. Traditionally, individual isoelectric points have been gathered by testing pure, synthetic minerals. These values can vary widely depending on the mineral synthesis procedure and the water quality used during the isoelectric point analysis. A more robust approach for determining the actual isoelectric point of a particular mineral in a mixture of minerals is needed. This paper details a method for determining the isoelectric point of an iron oxide mineral in a siliceous iron ore. The method uses a laser scattering particle size analyzer and a pH electrode to determine the pH at which the liberated mineral particles begin to flocculate as pH is decreased. The pH at which the average particle size rises dramatically is the isoelectric point of the mineral with the highest isoelectric point in the ore. This measurement technique was used on natural hematite, goethite and siderite ores as well as a synthetic mixture of pure silica and pure hematite. The results for synthetic hematite mixtures were comparable to literature values.IntroductionRecently there has been an increased interest in the processing of low-grade iron ores (Bolen, 2014; Carlson and Kawatra, 2008, 2011, 2013; Halt et al., 2014; Halt and Kawatra, 2014; Haselhuhn 2012, 2013; Haselhuhn et al., 2012a, 2012b; Kawatra and Halt, 2011; Liu et al., 2014; Manouchehri, 2014; Sandvik and Larsen, 2014; Semberg et al., 2014). The zeta potential of iron ore minerals is a very important and often overlooked aspect of iron ore mineral processing. Zeta potential is the charge at the shear plane of a surface in an aqueous environment (Carlson and Kawatra, 2013). Many ores consist of a variety of minerals differing in zeta potential. This property of a particle surface in water is responsible for either keeping the particles dispersed from each other or flocculated to each other. This is important during many operations such as flotation, desliming and thickening. Zeta potential is primarily a function of the pH of the water and the mineralogy of the particles, though certain ions within the water can also have a significant impact (Haselhuhn, 2012). Consider the following situation: silica (SiO2) particles and hematite (Fe2O3) particles are suspended in an aqueous solution. These two types of minerals have drastically different zeta potentials throughout the pH spectrum (Esumi et al., 1988). In alkaline conditions, both types of particles exhibit negative zeta potentials and will tend to disperse from each other. In acidic conditions (between pH of 3 and 6), silica has a negative zeta potential while hematite has a positive zeta potential, so these surfaces will tend to be attractive to each other and the particles will flocculate and settle. This phenomenon is visually described in Fig. 1. The pH at which the two minerals begin to attract to each other, or destabilize, is near hematite’s isoelectric point. The isoelectric point is defined as the pH at which the surface has a net zero zeta potential (Carlson and Kawatra, 2013)."

Jan 1, 2015

By J. E. Gebhardt, L. Piga, G. Schena

The possibility of beneficiating a low-grade alunite ore from the Tuscany region of Italy was examined. Flocculation and flotation techniques were investigated to separate alunite and kaolinite from the ore, which also contained feldspar and quartz. Flotation was performed at pH 6.5 with oleic acid as collector and sodium silicate as dispersant. A concentrate containing 12% alunite with a recovery of about 65% and a concentrate containing 28% alunite with a recovery of 84% were achieved from the -38-µm feed samples containing 5.0% and 12.9% alunite, respectively. Poor recovery of alunite was achieved by flocculation methods.

Jan 1, 1999

By S. Behl, S. Mathur

It was previously reported that dolomite samples from different locations showed varying flocculation behavior with poly(ethylene oxide) (PEO). In this study, a Florida dolomite sample was examined, and it was determined that palygorskite associated with dolomite was responsible for its flocculation with PEO. A detailed characterization of dolomite samples from different locations was made by electrokinetic, XRD and FT-IR analyses, and the relevance of these characteristics to flocculation with PEO is discussed.

Jan 1, 1996

It has been reported previously that dolomite samples from different locations showed varying flocculation behavior with Poly(ethyleneoxide) (PEO). In this study it is determined that palygorskite associated with the Florida dolomite samples is responsible for their flocculation with PEO. A detailed characterization of the dolomite samples from different locations and its relevance to flocculation with PEO is discussed.

Jan 1, 1994

By Behl S

Flocculation behaviour of six different dolomite samples, four from the Florida mining district, one from Perry, South Georgia and another from New Jersey was examined using polyethylene oxide (PEO) as a flocculant. The samples were similar in chemical composition, however the porosity of the samples from the Florida mining district was higher than the others. FT-IR, adsorption and surface modification by leaching revealed that flocculation was directly related to the presence of isolated hydroxyl groups on the surface. The adsorption mechanism was believed to be hydrogen bonding of the ether oxygen of PEO with isolated -OH sites on the solid.

Jan 1, 1993

By D. Tao, R. Honakey, B. K. Parekh

The dewatering of stable phosphatic clay suspensions generated from phosphate beneficiation in the central Florida is an issue of practical and theoretical importance. Because of its tiny particle size and surface charge, the phosphatic clay takes up to 20-30 years to settle in water and causes environmental, aesthetic, economic, and handling problems. An efficient and cost-effective dewatering/consolidation process for phosphatic clay is of great interest to the phosphate industry in Florida. In this paper, the consolidation and dewatering behavior of phosphatic clay was studied by use of anionic flocculants with and without sand addition. The effects of pH, initial polymer concentration, polymer dosage, polymer addition steps, and metal cations (K+, Ca2+, and Al3+) on the flocculation of phosphatic clay have been studied. Experimental results indicated that clay suspensions were well flocculated at pH 10.5 by DPW-1-1355 and Magnafloc 5250 flocculants acquired from Ciba Specialty Chemicals. Sand particles from phosphate flotation added to the clay slurry promoted flocculation and increased clay consolidation. K+ showed good performance to improve the flocculation characteristics by neutralizing clay surface charge. The adsorption mechanisms of flocculants on clay particles were also discussed in this paper.

Jan 1, 2006

By Vladko Panayotov, Marinela Panayotova

"Recently, in order to extract metals, the industry is trying to process old metallurgical slag. The material requires very fine grinding that results in enhanced slime-formation. This in turn leads to problems in the course of the flotation process and to a loss of metal. In addition, it causes difficulties in the wastewater treatment aimed at water reuse. The aggregation and separation of the fine particles and their further subjecting to mineral processing would result in more efficient use of raw materials. Closing the water cycle also would be facilitated. The paper presents results from studying sixteen flocculation reagents, commercially available for treating municipal wastewater, including products based on nanotechnology, for their ability to rend the production wastewater in suitable for reuse in the flotation. It turned out that, from all studied reagents, the cationic C-587 is suitable for the purpose. Some of reagents were studied for their ability to flocculate selectively, in presence of coke fines, rich in copper fines which are produced at grinding of a slag from lead-zinc metallurgy. Most promising reagents are chosen, based on the chemical analysis of the flocculated materials. Open-cycle rough copper flotation experiments with the flocculated fines and recycled wastewater gave encouraging results."

Jan 1, 2014

By H. Suharyono, R. Hogg

A laboratory investigation was performed on flocculation following the addition of polymer to slurries flowing through pipes and in-line (static) mixers. Results are presented showing the effects of flow velocity, pipe length, in-line mixer elements and the use of multiple addition points. Flocculation performance was measured by the settling rate and the supernatant turbidity. The effects of agitation and mixing time are shown to be generally consistent with the results of equivalent tests (both batch and continuous) conducted in stirred tanks.

Jan 1, 1997

By H. Suharyono

A laboratory investigation of flocculation following polymer addition during slurry flow through pipes and in-line (static) mixers is described. Results are presented showing the effects of flow velocity, pipe length, in-line mixer elements and the use of multiple addition points on flocculation performance as measured by settling rate and supernatant turbidity. The effects of agitation and mixing time are shown to be generally consistent with the results of equivalent tests, both batch and continuous, conducted in stirred tanks.

Jan 1, 1995

By K. N. Han

Coal is becoming increasingly important as a major energy source in the face of the world's depleting energy mainly based on oil reserves. Coal is by far the most abundant fossil fuel both in the United States and abroad. Currently, because of increased mine mechanization, the fineness of preparation plant feed is increasing. Further, in the future as the grade of coal diminishes and the sulfur content increases, upgrading preparation of coal is very important. Because the density of coal is less than that of rock materials that occur as impurities, coal is separated from such waste largely by gravity-controlled processes for particle size between 5 inches and 28 mesh. If the size of coal particles is below 28 mesh, froth flotation is a good method for upgrading fine coal. Previously, numerous investigators have tried to upgrade coal values by froth flotation(1-16) and have achieved moderate success. However, the recovery and grade of coals in the concentrates are not always satisfactory, especially when the particle size is small. In general, when the size of coal is below 100 mesh, the above methods suffer from poor grade and low recovery. The reason for this is that as size decreases, the effects of gravity diminish, and other forces take effect.

Jan 1, 1985

By R. W. Smith, S. A. Davis, A. M. Raichur, M. Misra

The flocculation of coal is typically accomplished by the addition of commercially available polymeric flocculants. Recently it was shown that biopolymers derived from microorganisms can also be used. The biopolymers flocculate coal efficiently and make the coal more hydrophobic. This increase in hydrophobicity can be utilized to separate coal flocs and can be used for reducing the moisture content of the flocculated coal. In this regard, flocculation and settling tests using biopolymers and synthetic flocculants were performed on fine coal. The experimental results are discussed and a transport model is presented for the time-dependent settling of fine coal.

Jan 1, 1998

By A. M. Raichur

Flocculation of fine coal is usually accomplished with the addition of commercially available organic flocculants. Recently it has been shown that biopolymers derived from microorganisms can be used to flocculate coal. The biopolymers flocculate coal efficiently and render the coal surface hydrophobic. The increase in hydrophobicity can be utilized either to separate the coal flocs from mineral matter. It can also be used for reducing the moisture content of fine coal. In this regard, flocculation and settling tests of fine coal with biopolymers and synthetic flocculants was undertaken and the results are discussed here. Also, a transport model was developed for the time-dependent settling tests for fine coal.

Jan 1, 1996

By B Scheiner, D. A. Stanley

Introduction Treatment of ores to recover metal and mineral values results in waste materials usually in the form of dilute slurries. The US Bureau of Mines (USBM) investigated a technique for dewatering phosphatic clay waste by flocculating with polyethylene oxide (PEO) and dewatering the resulting floes on a static screen and/or trommel screen (Schemer et al., 1985). In the investigation, it was determined that PEO was far superior to polyacrylamide polymers for this type of dewatering. This paper discusses reasons for this superior performance. Comparison of PEO with polyacrylamides Dewatering experiments were conducted by adding PEO solution from a burette to a stirred clay slurry. The dewatering endpoint was characterized by rotation of the floc mass as a unit, a clear supernate, a maximum floc size, and a minimum floc volume. Additional water was removed from the floes by hand squeezing (Schemer et al., 1985). The clays investigated were sodium, potassium, magnesium, calcium, and aluminum exchanged montmorillonite and attapulgite. Nine commercially available (Superfloc) polyacrylamides were compared with PEO at two polymer concentrations. Results are summarized in Table 1. The solids content of the dewatered clays ranged between 24% and 33% and was highest for PEO-treated material. These results and the data in Table 1 indicate that PEO is superior to polyacrylamide in terms of polymer dosage required. Superflocs 16 through 128, like PEO, are nonionic and should give similar results to those for PEO if the flocculation mechanism is the same for both type polymers. Superflocs 204 through 214 are anionic with increasing anionic character from 204 to 214. Generally, the anionic polymers gave the best results for the polyacrylamides tested, but in terms of dosage they were not as good as PEO. Correlation between flocculation and dewaterability of waste slurries The overall mechanism for mechanically induced clay dewatering is not completely known, but certain observations can be made. For instance, when a polymer is adsorbed on a clay such as montmorillonite, the polymer desorbs interlayer water. Polymer adsorption is driven by favorable entropy changes associated with this water desorption. It is also known that the -CH2-CH2- links of the PEO chain are sufficiently hydrophobic to lead to physical adsorption of the polymer (Theng, 1979). For montmorillonite slurries, the sheet-like fundamental particles, called tactoids, consist of a small, variable number of aluminosilicate layers together with interlayer water and exchange ions. The flocculation process consists of adsorption of polymer on the tactoid. Loops and tails of polymer that extend into solution then adsorb on another tactoid, forming a bridge. Mechanical action, induced by hand squeezing or in a trammel, joins the bridged tactoids face-to-face and edge-to-edge to form regions of high density. Similar orientation effects are observed for the needle-like attapulgite crystals (Schemer et al., 1985). Proposed flocculation model Generally, statements concerning flocculation and dewaterability apply to both PEO and the polyacrylamides. However, PEO has additional interaction with the clay material when compared with polyacrylamides. PEO is a polymer with repeating -CH2-CH2-O- groups and interacts with montmorillonite through a water bridge whose strength is greatly influenced by the exchange ion. To obtain insight into this interaction, a series of experiments were conducted in which different ion exchange forms of montmorillonite and attapulgite clays

Jan 1, 1987

By H. A. Hamza

An experimental study of the settling characteristics of a washery effluent originating as tailings from a froth flotation circuit was undertaken by using a systematic approach to select the most appropriate flocculant(s) under predetermined conditions. Selection and evaluation procedures which greatly reduce the effort required to select flocculants are described. The results show that, although different flocculants display superiority at different ranges of dosage. Separan MG 700 (Dow) is the most suitable on absolute economic grounds. Flocculant evaluation is based on a Cost Performance Index (CPI) which expresses the cost of flocculant (¢/ton) required to produce a unit settling rate (in./hr). From experiments carried out with a number of flocculant aid and flocculant combinations, it was concluded that the use of flocculant aids can be economically justified only if the settling rates required are higher than those obtainable at the optimum flocculant dosage. Otherwise, the value of the flocculant aid appears to be limited largely to the reduction of supernatant turbidity.

Jan 1, 1979