Dewatering of coal plant tailings: Flocculation followed by filtration

A sustainable alternative to tailings dam disposal of coal refuse is mechanical dewatering of tailings, which provides fast production of dry solids and water reuse. In this study, flocculation followed by filtration of coal plant tailings, a new concept in tailings dewatering is investigated in detail. This paper focuses on the effect of preconditioning tailings with varying flocculants and dosages on filtration kinetics and the resultant moisture content of the filter cake. The results show that the cationic flocculant, MAGNAFLOC LT 425, requires a high dosage to produce a low moisture content filter cake and clear filtrate. Optimal sized flocs were produced with the anionic flocculant, MAGNAFLOC 5250, even though the particles are negatively charged. The kinetics of the filtration was dependent on the composition of process water as indicated by supporting sedimentation tests. The concentration of divalent alkali earth metals such as Ca²⁺ and Mg²⁺ allow for large floc growth by a bridging mechanism, which involves binding of the polymer and the negativity charged particle. Filtration and settling curves at this dosage were also supported by filter cake analysis using Darcy plots. It was found that the large floc size significantly increases the permeability of the filter cake. Floc size measurements and fractal dimension showed that while the large flocs were produced with anionic flocculant, the flocs produced with the cationic flocculant were small and weak. The results indicate that the optimum dosage and flocculant type for effective and efficient filtration of coal plant tailings is approximately 350 g/t of anionic flocculant at a 35% solids content and 40 kPa filtration pressure.     

The Effect of Polymeric Flocculants on Settling and Filtration of Iron Ore Slimes

Abstract

During the wet processing of iron ores, a substantial amount of fine particles known as slimes are generated in downstream which need to be recovered effectively for their usage and beneficiation. Besides water from slime ponds overflow remains contaminated with very fine particles which are difficult to settle and cause environmental pollution when contaminated water is discharged to the downstream river. The settling behaviour in the slime pond gets affected in particular when ore contains hydrated oxides. The above problems necessiatate to study the settling and filtration behaviour of the slimes by means of effective flocculants. The flocculants namely, amylopectin-g-polyacrylamide (Ap-g-PAM), sodium alginate-g-polyacrylamide (SAG) were synthesized by graft copolymerization using redox initiated catalyst. The high molecular weight flocculants, namely, magnafloc (1011) superfloc (N 300) were used for comparative studies. The present paper reports the settling and filtration behaviour of iron ore slimes.

The experiments show that sedimentation rate increases with increasing flocculant dose upto a certain limiting value. The settling rate decreases with increasing the pulp density. The volume of filtrate increases with increasing flocculant dose. The filtration efficiency of synthesized polymer is comparable with the commercial one, i.e., magnafloc (1011) at natural pH.     

The Vacuum Filtration of Iron Ore Ultrafines

ABSTRACT

The dewatering of fine particles (? 0.5 + 0 mm) derived from iron ore processing is a topic of increasing importance to Australian producers. With little previous published work in this area, it is difficult to predict how these materials are going to dewater, in particular during vacuum filtration. The work described in this paper was therefore undertaken in order to help overcome this paucity of background information. The sample of iron ore that was tested responded well to vacuum filtration provided that anionic flocculants were used as a filter aid. In the presence of these polymers, cake formation times were very short (mainly below 10 seconds) and the moisture levels of 18 mm thick filter cakes were reduced to 10–11 wt% after dewatering times of only 40 seconds. By comparison, the cationic and nonionic flocculants tested were much less effective. The mathematical model devised by Wakeman shows considerable promise as a toolfor predicting the kinetics of desaturation.     

Polymer aids for settling and filtration of oil sands tailings

Commercial Magnafloc 1011 (Percol 727) polymer and in‐house synthesised Al‐PAM polymer were used to flocculate oil sands tailings that were derived from low and high fines oil sands ores. Fines are defined as mineral solids less than 44 µm. The performance of polymers was evaluated in terms of tailings settling, filtration rate, and final moisture content of tilter cakes. Both polymers were shown to effectively flocculate the derived oil sands tailings and hence to enhance tailings settling. Al‐PAM performed very well as a filtration aid. The final moisture content of the filter cake obtained from tailings derived from the low fines ore was 6.6 ± 1.2 wt.% and that from the high fines ore was 16.9 ± 0.8 wt.%. This class of polymer can provide an alternative approach for oil sands tailings disposal that has the potential to eliminate tailings ponds. However, the commercial Magnafloc 1011 polymer was found ineffective as a filtration aid for the two tailings tested in this study.     

Interaction mechanism of flocculants with coal waste slurry

Coal tailings are the inevitable by-product of coal mining and preparation plants, and often are problematic in terms of dewatering and solid-liquid separation. The interaction of multi-component fine coal tailings with various coagulants and flocculants are important in dewatering processes. Tunçbilek coal preparation plant wastes are composed of 81% inorganic solids with negative surface charges dominating at all pHs. The highest settling rate and turbidity values without flocculant are obtained at natural pH of 8.3 due to the presence of inorganic ions in the suspension particularly Mg²⁺and Ca²⁺that act as natural coagulants. Additon of medium and low charge density anionic flocculants with high molecular weight at natural pH produced higher settling rates at lower dosages than nonionic and cationic flocculants. It shown that the charge density of anionic flocculants has a significant effect on both settling rate and supernatant turbidity, also the settling rate increases with increasing the degree of anionicity. Anionic flocculants having high molecular weight and high anione charge density produced flocs at sufficient size necessary for settling conditions, yet anionic flocculants having low charge density were more effective in the clarification of suspensions containing clay minerals of high stability. The multivalent ions act as a bridge between negatively charged coal, quartz and clay minerals with anionic groups (-CH₂-(CH-CO)-COO groups) of the polymer. Non-ionic flocculants required higher dosages than other flocculants to achieve equivalent settling rates; though excellent turbidity values were obtained in most common pH values. Cationic flocculants of higher charge densities (%70) achieved good settling rates and low supernatant turbidities (9.9 NTU) at natural pH for a dosage of 119.7 g/t-solids flocculant. An interaction mechanism of each polymer type with different components of the tailings is proposed.     

Coagulation and Flocculation Study of Iron Ore Fines

ABSTRACT

A comparative study of the flocculation and coagulation response of an iron ore fines suspension has been carried out, and the extent of flocculation has been assessed by measurement of electrophoretic mobility, supernatant clarity, and settling rate. Of the several commercial flocculants and polyelectrolyte studied, the combination of medium molecular weight anionic flocculants Magnafloc 1011 and Rishfloc 258 (1:1), and coagulant aluminum nitrate was most effective in terms of enhancing settling rate and supernatant clarity.     

Influence of surfactants on flocculation and dewatering of kaolin suspensions by cationic polyacrylamide (PAM-C) flocculant

This paper reports the result of studies on flocculation and dewatering of kaolin suspensions by cationic polyacrylamide (PAM-C) flocculants in presence of surfactants. The surfactants used were namely anionic sodium dodecyl sulphate (SDS), cationic cetyl trimethyl ammonium bromide (CTAB) and non-ionic TritonX 100, which is a polyoxyethylenic ether compound. The unflocculated kaolin has a very slow settling rate of about 0.03 cm/s and can be improved by more than ten times using PAM-C as a flocculating agent. PAM-C adsorbs on kaolin primarily through electrostatic attraction and the flocculation is governed mainly by charge neutralisation and bridging. Partial pre-coating of kaolin with all three surfactants leads to both physical adsorption as well as chemisorption at PAM-C. Pretreating the kaolin with surfactants can further increase or decrease settling rate depending on the type of surfactant used. However, the flocs thus formed shows better filtration and dewatering behaviour estimated in terms of reduction in specific resistance to filtration (SRF) and cake moisture. The minimum SRF occurs under conditions corresponding to far lower adsorption of PAM-C than that for best flocculation. Simultaneous addition of PAM-C and each of the three surfactants decreases settling rate and sediment volume markedly and does not reduce SRF any further but they all reduce cake moisture substantially. The reduction in cake moisture for different PAM-C: surfactant mixture is in the following order: PAM-C: SDS (1:1)>PAM-C: TX 100(1:1)>PAM-C: CTAB(1:1). Low cake moisture in comparison with PAM-C alone, may be a result of reduction in entrapment of excess water in the smaller flocs formed by simultaneous addition with surfactants and to some extent due to hydrophobicity caused by adsorption of surfactants.     

Statistical evaluation of hyperbaric filtration for fine coal dewatering

A statistical design of parametric study of pressure filtration for fine coal dewatering is presented. The effects of five major parameters of the dewatering, i.e. applied pressure, filtration time, cake thickness, solids concentration and slurry pH, on cake moisture reduction and air consumption were investigated. The study was conducted starting with two level factorial experiments to identify the most significant parameters, and concluding with response surface methodologies to establish an optimum operating condition for the dewatering of fine coal. It was observed that applied pressure, cake thickness and filtration time were identified to be the key operating variables for reduction of filter cake moisture as well as air consumption. With the key parameters, an optimum condition for the dewatering was determined to be an applied pressure of 93 psi with a cake thickness of 2.5 cm and a filtration time of 4.8 minutes for the laboratory filtration system. At these optimum conditions the filter cake containing about 22 percent moisture by weight and consuming air by 4.1 m³/(m²·min·kg) on dry solid basis was obtained.     

The Effect of Reagents on Ultrafine Iron Ore Vacuum Filtration

Continuous vacuum filters normally carry out the final removal of water from iron ore products. The objective of this investigation is to check the possibility of enhancing the industrial performance of a horizontal belt filter by adding one flocculant and two surfactants to the filtration feed slurry. The mineral sample came from the Iron Quadrangle (State of Minas Gerais, Brazil). X-ray diffraction showed a predominance of hematite and small amounts of quartz and goethite. The filtration tests were performed at laboratory scale using a modified Büchner funnel apparatus, which was connected to a scale/computer system. The results indicated: a) the best filtration condition was achieved near the zero charge condition; b) cake moisture, cake porosity, cake formation time and the specific cake resistance were pronouncedly influenced by the flocculant addition; and c) surfactants tested were not able to significantly reduce the cake moisture.     

Application of Enhanced Vacuum Filtration to Dewatering of Fine Coal Refuse

Abstract

It is difficult to reduce the moisture content of fine coal refuse to a satisfactory level because of the high mineral content and the large capillary forces associated with small particle sizes. An experimental investigation of important operating variables on dewatering of fine coal refuse is reported. The cake permeability, cake formation time and final moisture content are used to measure the efficiency of moisture removal. Factors that were studied are the addition of coarse particles, level of vacuum, pH and the use of coagulants, flocculants and surfactants as additives. Addition of a flocculant was the most effective single means of improving dewatering and the permeability could be increased by more than an order of magnitude and the moisture content lowered by as much as 0.05 kg water/kg dry cake. It was found that the ionic nature and molecular weight of the flocculant, the flocculant dosage, the mixing time and the mixing intensity must be carefully studied to obtain optimal performance.     

不同絮凝剂对剩余污泥水解和脱水特性的影响

研究了无机和有机絮凝剂对剩余污泥水解和脱水性能的影响。分别投加浓度为20g/L的CaO和CPAM（阳离子型聚丙烯酰胺）调节剩余污泥,溶出的有机质规律如下：溶解性COD（SCOD）的溶出量表现为CPAM>CaO>空白;溶解性蛋白质（SPN）的溶出量表现为CPAM>CaO>空白;溶解性碳水化合物（SPS）的溶出量表现为CaO>CPAM>空白。污泥的脱水性能指标——比阻（SRF）和滤饼含固率的变化分别为：SRF表现为CPAMCaO>空白。从SPN、SPS和SCOD的溶出量、比阻和滤饼含固率的变化说明：加入CaO和CPAM都能改善剩余污泥的水解和污泥脱水性能。     

A study of the improvement in dewatering behavior of wastewater sludge through the addition of fly ash

Wastewater sludge is classified as a difficult dewatering material (DDM) due to the high cake specific resistance (CSR). On the other hand, fly ash is classified as an easy dewatering material (EDM), which suggests that it might be able to improve the dewaterability of wastewater sludge. The water content and cake specific resistance of dewatered sludge without the addition of fly ash were 80% and 2.9×10¹⁴ kg/m, respectively. When 50% (by dry weight) fly ash was added to the sludge, the water content and cake specific resistance decreased to 29.4% and 2.9×10¹³ kg/m, respectively. The cake specific resistance and water content decreased with increasing fly ash additions. Therefore, the production of sludge cake can be reduced by adding fly ash, which can help minimize the social and environmental problems caused by the need to dispose of wastewater sludge.     

有机絮凝剂对铁矿相沉降性能影响及其吸附机理

通过模拟拜耳法赤泥沉降过程研究了聚丙烯酸铵(PAAA)、阴离子聚丙烯酰胺(APAM)和氧肟酸絮凝剂(HPAM/HCPAM)对赤铁矿和针铁矿沉降性能的影响规律和絮凝后絮体的粒径分布及分形维数,并利用傅里叶变换红外光谱探讨了絮凝剂与铁矿相的吸附机理。在不同类型絮凝剂中,添加氧肟酸絮凝剂铁矿相沉降速度最快,且氧肟酸含量越高,沉降性能越好;聚丙烯酸铵和阴离子聚丙烯酰胺絮凝剂对铁矿相沉降性能影响较小;同等条件下赤铁矿沉降速度要远高于针铁矿,增加絮凝剂添加量有助于提高针铁矿沉降速度。在赤铁矿絮体中,添加PAAA絮体粒径最大,HPAM絮体分形维数最大、致密性最好;在针铁矿絮体中,添加APAM絮体粒径最大,HCPAM絮体分形维数最大、致密性最好。氧肟酸絮凝剂与铁矿相形成结构稳定、吸附能力强的五元环状螯合物,增强了赤铁矿和针铁矿的絮凝效果;PAAA通过双齿桥接配位与赤铁矿表面发生吸附,通过单齿配位与针铁矿表面发生吸附,其吸附能力弱于五元环;APAM与赤铁矿和针铁矿表面发生化学吸附,沉降性能差。     

有机絮凝剂对铁矿相沉降性能影响及其吸附机理

通过模拟拜耳法赤泥沉降过程研究了聚丙烯酸铵(PAAA)、阴离子聚丙烯酰胺(APAM)和氧肟酸絮凝剂(HPAM/HCPAM)对赤铁矿和针铁矿沉降性能的影响规律和絮凝后絮体的粒径分布及分形维数,并利用傅里叶变换红外光谱探讨了絮凝剂与铁矿相的吸附机理。在不同类型絮凝剂中,添加氧肟酸絮凝剂铁矿相沉降速度最快,且氧肟酸含量越高,沉降性能越好;聚丙烯酸铵和阴离子聚丙烯酰胺絮凝剂对铁矿相沉降性能影响较小;同等条件下赤铁矿沉降速度要远高于针铁矿,增加絮凝剂添加量有助于提高针铁矿沉降速度。在赤铁矿絮体中,添加PAAA絮体粒径最大,HPAM絮体分形维数最大、致密性最好;在针铁矿絮体中,添加APAM絮体粒径最大,HCPAM絮体分形维数最大、致密性最好。氧肟酸絮凝剂与铁矿相形成结构稳定、吸附能力强的五元环状螯合物,增强了赤铁矿和针铁矿的絮凝效果;PAAA通过双齿桥接配位与赤铁矿表面发生吸附,通过单齿配位与针铁矿表面发生吸附,其吸附能力弱于五元环;APAM与赤铁矿和针铁矿表面发生化学吸附,沉降性能差。     

Effect of entrapped air bubbles on fine coal dewatering via filtration

An experimental study was conducted to obtain detailed information concerning entrapped air bubbles in fine coal filter cakes and their effects on filtration and the dewatering process. Four size fractions of coal samples (?80 mesh, ?42 mesh, ?82 mesh and ?100 +200 mesh) were investigated. An image analyzer with the aid of quantitative stereology was used to measure the entrapped air bubbles in relation to the microstructure of the filter cake (i.e., the particle and pore size distribution in the filter cake).The results show that the size and number of air bubbles entrapped in the filter cake can be controlled by the degree of aeration/deaeration of the coal slurry prior to filtration. Both the rate of filtration and the extent of dewatering are adversely affected by the presence of air bubbles in the filter cake. These adverse effects can best be understood in terms of the alteration of cake structure caused by air bubbles. Specifically, the reduction in connectedness of pores within the cake matrix tends to impede the flow of filtrate through the filter cake.     

Involvement of Gypsum (CaSO4 · 2H2O) in Water Treatment Sludge Dewatering: A Potential Benefit in Disposal and Reuse

Abstract

This research assessed the use of gypsum (CaSO₄ · 2H₂O) as a skeleton builder for sludge dewatering since polymer conditioning of sludge affected only the rate of water release, not the extent of dewatering. The use of gypsum as a physical conditioner, in association with a polymer, could improve sludge filterability. More significantly, gypsum serves as a skeleton builder, forming a permeable and rigid lattice structure that can remain porous under high positive pressure during the compression step after the cake growth of the filtration, thereby maintaining the size of the micro‐passages through which water is expressed. Experiments using a high pressure cell apparatus showed that a further decrease of two to seven percent of the equilibrium moisture content of the sludge cake was achieved, for sludge thicknesses for dewatering of 1 to 10 cm, by the addition of gypsum with 60% of the original sludge solids when compared to the single polymer conditioning. The importance of the addition of gypsum in alum sludge dewatering is not only the improvement in the extent of dewatering, but also the potential application of transforming dewatered alum sludge from “waste” for landfill to useful “fertilizer” or to be used as a filter medium/adsorbent for wastewater treatment engineering.     

Influence of coagulants and flocculants on contact angles of coal surfaces

Contact angles on both natural, flat and prepared, polished surfaces of coal were measured for distilled water, solutions of several Al³⁺ and Fe³⁺ coagulants, and commercial flocculants. The pH value was varied also. Contact angles increase up to coagulant and flocculant concentrations of ≈ 60 ppm and remain practically constant at higher concentrations. Coagulants probably adversely affect flotation of coal fines whereas flocculants have an effect on contact angles similar to that of surfactants.     

Magnetic field enhanced press-filtration

The proposed hybrid process represents a new application of a magnetic field which directly influences a classical press filtration. The new technology offers high potential in the field of magnetic pigment production and iron oxide processing as well as bio-separation with functionalized magnetic particles. Especially in the field of fine-scale particulate product systems high specific cake resistances result in slow cake building and dewatering kinetics, which leads to economic inefficiency.Experimental and theoretical investigations show that the magnetic field has strong influence on cake building. Two major effects were observed: (I) In inhomogeneous magnetic fields magnetic particles experience a magnetic force counter directed to the pressure force, that results in slow down of cake formation; (II) Interparticle magnetic forces lead to structured cake formation.This gives on one hand the possibility to uncouple fluid and magnetic particle motion to force a cake built-up in designated location of the filter chamber. The result is a big increase of the overall filtrate mass flow and therefore an improvement of filtration kinetics. On the other hand due to the particle's magnetization including the formation of an attracting north and south-pole chainlike agglomerates can be observed. This leads to a “structured” cake building and therefore higher permeability.This work will show the effect of a superposed magnetic field on press filtration of ferromagnetic iron oxide particles (Fe₃O₄) in a lab-scale filter press.     

壳聚糖絮凝剂的投加量对污泥脱水性能的影响

通过污泥比阻的测定,分析絮凝剂剂量对污泥脱水性能的影响。同时对三氯化铝、阳离子聚丙烯酰胺、壳聚糖以及复合絮凝剂的絮凝效果进行比较。结果表明,无论是无机絮凝剂和有机絮凝剂都存在最佳剂量,小于或大于最佳投加量,絮凝效果都不好。阳离子聚丙烯酰胺(CPAM)、壳聚糖、三氯化铝的最佳投加质量浓度分别为0．2g/L、10g/L、35g/L。与三氯化铝相比,阳离子聚丙烯酰胺的药剂消耗量要低得多。壳聚糖与CPAM相比,在达到相同的絮凝效果时,壳聚糖的用量大于CPAM的用量。将壳聚糖与氯化铝复合,用两段法应用于污泥调理,研究这种复合絮凝剂的脱水性能,实验表明壳聚糖和三氯化铝复合,能大大提高污泥的脱水性能。     

盐酸分解高硅混合型胶磷矿工艺研究

中低品位磷矿的开发利用是中国磷化工产业可持续发展的基本保障。采用盐酸浸取高硅磷矿,通过单因素实验对其酸解工艺和过滤强化过程做了研究。结果表明,磷矿粒径≤180 μm、在反应温度为40 ℃、酸比（实际投入的盐酸量与理论耗酸量的质量比）为1.1、盐酸质量分数为20%以上、浸取10 min,此时P₂O₅浸取率可达到99%以上。盐酸浸取速率快,酸解率高。高硅磷矿酸解料浆中二氧化硅含量高、粒度小、沉降速度慢,导致过滤困难。添加非离子型聚丙烯酰胺絮凝剂,控制絮凝剂为酸解料浆质量的1.0%,沉降2 min之后,可显著强化过滤。