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.     

Flocculation of fine particles in ceramic wastewater using new types of polymeric flocculants

It appears to be quite a few national and international studies were reported regarding flocculation and settling properties of ceramic industry wastewater containing various mineral matters. Cleaning of ceramic industry wastewaters with ever increasing environmental standards needs effective and economical solid–liquid separation processes. In this study, quantity and type of optimum flocculant concentration were investigated for solid–liquid separation of Umpac ceramic plant (located at Usak, Turkey) wastewaters. A new generation of flocculants namely unique molecular architecture (UMA) are used to obtain high settling velocity along with high solid content waste and circulation water with low turbidity values. Zeta potential of the tailings including quartz, feldspar, clorite, and mica was also measured at different pH values. The flocculation tests were performed in the presence of different types of polymers at different polymer dosages. It seems that Magnafloc 5250 shows higher performance than the anionic flocculant SPK 508 and other anionic UMA flocculants Magnafloc 6260 and Magnafloc 3230. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Settling characteristics of coal preparation plant fine tailings using anionic polymers

The objective of solid-liquid separation in thickeners in coal preparation plants is to obtain both a clear supernatant liquid with a low turbidity for reuse and a dense slurry. It is important for the smooth operation of the plant to produce good-quality recirculation water. In this study, settling characteristics of coal tailings (d₈₀=70 μm) taken from the thickener feed of Derekoy Coal Preparation Plant (Manisa, Turkey) were investigated with the use of anionic polymers. In the tests we determined the effects of the process parameters including polymer type, polymer dosage, temperature, suspension pH, and pulp density on the flocculation of the fine tailings of the coal preparation operation. Minefloc anionic polymer showed a better flocculation performance in comparison with other polymers. An optimum settling rate of 300 mm/min was reached at a dosage of 30 g/t-solids, a pulp density of 5%, pH 7.9, and temperature 25 °C using Minefloc polymer.     

Influence of flocculant molecular weight and anionic charge on flocculation behaviour and on the manufacture of fibre cement composites by the Hatschek process

Although in the industrial Hatschek process it is necessary to use flocculants to improve retention, dewatering and formation, the use of flocculants may also decrease the strength of the final product. This paper studies the influence of the molecular weight and the anionic charge of anionic polyacrylamides on the flocculation behaviour of fibre cement suspensions and on the bending strength of the final product. Flocculants influence the density of the final product and in-turn the lowering of the density results in strength reduction. Results showed that an increase in the flocculant molecular weight reduces the bending strength of the composites significantly due to its density reduction. However, an increase in flocculant anionic charge increases the bending strength of composites. Therefore, in order to optimise the fibre cement process, it is necessary to use flocculants with high anionic charge and medium molecular weight.     

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.     

The Effect of Flocculants and Surfactants on the Filtration Dewatering of Iron Ore Fines

Abstract

The filtration and separation characteristics of iron ore fines have been investigated. The experimental work included: characterization, evaluation of suitable flocculants to enhance settling and dewatering rate, determination of optimum dosages of flocculants, and influence of surfactants on nitration dewatering of both flocculated and unflocculated iron ore fines by vacuum filtration. The results showed that 1) the settling rate can be enhanced many-fold (from 2.52 to 90 m/h) by a suitable flocculant, 2) the residual filter cake moisture content can be reduced from 18.2% without reagents to 12.6% with suitable surfactant dewatering aids while the filtration rate can be enhanced from 4.8 to 97.2 L/h with suitable dewatering filter aids, and 3) the specific cake resistance to filtration can be brought down from 8.6 × 10⁹ to 1.0 × 10⁹ m/kg by using a surfactant sodium petroleum sulfonate at a concentration of 1.47 × 10^?3 kg/t. The economics of using flocculant filter aids and surfactant dewatering aids before thermal drying is described and discussed.     

Polyacrylamide-induced coagulation process removing suspended solids from palm oil mill effluent

Palm oil mill effluent (POME) is a colloidal suspension with 2–4% suspended solids. About 50% of the suspended solids are cellulosic compounds, which are not degraded in the typical biological treatment systems. Chemical (polymer-induced coagulation) and physical (settling) pretreatment methods were examined to remove the suspended solids in this study. A novel physicochemical treatment with high water recovery and sludge compressibility including three cationic polyacrylamides (C-PAM; as coagulant) and three anionic polyacrylamides (A-PAM; as flocculant) with different molecular weights and charge densities was used. The coagulants used were biodegradable. The combination of a C-PAM (Chemfloc1515C) with medium molecular weight and charge density and an A-PAM (Chemfloc 430A) with high molecular weight and charge density at doses of 300 and 50 mg/dm³ showed the best total suspended solids (TSS) and chemical oxygen demand (COD) removal (96.4 and 70.9%, respectively). The optimal condition was found at pH 5, rapid mixing at 150 rpm for 1 min, and slow mixing at 40 rpm for 30 s. As a conclusion, the physiochemical pretreatment using biodegradable coagulants was a promising alternative to effectively separate TSS (96.4%) with high water recovery (76%).     

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.     

Parameters affecting the performance of polyelectrolytes as aids to water clarification

An investigation of the flocculation of silica and alumina suspensions by a series of synthetic flocculants of a wide range of charge density both anionic and cationic in nature has been carried out. The extent of flocculation was determined by measurements of settling rate, sediment volume and supernatant clarity. The effect of the pH of the suspension on the performance of a number of selected polymers has been investigated. In the systems examined, flocculation was largely controlled by the charge carried by the suspended particles and polymer molecules. The dosage/settling rate characteristics of kaolin suspensions flocculated with non-ionic polymers of varying molecular weight are reported. The dosages of non-ionic polymers required for optimum flocculation of kaolin suspensions of varying solids content have been measured. At low particle concentrations bridging is less effective, and is probably reduced due to the adsorption of polymer molecules on to single particles.     

Water soluble polymeric nanofibres for rapid flocculation and enhanced dewatering of mature fine tailings

Water-soluble polymer flocculants have been used to efficiently release entrapped water in oil sands tailings by bridging fine particles to create large heavier flocs which can then settle faster and release water more efficiently. Due to their initial interaction with the fine particles suspended in tailings, polymer nanofibres may perform better than their parent polymers because of the entire surface of the nanofibres being fully accessible to the fine particles. In this work, commercially available poly(acrylamide-co-diallyl dimethylammonium chloride) was chosen as a basis for this study. Initial settling rate, supernatant turbidity, water recovery, capillary suction time, and solids content were measured to determine the effect of polymer nanofibres on solid-liquid separation. The solid forms of the polymer (either as nanofibre or powder) perform better than the polymer solution in each test, with optimum dosages of 5 wt% mature fine tailings (MFT) loading. Nanofibres could achieve settling rates of 60 m/h, while the other forms were only able to achieve 42 m/h. Additionally, the turbidity of the supernatant obtained after flocculation with nanofibres was 15 nephelometric turbidity units (NTU), while the polymer solution and powder produced turbidites of 162 NTU and 70 NTU, respectively. In addition, polymer nanofibres and powders generated larger flocs compared to the polymer solution, which produced small, homogenized flocs.     

阳离子絮凝剂PDA的合成与应用——对再生造纸废水的污泥脱水处理

研究了阳离子聚丙烯酰胺絮凝剂PDA对一种废纸再生造纸废水中的污泥的絮凝脱水处理过程，探讨了絮凝剂PDA的投加量，电荷密度，平均相对分子质量对絮凝脱水效果的影响，并比较了各种不同絮凝剂的处理效果，研究结果表明，絮凝剂PDA的电荷密度越大，相对分子质量越高，其絮凝脱水效果越好，在与无机絮凝剂PAC复配使用的相同条件下，实验室自制的絮凝剂PDA的絮凝脱水效果优于其他作对比的市售多种阳离子聚丙烯酰胺类絮凝剂。     

两性聚电解质在黄河高浊度水中的应用

本文合成了一系列不同阴、阳离子度的强碱弱酸型的两性聚电解质[丙烯酰胺(AM)-二甲基二烯丙基氯化铵(DMDAAC)-丙烯酸(AA)共聚物]。研究了阴、阳离子单体的配比对两性聚电解质分子量的影响;以及两性聚电解质阴、阳离子度对絮凝效果的影响。并将所合成的两性聚电解质作为絮凝剂,首次应用到黄河高浊度水的处理中。填补了国内两性聚电解质高分子絮凝剂应用于上水的空白。研究结果表明:在等电点范围内的两性聚电解质对黄河高浊度水的絮凝效果明显优于传统的非离子型、阳离子型及阴离子型絮凝剂。     

天然改性植物阳离子絮凝剂对洗煤废水的处理研究

基于洗煤废水对环境所造成的危害,研究了一种以植物木粉为原料,通过与醚化剂接枝共聚制得的易降解、且不产生二次污染的天然改性植物阳离子絮凝剂。其对洗煤废水的处理,研究表明,常温下,当pH=6～8,该絮凝剂和聚铝的投入量分别为10 mg/L和5 mg/L时,洗煤废水的浊度、CODCr、固体悬浮物的去除率分别可达到96.8%6,9.3%9,7.9%。     

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.     

Synthetic polyelectrolytes of varying charge densities but similar molar mass based on acrylamide and their applications on palm oil mill effluent treatment

Cationic polyacrylamides of varying charge densities but similar molar mass were synthesized using free radical polymerization and Mannich reaction, characterized by different methods and applied as flocculants for palm oil mill effluents (POME). Flocculant performance was assessed by determining the polymer dosage, pH of POME and the removal efficiency of the resulting supernatants using turbidity, suspended solids and chemical oxygen demand as indicators. The pH of POME was adjusted to 3 prior to flocculation. It was found that varying the charge density of the polymer from 48.2-485 C/g affects flocculant performance significantly. Polymer adsorption increased as the charge density of the polymers increased. High charge density cationic polyacrylamide (485 C/g) is the most effective polymer as it obtains 98% turbidity removal, 98.7% suspended solids removal and 54% chemical oxygen demand removal with a dosage as low as 32 mg/l at pH 3 of POME.     

天然改性植物阳离子絮凝剂的制备研究

以天然植物木粉为原料,合成了一种天然改性植物阳离子絮凝剂,合成的最佳工艺条件为:木粉/NaOH质量比为2∶1,木粉/醚化剂质量比为1.5∶1,反应温度40℃,反应时间为3.5 h;该阳离子絮凝剂与PAC复配后处理洗煤废水,在常温下,当pH=6～8,絮凝剂和PAC的投入量分别为10 mg/L和5 mg/L时,洗煤废水的浊度、CODCr、固体悬浮物的去除率分别可达到96.8%,69.3%,97.9%。     

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。     

Polyacrylamides revisited: flocculation of kaolin suspensions and mature fine tailings

A series of acrylamide‐based water‐soluble (co)polymers was synthesized and they were investigated as flocculants of model kaolin suspensions and mature fine tailings of oil sands. The effects of molar mass, charge density, and polymer concentration on flocculation efficiency were studied by monitoring the initial settling rate during sedimentation. Hydrolyzed polyacrylamide (HPAM) with high molar mass and intermediate acrylic acid contents (0.14–0.41 mol/mol (14–41 mol%)) performed better in flocculation tests on kaolin suspensions requiring lower dose for maximum initial settling rate than native polyacrylamide (PAM). Surface force measurements showed that at low polymer concentrations (1 ppm), the partially‐adsorbed polymer induced a bridging attraction between the mica surfaces. Increasing the polymer concentration to 10 and 50 ppm caused purely repulsive forces. The presence of anionic groups in HPAM led to stronger repulsion, which was also demonstrated by the higher viscosity and larger hydrodynamic radius of the charged polymer. The charge‐induced increase in the viscosity of polymer solutions was suppressed by the screening effect of salts in a buffer solution and reducing the viscosity is desirable in the injection of flocculants in the industrial process.     

Preparation of Quaternized Lignin Derived from Oil Palm Empty Fruit Bunches and its Flocculation Properties

Quaternized lignin-based flocculant (QL) was prepared by a single-step reaction of an extracted lignin (EL) derived from oil palm empty fruit bunches (OPEFB) with 3-chloro-2-hydroxypropyl trimethylammonium chloride (CHPTAC) under alkaline condition. The performance of QLs was studied for various β values (molar ratios of CHPTAC to phenylpropanoid unit of lignin), flocculant dosages, pH values, kaolin concentrations, slow mixing rates and sedimentation times. The QL10 achieved the highest turbidity removal efficiency (ε_t) with increasing flocculant dosage, pH and kaolin concentration to the optimal conditions of 5?mg?L^?1, pH 7 and 1000?mg?L^?1, and required 20?min of sedimentation time at all the mixing rates tested. The flocculation kinetics agreed well with the particle collision model. The QL10 has good sludge dewatering properties compared to the alum. It also showed encouraging results in water quality analysis for sewage wastewater flocculation in comparison to that of the alum. This indicates the potential application of QL in treating water and wastewater.     

二甲基二烯丙基氯化铵聚合物的除浊性能研究

研究了二甲基二烯丙基氯化铵聚合物（PDMDAAC）系列絮凝剂对高岭土模拟水样的除浊效果及其影响因素；借助于微电泳技术，探讨了该系列絮凝剂的絮凝机理，并考察了其与PAC复配的除浊效果。实验结果表明：PDMDAAC系列絮凝剂具有优良的除浊效果，尤其对于高浊水；絮凝剂的特性粘度越高，阳离子度越高，除浊效果载好；PDMDAAC系列絮凝剂具有电中和和吸附架桥两种功能，与PAC复配，PDMDAAC系列絮凝剂可使除浊效果更佳而且可以降低处理成本。