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.     

铁盐絮凝剂磁絮体形成的最佳参数及性能研究

本文系统研究了失盐及有机高分子絮凝剂与磁粉在高浊度原水中复合投加的絮凝效果和含磁絮体形成的最佳参数，并通过比较处理效果，出水沉降时间和含磁絮体的显微结构，验证了本磁絮凝方法处理高浊度原水效果更好，停留时间更短的预估，且絮体含磁易分离、为管式絮凝器采用磁絮凝和高梯度磁分离工艺提供了参数依据和高效絮凝分离一体化，管经的可行性证明。     

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.     

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.     

Coagulation of Particles Through Rapid Mixing

As is often assumed, rapid mix effectively distributes the dosed coagulant in suspension to promote subsequent flocculation of suspended particles and coagulant molecules. This study determined that the role of rapid mix is considerably more complex than conventionally assumed. Particles in the raw water samples from the Banxing Water Works of Taipei City were coagulated at high shear environment, during which flocs of size 40–70 μm were produced. The produced floc interior was compacted, and residual turbidity and the amount of dissolved natural organic matter (NOM) in suspension were substantially reduced. The subsequent stage of rapid mix slightly reduces floc size, further compacts the floc interior, and expels fine particles and some adsorbed NOM from the flocs. A sudden reduction in shearing rate produced large sized flocs with not so compact structures. Moreover, this action released fine particles from flocs into the suspension and enhanced adsorption of NOM onto solid surfaces.     

Coagulation of Particles Through Rapid Mixing

As is often assumed, rapid mix effectively distributes the dosed coagulant in suspension to promote subsequent flocculation of suspended particles and coagulant molecules. This study determined that the role of rapid mix is considerably more complex than conventionally assumed. Particles in the raw water samples from the Banxing Water Works of Taipei City were coagulated at high shear environment, during which flocs of size 40-70 μm were produced. The produced floc interior was compacted, and residual turbidity and the amount of dissolved natural organic matter (NOM) in suspension were substantially reduced. The subsequent stage of rapid mix slightly reduces floc size, further compacts the floc interior, and expels fine particles and some adsorbed NOM from the flocs. A sudden reduction in shearing rate produced large sized flocs with not so compact structures. Moreover, this action released fine particles from flocs into the suspension and enhanced adsorption of NOM onto solid surfaces.     

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.     

聚二甲基二烯丙基氯化铵对聚合硫酸铁处理冬季长江水的助凝效果

采用聚二甲基二烯丙基氯化铵(PDM)与聚合硫酸铁(PFS)复合制得的稳定型复合混凝剂,用于冬季低温长江水强化混凝脱浊处理。通过混凝烧杯试验,考察了PDM对PFS在脱浊效果和沉淀性能上的改进程度。结果表明:对温度为5～7℃,浊度为45 NTU左右的冬季长江水,PDM助凝效果明显,同时PFS与PDM的复配比例越低,复合混凝剂混凝脱浊效果越好。复合混凝剂中PFS的用量比单独使用PFS时的少。复合混凝剂能增大絮团的沉淀速度,克服冬季低温条件下单独使用PFS时絮体轻而细小、沉淀慢、破碎现象严重的问题,从而使沉淀出水水质能够迅速稳定地达标,同时,还可明显改善PFS处理时出水带色、腐蚀设备等问题。     

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.     

絮凝污泥制备TiO2/MCM-41复合光催化剂及降解罗丹明B

研究了以聚硅硫酸钛为絮凝剂,处理掺杂MCM-41型分子筛的长江水,将产生的大量絮体经抽滤、烘干和一定温度下煅烧,制备了具有光催化活性的TiO2/MCM-41复合光催化剂,并用X射线衍射（XRD）对其进行了表征。结果表明,在长江水浊度为86.7NTU,MCM-41分子筛掺杂量为0.7g/L时,经聚硅硫酸钛絮凝产生的絮凝污泥在700℃下煅烧2h后制备的复合光催化剂活性最高,光催化氧化浓度为20mg/L的罗丹明B 40m in后脱色率达97.6%。     

Acrylamide-sodium acrylate copolymers: A comparison between copolymerization and hydrolysis

Polyacrylamide-co-sodium acrylate has been prepared via copolymerization of acrylamide and acrylic acid, or the hydrolysis of a pre-formed nonionic polymer. Both macromolecules had a charge of 24 mol% with a molar mass of 25 million g/mol. While one might expect similar performance, the hydrolyzed materials were superior in rheology modification, while the copolymerized samples worked better as flocculants. This hydrolysis reaction is influenced by the dyad sequence and produced a relatively uniform charge distribution along the backbone. These partially hydrolyzed polyelectrolytes had approximately 40% higher solution viscosities compared to the copolymerized samples. The rheological properties were also more tolerant to temperature, electrolytes, and hardness. Such molecules would be expected to perform well as pushing fluids as used in enhanced oil recovery processes. In contrast, when tested on an inorganic sludge, with a high level of polar and soluble hydrophobic molecules, the copolymerized sample provided larger flocs, a clearer filtrate, and faster settling. The hydrolyzed macromolecules essentially functioned only as a coagulant generating pin flocs. Depending on the application, polymer structure can be tuned by the method of synthesis. To the authors' knowledge, this is the first report comparing the influence of synthesis method on polyacrylamide solution properties and application performance.     

Effect of molecular weight and charge density on the performance of polyacrylamide in low‐grade oil sand ore processing

The effect of charge density and molecular weight (MW) of partially hydrolyzed polyacrylamide (HPAM) polymers on their performance in processing low‐grade oil sand ores was investigated. Bitumen extraction and tailings settling tests were carried out and an atomic force microscope (AFM) was used to directly measure the bitumen‐solid and solid‐solid interaction forces. It was found that HPAM polymers with a low MW acted as dispersants in the bitumen extraction process, resulting in low bitumen recovery and slow tailings settling but improved froth quality. In contrast, the use of HPAM polymers with a high MW improved both bitumen recovery and tailings settling but deteriorated froth quality. To achieve high bitumen recovery and fast tailings settling, a HPAM polymer must have a low to medium charge density (～30%) and a high MW (17.5 million Daltons). A stronger clay‐bitumen adhesion force normally resulted in a lower bitumen recovery. Fast tailings settling was achieved in the presence of a strong solid‐solid adhesion force.     

准能选煤厂煤泥水絮凝沉降优化试验研究

为改善准能选煤厂煤泥水沉降效果,在对选煤厂一系统煤泥水中煤泥矿物组成和粒度特性进行研究分析的基础上,对煤泥水进行了絮凝沉降试验,分别比较了絮凝剂类型、分子量(离子度)和用量对煤泥水沉降效果的影响;结果表明:选择阳离子度为70%~80%的阳离子型聚丙烯酰胺,用量为1 g/L时,上清液浊度为12.24 NTU,煤泥水体系Zeta电位最接近于零,煤泥水沉降效果达到最佳。     

Preparation of a new polymer-modified adhesive mortar using fine iron tailings as aggregate

In this paper, a new polymer-modified adhesive mortar is prepared using the fine iron tailings, eco-cement, redispersible latex powder, additives, and water. In our study, the fine iron tailings are used to replace the natural river sand as the mortar aggregate and the optimal process conditions are determined by the orthogonal experiment. The obtained results are shown as follows: The ratios of cement–sand and polymer–cement are 1:2.5 and 4%, respectively, with the aggregate modulus 0.81 and water reducing agent 0.5% (cement-based). The properties of the polymer-modified adhesive mortar obtained under the optimal process conditions conform to JC/T 547-2005 (China Professional Standard: Ceramic Tile Adhesive). Moreover, the microstructure of the polymer-modified adhesive mortar is studied and discussed. The results show that the network formed by the intertwined polymer film can prevent the merger of micro-cracks and improve the adhesive mortars’ overall cohesion. Therefore, adding polymer to the adhesive mortar can improve its failure stress and enhance its bonding strength.     

新型溢流器高效回收钛白酸解尾渣中的钛

中国是世界上最大的硫酸法钛白生产国,目前已累计堆积超过千万吨副产品酸解尾渣。酸解尾渣中含有大量未反应的粒径大于25 μm的钛铁精矿,酸解尾渣堆积而不利用就造成了严重的环境污染和资源浪费。根据酸解尾渣颗粒沉降实验分析,发现酸解尾渣料浆具有良好的沉降和易分层特性。通过建立干扰沉降末速度计算式,得出酸解尾渣中颗粒切割粒度25 μm的沉降速度为0.60 mm·s^-1。基于流动、分选机理和沉降特性分析,设计了适用于酸解尾渣分离工艺的新型DTB（draft tube babbled）溢流分离器,并进行了结构参数优化,获得了溢流器最优结构参数和最佳分离效果。结果表明,外排溢流含有极少量大于25 μm的钛铁精矿颗粒,回收的钛品位达27%,回收率为73%。这些结果为大规模回收酸解尾渣中钛资源提供了基础数据。     

铁尾矿干排应用倾斜板浓缩机的研制

重力浓缩是固液分离的第一道工序,为满足铁尾矿干排处理工艺中含有大量微细颗粒且浓度较低的矿浆对浓缩技术的要求,基于"浅层沉降"原理对浓缩机的结构进行改进,利用一组表面光滑的特制倾斜板面,改变固体颗粒的沉降路径,缩短沉降距离,减少沉降时间,提高沉降速度,改善液流条件,强化浓缩机工作效率,增加浓缩机自然沉淀面积及单位面积生产能力,提出一种新型高效倾斜板浓缩机。     

微砂强化结团絮凝处理模拟工业废水的试验研究

采用微砂强化结团絮凝工艺处理模拟工业废水,研究了投药量、加砂量以及微砂粒径对除浊性能的影响,并分析了结团絮体的形成机理。结果表明,聚合氯化铝的最佳投加量为0.875 g/L,微砂最佳粒径范围为50~100μm,微砂最佳投加量为1.0 g/L,在此最佳条件下处理低浊废水,浊度由进水时的21.6~25.3 NTU降低至出水时的0.47 NTU以下,去除率达98.0%~98.8%。     

含沙高浊水最佳絮凝条件的确定

在含沙量为85kg／m^2的悬浊液中投加阳离子高分子聚合物,研究不同絮凝条件下絮体的自由沉速、结构密实程度、浑液面沉速与上清液余浊等的变化规律。利用“分维”作为定量控制参数研究含沙高浊水絮凝效果迭最佳时的絮凝条件（如搅拌速率、搅拌时间、高分子浓度等）,探讨了最佳絮凝条件下不同原始泥沙浓度对絮体分形结构的影响规律。实验得出85kg／m^2泥沙絮体结构密实性达最佳时的水力剪切强度Ct值存在两个临界值：快速絮凝阶段C1t1=2350,慢速絮凝阶段G2t2=12420。     

Using polymer adsorption data and a population balance model to estimate how polymer dosage affects the flocculation of oil sands tailings

Population balance models can describe how particles aggregate and fragment during the flocculation of mineral tailings. We used a new method to estimate some of the parameters in a population balance model describing the flocculation of oil sands mature fine tailings with poly(vinyl benzyl trimethylammonium chloride). Differently from previous population balance models, the polymer adsorption data onto the particles suspended in the tailings were used to estimate a fundamental parameter relating polymer dosage to the mean diameter of the aggregates formed during flocculation. The model could predict the flocculation behaviour of three polymer samples with different molecular weights. This model is another step toward a quantitative understanding of how polymer properties affect the flocculation of mineral tailings.     

Effect of molecular weight of poly(N‐isopropyl acrylamide) temperature‐sensitive flocculants on dewatering

The influence of molecular weight (MW) and dose of Poly(N‐isopropyl acrylamide) (PNIPAM) (temperature‐sensitive flocculant) on sedimentation rate, sediment density, and supernatant clarity of silica suspensions was investigated. The addition of PNIPAM resulted in rapid sedimentation (T > critical solution temperature, CST) and low sediment moisture (T < CST). Higher MW polymers resulted in more effective flocculation and sediment consolidation. At 10 ppm, PNIPAM (3.6 million Da) produced 20 m/h settling rate and 48 vol % solids sediment density, whereas 0.23 million Da polymer produced 0.1 m/h settling rate. PNIPAM produces effective flocculation and consolidation by cycling the interparticle interactions between repulsion and attraction as temperature is cycled around the CST. The change in temperature produces a hydrophilic/hydrophobic transition of the polymer, influencing adsorption onto the surface and the inter‐particle forces. Conventional polyacrylamide flocculants (not influenced by temperature), cannot be used to produce both rapid sedimentation and dense sediments. © 2009 American Institute of Chemical Engineers AIChE J, 2009