An investigation of the recovery of cryolite from alumina-electrolyte froth by flotation

In the industrial production of aluminium by the electrolysis of alumina, electrolyte froth, which is a mixture of carbon and cryolite is obtained at a rate of 50 kg of froth per ton of aluminium produced. Cryolite can be recovered from this mixture by flotation. In this study, the effects of the following parameters on flotation were experimentally investigated: particle size, type, combination, dosage and ratio of reagents, and conditioning time. It is found that it is possible to decrease the carbon content of cryolite below 1% by suitably choosing the operating parameters. Electrolyte froth must be ground to —100 mesh size for the liberation of carbon particles captured in the cryolite matrix. Any combination of two of the reagents, kerosene, fuel oil, creosote and terebenthene yield good results if used together with pine oil. Pine oil is found to be a more effective frother compared to Pril, a commercial detergent. Satisfactory separations are obtained when a kerosene-fuel oil mixture (50:50, v/v) is used as the collector with a dosage of 3.7 kg per ton of feed together with pine oil, the frother, with a dosage of 0.095 kg per ton of feed.     

Removal of sulfur from Assam coal by bacterial conditioning and froth flotation

Reduction of sulfur by bacterial leaching from a high sulfur‐bearing coal sample from Assam was attempted. Flotation of the sample with light diesel oil could not depress the pyrite and also the Thiobacillus ferrooxidans was found to be ineffective in leaching the sulfur from the flotation concentrate. Conditioning of the same coal sample with Thiobacillus ferrooxidans was found to assist in selectively depressing the pyrite, thereby reducing nearly 60% of the pyritic sulfur present in the sample. © 1999 Society of Chemical Industry     

Removal of motor oil by continuous multistage froth flotation: Effect of operational parameters

A continuous multistage froth flotation column was employed to remove motor oil from water at a low concentration (500 mg/L) using an extended surfactant – branched alcohol propoxylate sulphate sodium salt (C_14-15–8PO–SO₄–Na) – as a frother. The highest separation efficiency (97% motor oil removal with the enrichment ratio of 16 for motor oil) was obtained at a foam height of 60 cm, an air flow rate of 40 L/min, a feed flow rate of 60 mL/min, a surfactant concentration of 0.3% (w/v), and an NaCl concentration of 1.5% (w/v). The process performance increased with increasing tray number but beyond 4 trays, the system could only offer lower concentrations of motor oil and surfactant in the effluent.     

Separation of unburned carbon from fly ash using a concurrent flotation column

In this study, a new concurrent flotation column that simulates the plug flow reactor was designed with the use of a static mixer, a froth separator column and an optional additional bubble generator for fly ash beneficiation. The objective was to improve the efficiency and effectiveness of unburned carbon removal from fly ash by minimizing energy costs. Cleaning tests were performed with and without the additional bubble genarator. Without the additional bubble generator unburned carbon in the ash product could be reduced to only 2.53%. Incidental loss of carbon particles and insufficient bubble generation were the main causes of poor carbon separation performance. By turning on the additional bubble generator it was aimed to assist bubble generation, to compensate bubble rupture and to recapture the detached or free carbon particles leaving the froth phase. With the additional bubble generator and under optimized conditions a froth product with 95% carbon recovery and a cleaned ash product with less than 1% unburned carbon was obtained. The separation process through the static mixer (feeder) and the separator column and the energy consumption of the unit were analyzed. It was seen that around 80% energy could be saved with the concurrent flotation column compared to conventional flotation.     

The effect of different flotation operating parameters on the froth properties and their relation to clean coal ash content

Froth properties and their relation to the concentrate grade play an important role in monitoring flotation running conditions and predicting flotation concentrate quality. In this paper, the correlation between the froth properties and clean coal ash content was investigated under complicated conditions where the frother dosage, gas velocity, and froth height were changed together. For the froth properties under study, their degree of correlation with clean coal ash content decreased in the order of homogeneity, water recovery, gray value, and froth velocity. The coefficient of determination (R²) of the fitting relationship between homogeneity and clean coal ash content was as high as 0.9028, because homogeneity has a close correlation with the foam structure and foam destabilization behaviors.     

Facile determination of foamability index of non-ionic and cationic frothers and its effect on flotation of quartz

ABSTRACT

In this work, a facile method for determination of foaming properties of frothers was used. It was based on measuring the foam height in a flotation machine at different concentrations of frothers. Based on the foam height-concentration curve, a new foaming parameter, so-called concentration at half of the maximum foam height CMH, was proposed. Assessment and usefulness of CMH were shown in flotation of quartz. The concentration of amine at the critical contact angle CCA, at which amine starts to be a collector, was also determined. The determined values of CCA were similar to CMH and were equal to 1.3, 0.14 and 0.03 mM for ButNH₂, HexNH₂ and OctNH₂, respectively. The values of CMH and CCA depended on the alkyl chain of frothers.     

Effect of flotation on the dioxin distribution in size-fractioned fly ash of hospital solid waste incineration

After the flotation of hospital solid waste incinerator (HSWI) fly ash, two types of solid products, froths and tailings, are produced. This paper reports the effect of flotation on the dioxins distribution patterns in different particle size fractions (?25, ?38, +25, ?75, +38, ?106, +75 and +106 µm) of fly ash. The results showed that the froths had a higher small-size particle distribution than that of the raw fly ash. The dioxin content with particle size in the flotation products depended on the partition behavior of powder-activated carbon (PAC). The dioxin content in the fine particles of the froths was higher than that in the coarse particles, and the highest content was in the finest particles (?25 µm). The dominant dibenzo-p-dioxins and dibenzofurans (PCDD/F) congeners in the froths and tailings were similar to those in the raw fly ash. A positive correlation between carbon removal and PCDD/F removal with different size fractions was observed. The carbon removal efficiencies of the fractions of ?25 and ?38, +25 µm were evidently higher than those of the other particle size fractions. Similarly, the PCDD/F removal efficiencies in fractions of ?25 and ?38, +25 µm could reach 156.9% and 115.0%, respectively.     

Effect of pH on the flotation performance of incinerator fly ash

Flotation was proved to be effective for decarburization and removal of dioxins from hospital solid waste (HSW) incinerator fly ash, but weathering makes it difficult. The effects of three types of surfactants including nonionic (Tween 80), anionic (SDS), and cationic (CTAB) at different pulp pH values on the flotation performance of weathered HSW incinerator fly ash were investigated. Results showed that the corresponding optimal pH values of Tween 80, CTAB, and SDS were 7, 5, and 9 in terms of decarburization performance, respectively, which were validated by the measurement of Zeta potential. The total dioxins and carbon removal efficiencies showed good correlation at various pulp pH values with surfactant of Tween 80. The optimum surfactant type and pH value should be selected as Tween 80 and pH = 7 from the standpoints of the dioxin removal. Under the optimum condition, the lowest content of dioxins (2.7 ng I-TEQ/g) in the tailings was obtained. The content of heavy metals in the froths exhibited higher with addition of SDS compared with that with Tween 80 and CTAB.     

Physical and chemical analyses of unburned carbon from oil-fired fly ash

In the hydrometallurgy process of extracting vanadium and nickel products from oil-fired fly ash, a large amount of unburned carbon remains as a by-product. Because of insufficient knowledge of the physical and chemical properties and related applications of the unburned carbon, the residue has been disposed to landfill or incinerated. In order to explore the utilization of unburned carbon, this preliminary study analyzed its morphology, particle size distribution, specific surface area, pore size distribution, density and chemical composition. The results indicate that the chemical composition is 73-91% carbon, 5-19% ash, 2.5-11.5% volatile substances, and 0.7-1.9% water, it consists of porous spherical particles and some crumbled particles with particle sizes mainly in the range 1-100 μm, the specific surface area is 16-33 m²/g, the pore size ranges between 0.02 and 10 μm, the real density is about 2.05-2.16 g/cm³, the apparent density about 0.15 g/cm³ and it can be characterized as a puffy, readily wind-blown powder.     

改性粉煤灰对燃煤电厂脱硫废水中氯离子的吸附性能

为了将"以废治废"的理念融入实际工业应用中,开展对燃煤电厂固体废弃物粉煤灰改性后在不同条件下进行脱硫废水的吸附实验研究.结果表明,改性粉煤灰的最佳投加量为25 g/L,此时对废水中Cl-的去除率最大,为56％;在45°C和pH为5的条件下,粉煤灰对Cl-的吸附量最大,在反应约280 min时达到吸附平衡.该吸附过程为吸...     

起泡剂性能及其对煤泥浮选的影响研究

为提高煤泥浮选效果,利用充气法和TRACKE界面张力仪研究了仲辛醇和GF油的起泡能力及泡沫稳定性,分析柴油对起泡剂起泡能力和泡沫稳定性的影响,并采用2种捕收剂对山西煤样进行煤泥浮选试验研究。结果表明:起泡剂质量分数相同时,GF油的起泡能力要高于仲辛醇,GF油的界面张力比仲辛醇低,但界面张力曲线的斜率比仲辛醇大,因此,GF油的泡沫稳定性大于仲辛醇。起泡剂质量分数相同时,GF油产生泡沫的半衰期要高于仲辛醇,说明其泡沫稳定性要好于仲辛醇。在仲辛醇和GF油中加入柴油后,溶液界面张力下降明显,泡沫半衰期增加,提高了起泡剂的起泡能力和泡沫稳定性。煤泥浮选试验表明,起泡剂用量相近时,GF油作起泡剂的煤泥浮选精煤产率和精煤灰分均高于仲辛醇。     

Plerosphere and its role in reduction of emitted fine fly ash particles from pulverized coal-fired power plants

Fine particles (PM_2.5) emitted from the stacks of the coal-fired power plants are of environmental concern since they can easily enter the human respiratory track. The detailed study of the fly ash particles using scanning electron microscope/electron dispersive spectrometry (SEM/EDX) show that fine solid spherical particles (microspheres) are contained by the large cenosphere particles (>50 μm) during the combustion process. The resulting macro particles are known as “plerosphere”, which are typically impregnated by the fine microspheres. The coal-fired power plants’ particle control devices such as the electrostatic precipitators (ESP) and baghouse filters tend to capture the large plerospheres, more efficiently. Therefore, the result of this study suggests that the containment of the microspheres by plerospheres during the coal combustion process can effectively reduce the amount of fine particles and associated elements released into atmosphere.     

Influences of Jameson flotation operation variables on the kinetics and recovery of unburned carbon

The purpose of this study was to investigate the influences of Jameson flotation operation variables on the recovery and kinetics of unburned carbon (UC). The waste sample of petroleum coke, filter powder or fly ash, used in the experiments was collected from lime calcination plant tailings. The effect of Jameson flotation parameters on the recovery and kinetics efficiencies of UC was systematically studied. The feasibility of separating unburned carbon and refuse was determined from the combustible recovery (CR) and ash reduction (AR) (%) curves. Within the range studied, the optimum diesel oil dosage was 3500 g/tonne, pine oil dosage was 2500 g/tonne, pulp density was 15%, wash water rate was 0.17 cm/s and downcomer immersion depth was 50 cm. The results indicate that the Jameson flotation technique is effective in removing the UC from waste filter powder. Furthermore, the classical first-order kinetic flotation model (R = R_∞ [1 − exp (− k ? t)]) was applied to data from the tests. The model was evaluated by statistical technique, after non-linear regression on the model parameters. It is found that the classical first order flotation kinetic model, most extensively used among flotation models, fits the tests data very well.     

火力发电厂燃煤飞灰润湿性能

化学团聚是控制燃煤电厂细微颗粒排放最有效的方法之一。颗粒物被团聚剂润湿是化学团聚的首要步骤。以小龙潭电厂燃煤飞灰为对象,采用激光粒度仪研究了燃煤飞灰在十二烷基硫酸钠(SDS)、十二烷基苯磺酸钠(SDBS)和Triton X 100(TX100)三种润湿剂溶液中的润湿性能,考察了润湿剂浓度、温度对燃煤飞灰润湿性能的影响。结果表明：水仅能将飞灰颗粒中的PM^₁₀+部分全部润湿,0.25%的SDS溶液中PM_2.5⁺可全部润湿,1%的SDS及0.4%的SDBS溶液中PM₁⁺可全部润湿;TX100溶液在低浓度条件下具有较强的润湿飞灰颗粒的能力,且0.1%的TX100溶液对细微颗粒的润湿性能较好;温度从20℃上升到60℃,润湿剂溶液表面张力降低,飞灰的润湿性能增强。鉴于飞灰在三种润湿剂中良好的润湿性能,三种润湿剂均可作为团聚剂组分以促进燃煤飞灰中的细微颗粒润湿进而被团聚成为容易脱除的大颗粒。     

Effects of residual concentration of collector CTAC on flotation behavior of illite

ABSTRACT

In present study, illite flotation behavior with Cetyl Trimethyl Ammonium Chloride (CTAC) as the collector has been studied to investigate the effects of its residual concentration on froth stability and flotation. Results showed that, with increasing conditioning time, the residual concentration (frother concentration) and froth height decreased simultaneously, while the adsorbed amount (particle hydrophobicity) increased. Increasing CTAC conditioning time decreased the residual concentration in solutions, resulting in poor froth stability and flotation recovery at high pH; the adsorption rate of CTAC on illite surface was relatively high at higher pH due to strong electrostatic mechanism, making CTAC residual concentration decrease.     

Characterization and column flotation of bottom ashes from Tuncbilek power plant

Bottom ashes from the Tuncbilek power plant have been characterized by size fraction, X-ray diffraction and X-ray Fluorescence. These samples are potentially of class F type and have significant amounts of unburned coal. The unburned coal specimens studied using Fourier Transform Infrared Spectroscopy indicated a significant loss of the aliphatic hydrocarbon groups (C-H) and the carbon bond CC during their stay in the combustion environment. In contrast, they indicated insignificant levels of carbonyl group, CO, possibly due to the loss of CO₂ to air as well as carboxylic ions to disposal water. The effects of various operating variables on the combustible recovery and ash content determined using column flotation were limited due to severely oxidized state of unburned coal. Best set of results was obtained with the bottom ash sample from unit 3, which brought the ash content from 77.6% down to 42.6% at a combustible recovery of 53.8%, and the calorific value was increased from 1270 kcal/kg to 3840 kcal/kg.     

烟气及飞灰组分对溴改性飞灰脱汞特性的影响

燃煤飞灰中的未燃碳（unburned carbon,UBC）和金属氧化物因对汞有一定的吸附和氧化作用而被认为是燃煤电厂廉价的潜在脱汞吸附剂,但效率有待提高。文章选取两种UBC含量不同的飞灰,采用质量分数1%的NH₄Br溶液对其浸渍改性,利用固定床汞吸附实验台探究了烟气组分（O₂、SO₂和NO）以及飞灰中无机金属氧化物对汞吸附和氧化的影响,以期获得高效脱汞吸附剂吸附机理。结果表明,O₂对于溴素改性飞灰氧化汞有较小的促进效果,SO₂具有一定的抑制作用,NO促进Hg⁰的氧化效果明显;溴素改性飞灰中的Fe₂O₃和TiO₂对Hg⁰的氧化起着主要作用,原因在于溴素改性增加了金属氧化物Fe₂O₃和TiO₂中的晶格氧含量,促进了Hg⁰的催化氧化,主要遵循Mars-Maessen机理。另外,UBC含量对飞灰脱除Hg⁰的影响很大,溴素嵌入飞灰表面的UBC时,会使其邻域的活性加强,从而增强碳质表面对Hg⁰的吸附能力,促进了后续反应的进行。     

The effect of fly ash on fluid dynamics of CO2 scrubber in coal-fired power plant

Uncaptured fly ash and/or suspended solids from wet flue gas desulfurization (WFGD) scrubbing solutions are one of several factors that will influence the performance and robustness of carbon dioxide capture systems in coal-fired power plants which will be installed prior to the exhaust stack. In this study, a 100 mm ID packed column scrubber was tested with different concentrations of ash in various chemical solutions to evaluate the influence of solids on the fluid dynamics of the packing material. Data reported here are collected from three solutions including water, 30 wt% MEA (monoethanolamine), and 20 wt% potassium carbonate. The packing selected for this study was a 16 mm polypropylene pall rings. Compressed air was used to simulate flue gas at near ambient temperature and pressure.     

Emission characteristics of NOx and unburned carbon in fly ash on high-ash coal combustion

Three coal sources, two high-ash coals from South Africa and one bituminous coal from Australia, were evaluated at a pulverized coal combustion test furnace. These combustion trials were carried out on different blending ratios with the two South African coal sources. The NOx emission characteristics of these high-ash coals are similar with those of bituminous coals. The combustion efficiencies on the high-ash coals are lower than those of bituminous coals. The high-ash coals do not affect bituminous coal combustion on the blending combustion.     

燃煤电厂干化灰渣中氯的脱除研究

干化灰渣是燃煤电厂脱硫废水零排放的固态废弃物,但由于氯含量高限制其资源化利用。再加之脱硫废水零排放技术渐成主流,研究干化灰渣高效脱氯的方法具有重要的现实意义。通过XRF和XRD对干化灰渣进行元素成分和物相表征,通过IR分析灰渣的结构特性,采用添加脱氯剂三氧化二铝（质量分数为2.5%~10.0%）并结合高温煅烧（600~900 ℃）研究了干化灰渣中氯去除过程。得到的优化工艺参数为：煅烧温度为700 ℃、煅烧时间为2 h、三氧化二铝添加量为7.5%,优化工艺下脱氯率可达96.9%。并对脱氯剂三氧化二铝的作用机理作了初步分析。