The effect of froth stability on the beneficiation of low-rank coal by flotation

The nature and type of minerals associated with a low-rank (NCB 902) coal were determined by scanning electron microscopy and dispersive X-ray analysis.

The mineralogical examination showed the presence of fluorapatite and other minerals which would be troublesome on combustion. It also showed that the minerals would, to a large extent, be liberated by fine grinding.

The effect of kerosine and a branched chain aliphatic alcohol (2-ethyl-hexan-1-ol) on the beneficiation of finely ground samples of this coal under conditions of agglomeration flotation were studied.

A relationship between beneficiation and froth stability was noted and results are reported for the beneficiation of individual wet-screened fractions for selected runs.

A mechanism for beneficiation is proposed which is consistent with the experimental observations.     

Collector adsorption during froth flotation

The adsorption of oleate on ferric oxide, conditioned in aqueous solution at pH 9.0, has been determined from the heat of combustion of the adsorbed oleate by differential thermal analysis. Measurements were made over a range of oleate concentrations on the conditioned material prior to flotation and on floated ferric oxide. The resulting adsorption isotherms show that the floated material usually carries less, and never more, adsorbed oleate than the conditioned but unfloated material. This is contrary to what would have been expected front the work of Digre and Sandvik; the explanation is probably that sorption equilibrium conditions hare been established in our measurements, but not in those of the workers mentioned above.     

Oil shale beneficiation by froth flotation

It was found that froth flotation is capable of upgrading oil shale to improve the oil yield in the Fischer assay from 0.117 to 0.175 1/kg at 75% organic recovery in 50% of the rock. Feed particle size affected the float yield and grade and thus the separation efficiency. For economic reasons, grinding to very small particle sizes was avoided. With moderate grinding, particles < 75 μm required less frother and collector to float than particles ? 150 μm and the selectivity was lower for < 75 μm particles. The best separation efficiency was achieved at a feed particle size of 500-150 μm. As the quantities of frother and collector increased, both the float yield and the percentage organic recovery increased, but the percentage mineral rejection decreased. As a result, the separation efficiency reached a maximum at float yields of 40–50%. The types of frother and collector affected the float yield. However, they had no significant effect on the grade of float if the amounts of frother and collector were controlled to achieve the same float yields.     

Convective-dispersive gangue transport in flotation froth

The transport of gangue through flotation froth has been described by solving the convection-diffusion equation. Gangue recovery is predicted to be proportional to liquid recovery, which is consistent with experimental observation. In addition, it is seen that the dependency of gangue recovery upon particle size is due to processes within the pulp phase rather than the froth, insofar as the transport of particles in a given froth is approximately independent of size. The importance of maintenance of positive bias in column flotation, previously stressed by other workers, is reinforced. This model utilises a simplified representation of the froth and, as a consequence, it does not necessarily give accurate gangue recovery estimates for practical flotation processes. However, the convective-diffusive model does illuminate the physical processes behind gangue recovery in the concentrate which will aid the development of automatic control strategies.     

基于图像空间结构统计分布的浮选泡沫状态识别

通过泡沫图像统计建模,实现了基于图像空间结构感知的浮选泡沫状态自动识别与客观评价。首先,采用Weibull分布建立了泡沫图像各方向边缘响应结构的统计分布模型,有效获取了泡沫图像空间结构的统计分布细节;然后,通过统计学习获得各典型工况状态下的泡沫图像边缘响应统计分布的混合高斯（MoG）模型;最后,通过简单的贝叶斯推理推断出测试泡沫图像对应的工况状态。结果表明：所提出的方法因有效获取了与浮选生产性能直接相关的泡沫空间结构的统计分布特征,可以实时监视泡沫空间结构的变化情况,泡沫生产状态识别准确率高。     

Electro-osmotic dewatering of coal froth flotation concentrates

Two coal flotation concentrates were dewatered by electroosmosis in small-scale laboratory tests to 84 and 88 wt% solids at an energy consumption of 25 and 69 kW h/dry tonne, respectively. Vacuum filtration at the washeries yielded 70–75 wt% solids.     

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.     

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     

Coal microlithotype response to froth flotation in selected Western Kentucky coals

Seven coals representing four western Kentucky coal seams and the coal rank range from high volatile C to high volatile A bituminous were selected for bench-scale froth flotation processing. Each coal was represented by two splits of the run-of-mine coal: a 12.7 mm × 0 fraction (crushed to 28 mesh × 0) and a 28 mesh × 0 fraction. The original 28 mesh × 0 split was found to be higher in the inertinite macerals fusinite and semifusinite than the coarser fraction. The separation of the inertinite macerals, expressed as the microlithotype inertite, from the vitrinite-rich vitrite and clarite microlithotypes proved to be markedly rank dependent. In the higher rank coals vitrite and clarite were concentrated in the clean coal while inertite was concentrated in the clean product in the high volatile C coals. Whereas in gravity-based coal cleaning only the finest pyrite usually remains in the clean coal, in this study no consistent trend in pyrite-size or pyrite-quantity partitioning was noted.     

Macro-pore structure characteristics of a low-rank coal and its froth flotation fractions

A high pressure Mercury Porosimeter (M.P.) (max. oper. press: 2000 atm) and an optical microscope interfaced with a Quantimct image analyser were employed to investigate the internal macro-pore structure of froth flotation concentrates of low-rank coal. The objective of the froth flotation process is to produce a demineralized product from a pulverized low-rank feed coal suitable for use in industrial combustors as the solid component of a coal-oil mixture (COM). The effectiveness of the coal for this use is associated with a rapid rate of combustion for which a knowledge of macro-pore distribution is useful. It is also of interest to know whether the pore-size distribution of the treated coal influences in any way the froth flotation process, possibly leading to selective separation based on internal pore structure. The experimental distributions showed a bimodal configuration with maxima located at pore sizes of ≈ 10 and ≈ 5500 nm. Overall specific surface areas ranging between 3.50 and 11.80 m²/g_c are substantially higher in comparison with results from literature obtained by M.P. and N₂ adsorption at ?196 °C. M.P. hysteresis results are discussed and a low mercury entrapment of ≈ 5% of the ultimate detected porosity was observed on froth flotation tailings with an ash content approaching ≈ 77%.     

胶磷矿浮选过稳定泡沫消泡技术初探

以王集磷矿浮选精矿泡沫为研究对象，通过物理方法和化学方法的组合旨在找出胶磷矿浮选过稳定泡沫的最佳消泡技术，以达到最佳的消泡效果，并对胶磷矿浮选泡沫过稳定原因及消泡技术机理进行了初步探讨。     

Optimization of froth flotation procedure for poly(ethylene terephthalate) recycling industry

This article addresses the separation of polyethylene terephthalate (PET) from ternary blends with polyvinyl chloride (PVC) and polystyrene (PS) by froth flotation. The experimental work was carried out with representative samples from post‐consumer waste packages collected at drop‐off‐points. Previous to froth flotation, PET selective wetting was achieved by alkaline treatment followed by surfactant adsorption. For this purpose, an aqueous solution of NaOH and an industrial detergent commonly used for waste plastic washing were tested as alkaline treatment, and calcium lignosulphonate and Hostaphat were tested as surfactants. An enriched product with 98.9% grade in PET and only 0.6% in PVC was recovered in the nonfloated product. The PET recovery in this product was 97% while ～96% of PVC and 91% of PS were recovered in the floated product. An analytical method was developed for the quantification of the waste plastic composition. The method was based on the selective dissolution of the plastics in the mixture. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Performance of classic oils and lubricating oils in froth flotation of Ukraine coal

In this study, the appropriate collector and collector amount for Ukraine coal in froth flotation was determined. For this purpose, the performance of classic oils (kerosene, diesel-oil and fuel-oil) and lubricating oils (spindle oil, bright stock and heavy neutral) was evaluated by combustible recovery, ash rejection and efficiency index. It was found that the combustible recovery and ash rejection changed, depending on the type and concentration of oil. The maximum combustible recovery was obtained by using bright stock. It was determined that bright stock, fuel-oil and kerosene were suitable for the flotation of Ukraine coal. On considering the flotation efficiency index values, the best results were obtained with bright stock and diesel-oil. Consequently, it was shown that bright stock and spindle oil could be used as alternative oils instead of classic oils for cleaning of Ukraine coal by the froth flotation.     

Selective froth flotation of PVC from PVC/PET mixtures for the plastics recycling industry

It was found that strongly alkaline solutions of sodium hydroxide are able to destroy the hydrophobicity of polyethylene terephthalate (PET) whereas the hydrophobicity of polyvinyl chloride (PVC) remains only slightly affected by these solutions. On this basis, a technology involving treatment of PET and PVC particles with alkaline solutions followed by froth flotation of PVC with nonionic surfactants has been developed and tested at a laboratory scale. In both steps of this technology, appropriate experimental conditions, such as concentration of reagents, temperature and residence time, have been optimized through a detailed examination of all these variables on the efficiency and selectivity of PVC separation from PVC/PET mixtures of varying composition. It is demonstrated that using this technology 95–100% recovery of PET and PVC can be achieved in separate products from a variety of PVC/PET mixtures.     

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.     

一次浮选作业泡沫分室处理工艺在淮北选煤厂浮选系统改造中的应用

介绍了淮北选煤厂(南区)浮选入料特性,分析了一次浮选作业分室泡沫的粒度组成以及沉降过滤式离心机脱泥的局限性;将煤泥二次浮选、精煤泥二段脱水工艺流程进行了优化,即一、二室粗选泡沫由沉降过滤式离心脱水机脱水、脱泥,三、四室粗选泡沫直接由二次浮选作业精选,有效提高了精煤产率。     

Effect of frothers on removal of unburned carbon from coal-fired power plant fly ash by froth flotation

The effect of single frothers and their blends on bubble size, froth stability, and unburned carbon (UC) flotation performance was studied. Methyl isobutyl carbinol that produces smaller bubbles is efficient in floating ultrafine particles and producing concentrate. DF-250 that gives higher froth stability is effective for recovering coarse particles and improving recovery. The presence of DF-250 in the blend increases bubble size and significantly enhances froth stability, and hence the optimal flotation performance is achieved with 75% DF-250. It indicates that the frother giving high froth stability is better in UC flotation due to the little effect of UC on froth stability.