Improving the flotation performance of coking coal using the reverse-direct flotation process

In order to improve the flotation performance of the coking coal particles, the flotation tests of the coking coal particles were conducted in the direct flotation, reserve flotation, and reverse-direct flotation processes. It was found that the concentrate ash content of coking coal particles was higher than 20%, which cannot be effectively reduced using the direct and reserve flotation processes. However, the flotation concentrate with the ash content of 12.53% can be obtained from the reverse-direct flotation process. In the reverse-direct flotation process, the surface hydrophobicity was reduced with the dextrin and 1-dodecylamine (DDA) addition at the reverse flotation process stage. For the addition of diesel collectors at the direct flotation process stage, the surface hydrophobicity of the coking coal samples was improved.     

Recovering clean low-rank coal using shale oil as a flotation collector

Shale oil (SO) was adopted as flotation collector to recover clean low-rank coal. Gas chromatography-mass spectrometry, flotation, X-ray photoelectron spectroscopy and contact angle measurements were performed to identify the chemical constituents and flotation performance of SO, and the surface properties of low-rank coal. The results indicated that the long-chain hydrocarbon and high viscosity of SO may lead to the higher combustible matter recovery and lower ash content of clean coal. The adsorption of SO significantly enhanced the carbon-bearing content and decreased the C?O content, which was favorable to enhance the hydrophobicity, and thus improve the flotability of low-rank coal.     

Oxidized coal flotation enhanced by adding n-octylamine

Oxidized coal is difficult-to-float using conventional diesel as the collector due to the abundant oxygen-containing groups on coal surface. In this study, a short-chain cationic amine, n-octylamine, was added into diesel in 1:4 ratio for enhancing oxidized coal flotation. X-ray photoelectron spectroscopy (XPS) was used to identify the interaction mechanism between diesel-n-octylamine mixture (DO) and oxidized coal. The results showed that the flotation yield using 500 g/t DO mixture was much higher than that of using 2000 g/t diesel under a similar ash content of clean coal. The addition of n-octylamine was proven to be an effective way to lower the oily collector consumption in oxidized coal flotation. XPS showed that electrostatic bonding between n-octylamine and negative-charged hydrophilic sites on oxidized coal surface was responsible for the enhancement of flotation recovery using DO as the collector.     

Recovery of clean coal from tailings by flotation with aid of ultrasonic

In this paper, clean coal was recovered from tailings by flotation with the aid of ultrasonic irradiation. Flotation test, coal surface scanning and collector adsorption measurement were carried out. The results show that ultrasonic alleviated slime coating and decreased collector adsorption on coal surfaces. Meanwhile, the combustible recovery increased while the recovery of ash-formed minerals decreased. Particles with different size and density fractions have different flotation behaviors, which were also analyzed by measuring size fraction distribution and density fraction distribution of clean coal. This practice saved coal resources and benefitted environment.     

A new process for the production of medium quality fuels from coal washing plant coarse tailings

Turkey’s proven bituminous coal reserve is very low, and it is about 1.3 billion tons. The annual bituminous coal production is 2 million tons, and the annual import amount is 30 million tons. Turkey is a foreign-dependent country in its bituminous coal requirement. In this respect, the highest recycling of coarse and fine plant tailings is important in respect of the efficient use of limited natural resources. In this study, a novel process was developed for medium quality fuel production from coarse plant tailings. By the developed process, from coarse plant tailings with an ash content of 78.21%, medium quality fuel was produced which has ash content between 29.20 and 44.38% and which has economic value in the current market. The upper calorific values of these fuels change between 5620 and 4350 kcal/kg. The developed process basically includes the stages of micronized grinding and then froth flotation applied to the obtained powder tailing material.     

A suitable process for clean coal recovery from tailing pond deposits

This study aims to recover ?ne coal process with efficiency at a very low reasonable investment and operational costs. In the present study, the sample was taken from a tailing pond of an operating coal preparation plant, cleaned using an enhanced gravity separator to produce a clean product of low ash content. The experimental results indicated that a good amount of clean coal recovered from tailing pond with an ash content of 16.24% could be produced from a feed of 33.5% ash with an appreciable yield of 69.15%. The multi-gravity separator (MGS) has an advantage of utilizing the fine- and ultrafine-sized refuse coal with minimum environmental pollution.     

Biodiesel as a renewable collector for coal flotation in the future

Biodiesel is a renewable and clean energy which is being developed day by day. However, oil and coal reserves are decreasing due to an increase in energy demand for the development of social economy. Additionally, fine coal is usually beneficiated by flotation using diesel or kerosene as collectors, which may be a waste of energy. Therefore, using biodiesel as a collector for coal flotation has its potential value. In this investigation, biodiesel was used as a collector for coal flotation. Three bituminous coal samples with different coal ranks were selected, that is, gas coal, coking coal, and lean coal. FTIR results showed that biodiesel contained much more abundant unsaturated fatty acids than diesel. Flotation results showed that the flotation performances of three coal samples using biodiesel as collector were similar to that using diesel as collector. Even better, the concentrate yields of three coal samples using biodiesel as collector were a little higher than that using diesel as collector, while their concentrate ash contents were similar. Throughout this paper, it was proved that biodiesel could have a potential application in coal flotation.     

Valuation of chloride salts and their mixtures in coal flotation without collector

Scarce of good quality water for processing especially in the surrounding area of the mining sites dictates searching for new water resources. One of the available solutions is saline water as a flotation medium particularly in the regions close to the sea. Using the saline water, the most likely, enhances the flotation of naturally hydrophobic coal particles. Therefore, in this study, MgCl₂, NaCl, and CaCl₂ were tested for coal flotation and for reducing its ash content. The coal sample was characterized by size analysis as well as proximate and ultimate analyses to determine the ash content, volatile matter, moisture, and fixed carbon. Flotation experiments were conducted using salts either separately or in a mixture. The statistical design was mainly used to study the main effect of each salt as well as the interactive effects of binary and tertiary mixtures. The results showed that the MgCl_2, as a single salt, is the best among the used salts in decreasing the ash percentage. On the other hand, the binary and tertiary mixtures negatively affect the ash removal especially when the CaCl₂ is present in the mixture. Therefore, the usage of saline water in flotation depends on its composition in terms of salts concentration, especially the presence of Ca-containing salts.     

Effects of calcium chloride and sodium chloride on the flotation removal of unburned carbon from coal fly ash

The effects of calcium chloride and sodium chloride on the coal fly ash flotation were investigated by studying the surface properties of coal fly ash. X-ray photoelectron spectroscopy and scanning electron microscopy showed the presence of many lime particles in the coal fly ash, which, together with Ca(OH)₂(s), could be adsorbed on the rough surface of unburned carbon particles. The flotation results indicated that calcium chloride reduced the performance of unburned carbon removal from the coal fly ash, whereas sodium chloride increased froth stability thereby improving the flotation performance.     

粗煤泥回收工艺及其设备应用

随着国内外采煤机械化程度的提高,洗煤厂入选原煤中的末煤含量也随着增高,若是粗煤泥不进行再次分选回收,则会造成精煤损失,如果直接掺入精煤,就会导致总精煤灰分升高,使重选和浮选为其＂背灰＂,从而导致总精煤产率降低;而且再次分选的方法也是提高精煤产率和经济效益的关键。     

Effects of ultrasonic pretreatment on the flotation performance and surface properties of coking middlings

The effects of ultrasonic pretreatment on the flotation performance of coking middlings were investigated through a flotation cell. The surface properties of coking middlings before and after ultrasonic pretreatment were indicated using X-ray fluorescence analyzer (XRF), scanning electron microscope (SEM) and DSA100 contact angle analyzer. The flotation results demonstrated that the combustible recovery increased by 7.18%, while the ash value of flotation tailings decreased by 2.74% at most after ultrasonic pretreatment. Flotation results were supported by XRF analysis, SEM analysis, and contact angle measurements results. These results show that the ultrasonic pretreatment has a beneficial influence on the flotation of coking middlings.     

Effect of ultrasound on the true flotation of lignite and its entrainment behavior

In this study, the ultrasound was fixed in the pulp zone of flotation cell and its effect on the true flotation of lignite was analyzed. Flotation results indicated that the simultaneous ultrasound treatment increased the concentrate yield and decreased the concentrate ash content. Screening analysis of flotation products revealed that the ultrasound could crush coarse coal to fine coal and scanning electron microscopy (SEM) tests indicated that the ultrasound could reduce the coverage of high-ash coal fines on the coarse particle surface. Thus, the flotation recovery of coarse lignite particle was increased. In addition, the true flotation and entrainment of ?0.074 mm fine particles were studied by the sink-float test and the method of Trahar. It was found the ultrasound significantly enhanced the true flotation of fine particles and improved the overall water recovery in lignite flotation.     

The effect of coarse gangue particles during the coal flotation process

It is well known that fine gangue particles play an important role in contaminating the concentrate during coal flotation process. However, the contamination behavior of coarse gangue particles in the concentrate has been neglected in the past. In this paper, the contamination behavior of coarse gangue particles in the concentrate during coal flotation process was investigated using a mixture of coarse gangue particles and low ash coal particles at a proportion of 1:1. The size fraction of coarse gangue particles was 0.5–0.25 mm. The size fraction of low ash coal particles was 0.5–0.25, 0.25–0.074, and ?0.074 mm, respectively. The results of XRD showed that coarse gangue particles were composed of quartz, pearl clay, kaolin, mica, and dickite. The results of contact angle measurements showed that the contact angle of coal particles was about 89° while that of gangue particles was only 30°. The results of flotation tests indicated that the contamination behavior of coarse gangue particles in the concentrate during the coal flotation process cannot be neglected.     

Preparation of clean coal by flotation following ultra fine liberation

This paper reports the results of current fundamental research at the Department of Process Engineering, University of Miskolc on the processing of clean coal from Mecsek bituminous coal, Southern Hungary. The theoretical possibility of the separation of different petrographic components was proven experimentally and their liberation degree was determined based on the petrographic composition, flotation kinetic study of isolated components (groups of components), scanning electron microscopy and microprobe analyses. The mill with stirred ball media was chosen for the ultra-fine liberation of the coal components. It was revealed that along with the liberation of coal components, their surface oxidation and spontaneous agglomeration, entrapping the mineral impurities take place in ultra-fine grinding. This paper discusses the interfacial phenomena occurring in the ultra-fine grinding process and their influence on the flotation. The concept for the advanced preparation of clean coal was developed, tested and proved. The main steps of this concept are the ultra-fine liberation in the stirred-media mill, the de-agglomeration of flocs spontaneously formed during the ultra-fine grinding and the induced (hydrophobic) flocculation with the following two-step flotation in a flotation column.     

Effect of different grinding conditions on the dissociation and flotation of difficult-to-float coal

The recovery of clean coal can be improved through grinding. In this study, grinding and flotation experiments were conducted on difficult-to-float coal. Results show that the particle size obtained from ball milling is finer than that obtained from rod milling. However, the particle size distribution obtained from rod milling is more evenly distributed than that obtained from ball milling. The contact styles of steel rod and steel ball are “line contact” and “point contact,” respectively. Results from the flotation experiments are consistent with those from the orthogonal experiments.     

Effects of flotation on the release behavior of sulfur and nitrogen during coal pyrolysis

Two Chinese coals were selected to investigate the effects of flotation on the release behavior of sulfur and nitrogen during pyrolysis. The results show that the removal rate of minerals and sulfur-containing compounds from raw coal by flotation are closely related to coal properties. The significant alterations of sulfur and nitrogen forms on coal surface are mainly presented in the decrease of sulfidic-S, thiophenic-S, and pyridinic-N, the increase of sulfones-S and quaternary-N after flotation. The release of sulfur- and nitrogen-containing gases during pyrolysis of raw and clean coals has evident differences, which are mainly caused by the change of the relative proportions of different sulfur and nitrogen forms in the process of flotation.     

Flotation kinetics of the removal of unburned carbon from coal fly ash

Unburned carbon (UC) in coal fly ash indicates the waste of energy source and is an obstacle to the utilization of coal fly ash. The purpose of this study was to investigate the flotation kinetics of the removal of UC from coal fly ash. The collector and frother dosage are key factors for coal fly ash flotation. Six flotation kinetic models were applied to fit the flotation kinetic tests data. The fitted results showed that the classical first-order model had better consistency with the experimental data. The contact angle of flotation concentrates decreased as the flotation time was extended which revealed the decrease of flotation rate.     

Recovery of coal values from the refuse pond coal slurry using flotation

The objective of the present investigation is to explore the possibility of recovery of coal values from the tailing dump, so as to recover the coal values from the discarded product for sustainable development and optimum utilization of coal reserves. The influence of two important variables which commonly fluctuate in the operating plants, such as feed solid concentrations and collector dosage, has been varied and analyzed to study their influence on flotation performance. Among the variables studied, the pulp density of 8% of feed solid concentration was found to be most suitable level. A collector dosage of 0.105 kg/ton of coal gave the best result in term of ash reduction.     

The production of ultra-clean coal from Zonguldak bituminous coal by chemical leaching

From run-of-mine coal with an average ash of 50% being produced at Zonguldak coal basin, clean coal with 7% ash can be produced through physical enrichment methods such as jig and heavy media. However, for the production of coal with an ash content of lower than 7%, it is required for the coal to be first ground and then subjected to chemical leaching operation. In this study, chemical leaching tests were performed with aqueous HF, HCL, HNO₃, and citric acid (CA) in order to produce ultra-clean coal (UCC) from Zonguldak bituminous coal. The effects of type of chemical, grain size, temperature, and leaching time in the leaching process were studied. It was observed that UCC with 0.82% ash could be produced from sample coal with 8.84% ash as the result of leaching operation with aqueous HF.     

在选煤中如何通过浮选指标来预测快灰数据

为了提高煤炭的使用率，降低燃烧产生的烟尘对环境的污染，需要通过选煤进行洁净处理。叙述了选煤中如何通过浮选指标来预测快灰数据的方法。