Characterization of Flocs in Dewatering of Coal Plant Tailings

Flocculation is a widely used method for dewatering fine coal tailings. Flocs must resist to the shear stresses during the following processes such as flotation, cyclone separation, and pumping. Therefore, the strength of the flocs must be considered during flocculation. In this study, the fine coal tailings were dewatered with an anionic flocculant SNF-923 at various dosages, and the floc size of the coal tailings was characterized using a laser diffraction particle size analyzer with respect to time in order to determine the change in the floc size and hence the floc strength. The results of this study clearly indicated that the determination of the floc size with a laser particle size analyzer could be a simple and good method to observe the flocculation efficiency in terms of the floc strength

An investigation of air/water interface in mixed aqueous solutions of KCl, NaCl, and DAH

Flotation of soluble salts such as borax, potash, and trona is carried out in their saturated solutions. The high ion concentration of the flotation suspension can affect the floatability of the minerals as well as the coalescence behaviors of the bubbles. The bubble coalescence can be inhibited in the presence of dissolved ions at high ion concentrations as well as with the use of surfactants. In this study, the effect of the mixtures of KCl, NaCl, and dodecyl amine hydrochloride (DAH) on air/water interface was investigated with surface tension and bubble coalescence time measurements for potash flotation. The surface tension measurements indicated that lower surface tension values obtained with mixed KCl and NaCl solutions than their single solutions. In addition, the surface tension of the mixed KCl and NaCl solutions increased with the NaCl and the ionic strength of the solution. The dynamic surface tension measurements indicated that while ion adsorption on air/water interface was so fast, DAH molecules required more time for adsorption probably related to the viscosity of the solution. In addition, the bubble coalescence time measurements showed that the bubble coalescence could be inhibited with the use of DAH in the absence and presence of KCl and NaCl. In the absence of DAH, the bubble coalescence time was determined as 100 ms, 270 ms, and 650 ms, respectively for 100% KCl, 100% NaCl, and 50%KCl+50% NaCl salt solutions. Therefore, the trend in the success of the salt solutions for the inhibition of bubble coalescence can be written as 100%KCl+ ions, it was 100 ms in the presence of K+ ions 100 ms. It can be concluded from the results obtained from this study that the bubble coalescence phenomena may be managed by the specific ion pairing types in solutions which significantly affect the flotation recovery of minerals

INVESTIGATION OF ULTRASONICS USE FOR COLEMANITE FLOTATION

The aim of this study is to investigate ultrasonics use for colemanite flotation. The samples used in the study were provided from Eti Mines Inc.'s Emet Boron Works. The samples were 0-3 mm concentrates which could have not been increased to desirable B2O3 % grades. At first, determination of moisture and grinding experiments were carried out. The liberation size of the ore was determined as minus 250 mu m and minus 38 mu m was removed because of the negative effect of slime coatings in flotation. Then, it was decided to use -250 +38 mu m fractions in flotation tests. Flotation tests were carried out in two different approaches for purpose of determination of the effects of ultrasonic pre-treatment in colemanite flotation. Conventional flotation tests were carried out in the first step. After that, ultrasonically pre-treated samples were floated. The reagents were a sodium sulphonate type collector and an alcohol type frother. The frother quantity was kept at 100 g/t. However, the collector was tested in four different dosages: 500, 1000, 1500 and 2000 g/t. In conclusion, ultrasonic pre-treatment was found to have positive effects on B2O3% grade and % recovery values. 41% B2O3 feed grade was increased to 49% by ultrasonic pre-treated flotation with 85 B2O3 recovery

ENHANCEMENT OF COLEMANITE FLOTATION BY ULTRASONIC PRE-TREATMENT

Ultrasonic treatment methods are widely used for surface cleaning purposes prior to application of flotation. In this study, enhancement possibility for colemanite recovery was investigated with use of an ultrasonic bath prior to flotation. Representative colemanite ore samples from Hisarcik and Espey open pit mines, located in Emet, Turkey were used for this purpose. Ultrasonic flotation experiments were carried out by using circularly shaped RK-106 model of ultrasonic bath with constant frequency and power, manufactured by Bandelin GmbH in Germany and Denver Sub-2A type flotation machine with an impeller speed of 1200 rpm and 1 cubic decimeter capacity. The reagent for colemanite flotation was Cytec-R825 with variable dosages during conventional and ultrasonic flotation experiments. The results showed that ultrasonic pre-treatment helps desliming and hence yields more borate recovery in floated part with lower borate content in tailing than under conventional flotation conditions by using similar reagent dosages

Effects of temperature during ultrasonic conditioning in quartz-amine flotation

In this study, the effect of ultrasound on flotation recovery of quartz- amine flotation was investigated in terms of temperature influence. For this purpose, an ultrasonic probe was used for conditioning quartz surfaces in presence of dodecylamine hydrochloride ( DAH), and the change in the temperature was recorded. The temperature- controlled ultrasonic conditioning tests were also carried out at various ultrasonic powers ( 30, 90, and 150 W) to investigate the effect of increasing temperature on the quartz- DAH flotation. The results showed that temperature of the suspension sharply increased from 23 up to 75 degrees C at the end of 10 min of conditioning at 150 W ultrasonic power. The flotation results for the temperature controlled and uncontrolled samples indicated that the flotation recovery increased from 45 to 65% by 90 W ultrasonic power. However, higher ultrasonic power levels affected the flotation recovery negatively. On the other hand, the ultrasonic application decreased the flotation recovery at all ultrasonic power levels in the temperature- controlled tests. Finally, the shape analysis was also performed for the particles treated with the ultrasound at various ultrasonic powers. As a conclusion, the positive effect of ultrasound on the quartz- amine flotation recovery could be related to temperature increase during conditioning

Investigation of flocculation properties and floc structure of coal processing plant tailings in the presence of monovalent and divalent ions

Low-rank coals are generally processed with wet methods including washing, flotation, etc. Fine-sized tailings of these processes are discharged to tailing ponds with a significant amount of associated water which contains a high amount of dissolved ions. These tailings should be dewatered employing coagulation/flocculation in terms of technological and environmental aspects. In this study, the coagulation/flocculation behavior of coal processing plant tailings obtained from Manisa, Turkey was investigated in the presence of monovalent (Na+, K+) and divalent (Mg2+, Ca2+) ions and an anionic flocculant (SPP-600). First, the coagulation properties of coal tailings were determined. Then, the flocculation experiments were carried out, and the turbidity values of the suspensions were measured. Moreover, the sizes of the flocs were determined using a laser diffraction particle size analyzer to analyze the strength of the flocs. The results of the coagulation experiments showed that while divalent ions were more effective at 10-1 mol/dm3, higher settling rate and lower turbidity values were obtained in the presence of monovalent ions at 1 mol/dm3 concentration. The optimum flocculant dosage was obtained as 150 g/Mg from the flocculation experiments. The floc size and strength measurements indicated that the larger flocs were obtained with Na+ than Ca2+ in the presence of the flocculant. The strongest flocs were obtained at 10-1 mol/dm3 Ca2+ + 150 g/Mg flocculant. It can be concluded from this study that the coagulation followed by the flocculation method can be employed to obtain fast flocculation behavior and low turbidity for the dewatering of coal tailings

An investigation of the effect of clay type on coal flotation along with DLVO theoretical analyses

Coals generally exist with clay minerals, which are very fine-sized minerals, and adversely affect the flotation of coal. For instance, they make the coal surface hydrophilic by coating coal surfaces and therefore, they inhibit bubble-particle attachment. Clay minerals can also cause over-consumption of reagents due to their high surface area. Additionally, clay minerals can transfer into the concentrate during the flotation process by entrainment because of their low weight and small particle size, and thus, increase pulp viscosity and changing froth stability. In this study, the influence of various clay minerals (kaolinite, illite, and bentonite) on the flotation behavior of coal sample was studied in detail by conventional flotation tests. In addition, the values obtained from flotation tests were correlated with theoretical energy barrier values established with classical DLVO theory based on zeta potential values of coal and clay samples measured at different pH values. According to the results of this study, no significant effect of clay minerals was observed on coal flotation. This was probably because of the high floatability of the coal used for this study. Both the results obtained from the experiments and theoretical analysis, DLVO calculations, showed that the type of clay mineral is the main indicator parameter for coal flotation

A novel technique to investigate the bubble coalescence in the presence of surfactant (MIBC) and electrolytes (NaCl and CaCl2)

An efficiency of flotation process is strongly dependent upon the collecting ability of air bubbles. On the other hand, the liquid film formed between two fully or partially mobile air/liquid interfaces being in contact has low stability, which leads to fast liquid drainage. Therefore, when they approach to each other, they tend to coalescence. Therefore, bubble coalescence is usually controlled with frothers in flotation process. Meanwhile, it is known that dissolved ions inhibit bubble coalescence. In this study, the bubble coalescence in the presence of MIBC was determined using a novel technique with a modified bubble-particle attachment timer. Additionally, the effect of NaCl and CaCl2 on bubble behavior was investigated along with surface tension and bubble coalescence time aspects. As a result of study, it is seen that the bubble coalescence time can be successfully determined with a bubble-bubble coalescence timer

Effect of conventional and microwave thermal treatments on floatability of low- and high-rank lignites

Thermal treatment is one of the well-known methods used before froth flotation to remove the polar groups from coal surfaces to make them more hydrophobic. In this study, the effect of conventional and microwave thermal treatments on the wettability of low and high-rank lignite was investigated using flotation experiments, zeta potential, and bubble-particle attachment time measurements, as well as hydrophilicity index analyses. The results showed that both of the thermal treatments increased hydrophobicity, and therefore floatability of the coal samples. The optimum results were achieved with conventional and microwave thermal treatment for the low and high-rank coals, respectively