Daniel Tao

Nanobubble generation and its applications in froth flotation(part II):fundamental study and theoretical analysis

Abstract Froth flotation is a commonly employed technology to improve the quality of raw coal and minerals. Coal and minerals particle size and surface hydrophobicity are two main parameters that affect three key steps in froth flotation process: particle-bubble collision, adhesion, and detachment. This paper fundamentally investigated the effects of nanobubble on coal and phosphate flotation. It has been found that the presence of nanobubble in flotation pulp could widen the coal and phosphate flotation particle size range, increase the particle surface hydrophobicity, and thus improve the coal and phosphate froth flotation recovery.

Nanobubble generation and its application in froth flotation （part I）： nanobubble generation and its effects on properties of microbubble and millimeter scale bubble solutions

Abstract A special nanobubble generation system has been developed for evaluating the effect of nanobubble on froth flotation. In this study, an eight-factor five-level Central Composite Experimental Design was conducted for investigating eight important parameters governing the median size and the volume of nanobubbles. These process parameters included surfactant concentration, dissolved oxygen (O 2 ) content, dissolved carbon dioxide gas (CO 2 ) content, pressure drop in cavitation tube nozzle,

A STUDY OF ROTARY TRIBO-ELECTROSTATIC SEPARATION OF SOUTH AFRICAN FINE COAL

This article presents an experimental study of rotary tribo-electrostatic separation (RTS) as an alternative approach for beneficiating steam coal mainly used in South African power plants. An RTS with an octagonal charger developed at the University of Kentucky, USA has been used in beneficiating two types of South African coals containing nearly 37% and 32% ash, respectively. System parameters, such as applied charger potential, separation chamber voltage, rotation speed of the copper-plated rotor, and splitter distances were investigated for their effects on the separation performance. It was found that better separation was observed at 5000 rpm rotation speed, no applied potential to the charger, and 25 KV separation voltage. The RTS process reduced the ash content of the −177 µm coal fraction by nearly 14.9% for the Klipfontein coal and 12.2% for the Liketh Townlands coal, with corresponding combustible recovery values of 10.7% and 8.9%, respectively. Total sulphur content was also reduced from 2.1% to 0.9% for the Klipfontein coal and from 2.8% to 0.4% for the Liketh Townlands coal at corresponding combustible recovery values of 5.7% and 8.9%, respectively. The x-ray diffraction analysis of the cleaned-coal samples confirmed a reduction in the mineral content with an improvement in the organic composition for both coal samples.

Nanobubble generation and its applications in froth flotation (part III): specially designed laboratory scale column flotation of phosphate

Abstract Froth flotation is used widely for upgrading raw phosphate. The flotation recovery of coarse phosphate (−1.18+0.425 mm) is much lower than that achieved on the −0.425+0.15 mm size fraction. Enhanced recovery of coarse phosphate particles is of great economic and environmental importance for phosphate industry. In this investigation, four different phosphate samples were aquired, characterized and tested in a specially designed laboratory-scale flotation column. Significant recovery improvement of coarse phosphate flotation was achieved using cavitation-generated nanobubble though its effects differ among the four testing phosphate samples. The laboratory-scale flotation column test results indicate that nanobubble increased P2O5 recovery by up to 10%∼30% for a given Acid Insoluble (A.I.) rejection, depending on the characteristic of phosphate samples. The improvement effect of nanobubble on the hard-to-float particles was more significant than that on easy-to-float particles, especially at lower collector dosages. Nanobubbles reduced the collector dosage by 1/3 to 1/2. Nanobubbles almost doubled the coarse phosphate flotation rate constant and increased the flotation selectivity index by up to 25%.

Dry coal fly ash cleaning using rotary triboelectrostatic separator

More than 80 million metric tons of fly ash is produced annually in the U.S. as coal combustion by-product. Coal fly ash can be converted to value-added products if unburned carbon is reduced to less than 2.5%. However, most of fly ash is currently landfilled as waste due to lack of efficient purification technologies to separate unburned carbon from fly ash. A rotary triboelectrostatic separator has been developed and patented recently at the University of Kentucky with unique features. Several fly ash samples have been used to understand the effects of major process parameters on the separation performance. The results show that compared to existing triboelectrostatic separators, the rotary triboelectrostatic separator has significant advantages in particle charging efficiency, solids throughput, separation efficiency, applicable particle size range.

Beneficiation study of Eshidiya phosphorites using a rotary triboelectrostatic separator

Abstract This study was performed to investigate the feasibility of applying a Rotary Triboelectrostatic Separator (RTS) to the beneficiation of Eshidiya phosphate minerals. RTS separation tests were carried out on phosphatic bed A1, phosphatic bed A3 and slime samples. The bed A1 and slime samples were tested without desliming. Two sets of tests were performed using the A3 sample: one was performed without desliming and the other with the A3 sample deslimed. RTS separation tests as initially performed on the bed A1 and slime samples gave products that had essentially the same P2O5 content. This indicated that adsorbed clay particles on the phosphate surface are responsible for the poor separation of un-deslimed phosphates. Better triboelectrostatic separation was observed with the undeslimed A3 phosphate sample; these tests resulted in a highest product grade of 26% P2O5. The deslimed A3 sample showed far more effective separation than the undeslimed A3 one. In fact, a concentrate of 34% P2O5 was obtained from the triboelectrostatic separation of deslimed A3. The results indicate that with deslimed A3 P2O5 recovery was about 65% for a concentrate of 28% P2O5 and about 45% for a concentrate of 30% P2O5. These results clearly show the importance of desliming for effective beneficiation of phosphate by the RTS. A more efficient separation can be expected from optimized operating conditions and circuit configuration.

Parametric study of electrostatic separation of South African fine coal

Abstract The fact that water requirements are a major problem for present and future developments in material beneficiation, and the construction of a new power plant in South Africa, forms the basis for the utilization of a Rotary Triboelectrostatic Separator (RTS) for beneficiation of South African pulverized coal. The cleaning potential of Majuba and Koorfontein coal was first evaluated using kinetic froth flotation tests on the −177 μm coal fraction. The RTS tests were conducted under varied process parameters. Parameters such as applied separating voltage, air injection velocity, particle feed rate and splitter position were investigated. Two stage separation results show that the RTS reduced Majuba coal initially containing about 30% ash to a clean product of 14.30%, or 19.46%, ash at a combustible recovery of 15.10%, or 53.02%, respectively. Similar separation performance was also achieved with the Koorfontein coal. The mineral and organic compositions in the feed, after single stage and after the second stage separations were characterized using X-ray diffraction analysis. The results show a better separation for the second stage coal products.