D. Tao

Role of Bubble Size in Flotation of Coarse and Fine Particles-A Review

Abstract Froth flotation is the dominating mineral beneficiation technique and has achieved great commercial success. This process has also found many applications in other industries where physical separation of materials is needed. However, its high process efficiency is often limited to a narrow particle size range of approximately 10–100 µm. Considerable efforts have been made to extend this size range to the lower limit of a few microns, even submicrons, and the upper limit of 1–2 mm, in response to increased needs for higher process efficiency and expanded applications of flotation. The particle–bubble collision, attachment, and detachment are the most critical steps in the flotation process. These individual elementary processes (microprocesses) and their effects on flotation efficiency are discussed and the most recent findings are reviewed. The low flotation recovery of fine particles is mainly due to the low probability of bubble–particle collision, while the main reason for poor flotation recovery of coarse particles is the high probability of detachment of particles from the bubble surface. Fundamental analysis indicated that use of smaller bubbles is the most effective approach to increase the probability of collision and reduce the probability of detachment.

A Study on Picobubble Enhanced Coarse Phosphate Froth Flotation

Abstract Effects of picobubbles on froth flotation of coarse phosphate particles (−1180 µm+425 µm) have been investigated with a specially designed flotation column. Cavitation generated picobubbles are characterized by inherently high probability of collision, high probability of attachment, and low probability of detachment during froth flotation due to their tiny size and high surface activity. Test results obtained with a 5 cm in diameter laboratory scale flotation column indicate that picobubbles are effective in enhancing the flotation of coarse phosphate particles, and increasing the flotation recovery by 10 to 23 absolute percentage points under various conditions. The required collector dosage and frother dosage for a given flotation performance were reduced by one‐half to two‐thirds.

Cyclo-microbubble column flotation of fine coal

Cyclo-microbubble flotation column (CMFC) is an advanced column flotation technology for fine coal cleaning developed by China University of Mining and Technology (CUMT). It combines cyclone separation with column flotation to enhance pyritic sulfur rejection and separation efficiency. A specially designed external bubble generator is employed to efficiently precipitate fine bubbles on particle surface. A set of screen plates inside the column produces nearly plug-flow condition, which is preferred for flotation process. The CMFC technology has been successfully employed to recover fine coal from discarded waste ponds and replace conventional mechanical cells. Typical commercial testing results are described and analyzed. The column is very effective in cleaning particles down to 45 μm. Laboratory- and pilot-scale testing of CMFC has also demonstrated that the CMFC process can produce a superclean coal product of 1.5∼1.6% ash content from a 9.8% ash feed.

An investigation on dewatering kinetics of ultrafine coal

Ultrafine coal dewatering is of great importance to the coal industry due to its impacts on the handling and utilization characteristics of coal products. Commercially available filtration techniques are either ineffective or costly for dewatering of ultrafine coal to the desired moisture level of about 20%. Considerable efforts have been devoted to understanding the dewatering process and developing new technologies for applications in the coal industry. Most of the previous work on ultrafine coal filtration was focused on the final filter cake moisture and few studies have been conducted to investigate the filtration kinetics. The present investigation was undertaken to better understand the kinetics of vacuum filtration of ultrafine coal under various conditions. The filtrate weight was continuously monitored using a precise load cell during the entire filtration process. Operating parameters such as vacuum pressure and reagent conditioning time were examined for their impacts on filtration kinetics. Use of cationic and anionic flocculants showed significant improvement in filtration kinetics. Kinetic data obtained from the study were used to determine the fundamental parameters of filtration such as cake permeability, specific cake resistance, and filter medium resistance using the integrated form of the Darcys law.

Picobubble Enhanced Fine Coal Flotation

Abstract Froth flotation is widely used in the coal industry to clean −28 mesh fine coal. A successful recovery of particles by flotation depends on efficient particle‐bubble collision and attachment with minimal subsequent particle detachment from bubble. Flotation is effective in a narrow size range beyond which the flotation efficiency drops drastically. It is now known that the low flotation recovery of particles in the finest size fractions is mainly due to a low probability of bubble‐particle collision while the main reason for poor coarse particle flotation recovery is the high probability of detachment. A fundamental analysis has shown that use of picobubbles can significantly improve the flotation recovery of particles in a wide range of size by increasing the probability of collision and attachment and reducing the probability of detachment. A specially designed column with a picobubble generator has been developed for enhanced recovery of fine coal particles. Picobubbles were produced based on the hydrodynamic cavitation principle. They are characterized by a size distribution that is mostly below 1 µm and adhere preferentially to the hydrophobic surfaces. The presence of picobubbles increases the probability of collision and attachment and decreases the probability of detachment, thus enhancing flotation recovery. Experimental results with the Coalberg seam coal in West Virginia, U.S.A. have shown that the use of picobubbles in a 2″ column flotation increased fine coal recovery by 10–30%, depending on the feed rate, collector dosage, and other flotation conditions. Picobubbles also acted as a secondary collector and reduced the collector dosage by one third to one half.

Dry Cleaning of Pulverized Coal Using a Novel Rotary Triboelectrostatic Separator (RTS)

Coal cleaning is often conducted using wet physical separation processes such as heavy medium vessels or spirals at coal preparation plants to remove impurities such as ash, sulfur, and mercury. However, the resultant clean coal product still contains a significant amount of impurity due to the fact that impurities are not well liberated from coal particles ranging from several millimeters to inches in size at which wet cleaning processes take place. A cleaner coal product can be obtained if a dry process is avaialble to further clean pulverized and thus better liberated fine coal at the power plant prior to its combustion. In this study, a novel rotary triboelectrostatic separator (RTS) was investigated for its application to dry cleaning of fine coal samples acquired from the power plants in the state of Illinois. The proprietary RTS is characterized by an innovative high-efficiency rotary charger, charger electrification, laminar air flow, etc. Compared to existing triboelectrostatic separators, the RTS offers significant advantages in particle charging efficiency, solids throughput, separation efficiency, applicable particle size range, etc. Important process parameters such as charger rotation speed, injection and co-flow rate, and feed rate were investigated for their effects on separation performance.

Reverse Flotation of Magnesite by Dodecyl Phosphate from Dolomite in the Presence of Sodium Silicate

Abstract Magnesite and dolomite are two salt‐type minerals. They show similar flotation behavior due to the same crystal structure, similar chemical composition, and high solubility. It is difficult to achieve effective flotation of magnesite from dolomite in a single stage. The present study was performed to develop a new and better flotation scheme for magnesite from dolomite. The flotation tests show that there exists a significant difference in flotability between magnesite and dolomite when dodecyl phosphate synthesized with dodecanol, phosphorus oxychloride, and other chemicals is used as collector. Modifiers are necessary to improve flotation selectivity. It was found that sodium silicate selectively depressed magnesite at a pH of 4.5 to 7.5. The flotation mechanism was investigated by characterizing surface electrical properties and measuring the adsorption density of the reagents on magnesite and dolomite.

Improved Phosphate Flotation Using Clay Binder

The presence of insoluble clay slimes in phosphate ore adversely affect phosphate flotation performance. In this study, the feasibility of using a clay binder as slime depressant for phosphate flotation was investigated by conducting batch mechanical flotation tests using a 16-200 mesh phosphate sample under various operating conditions. The flotation process parameters examined for their impacts on clay binder performance included collector dosage, binder dosage and conditioning time, flotation time, etc. Results have shown that use of 0.1 lb/t clay binder increased phosphate yield and recovery by 1.7% and 5.5% respectively with a two min. flotation time. The concentrate grade was essentially constant at about 24%. The highest yield of 16.09% and the highest recovery of 91.01% were obtained with 0.25 lb/t clay binder.

Pilot-Scale Demonstration of Deep Cone™ Paste Thickening Process for Phosphatic Clay/Sand Disposal

A pilot-scale Deep Cone™ thickener (DCT) from Dorr-Oliver EIMCO has been employed at a phosphate mine in central Florida to investigate the effects of key operating parameters, including feed rate, sand addition rate, flocculant dosage, and bed depth on waste clay thickening performance. The pilot-scale field testing successfully demonstrated the simultaneous production of an underflow paste product and a clear overflow water stream. Typical overflow water recovery and underflow solids recovery were more than 88% and 98%, respectively with a residence time of about 2 hours. The highest clay content and total solids content in the paste were higher than 25% and 35%, respectively, when the flotation sand tailing was added to the clay slurry at a clay/sand ratio of 2:1 by weight.

Statistical Analysis of Wear Rate of Phosphate-Grinding Mill

Abstract A statistical Box-Behnken design (BBD) of experiments was performed to evaluate effects of individual operating variables and their interactions on the wear rate of grinding ball mills used in the phosphate industry. The wear tests were conducted using a specially designed grinding mill. The variables examined in this study included grinding time, solution pH, rotation speed, mill crop load, and solids percentage. The most significant variables and optimum conditions were identified from a statistical analysis of the experimental results using response surface methodology. Experimental results show that solution pH has the most significant effect on the wear rate for both Type 1018 (UNS G10180) carbon steel (CS) and a high-chromium alloy. The optimum process parameters for minimum wear rate were solution pH at 7.36, rotation speed at 70.31 rpm, a solid percentage at 75.50, and a crop load at 71.94% for Type 1018 CS; for the high-chromium alloys, they include a solution pH at 8.69, rotation speed ...