Quality Improvement of Low-Grade Calcium Carbonate Using Induced Roll Magnetic Separator

Calcium carbonate (CaCO3) is an essential raw material in the manufacture of goods and industrial products like cement, rubber, paper, paints, food, and medicines. For this compound to be economically valuable, however, its quality needs to meet the standard market requirements. Among the various impurities found in natural CaCO3-bearing ores, iron (Fe) is one of the most problematic. In this study, the upgrading of low-grade CaCO3 from a processing plant in Thailand by magnetic separation was investigated. Detailed characterization of the low-grade material was also carried out to identify the solid-phase partitioning of Fe. The results showed that Fe was mainly associated with magnetite and pyrrhotite in the ore, and during processing, additional Fe was introduced from the ball milling process. To improve the quality of this low-grade CaCO3, the effects of magnetic field intensity, feed rate, and repetition on the induce roll magnetic separation were investigated. Based on the results, higher magnetic field intensity, lower feed rate, and more repetition are required for the upgrading of low-grade CaCO3

リサイクリングのためのアドバンスドジグ選別:選別に及ぼす粒子形状の影響とRestraining wallを用いた連続式ジグの開発

There are two common types of plastic recycling: (1) material recycling wherein plastics are recovered and reused, and (2) thermal recycling whereby plastics are used as fuel for power generation. Among the two, material recycling is a more sustainable and profitable approach, but different types of plastics must be separated to obtain very high purities. Most separation techniques for recycling were modified from techniques developed for mineral processing. Among of these techniques, jig separation, one of the oldest techniques that separates particles based on density differences, that is widely used in mineral processing especially in coal cleaning because of its simplicity, low cost, and high efficiency, was also applied for resources recycling. However, there is a critical challenge in the use of jig separation for secondary resources because of the wide variety of shapes formed after crushing, which is very different from the more uniform and sphere-like particles traditionally treated in mineral processing. In jig separation, the separation efficiency is dependent on particle motion, which is also a function of geometrical properties like size and shape. This means that understanding the effects of particle shape is important in the design of suitable jig separation process. This study investigated the effects of particle shape (disk-like plastics and rod-like metals wires) on the jig separation and identified the reasons why the particles shape affects to their behaviors and jig separation efficiency. Moreover, novel methods to estimate the jig separation efficiency using shape factors were proposed and modified waveform and shape separation methods to improve jig separation efficiency were developed. Finally, a discharge system for continuous jig separation of plastics using a restraining wall was developed. Chapter 1 describes the background and objectives of the study. In Chapter 2, previous studies on “the effects of particle geometry on physical separation” and “the application of gravity separation for coal cleaning and resources recycling” are reviewed. In Chapter 3, effects of particle geometry (size and shape) on jig separation efficiency of crushed plastics are investigated. The shape factors (flatness ratio etc.) and settling velocity of crushed plastics containing various size and shape were measured and the results showed that particles are more disk-like at coarser size fraction while the fine fraction is dominated by sphere-like particles. The results of jig separation of mixed plastics showed that separation efficiency was higher for the mixture of light, disk-like particles and heavy, sphere-like particles that was in line with the results of settling velocity experiments. These results indicate that settling velocity and jig separation are affected by both size and shape. In Chapter 4, empirical equation to calculate settling velocity of non-spherical particles using flatness ratio and projection area was developed, and a modified concentration criterion (CCs) is proposed to estimate jig separation efficiency of non-spherical particles. The experimental results showed that sharpness index decreased with increasing CCs calculated from the velocity of non-spherical particles. This result indicates that CCs can be used to estimate jig separation efficiency of non-spherical particles. Based on the CCs proposed here it was hypothesized that separation efficiency of the mixture of light, sphere-like particles and heavy, disk-like particles will be improved when the water rising velocity increase. This hypothesis was confirmed by the jig separation of the mixed plastic samples. In Chapter 5, separation of rod-like and sphere-like particles are discussed. Jig separation was applied to separate plastics and metals including copper (Cu) wires obtained from a recycling plant. The results showed that separation efficiency was low because of Cu wire entanglement that prevents particle motion in the separation chamber. The results of model experiments showed that the separation efficiency decreased with increasing the amount and length of Cu wires. To limit the effects of wire entanglement, two methods of shape separation were investigated. In addition, estimation of jig separation efficiency using the entanglement factor of rod-like particles is proposed. In Chapter 6, discharge systems for continuous jig separation of plastics are discussed. The purity of bottom layer products becomes lower when the heavy particles ratio in feed is low, because entrainment of light particles by a screw-extractor occurs. To suppress the entrainment, a new discharge system using a vertical restraining wall was developed. The restraining wall was installed to separate a chamber into two and particles can transfer from one to another through the channel under the wall. The results showed that purity of bottom layer products was improved with a restraining wall. Finally, Chapter 7 gives the general conclusions of this study

Development of Microencapsulation-Hybrid Jig Separation Technique as a Clean Coal Technology

In this study, the microencapsulation-hybrid jig separation technique was developed to improve the separation efficiency of pyrite and coal in the particle size range of 1–4 mm where conventional jig separation becomes inefficient. A hybrid jig is a gravity concentrator combining the concepts of jig separation and flotation to stratify particles based on their apparent specific gravity. Meanwhile, microencapsulation—a technique that encapsulates target materials with a protective coating—was applied to render pyrite hydrophilic and improve its separation from hydrophobic coal. The results showed that the required time for separation in the hybrid jig (0.5 min) was shorter than in conventional jig (2 min). Moreover, the effects of particle size on separation efficiency were reduced when a hybrid jig is used. However, the separation efficiency of hybrid jig separation was lower than that of the conventional jig because attachment of bubbles occurred to both pyrite and coal, which are hydrophobic. Using the microencapsulation-hybrid jig separation technique, the separation of coal and pyrite was significantly improved (~100%) because of the formation of hydrophilic iron phosphate coatings on pyrite that limited bubble attachment. This means that microencapsulation-hybrid jig separation is a promising clean coal technology that not only enhances the separation efficiency of the hybrid jig but also passivates pyrite and limits AMD formation in the tailings/rejects

Development of suitable product recovery systems of continuous hybrid jig for plastic-plastic separation

A modified jig called the hybrid jig was recently developed to separate mixed-plastics with similar specific gravities effectively using the concepts of bubble attachment, surface wettability and gravity separation. This method was effective in a batch-type jig setup, but when applied to a continuous-type jig setup, the efficiency of the process dramatically decreased. This drop in efficiency was attributed to the unintended negative effects of air bubbles on separation especially close to the screw-type extractor at the product end though this type of product recovery system was successfully applied to the RETAC and reverse jigs. To address this problem, a better product recovery system for continuous-type hybrid jig is proposed in this study, and the effects of air injection rate at different positions of the hybrid jig separation chamber were evaluated. The results showed that fluidization behavior of particles in the hybrid jig was influenced by not only water pulsation but also the rising motion of air bubbles. To improve the purity of heavy materials in the bottom layer products, two product recovery systems are proposed: (1) a screw-type extractor with one "separating" single-screen, and (2) a screw-type extractor with modified air injection and water pulsation (i.e., upward flow period was shortened)

Development of the reverse hybrid jig: Separation of polyethylene and cross-linked polyethylene from eco-cable wire

We have developed various types of jigs for resources recycling focusing primarily on plastic-plastic separation. The RETAC jig could be used to separate plastics heavier than water (specific gravity (SG) > 1.0) with different SGs while the hybrid jig-a process combining jig and flotation-was developed to separate plastics with similar SGs but different surface wettabilities. Meanwhile the reverse jig-a RETAC jig with a top screen-is used to separate plastics lighter than water with different SGs. In this study, a novel method that combines the principle of reverse and hybrid jigs, called "reverse hybrid jig separation" was developed to separate plastics lighter than water having similar SGs but different surface wettabilities. The tests were carried out with wastes from an eco-cable wire recycling facility in Japan, which is composed of polyethylene (PE) and cross-linked polyethylene (XLPE). The reverse hybrid jig separation results showed that bubble attachment to and detachment from plastic particles strongly influenced the separation efficiency. In addition, the effects of particle size on separation efficiency were also evaluated

Improvement of flotation and suppression of pyrite oxidation using phosphate-enhanced galvanic microencapsulation (GME) in a ball mill with steel ball media

Acid mine drainage (AMD) is one of the biggest and most challenging environmental concerns of the mining and mineral processing industries. In our previous study, we reported a new and promising approach to passivate sulfide minerals and limit AMD formation called galvanic microencapsulation (GME), a technique that forms protective coatings via galvanic interactions between sulfide minerals (e.g., pyrite) and metal powders (e.g., zero-valent iron and aluminum). In this paper, the possible application of GME in a ball mill with steel ball media and phosphate to suppress pyrite floatability during coal cleaning and limit pyrite oxidation after disposal is proposed. The results showed that adding phosphate and maintaining sufficient oxygen supply during GME treatment in the ball mill passivated pyrite and suppressed its oxidation via the formation of protective iron phosphate coatings. Moreover, the iron phosphate coatings on pyrite made the mineral more hydrophilic, which improved the separation efficiency during coal flotation

Improvement of hybrid jig separation efficiency using wetting agents for the recycling of mixed-plastic wastes

We have developed the hybrid jig which combines the principles of jig separation and flotation. However, the selectivity of bubble attachment in water was poor because most plastics have inherently hydrophobic surfaces; so, development of surface modification techniques for plastic particles would expand the application of hybrid jig to the material recycling of plastics. In this study, hybrid jig separation of polypropylene using glass fiber and high impact polystyrene having similar specific gravities and surface wettability were investigated with three wetting agents [Di-2-ethylhexyl sodium sulfosuccinate (Aerosol OT, AOT), sodium lignin sulfonate, and tannic acid]. The results showed that the probability of bubble attachment was influenced by wetting agents because of their strong effects on the surface tension of solution and surface wettability of plastics. The results also suggest that wetting agents could be utilized to control the selectivity of bubble attachment and improve the hybrid jig separation efficiency. In addition, since the hybrid jig separation of polyvinyl chloride and polyamide (nylon-66) using AOT was imperfect, a two-step approach, composed of a pre-wetting step (first step) in a solution containing the wetting agent (AOT) and hybrid jig separation in water (second step), is proposed