No.23 October 1997

STUDY ON SHAPE SEPARATION OF PARTICULATE MATERIALS

Chapter 1. INTRODUCTION

1.1 General introduction

The current development stage of renewable energy sources and various political, economic and environmental factors have until now dictated the use of fossil fuels as a major energy source well into the next century.

On the other hand, we have a developed and confortable civilization. It is supported by mass production and consumption. We have to change our life style to keep a sustainable development measured against the problems of the global environment [1-3].

The industrial activities that support society and the activities of our everyday life are the source of quite a remarkable amount of waste. In fact, it is estimated that the total amount of waste generated in 1990 by manufacturing industries in Japan amounted to as much as 243,220,000 tons.

In addition to this, the amount of general domestic wastes generated from households and other sources showed a steady increase of three or four percent a year since 1985, until it reached a total of 49,970,000 tons in 1991.

The processing plants and waste disposal sites are now reaching the point where they can no longer keep up with the ever increasing quantity of waste, and we now find ourselves in a position where we must either come up with a way to immediately reduce our total amount of waste or else face increasingly serious environmental problems. The addition to this, the cost to the average citizen for dealing with these wastes is yearly rising., therefore, this makes the rapid reduction in the amount of garbage we generate essential to the maintenance of a strong and healthy economy as well. While, on the one hand, Japan has come to be known as an economic superpower, it is also one of the few nations in the world which may be counted as a net consumer of resources. Also, Japan must rely on imports from overseas for a large part of these resources. If our nation is to continue following the path of a stable and rich life for everyone, then we must begin to give serious thought to using the limited resources of the Earth more wisely.

Many other countries in the world have the same social problems. Japan seems to be a small model of the world for resource recycling.

Figure 1.1 shows how the waste generated in 1990 by manufacturing industries throughout Japan were processed or recycled.

The total amount of industrial waste generated can be divided into three categories:

1. Waste processed immediately (18,663 million tons)
2. Waste immediately recycled as resource (68,134 million tons)
3. Waste subjected to burning, drying or some other form of intermediate waste processing (156,425 million tons)

Waste management systems are important for resource recycling, but at the core of these systems, we, the researchers, have to think about a good process in this technology field. The outline for resource recycling is

1. Research on waste characterization
2. Size reduction and handling before separation
3. Physical separation (density separation, size classification, electrostatic separation,...... )
4. Physical-chemical separation (flotation,...... )
5. Chemical separation (leaching, extraction,...... )

The numbers of process steps depend on the cost of the recycled materials. Processed 1 to 3 should be used for most of the generated industrial waste.

In the field of technology, mining engineering and chemical engineering have been changing and searching for new research subjects and applications. We do not develop any more mines in Japan. However, their technologies are applicable to the separation of waste [4-5].

Nanjo[6] calls it the urban mine instead of a real mine. Resource recycling is focusing on the important technology of recovering a resource from waste and diminishing the waste volume. It is necessary to solve social problems and maintain the global environment. We are attempting to undertake a big national project, named the total environmental process of zero emission, by the Ministry of International Trade and Industry.

In fact, we have to pay attention to recent research and development to keep our convenient life. Gross net product and the population have increased more than several hundred times since the beginning of the industrial revolution.

New functional materials have been developed into a variety of products in the ceramic and electric industries over the last few decades. Due to the growing demand for products with a very high degree of accuracy, fibrous or membranous materials rather than bulk ones are gaining attention. The production of fine particles with many kinds of physical and chemical properties is very important in the research and development of new materials.

In so far as particle shape has a close relationship to the function of the bulk materials, which are composed of the particles concerned, it is possible to enhance the function of the material by preparing the particle shape as desired[7].

Particle shape is also related to the bulk properties of powdered or granular materials and influences their behavior during handling and processing. In the case of particulate materials such as abrasives, glass beads, paints, foundry sands and catalysts, it is especially important to control not only particle size but also the particle shape in order to bring about the required function for these materials.

However, it is not practical to arrange the shape of every particle during the production stage, except for some special cases of very expensive materials.

Formerly, the separation of solid materials according to particle shape had been carried out to remove foreign materials from grains and seeds. Recently, the importance of particle shape as well as size has become a focus in the chemical, mineral processing and manufacturing industries, with an eye to improvement in the handling and functional characteristics of particulate materials.

Generally speaking, the word "classification" means the separation technique by size in the fields of mining and chemical engineering. At least, we often recognized it as such. But "classification" just means the separation of some parts on purpose. This means that most of the separation performed is size separation. Sometimes gravitational and shape separation is necessary to establish a good development of the product.

Focus on the shape is needed, for example, in spherical particles for ceramics, powder metallurgy, casting sand, solder beads and toner carrier; angular particles for abrasives, needle form of iron oxide for magnetic recording, needle form of titan dioxide for paints preventing electrostatic loading, and flattened particles for cosmetics and pigments.

Shape eparation can be applied not only to the development of materials, but also to recycling. Currently, particle shape separation or classification must become an important technique to maintain a good environment and develop functional materials.

It is important to control the particle shape, but in the literature, there are not many studies on this subject. In this report, current developments and investigations of particle shape separation are described.

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