ISSN:0734-9343    

DOI:10.1080/07349349008905178

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Magnetite heavy media processes are accurate, efficient and easy to control separators, capable of producing high quality clean coal. Magnetite recovery circuit operation and magnetite consumption are the main reasons for high capital and operating costs. Over the last two decades, several countries have been actively involved in establishing magnetite specifications for coal heavy media circuits and in developing working standards for test magnetite.

ISSN:0734-9343    

DOI:10.1080/07349349008905179

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A new device has been developed to measure the Theological properties of rapidly sedimenting suspensions. The utility of this device is illustrated by measurements of Theological properties of magnetite suspensions used in dense media separation of coal. These suspensions are characterized by solids concentrations ranging from 10% to 2% by volume, corresponding to media densities of 1.4 to 2.0 g cm-3, respectively. The tow solids concentration, coarse particle sizes and high density of the material causes the media to settle too rapidly for accurate measurements to be made with conventional rheometers.

ISSN:0734-9343    

DOI:10.1080/07349349008905180

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The importance of medium properties in dense medium separation is now a widely accepted fact. It has been proven in the laboratory on a number of occasions that medium rheology is critical for efficient separation. However, transfer of the theory to the plant environment is not a simple exercise. The lack of instruments capable of measuring the rheology of industrial suspensions on a continuous basis has been one reason for the time it has taken for the importance of rheology to be recognised. This paper reviews some of the literature on viscosity measurement of suspensions in mineral processing and gives examples which demonstrate the effect of changes in viscosity on some mineral separations. The author argues that variations in local conditions preclude a universal model of medium rheology — particularly for contaminated medium - and that the alternative is for viscosity to be monitored directly on the plant.

ISSN:0734-9343    

DOI:10.1080/07349349008905181

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

This paper reviews the literature on the influence of viscosity on separation in dense medium processes, for both baths and cyclones, in the context of the well-known fundamentals of particle motion in fluids. It is concluded that viscosity does play a role in determining both the separation density and the extent of separation inefficiency (Ep). because most DMS processes probably operate in the intermediate particle flow regime. A high viscosity increases particle misplacement in baths and cyclones. It increases or decreases the separation density of bath separators (depending on whether the bath is top or bottom fed. Respectively) and decreases the separation density in cyclones due to a reduction in the medium differential. The effects of viscosity are strongly size dependent. In practice, viscosity is not seen as a major problem in most coal preparation applications, as long as it is properly managed.

ISSN:0734-9343    

DOI:10.1080/07349349008905182

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The significance of keeping under control the rheological behaviour of the suspensions used in dense medium separation is highlighted. Some workable enhancements of the complex plant circuitry leading to the possibility to modulate the viscosity or operating media are proposed. With a stepwise procedure, the complexity or establishing a framework for the quantitative description or the medium viscosity is described. Adopting a simplified approach which considers the solid phase or the medium as made up by a binary blend (magnetite + contaminant), separate expressions have been defined for describing the dependence of the relative viscosity on the volume fraction of the disperse phase, its composition and the flow conditions (shear rate). Introducing some corrective parameters for taking account of more complex composition characteristics of the solid phase and combining the above mentioned expressions a final rheological model suitable for practical use is obtained. This model allows predicting the relative viscosity of dense media as a function of the major medium composition variables and of the operating Sow conditions.

ISSN:0734-9343    

DOI:10.1080/07349349008905183

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

It would be convenient to study the effects of changes in operating conditions on solid-solid separations within a free-settling-type device with a mathematical model that takes into account the changes in the physics of the separation process. One such model, the unsteady-state pulp-partition (USPP) model, based on a convection-diffusion equation, can be used to generate fractional recovery values. These values give the fraction of or probability that a given size feed material of known density will report to the product stream. Furthermore, curves generated from these values can be described by certain characteristic operating parameters — the density of separation and the mean probable error. By examining the variation of these characteristic parameters with systematic changes in the model variables such as the separation time, separation efficiency changes can be investigated.

ISSN:0734-9343    

DOI:10.1080/07349349008905184

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Although most of the magnetite used in dense-medium coal beneficiation can be recovered by magnetic separation, there are small but significant losses. The magnetite losses can be attributed to removal in the wash wastes or uptake into fractures of the coal particles. To determine the relative significance of these mechanisms we studied the magnetic properties of two samples of uncleaned Pennsylvanian bituminous coal and the same coal cleaned with water and also cleaned in a dense medium (magnetite) slurry. Magnetic susceptibility measurements made as a function of temperature indicate that the loss of magnetite during coal beneficiation in a magnetic slurry is due in part to the entrapment of magnetite in coal fractures.

ISSN:0734-9343    

DOI:10.1080/07349349008905185

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0734-9343    

DOI:10.1080/07349349008905186

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0734-9343    

DOI:10.1080/07349349008905187

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor