Elsevier

Powder Technology

Volume 140, Issues 1–2, 16 February 2004, Pages 68-78
Powder Technology

Effect of particle shape and roughness of talc mineral ground by different mills on the wettability and floatability

https://doi.org/10.1016/j.powtec.2003.12.012Get rights and content

Abstract

In this study, shape characteristics of talc particles produced by ball, rod and autogenous mills were investigated using Scanning Electron Microscope (SEM) and expressed by the shape descriptors such as elongation, flatness, roundness and relative width by measuring on the particle projections in two dimensions (2D). Approximately, 139 particles were measured for image analysis from each mill product. Surface roughness values of talc mineral have been expressed by the parameters of Ra value on the pelleted surfaces of the particles by employing Surtronic 3+ instrument. The wettability characteristics (γc) of talc mineral, produced by three different mills, were also determined by microflotation and the contact angle measurement techniques using the EMDEE MicroFLOT cell and Rame-Hart goniometer, respectively. Some correlations were established between the shape properties, surface roughness values and the wettability characteristics. The results have shown that elongation and smoothness helped to increase the hydrophobicity, while roundness and roughness caused a decrease in hydrophobicity or floatability for the talc mineral studied.

Introduction

Mineral ore comminution is generally a feed preparation step for subsequent processing stages. Grinding is most frequently done in rotating drums utilizing loose grinding media, lifted by the rotation of the drum, to break the ores in various combinations of impact, attrition and abrasion to produce the specified product [1]. In ball and rod mills, attrition is the main action; impact contributes to the comminution especially in primary mills, while abrasion is a negative factor causing wear of the grinding charge and the liners. In autogenous mills with moderate diameters, abrasion is the dominant grinding action. Impact and attrition are less importance and in some instances detrimental to the grinding processes, depending upon the characteristics of the ore feed [2].

In general, it can be said that there is a clear difference in the particle shape of different grinding methods [3]. It is known that the character of the material and the type of mill employed determine the shape of the particles produced.

The important variables in determining the behavior of a particle are size, density, surface properties and shape [4]. Because of the fact that there are no universally accepted definitions of shape of particles, particle shape parameter and its effect in processing have been neglected in most research [5]. In mineral processing, froth flotation, jigging, sieving, classification, shaking table, dense media separation, cyclone separation and the other most operation units are sensitive to particle shape. Minerals are separated from each other depending not only on mineral properties, but also particle shape [6].

Large tonnages of particles are made each year by crushing and grinding. Because shape has an effect on the chemical, physical and surface properties of particles, the usefulness of the crusher product for its intended purpose and degree of success of further processing is dependent on the product shape mix.

Since shape is a factor in the behavior of powders, the shape difference between the products of different mills is of particular significance to mineral processing recovery systems or any industry where particles are involved [7].

Particle morphology plays an important part in many aspects of powder technology. An image is the projection on a plane of the three-dimensional reality. Image analysis in connection with mineral processing includes analyzing unbroken and broken ores (to predict how the minerals may behave when they are ground and processed) and processed materials (to determine how the minerals respond to processing) [8], [9].

The shape and morphology of the products obtained during grinding and processing should be analyzed with the image analysis system to determine how the mineral behaved, to follow their flow through the grinding and concentrating circuits, and to predict what should be done to optimize the mineral recovery [10], [11].

Wetting of solid surfaces by liquids has many practical applications and consequently has been an important area of both applied and basic research for many years [12]. The wettability of solid or mineral particles, therefore, is known to be important parameter, which affects many technological processes such as flotation, agglomeration, solid–liquid separation and dust abatement [13]. Similarly, wetting properties also affect the behavior and performance of the particulate processing. The well-known contact angle measurement and flotation methods are used to assess the wetting behavior of minerals [14], [15].

Talc is a hydrous magnesium silicate mineral with the chemical formula Mg3Si4O10(OH)2 and the softest mineral on Mohs' scale of hardness. Since talc is used in a wide range of applications, notably as a filler, from animal feeds and fertilizers through cosmetics and detergents to technical ceramics, plastics and paper. Such versatility is because of talc's equally varied chemical and physical properties. That is, talc is hydrophobic, chemically inert, organophilic, platy, and has low electrical and high thermal conductivity [16]. Besides these properties, it will be worth determining the shape, morphological and wettability values of talc that are very important during breakage and flotation related processes. Therefore, this paper presents not only determining these properties such as elongation, flatness, roundness, relative width, surface roughness and wettability, but also sets a correlation between those shape and morphological properties with the wettability parameter [17].

Section snippets

Shape and morphology of particles

As mineral particles are made smaller and smaller, it follows that their surfaces assume a greater and greater importance, therefore surface characteristics and properties will clearly influence any fine particle processing operation. Size reduction causes new surfaces and this will be effective in any processing due to increasing interfacial area [18].

Particle shape characterization has the potential to become an analytical technique of significant importance to virtually all branches of

Mineral

Talc mineral having 59.2% SiO2 and 30.97% MgO from Turkey was used in this study (Table 1). The chemical analysis of the sample indicated that the sample was pure enough for this study as the shape may also be influenced by the particle mineral composition.

Grinding tests

All of the grinding tests were performed in dry conditions. A laboratory ball mill having 200 by 184 mm dimension with 5.475 kg of stainless steel balls of 30 and 26 mm in size were used. Feed sizes of the minerals were −850+600 μm with a

Results and discussion

Table 2 shows the values determined by SEM technique for the shape properties of talc mineral ground in different mills. After measuring about 139 particles from each mill product, the area and perimeter values were calculated using , followed by the shape properties such as elongation, flatness, roundness and relative width as already given in , , , , respectively. As shown in Table 2, rod milled product has the highest elongation and flatness values, whereas ball milled product has the

Conclusions

  • 1.

    The methods developed in this study set the possibilities of the correlations between the particle shape parameters (E, F, R, RW) and surface roughness values (Ra) with the critical surface tension of wetting values (γc) for talc mineral.

  • 2.

    The established correlation between the surface properties (i.e., flatness, roundness, relative width, elongation ratio and surface roughness) and critical surface tension γc of wetting values are in the form of γc=a (surface property)+b type, with a

Acknowledgements

The authors thank to CUBAP (The Scientific Research Projects Council of Cumhuriyet University) and TUBITAK (The Scientific and Technological Research Council of Turkey) for some part of the financial support of the study.

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