(200f) Investigation of Chemical Hydrophobisation Treatment of Solid Particles Surfaces in Organic Phase and Fluidized Bed

The hydrophobicity of solid particles plays an important role in a number of technological, environmental, and biological phenomena. For example, in the mineral flotation process, the hydrophobicity of minerals affects their floatability. In several cases, it is necessary to reduce particle wettability in order to make them hydrophobic. The most commonly used hydrophobization techniques can be divided into two treatments; the first treatment consists of coating or smearing surfaces with a thin layer of a product having specific hydrophobic properties; this process is easy to do. However, it is costly and does not last long. The second treatment is chemical; in this case hydrophobic molecules are grafted over the surface by means of chemical covalent bonds, thus making the chemical treatment significantly more durable. The reaction is commonly known as silanization an given below:

Si-OH + RSiXn -> RSiXn-1 R + HX

Si-OH is the hydrophilic group on the surface RsiXn the reagent (the hydrophobic group) : organosilanes

Most chemical treatments of surface particles are prepared in organic solvents that are often too expensive. This is the reason this treatment is still limited to the laboratory setting for a small amount of divided solids because waste treatment of the organic solvent is necessary afterwards. Therefore, in this present study we have substituted the hydrophobisation process conducted in an organic solvent with a new process carried out in a dry phase of a fluidized bed thus spending less time and consuming less reagents. We chose glass micro-balls as a model of hydrophilic divided solid (average diameter 125 µm). As a first step, we have treated the glass powder in an organic solvent (dichloromethane, hexane?) with different reagents and at several temperatures. The aim of this step was, on one hand to develop a convenient method for measuring the hydrophobic character of the micro-particles and on the other hand to establish a referential data base to evaluate the fluidized bed silanisation performances. The second step was the hydrophobization of glass powder in a fluidized bed (diameter 11 cm length 30 cm). It consists in treating the hydrophilic particles while mixing them, in a fluidized bed fed with hot air with an adequate amount of porous particles previously soaked in a grafting reagent. The quantity of reagent thus trapped is progressively released by evaporation coming into contact with the available hydrophilic functions of the target solid particles. Different hydrophobic reagents (having various chain lengths, different functional groups number and reactivity, such as trimethylchlorosilane TMCS, benzyltrichlorosilane BTCS?) and various kinetics parameters are studied to optimize the grafting yield. The hydrophobicity of treated particles is evaluated using the contact angle measurement from capillary rise, Dynamic Vapor Sorption, Environmental Scanning Electron Microscopy and goniometric tests.