Adsorption and flotation of hydrophilic and hydrophobic materials in the presence of hydrocarbon polyethylene glycol ethers

Polyoxyethylated alkanols (CnEm) and nonylphenols (CgPhE(m)), or generally hydrocarbon polyethylene glycol ethers (REm), are preferentially adsorbed on solids with pH(pzc) lower than 4. This is due to basic character of OH groups of RE(m)and acidic properties of the OH groups of the solids. The saturation adsorption of REm increases with the number of carbon atoms in the hydrocarbon part of the molecule and decreases with the increasing number of oxyethylenic groups. This pattern is not always reflected in flotation because of interplay of different parameters including surface tension of RE, solution and original hydrophobicity of the solid. The adsorption of RE, surfactants renders hydrophilic surfaces slightly hydrophobic. For instance, the induced hydrophobicity of hydrophilic materials such as quartz in the presence Of C16E23, expressed as contact angle, is less than 20 degrees. The flotation with REm usually occurs for solids with pH(pzc) < 4. The flotation of naturally hydrophobic solids such as coal is better than that of hydrophilic materials due to enhanced adsorption of the hydrocarbon part of REm on hydrophobic surfaces. There is no correlation between CMC and flotation of solids. The flotation above CNIC is a result of penetration and reorganization of the adsorbed layers of CnEm when the bubbles approach the solid. Cease of flotation at high CnEm concentrations mostly results from a decreasing surface tension of the solution. The separation of different mineral particles in the presence of RE, surfactants is possible only in gently agitated flotation cells due to low hydrophobicity caused by the surfactant. (c) 2007 Elsevier B.V. All rights reserved.