Mineral processing interactions interfacial

Table I Interfacial Interactions of Importance in Mineral Processing...

The intensity of intermolecular interactions at the interfaces between condensed phases is one of the critical factors determining the conditions for wetting and spreading. A large number of important technological processes, such as mineral processing (flotational enrichment and separation), are based on these phenomena. The ability to alter interfacial properties by surfactant addition allows one to gain fine control over these processes. 

Surfactant adsorption on saltlike minerals, such as calcite and dolomite, is a more complex process and is less understood than adsorption on oxide surfaces. These minerals are relatively soluble and when in contact with an aqueous medium develop an interfacial region of complex composition (41—43). In addition to the two mentioned mechanisms of adsorption, covalent bonding, salt formation between surfactant and lattice ions at the solid surface, ion exchange of surfactant with lattice ions, and surface precipitation have been suggested as adsorption mechanisms (36, 43—47). The dissolution products of sparingly soluble minerals may interact with the surfactant, precipitate or adsorb at the solid surface, or lead to mineral transformations that affect surface composition and electrochemical properties (46, 48—52). All these factors can be expected to influence surfactant adsorption. 

Inorganic-Organic Interfacial Interactions in Hydroxyapatite Mineralization Processes... 

Other Interaction Processes. The selectivity of flotation reagents in a pulp and their functions depend on their interactions with the mineral phases to be separated, but other physicochemical and hydrodynamic processes also play roles. AH adsorption—desorption phenomena occur at the sohd—hquid interfacial region. Surface processes that influence such adsorptions include activation and depression. Activators and depressants are auxiUary reagents. 

The recovery of petroleum from sandstone and the release of kerogen from oil shale and tar sands both depend strongly on the microstmcture and surface properties of these porous media. The interfacial properties of complex liquid agents—mixtures of polymers and surfactants—are critical to viscosity control in tertiary oil recovery and to the comminution of minerals and coal. The corrosion and wear of mechanical parts are influenced by the composition and stmcture of metal surfaces, as well as by the interaction of lubricants with these surfaces. Microstmcture and surface properties are vitally important to both the performance of electrodes in electrochemical processes and the effectiveness of catalysts. Advances in synthetic chemistry are opening the door to the design of zeolites and layered compounds with tightly specified properties to provide the desired catalytic activity and separation selectivity. 

The above forms for the Lennard-Jones surface-water interaction potential have been used as models of hydrophobic surfaces such as pyrophyl1ite, graphite, or paraffin. If the intention of the study, however, is to understand interfacial processes at mineral surfaces representative of smectites or mica, explicit electrostatic interactions betweeen water molecules and localized charges at the surface become important. 

The overall process of cement hydration and setting results from a combination of solution processes, interfacial phenomena and solid-state reactions which lead to the formation of complex products. Some of the hydration products formed from the different mineral components of cement are shown in Table 7.31 [125]. Admixture-cement interactions are essentially interactions between admixtures and the initially formed cement hydrates the influence of admixtures on cement hydration is best considered by reference to the evolution of the reaction with time. Five stages can be identified [125, 126] ... 

The other important interfacial process is ion exchange, during which the ions in the interlayer space or the external surfaces are changed to other ions. It happens in connection with the change of the composition of the liquid phase interacting on the solid. For example, the cation exchange of the interlayer space of a clay mineral is... 

Metal mobility in soils is governed by interfacial processes, such as dissolution. The role of DOM in such processes will be determined by the nature t organic matter-surface associations. The surface complexation model pro-odes a conceptual framework for estimating the contributions of specific DOM components, particularly LMW organic ligands, to the mobilization f metals in soils. With this framework, the effects of humic substances on mineral dissolution can be interpreted to provide some insight into hu--mate-surface interactions. 

The basic interfacial process in flotation is selective hydrophobization (or lepophiliza-tion) and hydrophilization of particulate matter. The role of the solution chemistry is very important in flotation as it is determined by the dissolution behavior of mineral particles in the aqueous solution (pulp) and subsequent dissociation, hydrolysis and precipitation of the soluble species the dissolution, association, dispersion and emulsion behavior of various flotation reagents in the pulp and interactions among reagents with both soluble and surface species of minerals. The efficiency of flotation and separation of mineral particles and consumption of reagents are thus controlled by the solution chemistry of the pulp. As other processes such as oil displacement are also governed by such interactions and in turn by the wettability of the solid surface, the study of solution chemistry of surfactant/mineral/additive systems become very important for the development of many technologies. 

---