Flotation of Minerals, Part J I. 311 



tures of galena and rhodonite, the oil collects the galena to form 

 granules, and the rhodonite remains as a sandy pulp which 

 could be washed out if desired. In cases of a mixture of a 

 sulphide which will attach oil and a gangue mineral which, in 

 an acidulated solution, will not aittach oil, some of the gangue 

 mineral is held mechanically by the sulphide aggregates, and 

 thus may be caused to float, although having no natural ten- 

 dency to do so. In such a case, what may be termed coad- 

 sorption may take place. For example, quartz sand by itself 

 will not float with oil in a non-acidulated solution, but the par- 

 ticles of c^uartz sand in a gangue with other minerals, as in the 

 case of Broken Hill tailings, are readily floated with oil in non- 

 acidulated water. This coadsorption will take place in feebly 

 acid solutions, and thus particles of rhodonite and other gangue 

 may be caused to float. 



From the above tests the following may be deduced : — 



Adsorption of oil in water. 



1. Finely divided sulphides when suspended in water will 

 adsorb varying amounts of oil. Large proportions of oil tend to 

 form magma, and smaller proportions plastic masses and co- 

 herent aggregates. TTie character of these oily magmas depends 

 upon the amount and the character of the oil used. Thick oils 

 give viscous coherent products, and thin oils give less coherent 

 products. Oily magmas containing considerable proportions of 

 oil will entangle and hold gaseous bubbles with a degree of per- 

 sistency which depends on the viscosity of the oil. 



Sulphides carrying an adsorption of about 5 per cent, of oil 

 tend to attach gaseous bubbles, and this tendency increases as 

 the proportion of oil diminishes, until a certain limit is reached 

 which is 0.5 per cent, or thereabouts. 



2. Th.e adsorption is more pronounced with sulphides than 

 with such minerals as quartz, felspar and most of the acidic 

 rocky minerals forming the gangue of ores. 



3. Some of the silicates and other gangue forming minerals 

 will adsorb oils in a manner approaching that of the sulphides, 

 for example, rhodonite, garnet, magnetite and calcite. 



4. As shown by the tests on sized minerals the amount of oil 

 adsorbed depends upon the extent of surface exposed. 



