The contact angle between a
nitrogen bubble and galena and pyrite surfaces immersed in methyl-, ethyl- or
butyl-xanthates has been determined as a function of the electrode potential
and of the quantity of xanthate species formed by interaction with the mineral
surface. For galena, the initial chemisorbed xanthate layer was found to be
hydrophobic when ethyl- or butyl-xanthates were employed, but hydrophilic for
the methyl homologue. The presence of dixanthogen enhanced the contact angle
but the metal xanthate diminished it. This conclusion was supported by contact
angle studies at a lead electrode. For pyrite the surface was hydrophilic
except when dixanthogen was formed, but a significant quantity was required on
the mineral surface before a finite contact angle was observed. This behaviour
is interpreted in terms of the presence of hydrated iron oxide on the pyrite
surface. ��� The potentials at which particulate bed
electrodes of galena and pyrite begin to float were determined for ethyl- and
butyl- xanthates. The potentials correspond to the regions where chemisorption
of xanthate takes place on galena and where significant quantities of
dixanthogen are formed on pyrite. ��� With butylxanthate,
flotation was inhibited when excessive quantities of xanthate species were
present on galena or pyrite. The inhibition arose from flocculation of the
mineral particles.
The contact angle between a nitrogen bubble and platinum or gold electrode surfaces immersed in xanthate solutions has been determined as a function of the quantity of dixanthogen on the metal surface for the methyl, ethyl and butyl compounds. Significant angles result from fractional coverages, but multilayers are required before the maximum angle, characteristic of the particular alkyldixanthogen, is reached.The quantity of dixanthogen required to float a particulate bed electrode of gold spheres was determined for a number of alkylxanthates. The required quantity varied from multilayers for methyl to low fractional coverages for the longer chain compounds. Nevertheless the static contact angle corresponding to these coverages was in each case found to be close to 55' for the three alkyldixanthogens studied.When butyl-or pentyl-xanthates were used at typical concentration levels applicable to practical situations (10 p.p.m.), flotation was inhibited when the quantity of dixanthogen formed was more than two to four times greater than the minimum amount necessary for flotation to occur. This inhibition arose from flocculation of the gold particles.
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