Adsorption mechanisms of modified thiol collectors on gold, silver,
and gold-silver alloys have been studied and compared with those of ethyl
xanthate (EX). The modified thiol collectors include dicresyl
monothiophosphate (DCMTP), dialkyl dithiophosphinate (DTPI) and monothiophosphinate
(MTPI).
In general, the adsorption mechanisms on silver and gold-sil ver
alloys can be explained by the EC-mechanism involving an electron transfer
step and a chemical reaction step. Thus, the adsorption should be
controlled by the Eh of the electrochemical oxidation of the electrode
involved and the pK of the metal collector complex. According to this
mechanism, DCMTP should adsorb on silver and gold-silver alloys at a lower
potential than DTPI and MTPI since the pK of sil ver-DCMTP complex is
larger than those of silver-DTPI and silver-MTPI. This has been verified
to be the case by voltammetry, FTIR and contact angle studies. Likewise,
EX adsorbs on silver at a lower potential than the modified thiol
collectors because the pK of silver-EX is larger than those of the silvermodified
thiol collectors.
Both EX and the modified thiol collectors adsorb on silver at lower
potentials than on the gold-silver alloys, which can be attributed to the
lower activity of silver on the alloy surface. For the same reason, the
potential for the onset of collector adsorption on alloys decreases with
increasing silver content.
next to an author's name indicates that all files or directories associated with their ETD are accessible from the Virginia Tech campus network only.
