Linear potential sweep

Hamilton IC, Woods R (1981) An investigation of surface oxidation of pyrite and pyrrhotite by linear potential sweep voltammetry. J Electroanal Chem 118 327-343... 

Linear Potential Sweep Infra-Red Spectroscopy (LPSIRS) is a variation of EMIRS techniques where the absorbance at a particular wavenumber is monitored during a potential sweep. 

Cyclic voltammetry belongs to the category of voltammetric techniques based on a linear potential sweep chronoamperometric technique. It certainly constitutes the most useful technique for a preliminary determination of the redox properties of a given species. 

Since the 1960s , various electrochemical methods such as linear potential sweep voltammetry, cyclic voltammetry etc. and various surface analysis apparatuses such as infrared spectra, X-ray photoelecfron spectroscopy etc. have been developed to investigate the electrochemical reaction mechanism involved in the flotation of sulphide minerals (Fuerstenau et al., 1968 Woods, 1976 Ahmed, 1978 Stm, 1990 Feng, 1989 Buckley, 1995 Arce and Gonzalez, 2002 Bulut and Atak, 2002 Costa et al., 2002). 

Abstract This chapter first explains the natural flotability of some minerals in the aspect of the crystal structure and demonstates the collectorless flotaiton of some minerals and its dependence on the h and pH of pulp. And then the surface oxidation is analysed eletrochemically and the relations of E to the composition of the solutions are calculated in accordance with Nemst Equation. The E h-pH diagrams of several minerals are obtained. Thereafter, electrochemical determination such as linear potential sweep voltammetry (LPSV) and cyclic voltammetry (CV) and surface analysis of surface oxidation applied to the sulphide minerals are introduced. And recent researches have proved that elemental sulfur is the main hydrophobic entity which causes the collectorless flotability and also revealed the relation of the amount of sulfur formed on the mineral surfaces to the recoveries of minerals, which is always that the higher the concentration of surface sulphur, the quicker the collectorless flotation rate and thus the higher the recovery. 

Keywords natural flotability collectorless flotation h pH diagram linear potential sweep voltammetry cyclic voltammetry XPS UV... 

Many investigators have used different techniques to study the electrochemical behavior of different sulphide mineral electrodes in solutions of different compositions. Linear potential sweep voltammetry (LPSV), and cyclic voltammetry (CV) have been perhaps, used most extensively and applied successfully to the investigation of reactions of sulphide minerals with aqueous systems. These techniques have provided valuable information on the extent of oxidation as a function of potential for various solution conditions and have allowed the identity of the surface products to be deduced. 

Figure 2.19 Linear potential sweep voltammograms for chalcopyrite electrode.

Figure 5.4 Voltammograms for a pyrite electrode in solutions at different pH conditions modified by CaO and NaOH (Linear potential sweeps at 20 mV/s)...

Buckley, A. N., Hamilton, I. C., Woods, R., 1985. Investigation of the surface oxidation of sulphide minerals by linear potential sweep and X-ray photoelectron. In K. S. E. Forssberg(ed.), Flotation of Sulphide Minerals, Elsevier. Amsterdam, 6 41 - 60 Buckley, A. N. and Woods, R., 1990. X-ray photoelectron spectroscopic and electrochemical studies of the interaction of xanthate with galena in relation to the mechanism. Int. J. Miner. Process, 28 301 - 311... 

Figure 6.23. Linear potential sweep voltammetry (a) input function (b) response function.

The rotating disc electrode is constructed from a solid material, usually glassy carbon, platinum or gold. It is rotated at constant speed to maintain the hydrodynamic characteristics of the electrode-solution interface. The counter electrode and reference electrode are both stationary. A slow linear potential sweep is applied and the current response registered. Both oxidation and reduction processes can be examined. The curve of current response versus electrode potential is equivalent to a polarographic wave. The plateau current is proportional to substrate concentration and also depends on the rotation speed, which governs the substrate mass transport coefficient. The current-voltage response for a reversible process follows Equation 1.17. For an irreversible process this follows Equation 1.18 where the mass transfer coefficient is proportional to the square root of the disc rotation speed. 

Again, application of the principle to the simple potential-step method appears trivial or superfluous. However, it is of quite great important for other types of potential control, namely double potential step, cyclic potential step [73], and especially the linear potential sweep method [21, 22, 73]. In all these techniques, sets of data Jf ( ) /f (f) E can be obtained, thus enabling kt(E) to be determined from eqn. (100). For more details, the reader is referred to the quoted textbooks. 

Values of ket were determined as previously reported for H20 or EtOH solvent (16). The derivatized electrode is first characterized by cyclic voltammetry in solvent/electrolyte solution without added I". The value of ket is then determined from the time dependence of the surface-concentration of (FeCp2+)surf. in the presence of variable I" concentration and as a function of solvent. The (FeCp2+)Surf. is generated in a linear potential sweep from -0.6 to +0.5 V vs. SCE while the... 

The term voltammetry refers to measurements of the current as a function of the potential. In linear sweep and cyclic voltammetry, the potential steps used in CA and DPSCA are replaced by linear potential sweeps between the potential values. A triangular potentialtime waveform with equal positive and negative slopes is most often used (Fig. 6.8). If only the first half-cycle of the potential-time program is used, the method is referred to as linear sweep voltammetry (LSV) when both half-cycles are used, it is cyclic voltammetry (CV). The rate by which the potential varies with time is called the voltage sweep (or scan) rate, v, and the potential at which the direction of the voltage sweep is reversed is usually referred to... 

An experimental example can be seen in Fig. 7.53 in which the DSCVC curves obtained for a staircase potential (AQ /AE — E curves, white dots) are plotted together with the LSV ones corresponding to the application of a linear potential sweep (7 v/ E curves, solid lines) to a solution of Phenantrenoquinone (PQ) in... 

The mercury-pool electrode. Mercury pools of sufficient diameter to approach a planar configuration obey the equations derived for linear diffusion to a planar electrode. This has certain theoretical advantages because of the large number of equations that have been derived for the planar electrode geometry, especially in terms of constant-current chronopotentiometry and linear-potential sweep chronoamperometry. 

The characterization of pure platinum catalysts and of Pt catalysts modified by lead was achieved in situ by linear potential sweep cyclic voltammetry. This technique allowed to measure the active platinum surface area in the absence and in the presence of deposited lead and to determine the surface fraction covered by lead adatoms (9-12). The adsorption stoichiometry of lead on platinum was also evaluated by electrochemical techniques and found to be equal to two (one lead atom covers two platinum atoms on the surface) (II). 

Linear potential sweep with hydrodynamic electrodes... 

Linear potential sweep in thin-layer cells... 

Linear potential sweep at a hydrodynamic electrode can lead to two extreme situations ... 

Fig. 16.6. Examples of BIA voltammetry, illustrated for the oxidation of 2 mM K4Fe(CN)6 in 0.4 M K2S04 electrolyte at a Pt electrode, dispension flow rate 24.5 p.Ls , cell parameters as in Fig. 16.5. (a) Consecutive injections of 16 p.L during a linear potential sweep, scan rate 10 mVs l (b) Background-subtracted cyclic voltammogram recorded during injection, scan rate 2 Vs-1 (c) Background-subtracted square wave (SW) voltammogram recorded during injection SW amplitude 50 mV, SW increment 2 mV, frequency 100 Hz.

Figure 6.12 shows a theoretical linear potential sweep voltammogram for a planar electrode, using the data of Table 6.3. The current drops beyond the peak ip shown in Fig. 6.12 because the species getting oxidized (or reduced) is depleted, in turn because the diffusion of analyte from bulk solution has not kept apace with the electrochemical process at the electrode. 

---