Electrochemical Leaching Research Articles

An investigation of the electrochemical nature of the ferric chloride leaching of sphalerite

Although considerable research has been reported on the hydrometallurgical behavior of zinc sulfide in chloride media, the electrochemical nature of the dissolution reaction involving a ferric/ferrous couple and the accelerating effects of the chloride ion and of cupric chloride have not been fully elucidated. It is shown that the decrease in dissolution rate of sphalerite in the presence of ferrous ions is due to a decreased cathodic half cell potential and therefore a less favorable mixed potential. The addition of chloride ion to the anodic half cell significantly increases the cell current, indicating that chloride ion plays a direct role in the anodic dissolution of ZnS and has relatively little effect on the cathodic half cell. It is also shown that Ag + has no effect on the dissolution of ZnS in a ferric chloride electrolyte. In addition the data suggests that cupric ion may accelerate the dissolution of sphalerite through a mechanism other than simply providing an additional oxidizing reagent to complement ferric ion. This investigation has demonstrated the utility of a relatively simple, dual cell technique for the study of electrochemical leaching reactions by separating the two half reactions. Although this technique would not replace standard leaching experiments, it does provide a useful complementary approach, and in some cases can provide data that would be particularly difficult or impossible to obtain through typical, standard leaching experiments.

Leaching of pure and cobalt bearing goethites in sulphurous acid: kinetics and mechanisms

The initial kinetics of sulphurous acid leaching of well characterised synthetic pure goethite (G–O) and goethites containing cobalt in sorption [GCo(S)] and co-precipitation [GCo(C)] modes have been studied. The interfacial reaction controlled nature of iron dissolution from different samples is indicated by the activation energy of about 65 kJ/mol. The rates of iron and cobalt dissolution from different samples showed a stronger dependence on the concentration of SO 2(aq.) compared with other solution species such as HSO 3 − and H +. The particles were found to be non-uniformly attacked, preferentially on multi-domain grain boundaries. The results of infra-red (IR) spectroscopy on leach liquors indicated that SO 4 2− is the major species formed during leaching. The half order of dependence of the iron dissolution rate on the concentration of SO 2(aq.) was corroborated by theoretical analysis of the electrochemical leaching reaction by the Butler-Volmer equation. It is proposed that chemically controlled leaching of cobalt ( E a≈82 kJ/ mol ) from GCo(S) may involve the reaction of two molecules of SO 2(aq.) with one molecule of surface Co(OH) 2 species. Cobalt and iron dissolve from GCo(C) congruently; the dissolution is controlled by the structure and leachability of the host goethite phase.

Treatment of chalcopyrite concentrates by hydrometallurgical techniques

A variety of hydrometallurgical techniques have been studied for the treatment of chalcopyrite concentrates. These include prior thermal treatment before leaching, direct leaching and direct electrochemical leaching. Thermal treatment to alter the mineralogical composition of the concentrate without oxidation with oxygen has been studied. In direct leaching, a variety of leaching systems like sulphate, chloride, nitric acid, ammoniacal systems and biological systems have been investigated. Direct electrochemical leaching of chalcopyrite concentrates with a view to recover copper and elemental sulphur has been proposed. Slurry electrolysis of chalcopyrite concentrates and basic studies to elucidate the mechanism of dissolution have been done. The development of a less polluting hydrometallurgical process as an alternative to smelting is the need of the future. The avoidance of air pollution as well as economic considerations such as capital cost, operating cost and recovery of byproducts will determine the adoption of these new processes.

The leaching of sintered CuS disks with ferric chlorides

A comparative study of chemical and electrochemical leaching of a sintered disk of CuS was carried out at 343 to elucidate the leaching mechanism of CuS with FeCl3. The leaching,rate of CuS exhibited a half order dependence on the FeCl3 concentration, but the addition of FeCl2 slightly reduced the leaching rate. The mixed potential of CuS exhibited a 53 mV decade-1 dependence upon the FeCl3 concentration; no significant effect on the mixed potential was observed by the addition of FeCl2. Based on these observations, an electrochemical mechanism is proposed which involves the oxidation of CuS and the reduction of FeCl2+ . The activation energy in chemical leaching of CuS was 46.7 kJ mol-1, while in electrochemical leaching, it was 50.4 kJ mol-1. By converting the leaching rate to electric current density,i, a 110 mV decade-1 dependence of mixed potential, E, against log i is obtained. This dependence of the mixed potential during chemical leaching of CuS on FeCl3 concentration agrees with the value theoretically expected from the electrochemical model of the leaching process. These findings strongly support an electrochemical mechanism for the FeCl3 leaching of CuS.

The leaching of chalcopyrite with cupric chloride

A comparative study of electrochemical leaching and chemical leaching of chalcopyrite was performed mainly at 343 K to elucidate the leaching mechanism of chalcopyrite with CuCl2. Also, the morphology of the leached chalcopyrite surface was studied by using a single chalcopyrite crystal. The leaching with CuCl2 produced a porous elemental sulfur layer on the chalcopyrite surface, showing a similar morphology to that produced during leaching with FeCl3. The leaching kinetics were found to be linear over an extended period, followed by an acceleration stage, as a result of an increase in the reaction surface area. The leaching rate of chalcopyrite was proportional to C(CuCl2)0.5, whereas it was inversely proportional to C(CuCl)0.5. The mixed potential of chalcopyrite exhibited a 66 mV decade−1 dependency upon C(CuCl2), and—69 mV decade−1 upon C(CuCl). Based on these observations together with other findings, an electrochemical mechanism involving the oxidation of chalcopyrite and CuCl − 2 and the reduction of CuCl+ was proposed. The Tafel plot between the mixed potential and the current density obtained by converting the rate of chemical leaching gave a straight line whose slope was in good agreement with that of the electrochemical leaching. These findings strongly support the electrochemical mechanism of chalcopyrite leaching with cupric chloride.

The photoelectrolysis of water using iron titanate anodes

Single-crystal and polycrystalline samples of the iron titanates FeTiO3, Fe2TiO4, and Fe2TiO5 have been studied as anodes for the photoelectrolysis of water. Band gaps and flatbands for the various compositions have been determined and aging studies have been conducted which indicate electrochemical leaching of iron atoms from the surface.