Jean Frenay

Leaching of oxidized zinc ores in various media

Abstract The leaching of various oxidized zinc ores in different solvents has been studied in laboratory tests by agitation leaching and in some cases by percolation leaching. Some tests have also been carried out on synthetic zinc compounds. The comparison of the leaching of four different Belgian ores in sulfuric acid, sulfurous acid, ammonium hydroxide and sodium hydroxide, shows that the better results are obtained with sulfuric acid and with caustic soda when the concentration of the latter is high enough. All the ores respond very well to leaching except one which is very rich in iron and can be processed only with concentrated caustic soda. Mineralogical studies have shown that smithsonite is completely leached but that hemimorphite is refractory to leaching in any solvent studied. The leaching in alkaline media (ammonia, caustic soda, diethylenetriamine) has been studied on five different ores. It is confirmed that hemimorphite is difficult to dissolve. Good results are obtained only with caustic soda at high temperature. In ammoniacal solutions, the presence of ammonium carbonate enhances the leaching of hemimorphite but decreases the leaching of smithsonite. The optimum concentration of diethylenetriamine is 250 g/l. Caustic soda leaching tests were carried out on pure compounds and showed that ZnO, Zn(OH)2, PbO, PbCO3 and 2PbCO3βPb(OH)2 dissolve very rapidly and completely, that the leaching of Zn2SiO4 is controlled by kinetics and that the leaching of ZnS, PbS and PbSiO4 is very poor, their solubility product being very quickly attained. The percolation leaching by sulfuric acid has been tested on Belgian ores and the good results obtained support the idea that this kind of ore could be successfully treated in this way.

Separation of Copper and Zinc by Solvent Extraction During Reprocessing of Flotation Tailings

Results from the solvent extraction of copper and zinc from pregnant solutions after bioleaching of re-floated tailings from the Kipushi concentrator in DR of Congo are presented. LIX984N has been used as extractant for copper, while D2EHPA as such for zinc, following prior removal of the ferric iron via precipitation. The McCabe-Thiele diagrams constructed for Cu and Zn extraction have theoretically suggested the need for two stages for copper and one for zinc. Stripping these metals to the aqueous phase by sulphuric acid has yielded rich electrolytes with 48.5 g/L copper and 85.5 g/L zinc. Thus, copper and zinc could be further recovered from the stripped solutions by electrolysis.

Oxidized copper phase precipitation in ammoniacal leaching — the influence of ammonium salt additions

Abstract In oxidative ammoniacal leaching of some copper sulfides, the dissolution of copper is slowed down by the precipitation of an oxidized phase which is identified as a hydrated tenorite. A simple set of mass balance equations permits determination of the stability limits of the copper ions in ammoniacal solutions with or without acidic ammonium salts.

Development of a pilot plant using clean technology for the recovery of gold from small scale mines

Abstract Previous experiments at laboratory scale showed that centrifugal gravimetry is able to recover gold at least as well as the usual mercury amalgamation methods used by small scale miners. From these results it was decided to build a pilot-plant with the help of a Belgian cooperation agency. This plant was built in 199–1997 near Copiapo, Chile, and has a capacity of 15 TPD.

INFLUENCE OF THE MAIN PARAMETERS ON ZINC POWDER ELECTROWINNING IN CAUSTIC SODA MEDIUM

ABSTRACT This work studies by SEM observations the influence of temperature, current density and some impurities on the morphology of zinc powder obtained by electrodeposition from NaOH solutions.

Kinetics of Ferrous Iron Oxidation by Moderately Thermophilic Microorganisms

The biological oxidation of ferrous iron is an important sub-process in the bioleaching of metal sulphides and other bioprocesses such as the removal of H2S from gases, the desulphurization of coal and the treatment of acid mine drainage (AMD). Owing to the numerous potential applications of ferrous iron biooxidation, several works were carried out with mesophilic microorganisms, especially with Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans, and only few studies were performed with moderately thermophilic and thermophilic microorganisms. The latter two have potential to be applied to the leaching of refractory sulphides such as chalcopyrite and requires a smaller degree of reactor cooling during bioleaching. The ferrous iron oxidation kinetics in the presence of Sulfobacillus thermosulfidooxidans (DSMZ 9293) was studied. The experiments were carried out in batch mode (2L CSTR) and the effect of ferrous iron concentration (2-20g/L) on the ferrous iron consumption and bacterial growth rate was studied. The Monod equation was applied to describe the growth kinetics of this microorganism and values of μ max and KS around 0.33 h -1 and 1.18g/L, respectively, were achieved, similarly to those reported for mesophilic microorganisms.