A. Uribe-Salas

Mechanism of adsorption of sodium dodecylsulfonate on celestite and calcite

Abstract The surface properties of celestite (SrSO4) and calcite (CaC03) in aqueous solutions of the anionic collector sodium dodecylsulfonate (NaDDS03) have been investigated making use of zeta potential, adsorption, infrared spectroscopy and microflotation techniques. A range of pH (3 to 11) and surfactant concentration (10−6 to 10−3 M) were tested. The experiments were performed at a constant temperature (25°C) and using regulated suspensions. The zeta potential studies showed that the isoelectric point (IEP) of celestite and calcite took place at pH 3 and 8, respectively. In the presence of dodecylsulfonate ion the IEP of both minerals shifted to lower pH values. The adsorption isotherms obtained for both minerals showed marginal adsorption up to certain surfactant concentration and precipitation of the salt (strontium or calcium dodecylsulfonate) onto the mineral surface beyond such a concentration. The microflotation studies showed that celestite was activated even at pH values where its surface was negatively charged. Compared to celestite, the activation of calcite was lower. It is suggested that the dodecylsulfonate ion adsorbed on the surface of celestite and calcite by a chemisorption mechanism giving rise, under certain circumstances, to the formation of the corresponding salt at the mineral-water interface.

On the sodium-diisobutyl dithiophosphinate (Aerophine 3418A) interaction with activated and unactivated galena and pyrite

Abstract The interaction mechanism of sodium-diisobutyl dithiophosphinate (DTPINa) with galena and pyrite was investigated using zeta potential, microflotation and FTIR measurements. To evaluate metal ion effects on both minerals, sulfides were conditioned in both water solutions and solutions containing Pb2+, Fe2+ or Fe3+. Results show that sodium-diisobutyl dithiophosphinate adsorbs onto galena and pyrite by a chemisorption mechanism. Collector shows a pronounced affinity toward lead species, either in the mineral lattice or adsorbed on the mineral surface as metal-hydrolyzed species. Pb-ions adsorb onto pyrite, thus promoting collector adsorption and a decrease in selectivity. DTPINa shows less affinity toward iron species.

Effect of dissolved oxygen and galvanic contact on the floatability of galena and pyrite with Aerophine 3418A

Abstract Tests were performed to evaluate the galvanic interaction of synthetic mixtures of galena (valuable mineral) and pyrite (gangue mineral) on their flotation response, both in air and nitrogen atmospheres, when the anionic collector sodium-di-isobutyl dithiophosphinate is added. The effect of lead activation of pyrite is also examined. Floatability of galena from mixtures is similar to that of galena alone indicating that the galena–collector interaction is not affected by the galvanic contact. In the presence of oxygen the floatability of pyrite from mixtures increases slightly compared to pyrite alone, due to the migration of Pb species, arising from galena dissolution, which adsorb onto pyrite as hydrolysed lead species. Galena–pyrite galvanic contact lowers the adsorption of lead species (from a Pb-bearing solution) onto pyrite, compared to that observed with pyrite alone. When the galvanic interaction is weakened due to the absence of oxygen (e.g., by using a nitrogen atmosphere), the concentration of lead onto pyrite surface increases to levels similar to those of pyrite alone. The collector chemisorbs onto galena forming a layer of low electroactivity that slows down the dissolution of the mineral; nevertheless, this layer does not completely prevent the galvanic interaction with pyrite.

On-line solids hold-up measurement in mineral slurries by the standard addition method

Abstract This paper presents the application of the standard addition method to on-line measure the solids hold-up at the laboratory scale. The method consists in measuring the electrical conductivity (mS/cm) of a two-phase dispersion using two conductivity cells: the first containing a known amount of dielectric material plus the solid–liquid dispersion and the second containing the solid–liquid dispersion only. A system of two equations are obtained by applying the Maxwells model to both cells, and the liquid conductivity and the solids hold-up may be evaluated by solving them. It is demonstrated that the studied method is a reliable option to estimate the solids hold-up on-line.

Gas dispersion in column flotation and its effect on recovery and grade

Abstract This paper reports the results of industrial test work performed in flotation columns of seven concentrators of Peñoles Group (México) on the relationship between gas dispersion parameters, namely gas rate (Jg between 0·5 and 3·5 cm s−1), gas hold-up (ϵg between 3·3 and 19·4%), average bubble size (d32 between 1·30 and 2·9 mm) and bubble surface area flux (Sb between 14 and 85 s−1), and the metallurgical performance of the columns (e.g. grade and recovery). Fifteen columns performing in the cleaning stages of lead and zinc circuits were examined. The results obtained show that the behaviour of dispersion parameters is consistent and that both Sb and ϵg correlate well with recovery and enrichment ratio c/f. Cet article rapporte les résultats d’un travail (essai) industriel effectué dans des colonnes de flottation de sept concentrateurs du Groupe Peñoles (México). On discute de la relation entre les paramètres de dispersion du gaz, soit la vitesse du gaz (Jg entre 0·5 et 3·5 cm s−1), la rétention de gaz (ϵg entre 3·3 et 19·4%), la taille moyenne de bulle (d32 entre 1·30 et 2·9 mm), et le flux de l’aire spécifique de la bulle (Sb entre 14 et 85 s−1), et le rendement métallurgique des colonnes (par exemple, teneur et récupération). On a examiné quinze colonnes d’étapes de nettoyage des circuits de plomb et de zinc. Les résultats obtenus montrent que le comportement des paramètres de dispersion est consistant et qu’il existe une bonne corrélation de Sb et d’ϵg avec la récupération et le rapport d’enrichissement c/f.

Pulp Potential Control in Flotation: The Effect of Hydrogen Peroxide Addition on the Extent of Xanthate Oxidation

Abstract The effect of increasing the redox potential by means of hydrogen peroxide additions upon the extent of oxidation of potassium ethyl xanthate (KEX: C2H5OCS2K) was investigated. The study was carried out at pH 7 in solutions of constant ionic strength (0.01 M NaNO3) using an initial surfactant concentration of 100 mg/L (6.176 × 10−4 M KEX). The Eh was varied in the range of 260 to 450 mV (vs SHE). The concentration of surfactant was determined by means of UV spectrometry at a wavelength of 280 nm. At shorter wavelengths it was observed that the absorbances of NaNO3 and H2O2 interfere with the measurement. It was determined that the main product of the oxidation of xanthate was perxanthate; no dixanthogen was detected regardless of the Eh of the solution.

Pyrite oxidation with ozone: stoichiometry and kinetics

ABSTRACT One of the most frequent causes of refractoriness in precious metals leaching is their occlusion or fine dissemination into a pyritic matrix. This study experimentally explores the acid leaching of pyrite with ozone, suggests the stoichiometry of the reaction, estimates its activation energy and defines the effect of the main variables on the leaching kinetics. The results of stoichiometry tests allow establishing that one mole of pyrite requires 7.7 moles of ozone to produce one mole of ferric ion and 2 moles of HSO4− ions. A decrease in the particle size, solution pH and solids’ concentration of the leaching system increases pyrite dissolution. The type of acid (nitric, sulphuric and hydrochloric) does not affect pyrite dissolution rate. Up to 60% of pyrite is dissolved when the optimal experimental conditions are employed (1u2005g pyrite (−25u2005µm), 800u2005mL of 0.18u2005M of H2SO4, 800u2005revu2005min−1, 1.2u2005Lu2005min−1 gas stream O2/O3 with 0.079u2005g O3u2005L−1 and 25°C). The apparent activation energy of the pyrite-ozone reaction is 14.92u2005kJu2005mol−1, and the absence of a passive layer on the pyrite surface and the linearity of the dissolution profiles suggest that the dissolution kinetics is controlled by the chemical reaction.

Role of pH on the adsorption of xanthate and dithiophosphinate onto galena

ABSTRACT In the concentrators of a Mexican mining company has been observed that the pH of the flotation has a significant effect on the galena recovery: the increase of pH from 7.5 to 9.5 in the Pb/Cu flotation circuit, resulted in a decrease of about 10% of lead recovery. In the present investigation, experimental models and techniques were developed to study the effect of pH on xanthate and di-isobutyl dithiophosphinate adsorption onto galena. The results obtained by UV / Vis spectroscopy showed that once galena surface has been slightly oxidised by the dissolved oxygen of the aqueous suspension, adsorption of both surfactants increases significantly, being adversely affected by the increase of pH from 5.5 to 9.5. Microflotation measurements performed for both surfactants support these findings. Thermodynamic simulation of the system suggests that the observed behaviour is due to the nature of the solid species formed on the galena surface at the particular pH: lead sulfate (PbSO4) under neutral and slightly acid conditions, and the basic sulfate (2PbO·PbSO4) under neutral and slightly alkaline conditions, as well as to their respective solubility. Infrared spectrometry confirmed the occurrence of sulfate onto galena particles, with a higher concentration for the acid pre-conditioning compared to the alkaline pre-conditioning.

Cyanidation kinetics of silver telluride (Ag2Te)

ABSTRACT The extraction of precious metals from tellurides by cyanidation is more difficult than when they are in their native form, nevertheless the reason for their refractory nature has not been adequately supported. In this study, the mechanism of the cyanidation kinetics of silver telluride (Ag2Te) was investigated. For this purpose, cyanidation experiments were carried out to: (1) study the difference between the cyanidation kinetics of elemental silver and silver telluride; (2) study the effect of temperature (i.e. 20, 25, 27, 30, 35 and 40°C) on silver telluride dissolution; and (3) elucidate the kinetic mechanism of the silver telluride cyanidation. The results obtained showed that: (1) while 83.5% of elemental silver was dissolved in 8u2005h, only 13.2% of silver from silver telluride was dissolved in the same time; (2) temperature has an important effect on silver extraction from silver telluride, but a minor effect on tellurium dissolution; and (3) at temperatures between 20 and 27°C, the process was controlled by the chemical reaction with an apparent activation energy of 191.9u2005kJu2005mol−1, whereas at temperatures between 30 and 40°C, the process was controlled by diffusion through a Ag5Te3 layer of products with an apparent activation energy of 25.2u2005kJu2005mol−1.

Decomposition kinetics of industrial jarosite in alkaline media for the recovery of precious metals by cyanidation

In the present study, the aqueous-slurry decomposition kinetics of industrial jarosite in alkaline media for the recovery of silver by cyanidation was investigated. For this purpose, aqueous-slurry decomposition experiments, using both NaOH and Ca(OH)2 as alkalinising agents, were carried out in order to (1) study the effect of pH (i.e. 8, 9, 10 and11), contact time and temperature (i.e. 30, 40, 60 and 70°C) on jarosite decomposition; (2) elucidate the rate-determining step of the process kinetics when using NaOH or Ca(OH)2, by applying the shrinking core model and Arrhenius equation and (3) study the effect of the aqueous-slurry decomposition on the recovery of silver by cyanidation. Results showed that when NaOH was used, the decomposition process was controlled by the chemical reaction with an activation energy of 40.42u2005kJu2005mol−1, whereas when Ca(OH)2 was used, the decomposition was controlled by diffusion through a porous layer of CaCO3 with an activation energy of 21.72u2005kJu2005mol−1. The alkaline decomposition emerges as a necessary step in order to recover up to 74% of the silver contained in the jarosite by cyanidation.