Thermodynamic simulation of the reaction mechanism of Mn2+ oxidation with an SO2/O2 mixture

Manganese oxides are essential in the production of electronic components and batteries. A promising alternative for their production from secondary sources is the leaching of the Mn and later oxidative precipitation of Mn2+ by an SO2/O2 mixture. The steps involved in this last reaction have not been fully understood. This work presents the reaction mechanism describing the oxidative precipitation of Mn2+ by an SO2/O2 mixture with MnO2 and SO4 2− as reaction products. The analysis was supported in thermodynamic simulations in which the formation and effect of the oxidant species was verified. The proposed reaction mechanism was validated with experimental batch tests and it was found that it describes satisfactorily the oxidation reaction. Experimental evidence revealed that this system is efficient at low concentrations of SO2 in the gas mixture composition; an optimal composition of 7.3% SO2 of the gas mixture was found

Selenium reaction mechanism in manganese electrodeposition process

A difficulty for the electrochemical deposition is the high negative electrolytic potential of the Mn+2/Mn° pair in aqueous solutions producing water reduction at any pH value; to resolve this problem it is necessary to use selenium dioxide (SeO2) as additive. However, there is little information about the selenium mechanism presenting discrepancies. Founded on linear voltammetry, cyclic voltammetry, chronoamperometry test, and impulses of constant potential and thermodynamic analysis, are experimental evidences of the reaction mechanism to explain the selenium action; from here the originality of this work. It is demonstrated that two reactions that occur in the selenium mechanism at −0.3 and −0.6 V, the first for the selenium deposition and the second for the selenium dissolution. On the active sites of the cathode the specie of selenium reduced at −0.3 V is the ion hydrogen selenite (H2SeO3−), while at −0.6 V the deposited selenium is reduced to selenide

Selenium reaction mechanism in manganese electrodeposition process

A difficulty for the electrochemical deposition is the high negative electrolytic potential of the Mn+2/Mn° pair in aqueous solutions producing water reduction at any pH value; to resolve this problem it is necessary to use selenium dioxide (SeO2) as additive. However, there is little information about the selenium mechanism presenting discrepancies. Founded on linear voltammetry, cyclic voltammetry, chronoamperometry test, and impulses of constant potential and thermodynamic analysis, are experimental evidences of the reaction mechanism to explain the selenium action; from here the originality of this work. It is demonstrated that two reactions that occur in the selenium mechanism at −0.3 and −0.6 V, the first for the selenium deposition and the second for the selenium dissolution. On the active sites of the cathode the specie of selenium reduced at −0.3 V is the ion hydrogen selenite (H2SeO3−), while at −0.6 V the deposited selenium is reduced to selenide

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

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

Removal of Te and Se anions in alkaline media in presence of cyanide by quaternary ammonium salts

Precious metals are currently associated with selenium (naumannite, Ag2Se) and tellurium (calaverite, AuTe2; sylvanite, (Au,Ag)2Te4) to form species refractory to cyanidation. The aim of this preliminary work was to study the use of the solvent extraction technique to recover tellurium and selenium ions from a synthetic solution similar to the cyanidation effluents to recycle the free cyanide back to the process. For the extraction of the Se and Te anions, the use of quaternary amines as extractants was evaluated (tallow trimethyl ammonium chloride, Quartamin TPR; hexadecyl trimethyl ammonium chloride, Amine F; and trioctyl methyl ammonium chloride, Aliquat 336) employing nonylphenol as a modifier in the organic phase (iso-octane). The results obtained showed that the extraction was strongly affected by the pH and that it was possible to recover up to 83% of Se and 10% of Te with Quartamin TPR from two synthetic solutions containing 23 mg/L of Te and 20 mg/L of Se with a molar cyanide:metal ratio of 1:4 at pH 11, a ratio of aqueous/organic (A/O) = 1 (V/V) and an extractant concentration of 0.022 mol/L. A maximum distribution coefficient (D) of 4.97 was obtained at pH 11. The McCabe-Thiele diagram indicates that two theoretical extraction stages are necessary to obtain a good extraction of Se complexes using Quartamin TPR.Precious metals are currently associated with selenium (naumannite, Ag2Se) and tellurium (calaverite, AuTe2; sylvanite, (Au,Ag)2Te4) to form species refractory to cyanidation. The aim of this preliminary work was to study the use of the solvent extraction technique to recover tellurium and selenium ions from a synthetic solution similar to the cyanidation effluents to recycle the free cyanide back to the process. For the extraction of the Se and Te anions, the use of quaternary amines as extractants was evaluated (tallow trimethyl ammonium chloride, Quartamin TPR; hexadecyl trimethyl ammonium chloride, Amine F; and trioctyl methyl ammonium chloride, Aliquat 336) employing nonylphenol as a modifier in the organic phase (iso-octane). The results obtained showed that the extraction was strongly affected by the pH and that it was possible to recover up to 83% of Se and 10% of Te with Quartamin TPR from two synthetic solutions containing 23 mg/L of Te and 20 mg/L of Se with a molar cyanide:metal ratio of 1:4 at pH 11, a ratio of aqueous/organic (A/O) = 1 (V/V) and an extractant concentration of 0.022 mol/L. A maximum distribution coefficient (D) of 4.97 was obtained at pH 11. The McCabe-Thiele diagram indicates that two theoretical extraction stages are necessary to obtain a good extraction of Se complexes using Quartamin TPR

Remoción de teluro y selenio de los efluentes de cianuración

Currently, processes are being developed to recover precious metals from refractory minerals, such as tellurides (e.g. AuTe2, Ag3AuTe2) and selenides (e.g. Ag2S). When Te and Se are found in the leaching solution, they interfere with subsequent processes, decreasing the recovery of precious metals. Therefore, they should be removed before continuing the process. Mexico has deposits of precious minerals associated with Te and Se; the most important are located in the state of Sonora. In this work it is proposed the removal of Te and Se from cyanide solution of gold leaching by solvent extraction and electrowinning techniques, with the aim of purifying the solution of cyanidation and recycling it back to the leaching process. With the solvent extraction technique, it was evaluated the use of quaternary amines (quartamin TPR and amine F) with a concentration of 0.022 mol/L to remove Te and Se complexes. It was extracted 83% of Se at pH 11 ([Se]0 = 20 mg/L, [CN]T = 26.36 mg/L at 25 °C) and 10 % of Te ([Te]0 = 23 mg/L, [CN]T = 16.31 mg/L at 25 °C) using quatarmin TPR. Amine F showed lower recoveries for the complexes of both elements. In the electrochemistry study, it was used the following techniques: cyclic voltammetry, linear voltammetry, voltammetry with rotating disc electrode and chronoamperometry. It was found that tellurite ion (TeO32-) is reduced to metallic tellurium at a potential of -1.062 V (vs saturated calomel electrode, SCE) in alkaline media. The selenite ion (SeO32-) is reduced to metallic Se at -0.80 V (vs SCE) in acidic media. Finally, it was performed massive electrowinning tests of Te in alkaline media and it was found the deposition of only metallic Te.En la actualidad, se están desarrollando procesos para recuperar metales preciosos a partir de minerales refractarios, tales como telururos (e.g. AuTe2, Ag3AuTe2) y selenuros (e.g. Ag2Se). Cuando el teluro y el selenio se encuentran en cantidades excesivas en la solución de lixiviación, interfieren en los procesos posteriores, disminuyendo la recuperación de los metales preciosos. Por lo tanto, éstos deben removerse antes de continuar el proceso. México cuenta con yacimientos de minerales preciosos asociados con teluro y selenio; los más importantes se encuentran localizados en el estado de Sonora. En este trabajo se propone realizar la remoción del teluro y selenio de solución de cianuración proveniente del proceso de lixiviación del oro mediante la técnica de extracción con solventes y electrodeposición, con el objetivo de purificar la solución con cianuro en solución y poder reciclarla de vuelta al proceso de lixiviación. Para la técnica de extracción con solventes se evaluó el uso de aminas cuaternarias (quartamin TPR y amina F) en una concentración de .022 mol/L para remover complejos de teluro y selenio. Se logró extraer un 83 % de Se a un pH de 11 ([Se]0 = 20 mg/L, [CN]T = 26.36 mg/L a 25 °C) y un 10 % de Te ([Te]0 = 23 mg/L, [CN]T = 16.31 mg/L a 25 °C) empleando la amina quartamin TPR. La amina F mostró recuperaciones menores para ambos elementos. En la técnica de electrodeposición se utilizaron las técnicas electroquímicas de voltametría cíclica, voltametría de barrido lineal, electrodo de disco rotatorio y cronoamperometría. Se encontró que el ion telurito (TeO32-) se reduce a teluro elemental a un potencial de -1.062 V (vs electrodo de calomel saturado, ECS) en medios alcalinos, y el ion selenito (SeO32-) es reducido a selenio elemental a un potencial de -0.80 V vs ECS en medio ácido. Finalmente, se realizó una prueba de electrodeposición masiva de teluro en medio alcalino, a nivel laboratorio y se encontró un compuesto formado únicamente por Te elemental