Francisco Patiño

Alkaline decomposition-cyanidation kinetics of argentojarosite

Abstract The cyanidation of argentojarosite in alkaline medium in the range 25–60°C and 5–30 m M NaCN, is a two-step process in series: a step of alkaline decomposition that controls the overall process, followed by a fast step of complexation of the decomposition products. The alkaline decomposition is characterized by the removal of sulfate ions from the lattice and the formation of a gel consisting of iron and silver hydroxides, which evolves to silver ferrite in the absence of cyanides. The decomposition curves show an induction period, followed by a conversion period. The induction period is independent of particle size and decreases exponentially with increasing temperature. The conversion period is characterized by the creation of a reaction halo of hydroxides around an unreacted jarosite core. The kinetic data are consistent with chemical control of the process. The rate expression obtained in NaOH media and Ca(OH) 2 media for [OH − ] ≤ 1 m M is: r 0 / V [1-(1-x) 1 3 ]=59.1 exp (−42,000/RT) [OH − ] 1 2 t . In Ca(OH) 2 the resulting expression for [OH − ] > 1 m M is: r 0 / V [1-(1-x) 1 3 ]=2.34 exp (−42,000/RT) [OH − ] 0 t .

Characterization and alkaline decomposition–cyanidation kinetics of industrial ammonium jarosite in NaOH media

Abstract A complete characterization was carried out on a jarositic residue from the zinc industry. This residue consists of ammonium jarosite, with some contents of H3O+, Ag+, Pb2+, Na+ and K+ in the alkaline “sites” and, Cu2+ and Zn2+ as a partial substitution of iron. The formula is: [Ag0.001Na0.07K0.02Pb0.007(NH4)0.59(H3O)0.31]Fe3(SO4)2(OH)6. Some contents of franklinite (ZnO·Fe2O3), gunninguite (ZnSO4·H2O) and quartz were also detected. The jarosite is interconnected rhombohedral crystals of 1–2 μm, with a size distribution of particles of 2–100 μm, which could be described by the Rosin–Rammler model. The alkaline decomposition curves exhibit an induction period followed by a progressive conversion period; the experimental data are consistent with the spherical particle with shrinking core model for chemical control. The alkaline decomposition of the ammonium jarosite can be shown by the following stoichiometric formula: NH 4 Fe 3 ( SO 4 ) 2 ( OH ) 6( s ) +3 OH ( aq ) − →( NH ) 4( aq ) + +3 Fe(OH) 3( s ) +2 SO 4( aq ) 2− . The decomposition (NaOH) presents an order of reaction of 1.1 with respect to the [OH−] and an activation energy of 77 kJ mol−1. In NaOH/CN− media, the process is of 0.8 order with respect to the OH− and 0.15 with respect to the CN−. The activation energy was 46 kJ mol−1. Products obtained are amorphous. Franklinite was not affected during the decomposition process. The presence of this phase is indicative that the franklinite acted like a nucleus during the ammonium jarosite precipitation.

Cyanidation kinetics of argentian jarosite in alkaline media

Abstract The cyanidation of argentian potassium jarosite in alkaline media is characterized by an induction period, followed by a conversion period, as was observed in other synthetic jarosites. The induction period shows an apparent order of 0.7 (NaOH) and 0.2 [Ca(OH) 2 ] with respect to the [OH − ], and an apparent activation energy of 86 kJ mol −1 (NaOH) and 36 kJ mol −1 [Ca(OH) 2 ]. The conversion period is characterized by the presence of a reaction front with an unreacted jarosite core. The decomposition products are amorphous. The process is chemically controlled in both media. In NaOH–CN − , the order of reaction is 0.6 with respect to the [OH − ] and the activation energy is 43 kJ mol −1 . In Ca(OH) 2 –CN − , the order of reaction with respect to [OH − ] is 0.5 and the activation energy is 80 kJ mol −1 . The order of reaction with respect to the [CN − ] concentration is zero in both media. The process is faster than that observed in natural arsenical potassium jarosite from gossan ores (Rio Tinto, Spain). The addition of potassium chloride to the reaction system increases the reaction rate; the order of reaction with respect to the [Cl − ] was 0.13.

Kinetics of alkaline decomposition and cyanidation of argentian ammonium jarosite in lime medium

Abstract The alkaline decomposition of argentian ammonium jarosite in lime medium is characterized by an induction period and a conversion period in which the sulfate and ammonium ions pass to the solution whereas calcium is incorporated in the residue jointly with iron; this residue is amorphous in nature. The process is chemically controlled and the order of reaction with respect to the hydroxide concentration is 0.4; the activation energy is 70 kJ mol−1. Cyanidation of argentian ammonium jarosite in lime medium presents the same reaction rate in the range of 0–10.2 mol m−3 CN−; in this range of concentration, the cyanide process can be described, as in other jarosites, in a two-step process: a step of alkaline decomposition that controls the overall process followed by a fast step of silver complexation. For higher cyanide concentration, the order of reaction with respect to cyanide is 0.65, and kinetic models of control by chemical reaction and diffusion control through the products layer both fit well; the activation energy obtained is 29 kJ mol−1; this is indicative of a mixed control of the cyanidation process in the experimental conditions employed. The process is faster than was observed in ammonium jarosite generated in zinc hydrometallurgy (Industrial Minera Mexico, San Luis Potosi, Mexico); it seems that the reaction rate decreases when the substitution level in the jarosite lattice increases; this behavior is similar to that observed for synthetic potassium jarosite and arsenical potassium jarosite from gossan ores (Rio Tinto, Spain) presented in a previous paper.

Alkaline reactivity of arsenical natrojarosite

Jarosites are compounds that can undergo substitutions with several elements of environmental importance (such as As5+) during precipitation. Arsenic integrated in the structure could influence the solubility of the jarosite, potentially stabilizing the structure under a wide range of conditions that are tolerated by pure jarosite. Alkaline reactivity is characterized by the removal of sulfate and sodium ions from the lattice and by the formation of a gel consisting of iron hydroxides with adsorbed arsenate. The decomposition curves show an induction period, followed by a conversion period. The induction period is independent from the particle size and decreases exponentially as the temperature increases. The conversion period is characterized by the formation of a hydroxide halo around an unreacted arsenical natrojarosite core. The kinetic data are consistent with the chemical control of the process. The expression obtained in NaOH medium for [OH-] concentrations ranging from 3.84 × 10-3 to 1.08 × 10-1 mol L-1 is the following: r0/-v[1 - (1 - x)1/3] = 3.11 × 109 exp(-57.110/RT) [OH-]0.7 t. The expression in Ca(OH)2 medium for [OH-] concentrations ranging from 2.21 × 10-2 to 6.98 × 10-2 mol L-1 is the following: r0/-v[1 - (1 - x)1/3] = 9.22 × 1011 exp(-48.610/RT) [OH-]1.51 t.

Kinetic modeling of the decomposition of beudantite in NaOH medium

This piece of work presents a study on the reaction of beudantite in NaOH medium under a wide range of experimental conditions. The partial decomposition of solids indicates the presence of an unreacted beudantite core, a reaction front and a halo of amorphous decomposition gel made of iron hydroxides and lead, through which sulfate and arsenate ions diffuse from the beudantite into the medium, while hydroxide ions from the medium diffuse through the gel onto the core of spherical particles of beudantite. We studied the dependence of the reaction rate on (OH−1) concentration, temperature and particle size in order to determine the reaction order and activation energy of the decomposition process of beudantite. A comparative study on the experimental rate constants of the alkaline decomposition of beudantite and other arsenic jarosites was conducted.

Estudio Cinético de la Lixiviación de Plata en el Sistema S2O3(2-)-O2-Cu2+ Contenido en Residuos Minero-Metalúrgicos

Resumen Se ha realizado un estudio sobre la cinetica de lixiviacion de plata en el sistema S 2 O 32- -O 2 -Cu 2+ que se encuentra contenida en las escombreras de Dos Carlos del Estado de Hidalgo en Mexico. La concentracion de [S 2 O 32- ] influye considerablemente sobre la velocidad de lixiviacion obteniendose un orden de reaccion de 0.98 en el rango de 15.8 a 126.4 gL -1 , logrando recuperaciones de plata en solucion del 73%. Se ha analizado tambien el efecto de la temperatura y la adicion de cobre en la cinetica. La temperatura tiene una marcada influencia sobre la velocidad global de la reaccion en el rango de 15 a 60°C. Se logro disoluciones de plata del 97% a la mas alta temperatura estudiada, obteniendo un valor de 43 kJ mol -1 para la energia de activacion. La adicion de cobre favorecio la velocidad de lixiviacion de la plata, obteniendo un orden de reaccion de 0.35 respecto a la [Cu 2+ ] y alcanzando un 95% de plata lixiviada. Palabras clave: lixiviacion, cinetica, orden de reaccion, produccion de plata, residuos minerales

Efecto de la Temperatura y Concentración de Tiosulfatos sobre la Velocidad de Disolución de Plata contenida en Desechos Mineros usando Soluciones S2O3(2-)-O2-Zn2+

The effect of the temperature and thiosulfate concentration on the dissolution rate of silver contained in mining wastes, using the system S2O3 2- -O2–Zn 2+ was studied. In the State of Hidalgo in Mexico, thousands of tons of waste mining having around 71 grams of silver per ton of waste have been accumulated over the years. This is the main reason that motivates this study. It was observed that the temperature drastically affects the leaching rate of the silver showing an activation energy Ea= 55.85 kJ mol -1 , implying that the dissolution reaction is controlled by the chemical reaction. The thiosulfate concentration shows a considerable influence on the precious metal dissolution rate. The maximum silver dissolution was found to be approximately 97% at 45 °C and 40 gL -1 of [S2O3 2- ]. It is concluded that the process studied represents a good alternative

Kinetic Analysis of the Decomposition of the KFe3(SO4)2-x(CrO4)x(OH)6 Jarosite Solid Solution in Ca(OH)2 Medium

The decomposition of the solid solution of potassium jarosite with chromium(VI) in Ca(OH)2 media was studied in the present work. According to experimental results, the incorporation of CrO42- into the crystal structure of jarosite resulted in a solid solution with the following approximate formula: [K0.86(H3O)0.14]Fe2.67[(SO4)1.23(CrO4)0.77][(OH)5.01(H2O)0.99]. The experimental data describe a reaction based on the shrinking core model with chemical control for spherical particles. A reaction order of n = 0.67 and an activation energy (Ea) of 63.75 kJ mol-1 were obtained in the induction period (tind). The progressive conversion period is characterized by the diffusion of K+, SO42- and CrO42- ions into the solution. In this stage, n = 1.99 with respect to OH-, and Ea = 51.56 kJ mol-1. The CrO42- diffusion is slower compared to that of sulfate, a slight amount of chromate is adsorbed in the layer of the solid residue consisting on Fe(OH)3. Finally, the equations that satisfactorily describe the reaction process were established from the data obtained.

Alkaline Reactivity of Solid Solution of NH4‐Na Jarosite with Arsenic

In this work, a kinetic analysis of the decomposition process of a solid solution of ammonium and sodium jarosite with arsenic incorporated into its structure in NaOH medium is presented. Atomic absorption spectroscopy (AAS), inductively coupled plasma optical emission spectroscopy (ICP-OES), elemental analysis and X-ray diffraction (XRD) were used for the characterization of the solid solution and the decomposition products. According to the results, the approximate stoichiometry of the jarosite synthesized is as follows: [(NH4)0.72Na0.06(H3O)0.21]Fe3 2.52(SO4)1.85(AsO4)0.15[(OH)4.41(H2O)1.59].