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Silver and antimony leaching from pyrargyrite (Ag3SbS3) by ozone in acid media was experimentally studied in order to evaluate this method as an alternative to the conventional cyanidation. When 1 g pyrargyrite was leached in 800 mL of 0.18 M sulfuric and 0.079 g O3/L gas was bubbled, it was observed that after 80% of metals dissolution the silver and antimony dissolution rates decreased until completely stopping. These results suggest the presence of a solid product layer onto the unreacted pyrargyrite cores. The SEM-EDS and XRD analysis showed that antimony oxides were formed as a layer covering the surface of pyrargyrite particles, hindering reactants transferring/diffusion to the unreacted surface. The chemical composition of the layer was identified as a silver/antimony oxide AgxSb2Oy (x = 0.51 ± 0.04 and y = 6.08 ± 0.43). For low solid/liquid ratios the pyrargyrite dissolution reached about 98%, however, for high solid/liquid ratios a maximum value of antimony concentration was found to be around 0.0008 mol/L. An activation energy of 27.88 kJ/mol was calculated, which is a typical value for mixed-control systems. The kinetic study showed that the controlling step changed as the reaction proceeds. The oxidation pretreatment with ozone is a promising alternative for pyrargyrite dissolution, currently under development.

This work characterizes raw and decopperized slimes, with the objective of identifying the phases in these two sub-products. The main phases in copper anodes are metallic copper, including CuO, which are present in free form or associated with the presence of copper selenide or tellurides (Cu2(Se,Te)) and several Cu-Pb-Sb-As-Bi oxides. During electrorefining, the impurities in the anode release and are not deposited in the cathode, part of them dissolving and concentrated in the electrolyte, and others form a raw anode slime that contains Au, Ag, Cu, As, Se, Te and PGM, depending on the composition of the anode. There are several recovery processes, most of which involve acid leaching in the first step to dissolve copper, whose product is decopperized anode slime. SEM analysis revealed that the mineralogical species present in the raw anode slime under study were mainly eucarite (CuAgSe), naumannite (Ag2Se), antimony arsenate (SbAsO4), and lead sulfate (PbSO4). In the case of decopperized slime, the particles were mainly composed of SbAsO4 (crystalline appearance), non-stoichiometric silver selenide (Ag(2−x)Se), and chlorargyrite (AgCl).

Arsenate-for-sulfate substitution in natroalunite has been investigated as the basis of a potential method for arsenic immobilization. The effects of temperature, reaction time and AsO4/(SO4 + AsO4) molar ratio in the initial aqueous medium were studied. The rate of precipitation increased with increasing temperature and AsO43− concentration, and it was practically complete in 180 °C. Natroalunite formation was faster and preferential than mansfieldite precipitation; the latter decreased when the temperature increased and the (AsO4/TO4)aq ratio (TO4 ≡ SO4 + AsO4) decreased. For (AsO4/TO4)aq 0.4, natroalunite was not precipitated, and other arsenate phases such as alarsite, mansfieldite and natropharmacoalumite appeared. AsO4 substitution in natroalunite in the interval 160–200 °C was practically independent of temperature and reaction time but it increased when increased (AsO4/TO4)aq. At 200 °C the substitution type was (AsO4/TO4)nat ≅ 0.5(AsO4/TO4)aq. The maximum arsenate substitution observed in the natroalunite structure was ~ 15% molar. The introduction of gypsum in the initial medium ends with the precipitation of anhydrite and natroalunite with a Ca-for-Na substitution about 4–6% molar and a similar degree of arsenate-for-sulfate substitution. In absence of Na+, Ca/As-rich alunite-type phases such as schlossmacherite or arsenocrandallite were not precipitated at reasonable rates in Ca2+/Al3+/SO42−/AsO43−media.

The effect of AsO4 substitution in natroalunite ((Na,H3O)Al3(SO4)2-x(AsO4)x(OH)6 − x, x ≤ 0.3) has been investigated by Rietveld refinement of the XRD patterns. Cell refinements confirmed a structural type R-3 m Z = 3, characteristic of alunite-type phases. AsO4-for-SO4 substitution slightly increased the c unit-cell parameter, in consistency with the cell expansion due to the differences between As-O1 and S-O1 distances in the crystal structure. The a cell parameter was practically independent of the AsO4 substitution. The arsenic leaching and stability of arsenical natroalunite compared with other related phases (mansfieldite, alarsite, natropharmacoalumite and amorphous Al-arsenate) was studied in the pH interval 1 to 12. The dissolution of arsenical natroalunite was congruent at pH

The stabilisation of calcium arsenate waste from a copper smelter by precipitation of arsenical natroalunite has been investigated. This procedure could solve the problem of arsenical gypsum production because it is transformed into arsenic-free anhydrite. Natroalunite precipitation was studied at 180-200 °C from the slurry obtained after H 2 SO 4 -leaching and ozonation of the original waste - using sodium and aluminum sulfates as reagents. Calcium arsenate waste and final precipitates were characterized by chemical analysis (ICP), SEM-EDS and XRD. Solubility tests were also performed on original waste and selected precipitates. The effects studied in the hydrothermal treatment were: initial pH, Al/As molar ratio, As concentration, reaction time and prior gypsum removal. For (Al/As) aq = 4.5, a complex natroalunite (~(Na,Ca)(Al,Fe) 3 ((S,As,P)O 4 ) 2 (OH) 6 )) was extensively formed. Under these conditions, As-substitution in TO 4 was 7-8% molar. Decreasing (Al/As) aq increased As-substitution in natroalunite (up to ~ 14% molar) but mansfieldite ((Al,Fe)(As,P)O 4 .2H 2 O) co-precipitated. Other effects such as the arsenic concentration in the range 3.5-7.0 g/L and prior gypsum removal did not significantly alter the arsenic phase ratio and the composition of the arsenic phases. However, treatment at 180 °C increased mansfieldite precipitation. Calcium incorporation in natroalunite was small (~ 0.04 in formula) and for initial pH = 1, precipitation of Cu, Ni and Zn was insignificant. Arsenical natroalunite can be effective for long-term storage. At its natural pH (4-5), arsenic solubility remained stabilized at ~ 0.1 mg/L in 6 months. Mansfieldite was not stable under the same conditions with arsenic solubility between 5-10 mg/L. The major disadvantage of natroalunite is the limited arsenic partition between solid and aqueous phases (~ 0.45 molar). However, as the precipitation rate is fast (

The hydrothermal treatment of Chilean Codelco-type copper concentrates with copper sulfate solutions was investigated as a mean of removal of impurities and subsequent increase of the copper assay. The behavior of the mineral phases (digenite, chalcopyrite, covellite, bornite, pyrite and sphalerite) was similar to those obtained in previous works from pure mineral samples. An almost complete transformation of bornite, chalcopirite, covellite and sphalerite into Cu 2 − x S phases was obtained at 225 °C–240 °C. The highest degree of elimination (around 80%) of impurities was in Zn, Cd, Tl and Bi. An intermediate elimination (40–70%) was achieved for Pb and Te, with only moderate elimination (20–40%) of Mo, Hg, Sb and As. Temperature was the variable having the greatest influence on the elimination of the impurities. A concentrate containing 33% Cu, 33% S, 22% Fe and 2% Zn was converted to a highly enriched concentrate containing 70% Cu, 19% S and 3% Fe. The advantages of a concentrate of this type would include: (1) raising by more than twice the smelting capacity due to the high copper content, (2) generation of a minimum amount of slag, (3) reduction by almost 50% in sulfur emissions, (4) substantial reduction of wastes containing hazardous metals and, finally (5), retention of the option to hydrometallurgical copper recovery since the neo-formed Cu 2 − x S phases are more reactive than chalcopyrite to the chemical or biochemical leaching.

The nature and basic kinetics of the hydrothermal reactions of bornite, covellite and pyrite with copper sulfate solutions were investigated, as a previous study on the behavior of the bulk Chilean copper concentrates. The reaction of bornite produced digenite at 2+ ] (aq) , and the activation energy was ∼ 100 kJ/mol. Covellite was transformed to digenite at 200 °C. The reaction was characterized for an irregular nucleation and growth of the products, which were non-protective. The order with respect the [Cu 2+ ] (aq) was 0.6 and the activation energy ∼ 110 kJ/mol. The pyrite reaction was significant at > 200 °C and extensive at 240 °C. It produced a mixture of digenite/chalcocite-Q, with small amounts of djurleite. The transformation has a high Philling–Betworth ratio (∼ 1.6), causing the break of the product layers. The reaction order and the activation energy were also 0.6 and ∼ 110 kJ/mol, respectively. The rate of the bornite reaction should be controlled by solid-state ionic diffusion, whereas for covellite and pyrite the rates should be limited by electrochemical processes. Towards the hydrothermal transformation, the reactivity of the main phases present in Chuquicamata-type concentrates was: bornite > chalcopyrite > covellite > sphalerite > pyrite.

The new mineral species barahonaite-(Fe) and barahonaite-(Al), simplified as (Ca,Cu,Na,Fe 3+ ,Al) 12 Fe 3+ 2 (AsO 4 ) 8 (OH) x · n H 2 O and (Ca,Cu,Na,Al) 12 Al 2 (AsO 4 ) 8 (OH) x · n H 2 O, respectively, occur at the Dolores prospect in Murcia Province, southeastern Spain. Barahonaite-(Al) also occurs at the former Gold Hill mine in Tooele County, Utah. The minerals form beads, coalesced beads, and crusts of submillimetric thickness whose surfaces commonly glisten because of the presence of plates, up to 50 μm in diameter (Utah), and razor-thin, tabular, composite crystals, up to 20 μm long (Spain). Barahonaite-(Al) is pale blue, brittle, transparent to translucent, soft, nonfluorescent, and has a white streak and D meas 3.03 g/cm 3 ; barahonaite-(Fe) is similar, but is yellow with a greenish tint and has a white to pale yellow streak. Both minerals are readily soluble in 10% HCl. Barahonaite-(Fe) is biaxial negative, α 1.664(2), β ≈ γ, γ 1.677(2), 2 V meas 45–80°; the indices of refraction of barahonaite-(Al) are α 1.616(2), γ 1.622(2). The compositions for barahonaite-(Fe) and barahonaite-(Al) from Spain, as determined with an electron microprobe, are, respectively, Na 2 O 2.07, 1.65, MgO 0.14, 0.00, CaO 12.96, 15.71, CuO 12.41, 14.59, Al 2 O 3 1.71, 9.52, Fe 2 O 3 13.78, 0.10, SiO 2 0.33, 0.14, P 2 O 5 0.42, 0.35, As 2 O 5 41.18, 42.16, SO 3 0.29, 1.24, Cl 0.91, 0.06, H 2 O (by difference) 14.01, 14.49, which correspond to (Ca 4.95 Cu 3.34 Na 1.43 Mg 0.07 Fe 3+ 1.70 Al 0.72 ) ∑12.21 Fe 3+ 2.00 [(As 0.96 P 0.02 S 0.01 Si 0.01 )O 4 ] 8 [(OH) 6.82 Cl 0.55 ] ∑7.37 ·13.2H 2 O and to (Ca 5.75 Cu 3.77 Na 1.09 Al 1.84 Fe 3+ 0.03 ) ∑12.48 Al 2.00 [(As 0.94 S 0.04 P 0.01 Si 0.01 )O 4 ] 8 [(OH) 7.95 Cl 0.04 ] ∑7.99 ·12.5H 2 O for X O 4 = 8. Indexing of the powder-diffraction patterns gave a 10.161(7), b 22.39(2), c 10.545(10) A, β 93.3(1)° for barahonaite-(Fe), and a 9.964(3), b 22.43(1), c 10.555(6) A, β 92.76(6)° for barahonaite-(Al). The strongest lines in the powder pattern [ d in A( I )( hkl )] are 22.0(100) (010), 11.2(70)(020), 5.068(20)(200), 3.345(20)(023, 310), 2.763(30)(053), 2.659(20)(172), and 2.541(20)(400) for barahonaite- (Fe), and 22.0(100)(010), 11.16(70)(020), 4.983(50)(200), and 3.333(45)(250,113) for barahonaite-(Al). The compositions and X-ray data suggest a possible overall relationship to the smolianinovite group, and a close relationship between attikaite and barahonaite-(Al). The new name barahonaite-(Fe) honors Antonio Barahona (b. 1937) of Madrid, Spain, who collected the original specimens, and barahonaite-(Al) is the Al-dominant analog of barahonaite-(Fe).

A study was made of the leaching of a sulfide copper ore in a NaCl–H 2 SO 4 –O 2 media after pre-treatment by agglomeration with H 2 SO 4(conc) and NaCl. The leaching variables evaluated included the amount of NaCl to be employed, the percentage of solids in the leaching solution, particle size of the raw mineral to be leached, and the preferable method of agitation in the leaching system. Mineralogical characterization of the material to be leached included analysis of the raw ore and of the leached ore residue using reflected-light microscopy, X-ray diffraction, and scanning electron microscopy. The soluble species included djurleite and digenite. The most important parameters in the leaching process proved to be particle size and type of agitation. A total percentage of copper extraction of 70% was achieved using mechanical stirring, which increased to 78% when using compressed air agitation. The best extraction of the copper was achieved when leaching with 3 g/L of chloride, room temperature of 20 °C, and when all particles were

Since ancient times, agriculture has had a significant impact on ecosystems in the Mediterranean basin. Current cultural landscapes are a result of these historical activities and they are sites where traditional human knowledge is reflected in both tangible and intangible heritage assets. The use of water for agriculture has always involved an understanding of the geographic space, hydrology management practices, and the engineering design of hydraulic devices such as small dams, weirs, irrigation channels, pools, or water mills, among other things. The intangible heritage is also especially relevant since the historical irrigation system provides the landscape with a structure characterized by orality, best practices, and traditional environmental knowledge. However, this heritage is at risk due to its wide territorial spread and in some cases loss of functionality. Urbanization, unsuitable land usage and loss of production are also factors that can be mentioned. This paper focuses on analysing the influence that the tangible and intangible heritage and the landscapes linked to the Rivers Jucar and Turia have on local development. The results indicate the existence of several resources with great cultural and recreational potential. They also continue to be key elements in the functioning of existing historical irrigation systems and, for this reason, these irrigation systems can still be considered fundamental drivers of the current sustainable development.

A study of leaching kinetics of djurleite (Cu 1.97 S) using Cu(II) solutions in a chloride medium was carried out. Copper sulfate and sodium chloride in an acid solution were reacted in order to obtain the aqueous solution medium for the study. Leaching of djurleite occurs as: Cu 1.97 S + 0.97Cu 2+ (chlorocomplexes) → CuS + 1.94Cu + (chlorocomplexes) Where the conditions were: copper concentration = 0.02–0.23 M, chloride concentration = 0.6–1.3 M, temperature = 20–80 °C. At room temperature, a complex solid-phase transformation with formation of intermediate Cu 1.97− x S phases is observed. Different variables such as total chloride and total copper concentrations, temperature, and particle size were used for obtaining kinetic data. The concentration of cupric chlorocomplexes using thermodynamic data available in the literature was calculated. The kinetics is governed by chemical reaction control, with activation energy of 35 kJ/mol (8.4 kcal/mol). The apparent reaction orders with respect to the total Cu(II) and total Cl − were 0.23 and 0.53, respectively.

The recycling of gold and palladium from metallic scraps can be carried out by ozone-leaching at ambient temperature and low (∼0.1 M) H+ and Cl− concentrations. Rh and Pt remain un-reacted, whereas metals such as Cu, Ni, Ag, can be previously eliminated through O2/H+ and O2/O3/H+ leaching pretreatments. Gold and palladium are dissolved in O3/Cl−/H+ with formation of AuCl4− and PdCl42−. Leaching studies showed a passive region, basically located at 2, as consequence of the influence of the [H+] on transfer control. The electric power consumption associated with O3 generation was in the range 4–8 kWh/kg metal leached.

The recycling of silver from metallic scraps can be performed through O 3 leaching at an ambient temperature and low (∼0.1 M) H 2 SO 4 concentration. The main by-product is O 2 , which can be recycled to the O 3 generation or used as leaching agent in a pretreatment step. The stoichiometry and the effects of the stirring speed, ozone and acid concentration and temperature on the leaching of silver were investigated. Silver dissolved as Ag 2+ (aq) in the range 10 −3 –1 M H 2 SO 4 , but for pH ≥4, insoluble Ag 2 O 2 was the main reaction product. Kinetics appeared to be controlled by mass transfer of O 3(aq) to the solid–liquid interface, showing first order dependency with respect to [O 3 ] aq and P O3 . Specific rates were only slightly dependent on the temperature in the interval 10–50 °C, but decreased at 60 °C due to the fall in O 3 solubility. The mass transfer coefficients showed an average activation energy of 17 kJ/mol. No significant effect of [H 2 SO 4 ] on mass transfer coefficients was observed for 10 −2 –1 M. Leaching rate gradually diminished for pH >2, as a consequence of the influence of the [H + ] in the transport control.

The nature of the hydrothermal reaction between sphalerite and copper solutions was investigated in the range 160–225 °C. Digenite (Cu 1.8 S) was the main reaction product at 160–212 °C, and chalcocite (Cu 2 S) at 225 °C. The reaction was characterized by the formation of a compact layer of copper sulfide around the sphalerite nuclei. Final particles retained the size and shape of the original ZnS. Reaction rate followed a parabolic kinetic law. No significant effect of aqueous copper concentration was observed in the range 1–10 g/L. An activation energy of 147 kJ/mol was obtained, indicating kinetic control by solid-state counter diffusion of Cu + and Zn 2+ ions through the copper sulfide layer. A possible electrochemical mechanism is discussed. The removal of zinc from digenite or chalcocite bearing copper concentrates is effective at ∼225 °C, in which a high sphalerite conversion can be achieved in times allowing autoclave processing (∼1 h).

The recovery of silver contained in electrolytic effluents is attractive due to its high economic value. These effluents are considered toxic wastes and it is not possible to dump them directly without any detoxification process. One of the most important way for silver recovery is the precipitation with sodium ditionite, sodium borohidride or hydrazine monohidrate. In this work, the most significant aspects related to the use of these reagents is presented. Results of silver precipitation with sodium ditionite from effluents containing thiosulfate without previous elimination of other species are also presented. Silver concentration in the final effluents was < 1 ppm.La recuperación de plata contenida en efluentes electrolíticos es atractiva por su alto valor económico. Estos efluentes son catalogados como residuos tóxicos y no pueden ser evacuados a cauces públicos sin un tratamiento previo de detoxificación. Una de las vías propuestas para recuperar plata de este tipo de efluentes es la precipitación química utilizando ditionito de sodio, borohidruro de sodio o monohidrato de hidracina. En este trabajo, se discuten los aspectos más signifícativos de la utilización de estos reactivos para el citado objetivo. Se presentan resultados de la precipitación de plata con ditionito de sodio en efluentes base tiosulfato, sin eliminación de otras especies presentes. Se pone de maniflesto la capacidad de este reactivo de cumplir los objetivos de alcanzar una precipitación, prácticamente total, de la plata, dejando el metal en el efluente a niveles de < 1 ppm, sin introducir substancias extrañas al sistema.

This work reports the results of copper concentrates leaching, which have high arsenic contents (up to 2.5 %). The treatments were carried out using chlorine that forms from sodium hypochlorite and sulphuric acid. The aim of this work is to obtain a solution having high copper content 4 to 6 g/1 and 5 to 7 g/1 free acid in order to submit it directly to a solvent extraction stage. In addition, this solution should have minimum content of arsenic and chloride ions. To carry out this investigation, an acrylic reactor was constructed where the leaching tests were made at constant temperature in a thermostatic bath under atmospheric pressure. The concentrate samples were obtained from mineral processing plants from Antofagasta, Chile. Typical variables were studied, such as leaching agent concentration, leaching time, pulp density and temperature among others. Some of the residues were analyzed by XRD and EPS. On the other hand, the solutions were analyzed by Atomic Absorption Spectroscopy. The results indicate solutions having the contents stated above can be obtained.Se ha estudiado la lixiviación de concentrados de cobre con alto contenido de arsénico (hasta 2,5 %), mediante un proceso de oxidación con cloro formado "in situ", por la reacción entre hipoclorito de sodio y ácido sulfúrico. El objetivo de estas experiencias es producir una solución de lixiviación, de características adecuadas para entrar a la etapa posterior de extracción por solventes (SX), es decir, entre 4 a 6 g/1 de cobre y 5 a 7 g/1 de ácido residual. Esta disolución, además, deberá contener cantidades mínimas de arsénico y cloruro. Las lixiviaciones se realizaron por agitación en un reactor de acrílico diseñado para tal efecto, a temperatura ambiente y a presión atmosférica. Se utilizaron concentrados de cobre de explotaciones mineras de Antofagasta (Chile). Se estudiaron algunas variables típicas de la lixiviación, como son: la concentración de agente lixiviante, el tiempo de lixiviación, el porcentaje de sólidos y la temperatura. La caracterización de algunos residuos sólidos, producto de las lixiviaciones, se realizó por DRX (Difracción de Rayos X) y EDS (Barrido de Energía Dispersiva de Rayos X). El cobre y arsénico en las disoluciones se analizaron mediante Espectroscopia de Absorción Atómica. Los resultados experimentales indican que es posible obtener soluciones de las características deseadas con este procedimiento, que utiliza reactivos comunes y de relativo bajo costo.

The kinetics of leaching of enargite (Cu 3 AsS 4 ) were studied in NaOCl solution for ranges of 20–60 °C, 0.07–0.47 M ClO − and 0.003–0.03 M OH − . The reaction is topochemical in nature with enargite particles converted to crystalline CuO. Complete conversion occurs according to: Cu 3 AsS 4 +11 OH − +35/2 ClO − →3 CuO + AsO 4 3− +4 SO 4 2− +11/2 H 2 O +35/2 Cl − The very fast reaction rates were limited by the chemical reaction; the kinetic equation was found to be: 1−(1−X) 1/3 = 3.57×10 2 exp (−58400/RT) r 0 [ ClO − ] 1/2 [ OH − ] 1/2 t A proposed electrochemical mechanism and a surface study by XPS was discussed. This leaching process could be used to remove arsenic from copper concentrates containing enargite.

Cobaltarthurite, of ideal end-member formula Co 2+ Fe 3+ 2 (AsO 4 ) 2 (OH) 2 ·4H 2 O, is a new Co-dominant member of the arthurite group and is named to reflect that relationship. The new species occurs predominantly as coalesced pellet-like spheres, up to 1½ mm across, that consist of straw-yellow to dark brown radial aggregates of fibrous crystals only a few micrometers in width. The mineral has a vitreous to silky luster, is brittle, translucent, nonfluorescent, has a hardness of 3½ – 4, a white to light brown streak, and is readily soluble in HCl. Cobaltarthurite is biaxial positive, α 1.741, β 1.762, γ 1.797, 2 V (calc.) 77°, with parallel extinction; the pleochroism is distinct, from almost colorless to medium yellow. Electron-microprobe analyses of yellow and dark brown material gave similar compositions, with the latter corresponding to (Co 0.50 Mg 0.12 Fe 3+ 0.11 Mn 0.08 Cu 0.01 □ 0.11 ) ∑0.93 Fe 3+ 2 [(AsO 4 ) 1.95 (PO 4 ) 0.04 (SO 4 ) 0.01 ] ∑2.00 (OH) 1.74 ·4H 2 O, for which D calc is 3.179 g/cm 3 for Z = 2; the measured density is 3.22(2) g/cm 3 . Indexing of the X-ray powder pattern, which is similar to those of the other members of the arthurite group, gave a monoclinic cell with a 10.27, b 9.72, c 5.545 A, β 94.46°. The strongest six lines of the powder pattern [ d in A( I )( hkl )] are: 10.2(95)(100), 7.04(100)(110), 4.81(65)(001), 4.24(60)(111), 2.89(25)(221), and 2.87(55)(311). The mineral is associated with pharmacosiderite, olivenite, conichalcite, jarosite, arseniosiderite, and several other products of oxidation in a near-surface, sulfide-depleted lens near Mazarron, in the Province of Murcia, southeastern Spain.

In order to explain the model of kinetics control on the dissolution of metallic copper, white metal, and natural chalcocite, the effects of the stirring speed, pH, initial chlorine and chloride concentrations, particle size, and temperature were investigated. The kinetics appear to be mass transport-controlled in conditions of full suspension of the particles, with activation energies of 17.9 kJ/mol (4.3 kcal/mol), 23.3 kJ/mol (5.6 kcal/mol), and 22.4 kJ/mol (5.4 kcal/mol) for copper, chalcocite, and white metal, respectively. The dependence of pH, temperature, and chloride concentration indicate that the rates were essentially determined by the concentration of chlorine.

The effects of the stirring speed, temperature, initial chlorine and chloride concentrations, particle size, addition order of the reactants and slags on the copper and iron dissolution from reverberatory and flash furnace slags were investigated. Extractions in the range of 75 and 80% Cu and about 5% Fe were obtained at room temperature. The most significant parameters were the particle size and the initial chlorine concentration. A mineralogical characterization of the reverberatory and flash smelting slags, using X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) coupled to an X-ray energy dispersive spectrometer (EDS) and microanalysis (EPMA), was made. This characterization indicated that most of the copper is in the form of metallic copper, chalcocite, bornite and other complex sulphides of very small size, mainly 5–10 μ m. Iron is present principally as the matrix of a vitreous phase, fayalite and magnetite. An average only 0.2–0.4% of the copper was found in the silicate phases.

The jarositic materials occurs as ores (such as gossan) or as residues from some hydrometallurgical processes. To recover silver contained in these materials, processes of alkaline decompositioncyanidation at room or high temperatures or under pressure have been proposed. A sulphidizingcyanidation study of jarosite-beudantite solid solutions from gossan ores is presented. The solid transformations have been determined using X-ray diffraction, optical and electron microscopy (SEM-EDS) and electron microprobe. During the first step of the process the jarosite phases are decomposed with the formation of lead and silver sulphides and amorphous iron hydroxide. The decomposition of potassium jarosite-beudantite and beudantite-plumbojarosite are carried out at pH ≥ 12 and pH = 14, respectively. An oxidation, to remove the excess of sulphide, followed by the conventional cyanidation process leads to the recovery of the silver.Los materiales jarosíticos pueden encontrarse en estado natural (minerales de gossan) o generarse en circuitos hidrometalúrgicos. Para recuperar la plata contenida en estos materiales, se han propuesto procesos de descomposición alcalina-cianuración a temperaturas moderadas, elevadas o a presión, según el tipo de jarosita. En este trabajo se presenta un estudio sobre el tratamiento de soluciones sólidas jarosita-beudantita con sulfuros alcalinos a temperatura ambiente, seguido de cianuración convencional para la recuperación de la plata. Las transformaciones en estado sólido se han determinado mediante difracción de rayos X, microscopía óptica y electrónica (SEM-EDS) y microsonda electrónica. Durante la primera etapa del proceso, tiene lugar la descomposición de las fases jarosita, con formación de sulfuros de plomo y plata y un gel de hidróxido de hierro. La descomposición de potasiojarosita-beudantita tiene lugar a pH ≥ 12 y la de beudantita-plumbojarosita, precisa de un valor más elevado (pH = 14). La oxidación posterior para eliminar el exceso de sulfuro, seguida de cianuración convencional, permite la recuperación de la plata contenida.

The stoichiometry and kinetics of AuCl 4 − cementation on arsenopyrite were studied. For solution potentials of 970–1020 mV (vs. SHE) the overall process is given by: 14/3 AuCl − 4 + FeAsS +8 H 2 O →14/3 Au + Fe 3+ + SO 2 4 + AsO 3− 4 + 56/3 Cl − +16 H + The kinetics are limited by transport in an aqueous phase with an activation energy of 20 kJ/mol. Kinetic constants are independent of the initial AuCl 4 − concentration.The pH and chloride ion concentration have an insignificant effect. The addition of thiourea in the ratio [Tio]/[Au[ III ]=4 inhibited the cementation process instantaneously. An X-ray photoelectron spectroscopy/Electron spectroscopy for chemical analysis (XPS/ESCA) depth profile study of the attacked arsenopyrite surface is included and a possible mechanism for arsenopyrite oxidation is discussed. Binding energies and quantitative analysis for S, As, Fe and Au are reported.

AsO4-for-SO4 substitution in alunite (KAl3(SO4)2(OH)6) and hydronium alunite ((H3O)Al3(SO4)2(OH)6) has been investigated by hydrothermal precipitation at 200 °C. Arsenical alunite presented a good precipitation yield and a significant AsO4 substitution (up to 15% molar). The degree of arsenate substitution depends on the solution composition. It increased as (AsO4/(AsO4 + SO4))alunite ≅ 0.5 (AsO4/(AsO4 + SO4))L. For (AsO4/(AsO4 + SO4))L < 0.26, arsenical alunite was the unique phase and, above this ratio, mansfieldite (AlAsO4·2H2O) co-precipitated. The a unit cell parameter is practically independent of the AsO4 substitution, but the c unit cell parameter increased consistently with the differences between the AsO1 and SO1 distances in tetrahedral sites of the structure. The maximum stability of arsenical alunite in short-term tests is between pH 5 and 8, with an As-solubilization of 0.01–0.03 mg/L in 24 h. Long-term tests were performed at some synthesized samples at its natural pH. Arsenical alunite was stabilized at 0.3 mg/L released As in 2.5 weeks. These values were similar to those obtained in pure and largely crystalline natural scorodite (0.4 mg/L released As), but lower than the obtained for synthetic scorodite (1.3 mg/L released As). Thus, arsenical alunite could be effective for arsenic immobilization, especially for effluents or wastes containing large SO4/AsO4 ratio. Hydronium alunite presents a low precipitation yield and a very low arsenate incorporation (up to 1% molar). This may be related by the difficulty of substituting protonated H2O-for-OH− groups, due to the location of the H-bridges of the H3O in the structure. These characteristics make hydronium alunite unsuitable for arsenic immobilization.

The effects of the particle geometry and size, stirring speed, pH, chlorine and chloride concentrations and temperature on the kinetics of the aqueous chlorination of gold were studied. Surface examinations of gold samples leached in different conditions were carried out by SEM/EDS and XPS. The kinetics appear to be chemically controlled in conditions of full suspension of the particles. The dependence of pH and the chlorine and chloride concentrations indicate that the rates were essentially determined by the concentration of the trichloride ion. The expression obtained for the specific rate was: Rate (mol cm−2 min−1) = 4.25 105 [Cl3−] exp ( −43.5 R T ) A discussion of the possible mechanism is included, based on the kinetic dependence, previously reported electrochemical studies and mixed potential measurements.

When actual solid systems are observed, be they organic, inorganic or mineral solids, all appear to have non-isometric crystalline and defined shapes. In this paper a general procedure for modelling the dissolution of any shape of crystalline solid in a chemical control regime is presented. The general equations are deduced for a triclinic prism, a body of the least symmetry, and are applicable to all bodies of the seven fundamental crystalline systems as particular cases. For simplicity, a radius of a kinetic sphere is defined and the relations between the radius and the fraction reacted are given to make it possible to follow chemically the reaction for all bodies of the seven crystalline systems. The influence of external shape (angles between faces and edges) and area of the surface/volume ratio in the kinetic behaviour are discussed.

The cyanidation of argentian natrojarosite in alkaline medium shows an induction period, followed by a conversion period. The induction period decreases exponentially with increasing temperature and [OH − ]. The conversion period is characterized by the unreacted core model, the reaction halo is formed by amorphous hydroxides and the core by jarosite. The kinetic data are consistent with chemical control of the process. In the experimental conditions employed, the order of reaction is 0.4 with respect to [OH − ] with an activation energy of 96 kJ mol −1 in NaOH medium. In Ca(OH) 2 medium the order of reaction with respect to [OH − ] is 0.5 and the activation energy is 39.6 kJ mol −1 . The alkaline decomposition–cyanidation of argentian natrojarosite, as for argentojarosite and plumbojarosite, is a two-step process in series: a slow step of alkaline decomposition, followed by a fast step of complexation of the silver from the decomposition solids. The addition of soluble salts such as NaCl or Na 2 SO 4 in the reaction system increases the reaction rate by a factor higher than 2 in the experimental conditions employed.

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 .

El coleccionismo de minerales es una actividad en expansión. El alto nivel de demanda de minerales y de sus derivados posibilita la creación de microempresas en países en vías de desarrollo que, con muy poca inversión de capital, pueden facilitar el desarrollo de áreas rurales sin producir apenas impacto en el medio natural. Un aspecto muy importante para la supervivencia de estas microempresas es que el material tenga la calidad adecuada para su óptima comercialización, cosa que no ocurre en la actualidad con la mayor parte del material que procede de los países en vías de desarrollo. En este trabajo se proporcionan, de forma ilustrada, los criterios que se deben usar para identificar el tipo de material que puede ser interesante para ser comercializado, así como los mecanismos de tratamiento de los minerales desde su lugar de extracción hasta el punto de venta. Mineral collecting is a growing activity. The high demand for minerals and their derivatives has resulted in the creation of microcompanies around the mineral trade in developing countries. This activity could facilitate the development of rural areas with no need of a large capital investment and with minimal environmental impact. The high quality of their products is the most important aspect for the survival of these micro-companies, but nowadays the material that comes from developing countries does not always arrive in the best condition. In this essay the basic criteria are provided for identifying the kind of minerals that are interesting enough to be commercialized, and also the procedures recommended for commercializing them from the place where they are extracted to their point of sale.

Plumbojarosite-containing hematite tailings from the sulfating roasting of complex pyrite ores comprise a porous hematite matrix impregnated with plumbojarosite, anglesite, ferric sulfate and elemental sulfur. About 70% of the silver content is in dilute solid solution in the plumbojarosite. Leaching of gold, silver and lead was studied in HClCaCl2 media. The extracion rates of silver and lead are controlled by the plumbojarosite leaching under conditions near equilibrium. The simultaneous leaching of gold was studied as a function of the solution potential. The extraction of 90–95% lead and noble metals can be achieved with a stoichiometric consumption of HCl with respect to the plumbojarosite content (HCli 0.3–0.5 M) and 0.6-4 kg Cl/t. Uner these conditions, hematite is only slightly attacked.

The development of new radiographic techniques and the refinement of microsurgery and reconstructive surgery have been the responsible of the establishment of craniofacial resection (CFR) as the standard treatment of anterior skull base tumors. Overall complication rates varies from 24-56%, according to a review of recently published series.To describe the complications of CFR in a series of 41 patients and to analyze the management and final outcome.From 1990 to 2002, 41 patients underwent CFR for tumors involving the anterior cranial base. The extent of the tumor was always assessed with craniofacial CT-scan and MRI. The objective of the surgical treatment was to achieve "on block" removal of the tumor.The average age was 57 years with a male preponderance (63.4%). Squamous cell carcinoma was the most frequent histopathological type of tumor. The tumors were localized in paranasal sinuses in 78% of the cases. Bifrontal craniotomy was performed in 85.4% and unilateral orbitofrontal craniotomy in 14.6% of the cases. The area of facial resection included: ethmoidectomy (60.9%), ethmoido-sphenoidectomy (24.3%), maxillectomy (39%) and orbital exenteration (14.6%). The reconstruction of the floor of the anterior cranial fossa was performed using pedicled pericranial flap (100%), local (34.1%) or microvascular free flaps (21.9%) and split calvarian graft (19.5%). 20 patients (48.7%) developed post-operative complications, CSF leaks (12.1%) and meningitis (7.3%) being the most frequent major complications. The mortality rate was 7.3%.CFR has become the standard approach for anterior cranial base tumors. Despite its widespread application, the complication's rate ranges between 24-50% and the procedure carries a risk of significant morbidity and even mortality. Improvement of specific aspects of surgical technique and more refined reconstructive methods will decrease the number of complications.

A study was made on the dissolution kinetics of metallic copper flat packs using solutions of Cu(II) in a chloride medium which was obtained via reaction between copper sulfate and sodium chloride. The effect of stirring, chloride and Cu(II) concentrations, distribution of Cu(II) chlorocomplexes and temperature were investigated. The leaching data showed the reaction to be under chemical kinetics control, with an activation energy of 28 kJ/mol (7 kcal/mol). Leaching occurred at an apparent order of −1 with respect to the total chloride concentration and an apparent first order with respect to the total copper concentration. The Cu(II) ion was the main active species based on calculation of copper species distribution and the solution kinetics may be interpreted as rate=k[Cu2+]. For ratios of CCl/CCu2+ of less than about 8, a layer of CuCl(s) formed which impeded the solubilization process.

Resumen Introduccion Los recientes avances en radiologia, tecnica microquirurgica y de reconstruccion han permitido que la cirugia craneofacial (CCF) se haya convertido en el tratamiento de eleccion de la patologia tumoral de fosa craneal anterior. A pesar de esto, continua asociandose a una incidencia de complicaciones considerable (24–56%). Objetivos . Revision, analisis y manejo de las complicaciones de la CCF en una serie de 41 pacientes. Material y metodos 41 pacientes diagnosticados de patologia tumoral infiltrativa de base craneal anterior, fueron intervenidos mediante CCF, entre 1990 y 2002. La extension tumoral fue valorada en todos los casos con TC y RMN de la region craneo-facial. Tras determinar el volumen y extension tumoral se diseno un tratamiento quirurgico radical, con el objetivo de conseguir una reseccion tumoral “en bloque”. Resultados El 63.4% de los pacientes eran varones con una mediana de edad de 57 anos (18–73). La histologia mas frecuente de los tumores fue carcinoma escamoso y la localizacion habitual fue en los senos paranasales en el 78% (32 de 41 casos). En el 85.4% de los pacientes se realizo una craneotomia bifrontal basal y en el 14.6% restante craneotomia frontoorbitaria unilateral, en un solo colgajo oseo. El area de reseccion facial incluia: etmoidectomia (60.9%), etmoido-esfenoidectomia (24.3%), maxilectomia unilateral (39%) y exenteracion orbitaria (14.6%). Para la reconstruccion se utilizo: colgajo pediculado pericraneal (100%), colgajos locales (34.1%), colgajos libres microvascularizados (21.9%) e injerto oseo autologo (19.5%). 20 pacientes (48.7%) presentaron complicaciones postoperatorias, entre las que destacan, como complicaciones mayores la fistula de LCR (12.1%) y la meningitis (7.3%). La mortalidad global fue del 7.3%. Conclusiones La CCF continua asociandose a una elevada tasa de complicaciones, en general de tipo infeccioso. El perfeccionamiento de las tecnicas de reconstruccion permitiran reducir la incidencia de las complicaciones mas frecuentes y peligrosas.

The viability of a pyroconsolidation process to render pyrite cinders inert and to co-inert pyrite cinders with a hazardous polymetallic residue such as electric arc furnace flue dusts (EAF) containing Pb, Cu, Zn, As, Cr, Ni and Mo were investigated. The effects of pyroconsolidation temperature (800-1200 degrees C), milling pyrite cinders and additions of both CaO and EAF on the resulting microstructure of the pellets were determined. The microstructural changes were then compared with the results of the standard leaching tests. Full inertization of pyrite cinders was achieved after milling to100 micron followed by a pelletization and pyroconsolidation process at a temperature of 1200 degrees C. This process also allows co-inertization of pyrite cinders with controlled additions of EAF (up to approximately to 10%). Following pyroconsolidation at 1200 degrees C, the metallic elements were inert components in the four main phases: traces of Cr in hematite; Cr, Cu, Zn and Ni in spinel-phase; traces of Cr and Zn in calcium ferrites; and Pb and traces of Cu, Zn and Ba in K-Ca-Al-Fe glassy silicate.

A study was made of the dissolution kinetics of enargite, Cu 3 AsS 4 , with chlorine generated in solution by the reaction between sodium hypochlorite and hydrochloric acid. The effects of stirring speed, initial chlorine concentration, particle size, and temperature were investigated. The kinetics of the dissolution were characterized by two sequential stages: relatively fast reaction initially, while later the reaction became very slow. In the first stage, the fraction of copper extracted varied linearly with time according to α = k 1 t , whereas in the second stage, the dissolution was well represented by the shrinking core model controlled by diffusion through a porous product layer with kinetic equation: 1−3(1− α ) 2/3 +2(1− α )= k 2 t . The S 0 product layer acts as a diffusion barrier. The calculated activation energies were 15.0 kJ mol −1 (3.5 kcal/mol) for the first stage and 21.0 kJ mol −1 (5.0 kcal/mol) for the second. For the first stage, an apparent reaction order of 1.0 was found with respect to the chlorine concentration; for the second stage, an apparent reaction order of 1.8 was obtained.

The tailings from the sulphatizing roasting of Spanish complex pyrites consist of an impregnation of ferric sulphate, argentian plumbojarosite and minor amounts of anglesite and elemental sulphur in a porous hematite matrix. The gold and silver contents are 1–4 g/t and 50–150 g/t, respectively. A two-step alkaline pretreatment and subsequent cyanidation was investigated.

The paper describes how to obtain an analytic approximation to the transfer function of a conduction calorimeter, namely, a procedure to identify the calorimetric system. In this case Pade approximants are used on the Laplace transform of the thermogram. The feasibility of the method is tested on two models which span the frequency range usually attained by actual calorimeters. The influence of random noise and baseline drift have also been analyzed. The results show that three or four time constants are correctly obtained.

This work analyses how the standard smoothing techniques affect the thermogenesis given by harmonic analysis or Z-transform methods. The analysis has allowed an optimization of their efficiency. The results concerning signal/noise ratios of 40, 60, 80 and 100 dB are tabulated and generalized to a reduced frequency representation.

The nature of argentian plumbojarosite contained in old tailings of sulfatizing roasting pyrites has been studied. HCl-CaCl2 leaching has been investigated over a temperature range of 60 to 90 °C with 0.175 to 1 M HC1 and 0 to 200 g/1 CaCl2 as a means of selective leaching. The analysis of experimental data, independent of the stirring speed and cinder particle size, shows that the chemical reaction on the surface of the plumbojarosite crystals is the rate limiting step. This is supported by an activation energy of 96 kJ/mole. A first-order dependence with respect to the hydrochloric acid activity was found with or without the addition of calcium chloride. A micrograin model was applied to explain the leaching behavior, which is in satisfactory agreement with the experimental data.