The sulfite pulping process is today practised in only a small number of pulp mills around the globe and the number of sulfite mills that use sodium as the base (cation) is less than five. However, due to the increasing interest in the wood based biorefinery concept, the benefits of sulfite pulping and especially the sodium based variety, has recently gained a lot of interest. It was therefore considered to be of high importance to further study the sodium based sulfite process to investigate if its benefits could be better utilized in the future in the production of dissolving pulps. Of specific interest was to investigate how the pulping conditions in the initial part of the cook (≥ 60 % pulp yield) should be performed in the best way. Thus, this thesis is focused on the initial phase of single stage sodium bisulfite cooking of either 100 % spruce or 100 % pine wood chips. The cooking experiments were carried out with either a lab prepared or a mill prepared cooking acid and the temperature and cooking time were varied. Activation energies for different wood components were investigated as well as side reactions concerning the formation of thiosulfate and sulfate. / Single stage sodium bisulfite cooking was carried out on either spruce or pine wood chips to investigate the influence of several process parameters in the initial phase of such a cook i.e. between 100 % and 60 % pulp yield. The cooking experiments were carried out with either a lab prepared or a mill prepared cooking acid and the temperature and time in the initial stage were varied. The influence of dissolved organics and inorganics components in the cooking liquor on the final pulp properties and side reactions were investigated. The impact of temperature and time on the pulp components were analyzed with respect to carbohydrates, lignin, extractives and thiosulfate. Kinetic equations were developed and the activation energies for delignification and carbohydrate dissolution were calculated using the Arrhenius equation. It was found that if using a mill prepared cooking acid, this had a beneficial effect with respect to side reactions, better extractives removal and higher pH stability during the cook, compared to a corresponding cook with a lab prepared cooking acid. Cooking with mill prepared and lab prepared cooking acids showed the same behaviour with respect to delignification and carbohydrate degradation, but the lab acid experiments resulted in a higher thiosulfate formation during the cook. The cellulose yield was not affected at all during the initial phase of the sulfite cook verifying earlier results by other researchers. The temperature had an influence on both the delignification rate and the rate of hemicelluloses removal.  The corresponding activation energies were found to increase in the following order; cellulose, xylan, glucomannan and lignin. / <p>Artikel 1: "The Initial Phase of Sodium Bisulfite Pulping of Spruce: Part 1" ingick i avhandlingen som manuskript. Nu publicerad.</p>

Hydrogen sulfide (H2S), is a gasotransmitter with several key roles in metabolism and vascular function. The effects of H2S are dependent on concentration and target organ. For example, increased H2S concentrations impair liver metabolic function but protect against vascular dysfunction and atherosclerosis. Thiosulfate sulfurtransferase (TST), a nuclear encoded mitochondrial matrix enzyme, is proposed to be a component of the sulfide oxidising unit (SOU) which metabolises H2S. Preliminary data has shown that Tst deletion in mice (Tst-/-) increases circulating H2S levels measured in whole blood. Therefore, it was hypothesised that Tst-/- mice would exhibit worsened metabolic function in the liver but also protection of vascular function under conditions of vascular stress e.g. atherosclerosis. Liver metabolism was assessed by extensive metabolic phenotyping of Tst-/-mice fed control diet and in conditions of metabolic dysfunction induced by a high fat diet (HFD). Tst deletion altered glucose metabolism in mice; gluconeogenesis was increased in liver from Tst-/-mice fed control diet. Glucose intolerance in HFD-fed Tst-/-mice was also more severe than HFDfed C57BL/6 controls. In vitro metabolic investigations in primary hepatocytes isolated from Tst-/-mice demonstrated that mitochondrial ATP-linked and leak respiration were increased compared to controls. The effect of Tst deletion on vascular function was investigated in Tst- /-mice fed control or HFD using myography. Tst deletion did not alter vessel function when mice were maintained on a normal diet. HFD feeding (20 weeks) reduced maximal vessel constriction in the presence of endothelial nitric oxide synthase and cyclooxygenase inhibitors in C57BL/6 aorta. However, in Tst-/-mice fed HFD there was no reduction in maximal constriction suggesting a protective action of Tst deletion. The effects of Tst deletion on atherosclerotic lesions was investigated by generating double knock-out (DKO) mice by deletion of the Tst gene in ApoE-/- mice and (ApoE-/-Tst-/-). Atherosclerotic lesion formation was accelerated by feeding mice a western diet. Within the brachiocephalic branch lesion volume and total vessel volume were reduced in DKO mice fed western diet for 12 weeks, indicating that Tst deletion reduced lesion formation. Plasma cholesterol was reduced in DKO mice compared to ApoE-/- controls and a trend towards reduced systolic blood pressure was also noted. Overall this work supported the hypothesis that Tst deletion engenders metabolic dysfunction but vascular protection. The findings are consistent with the reported effects of increased H2S signalling. Overall inhibition of TST represents a novel target for treatment of atherosclerosis, with the caveat that glycaemia may be worsened due to hepatic metabolic dysfunction.

This thesis presents results of studies using the technique of surface-enhanced Raman scattering (SERS) spectroscopy to investigate surface processes occurring on gold during electrochemical experiments in thiosulfate solutions and during leaching in ammoniacal copper(II) thiosulfate systems. The gold SERS electrode was characterised using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), linear sweep voltammetry (LSV) and cyclic voltammetry (CV). SEM investigations of the SERS activated gold surface showed the presence of electrodeposited dendrites with nanoscale features. XRD studies of the dendrites showed them to be polycrystalline with a large proportion of Au(111). Rotating disk electrode (RDE) studies of polished and SERS electrodes were undertaken in order to clarify the electrochemistry of various thiosulfate systems. The ex situ techniques of XPS and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy were used to determine the presence of sulfur, copper and nitrogen on leached or electro-oxidised surfaces. Voltammetric methods were used to determine sulfur and copper surface coverages at various potentials in sulfide, thiosulfate and ammoniacal copper(II) thiosulfate media. The electro-oxidation of sulfide was examined as a model system in order to identify spectral features and coverage associated with various potential-dependent sulfur layers. In the hydrogen evolution region, a surface layer formed by underpotential deposition in acid and basic media was characterised by a gold-sulfur stretching band, Au-S, attributed in the literature to a monoatomic stretching mode of sulfur bonded to gold. The surface coverage in this potential region was limited to 0.35 ML, representing adsorption in a (3x3)R30 structure. Bands were found to be absent that would have indicated the adsorption of SH– species as has been reported in the literature. A facile change in the position of the Au-S band with potential, unaccompanied by Faradaic processes, was seen when the adsorbed (3x3)R30 sulfur layer was examined in a sulfide-free solution. This may indicate a change in sulfur adsorption sites with potential in the hydrogen evolution region. At potentials above the S II/S0 reversible value in sulfide solutions, the surface coverage increased and S-S bands were observed, indicating the formation of an adsorbed polysulfide species, Au-Sn. A change in the position of the Au-S band was seen to accompany the formation of the S-S bands. As coverage further increased, bands due to S-S-S bending, S-S-S, developed that were characteristic of cyclo octasulfur, S8. On removal from sulfide solution and rinsing, a characteristic SERS spectrum was observed ex situ. The spectrum showed a characteristic S-S at 460 cm-1 and Au-S at 325 cm-1 and was assigned to an adlayer of S8 adsorbed on gold in a crown configuration, Au S8. Gold was polarised in thiosulfate solutions at a potential at which gold dissolution is known to occur. In situ SERS spectra showed bands characteristic of S-S bonding and Au2S to occur after 1 hr for thiosulfate with sodium and ammonium counter-ions and for both systems in the presence of ammonia. XPS studies of polished gold held in sodium thiosulfate under these conditions showed S 2p binding energies corresponding to metal sulfide and pyritic sulfur, S22-. After 72 hrs at the mixed potential in air saturated sodium thiosulfate, SERS investigations showed a spectrum with Au-S8 characteristics. XPS studies on a polished electrode under these conditions showed a third type of S 2p binding with a binding energy between that of pyritic sulfur and S8. The sodium thiosulfate system showed an adsorbed tetrathionate-like surface species, Au-S4O6, to be present at the mixed potential and to disappear with increased potential prior to the formation of bulk S8 via an Au-S8 intermediate. In the presence of the ammonium cation at high potentials, Au-Sn bands appear in the presence of a more intense and broad Au-S characteristic of gold sulfide, Au2S. This was assigned to a mixed gold sulfide/polysulfide phase, Au2S/Sn. With addition of ammonia, the surface species Au S4O6, Au2S/Sn and, tentatively, adsorbed NH3 were observed above the mixed potential. For gold in air-saturated copper(II) ammoniacal thiosulfate media, bands due S-S at 382 cm-1 and symmetric S-O stretching, symS-O, at 1017 cm-1 developed during leaching at the mixed potential. These modes diminished and, when rinsed and examined in water, were replaced by a single band at 255 cm 1 assigned to a metal sulfide stretch. In typical leach solutions, sulfur and copper coverages showed a 2:1 atomic ratio after leaching for 16 h. Ex situ ATR and XPS studies showed that ammonia was adsorbed to a surface copper sulfide. Kinetic studies using atomic absorption spectroscopy (AAS) to measure gold in solution showed that the ammoniacal copper(II) thiosulfate leaching solution exhibited higher dissolution rates in the presence of the sodium counter ion than the ammonium. Thiourea as an additive to thiosulfate solutions was seen to disrupt S-S bonding in both Au-S8 and Au2S/Sn surface structures.

The kinetics of the dissolution of gold and silver colloids in ammoniacal thiosulfate solutions has been studied using oxygen, copper(II) or oxygenated copper(II) as oxidants at pH 9 - 11 and temperature 22oC to 48oC. The effects of the concentration of the main reagents such as copper(II), ammonia and thiosulfate as well as various background reagents have been investigated. Gold and silver colloids have characteristic absorption peaks at 530 nm and 620 nm respectively. Thus, the extent of gold or silver dissolution in different lixiviant systems was monitored using an ultraviolet-visible spectrophotometer. A comparison of the behaviour of gold colloids and powders has also been made. The beneficial or detrimental effects of silver colloid, and background reagents such as silver nitrate, and sodium salts of nitrate, carbonate, sulfite, sulfate, trithionate, tetrathionate anions have also been investigated. Experimental results show that the relative rates and the extent of gold colloid dissolution at 25ºC in different lixiviant systems in a given time interval are in the order: oxygen-cyanide > copper(II)-ammonia-thiosulfate ≈ oxygen-copper(II)- ammonia-thiosulfate > oxygen ammonia-thiosulfate ≥ oxygen-ammonia > copper(II) ammonia. The analysis of electrode potentials shows that Au(S2O3)23- is the predominant gold(I) species in the lixiviant solutions containing oxygen or copper(II) as oxidant and thiosulfate or mixed ammonia-thiosulfate as ligands. During the reaction of copper(II) with thiosulfate in ammoniacal solution without oxygen, the measured potential using a platinum electrode represent the redox couple Cu(NH3)n2+/Cu(S2O3)m1-2m (n = 4 or 3, m = 3 or 2) depending on the concentrations of thiosulfate and ammonia. The initial dissolution rates of gold colloid by oxygen in copper-free solutions show a reaction order of 0.28 with respect to the concentration of dissolved oxygen, but independent of the concentration of ammonia and thiosulfate. The reaction activation energy of 25 kJ/mol in the temperature range 25°C to 48°C indicated a diffusion controlled reaction. The initial dissolution rates of gold colloid by oxidation with copper(II) in oxygenfree solutions show reaction orders of 0.41, 0.49, 0.60, 0.15 and 0.20 with respect to the concentrations of copper(II), thiosulfate, ammonia, chloride and silver respectively. The presence of silve (I) or chloride ions enhances the rate of gold dissolution, indicating their involvement in the surface reaction, possibly by interfering with or preventing a passivating sulfur rich film on gold surface. An activation energy of 40-50 kJ/mol for the dissolution of gold by oxidation with copper(II) in the temperature range 22°C to 48°C suggests a mixed chemically/diffusion controlled reaction. The dissolution of gold by oxidation with copper(II) in oxygen-free solutions appears to be a result of the reaction between gold, thiosulfate ions and the mixed complex Cu(NH3)p(S2O3)0. The half order reactions support electrochemical mechanisms in some cases. The initial dissolution rates of gold colloid, massive gold and gold-silver alloys by oxygenated copper(II) solutions also suggest a reaction that is first order with respect to copper(II) concentration. High oxygen concentration in solutions has a negative effect on the initial rate of gold dissolution and overall percentage of gold dissolution, indicating that oxygen affects the copper(II), copper(I) or sulfur species which in turn affects the gold dissolution. The surface reaction produces Au(NH3)(S2O3)- and Cu(NH3)p+. The mixed complexes Au(NH3)(S2O3)- and Cu(NH3)p+ re-equilibrate to the more stable complexes Au(S2O3)23- and Cu(S2O3)35- in solution. The dissolution of gold powder by oxidation with copper(II) in oxygen-free solutions shows the same trends as that of gold colloid. The presence of silver(I) or chloride ions enhances the initial rate and percentage dissolution of gold colloid and powder. The dissolution kinetics of gold powder and colloid follow a shrinking sphere kinetic model in solutions of relatively low concentrations of thiosulfate and ammonia, with apparent rate constants being inversely proportional to particle radius. The best system for dissolving gold based on the results of this work is the copper(II)-ammonia-thiosulfate solution in the absence of oxygen or in the presence of oxygen. In the absence of oxygen, copper(II) 1.5-4.5 mM, thiosulfate 20-50 mM, ammonia 120-300 mM and pH 9.3-10 are the best conditions. The presences of carbonate and sulfite have a significant negative effect on the dissolution of gold. The presence of sodium trithionate shows a beneficial effect in the first two hours, while sodium tetrathionate or lead nitrate have a small negative effect and sodium nitrate showed no effect on the dissolution of gold. Silver nitrate and sodium chloride also show beneficial effects. In the presence of oxygen, copper(II) 2.0-3.0 mM, thiosulfate 50 mM, ammonia 240 mM and pH 9.3-9.5 are the best conditions.

Obesity is associated with dysfunction of adipose tissue due to oxidative stress and inflammation, leading to insulin resistance. Thiosulfate sulfurtransferase (Tst) was previously identified as an adipose-expressed anti-diabetic gene that protects against diet-induced metabolic impairment when upregulated in adipose tissue of mice. TST is a mitochondrial enzyme involved in the metabolism of cyanide, reactive oxygen species (ROS) and endogenous hydrogen sulfide (H2S). This thesis tested the hypothesis that TST maintains metabolic health in the face of dietary obesity. To do this, I investigated the adipose-tissue phenotypes and metabolic consequences of Tst gene deletion (Tst–/– mice) and of adipose tissue-specific overexpression of human TST (Ad-hTST mice) after exposure to high fat diet (HFD). After 20 weeks of HFD, Tst–/– mice exhibited impaired glucose tolerance despite unchanged adipose tissue inflammatory cell infiltration, protein carbonylation and unfolded protein response activation. However, levels of mRNA encoding mitochondrial antioxidant enzymes including superoxide dismutase 2 and peroxiredoxin 3 were lower in Tst–/– mice on HFD. Unexpectedly, chow-fed Tst-/- mice had lower body weight and fat mass than wild-type controls highlighting a potential effect of Tst on fat accumulation with age. A new mouse model with high expression of human TST genetically targeted to adipose tissue (Ad-hTST) was developed using the LoxP / Cre recombinase expression system, with a parent line expressing Cre under the control of the adiponectin promoter to confer adipose specificity. The Ad-hTST mice were found to gain a similar amount of weight and fat mass to control mice when exposed to 6 weeks of HFD. However, Ad-hTST mice had impaired glucose tolerance with no change in inflammatory cell infiltration, mRNA levels of antioxidant enzymes or unfolded protein response genes. Thus, unexpectedly, overexpression of human TST in adipose tissue of mice results in a detrimental metabolic phenotype. In vivo and in vitro experiments were conducted to test the hypothesis that TST protects against ROS accumulation. Paraquat was tested as an inducer of oxidative stress in vivo in wild-type, Tst-/- and Tst+/- mice. At the doses used (25mg/kg and under), mice became unwell and lost weight, with no increase in markers of oxidative stress in adipose or lung. The production of mitochondrial ROS in response to exogenous hydrogen peroxide (H2O2) exposure was increased in primary adipocytes from Tst-/- mice in vitro. However, primary hepatocytes showed reduced mitochondrial ROS production in response to H2O2 exposure. ROS production in hepatocytes was unaffected by pre-incubation with a H2S donor, an inhibitor of H2S-producing enzyme CSE or N-acetyl-cysteine, an antioxidant. TST may therefore influence mitochondrial ROS production differently in cell types such as adipocytes and hepatocytes. Disposal of exogenous H2O2 was unchanged in primary adipocytes from Tst-/- and Ad-hTST mice, and this was not affected by pre-incubation with sodium thiosulfate, a TST substrate. Metabolic changes in response to HFD may be influenced by alteration in TST expression, however the current data suggest it is unlikely to occur through the prevention of excessive local ROS accumulation in adipose tissue. Mice lacking the Tst gene globally and mice with adipose-specific overexpression of the human TST gene have a similarly impaired metabolic response to HFD. The phenotype of adipose-specific human TST-overexpressing mice does not recapitulate the protective metabolic phenotype produced by overexpression of the endogenous mouse Tst gene. In conclusion, TST may influence adipose tissue due to its role in the oxidation of H2S, however, by the current means, it does not appear to substantially impact the response of this tissue to oxidative stress.

O objetivo deste trabalho é a extração de Au, Ag, Cu e Zn a partir de dois tipos de lodos galvânicos utilizando um processo híbrido de sulfatação seletiva e lixiviação com tiossulfato de sódio e amônio. Nos experimentos realizados, o lodo galvânico foi misturado com um agente promotor de sulfato (enxofre, sulfato de ferro ou pirita) e foi tratado por processos pirometalúrgicos a temperaturas até 750◦C. Nesta fase, este agente sulfatante é oxidado térmicamente, transformando a atmosfera do forno e os óxidos metálicos em sulfatos solúveis em água. Depois disso, os sulfatos foram tratados por lixiviação com água para a recuperação de Ag, Cu, Ni e Zn. Como o ouro não forma sulfatos nesta reação, foi realizada uma segunda fase de lixiviação utilizando tiossulfato de sódio e de amônio, reagentes eficazes e menos prejudiciais ao ambiente do que o cianeto. Diferentes parâmetros foram analisados como qual agente promotor de sulfatação apresentou a maior recuperação de metais em solução, a proporção ótima lodo galvânico/ agente sulfatação, a temperatura de forno, o tempo de aquecimento no forno e o tempo de lixiviação. Além disso, uma comparação da recuperação de ouro com cianeto e tiossulfato de sódio e de amônio foi realizada. A configuração que demonstrou a melhor recuperação de metal em solução tinha uma proporção de 1: 0,4 de lodo galvânico/enxofre, uma temperatura de forno de 550◦C, um tempo de aquecimento de 90 minutos e um tempo de lixiviação em água de 15 minutos. Usando estes parâmetros, as taxas de recuperação de 75% de prata, 68% de cobre, 52% de Ni e 67% de Zn foram obtidas. A lixiviação de tiossulfato de sódio resultou em uma recuperação de 78% do Au, próximos aos valores obtidos utilizando cianeto. / The purpose of this work is the selective extraction of Au, Ag, Cu and Zn from two types of galvanic sludge using a mixed process of sulfate roasting and sodium thiosulfate and ammonium thiosulfate leaching. In the experiments, the sludge was mixed with a sulfate promoter (sulfur, iron sulfate or pyrite) and treated by pyrometallurgical processes at temperatures up to 750◦C. At this stage, this agent is thermally oxidized, turning the furnace atmosphere and the metallic oxides into water-soluble sulfates. Afterward, the sulfates can be treated by leaching with water for recovery of Ag, Cu, Ni and Zn. The gold does not form sulfates in this reaction and was recovered through a second leaching stage using sodium and ammonium thiosulfate, an effective reagent and less harmful to the environment than cyanide. Different parameters as the sulfate promoter that achieves the highest recovery of metals, the proportion of galvanic sludge to sulfating agent, the temperature, the heating time in the oven and the leaching time were evaluated. Additionally, a comparison of gold recovery using cyanide versus sodium and ammonium thiosulfate was performed. The configuration that showed the best metal recovery included a 1:0.4 ratio of sludge to sulfur, an oven temperature of 550◦C, a roasting time of 90 minutes and a water leaching time of 15 minutes. Using these parameters, recovery rates of 75 % of the silver, 68% of the copper, 52% of Ni and 67% of the Zn were obtained. The sodium thiosulfate leaching resulted in a recovery of 78% of the Au, close to the values obtained using cyanide.

Salmonella enterica is an important cause of food poisoning and is responsible for approximately a billion human infections each year. Disease manifestation in humans varies from severe systemic enteric (typhoid) fever to self-limiting gastroenteritis depending upon the infecting S. enterica serovar. S. Typhimurium is responsible for acute gastroenteritis in humans but causes a typhoid-like disease in mice and thus serves as an important model for studying the pathogenesis of systemic salmonellosis. Following ingestion, S. Typhimurium employs a variety of virulence mechanisms to survive within its host and establishes infection in the intestinal tract by invading the epithelial cells. Recent studies have revealed the importance of sulfur compounds in the intestine, such as tetrathionate and thiosulfate for the disease progression. S. Typhimurium is capable of utilising these sulfur compounds as terminal electron acceptors for its anaerobic respiration and thus gains a growth advantage over host microbiota during infection. However, the regulation of sulfur availability within S. Typhimurium and the mechanisms involved in mitigating cellular sulfide toxicity are not well-defined. During this study, we have identified the sstRA operon in S. Typhimurium encoding a deduced SmtB/ArsR family of transcriptional regulatory protein (SstR) and a deduced rhodanese-family sulfurtransferase (SstA) and demonstrated a role in mitigating the effects of cellular sulfide toxicity. SstR has been confirmed to act as a transcriptional repressor from the sstRA operator-promoter and the SstR-dependent repression is alleviated by low pH and sulfide stress (sodium thiosulfate), consistent with a role for SstR in sensing sulfide stress to trigger gene expression. Electrophoretic mobility shift assays confirm binding of purified SstR to the sstRA operator-promoter region. Furthermore, a conserved pair of cysteine residues within SstR was identified to be crucial for alleviating SstR-mediated repression, with the substitution of either cysteine causing constitutive repression. This is consistent with SstR inducer-responsiveness involving a thiol-based redox switch. Importantly, S. Typhimurium mutants lacking the sstRA operon have reduced tolerance to sulfide stress, consistent with the sstRA operon having a role in cellular sulfide detoxification. Work is continuing to further characterise the roles of sstR and sstA in S. Typhimurium on their contributions to infections.

O objetivo deste trabalho é a extração de Au, Ag, Cu e Zn a partir de dois tipos de lodos galvânicos utilizando um processo híbrido de sulfatação seletiva e lixiviação com tiossulfato de sódio e amônio. Nos experimentos realizados, o lodo galvânico foi misturado com um agente promotor de sulfato (enxofre, sulfato de ferro ou pirita) e foi tratado por processos pirometalúrgicos a temperaturas até 750◦C. Nesta fase, este agente sulfatante é oxidado térmicamente, transformando a atmosfera do forno e os óxidos metálicos em sulfatos solúveis em água. Depois disso, os sulfatos foram tratados por lixiviação com água para a recuperação de Ag, Cu, Ni e Zn. Como o ouro não forma sulfatos nesta reação, foi realizada uma segunda fase de lixiviação utilizando tiossulfato de sódio e de amônio, reagentes eficazes e menos prejudiciais ao ambiente do que o cianeto. Diferentes parâmetros foram analisados como qual agente promotor de sulfatação apresentou a maior recuperação de metais em solução, a proporção ótima lodo galvânico/ agente sulfatação, a temperatura de forno, o tempo de aquecimento no forno e o tempo de lixiviação. Além disso, uma comparação da recuperação de ouro com cianeto e tiossulfato de sódio e de amônio foi realizada. A configuração que demonstrou a melhor recuperação de metal em solução tinha uma proporção de 1: 0,4 de lodo galvânico/enxofre, uma temperatura de forno de 550◦C, um tempo de aquecimento de 90 minutos e um tempo de lixiviação em água de 15 minutos. Usando estes parâmetros, as taxas de recuperação de 75% de prata, 68% de cobre, 52% de Ni e 67% de Zn foram obtidas. A lixiviação de tiossulfato de sódio resultou em uma recuperação de 78% do Au, próximos aos valores obtidos utilizando cianeto. / The purpose of this work is the selective extraction of Au, Ag, Cu and Zn from two types of galvanic sludge using a mixed process of sulfate roasting and sodium thiosulfate and ammonium thiosulfate leaching. In the experiments, the sludge was mixed with a sulfate promoter (sulfur, iron sulfate or pyrite) and treated by pyrometallurgical processes at temperatures up to 750◦C. At this stage, this agent is thermally oxidized, turning the furnace atmosphere and the metallic oxides into water-soluble sulfates. Afterward, the sulfates can be treated by leaching with water for recovery of Ag, Cu, Ni and Zn. The gold does not form sulfates in this reaction and was recovered through a second leaching stage using sodium and ammonium thiosulfate, an effective reagent and less harmful to the environment than cyanide. Different parameters as the sulfate promoter that achieves the highest recovery of metals, the proportion of galvanic sludge to sulfating agent, the temperature, the heating time in the oven and the leaching time were evaluated. Additionally, a comparison of gold recovery using cyanide versus sodium and ammonium thiosulfate was performed. The configuration that showed the best metal recovery included a 1:0.4 ratio of sludge to sulfur, an oven temperature of 550◦C, a roasting time of 90 minutes and a water leaching time of 15 minutes. Using these parameters, recovery rates of 75 % of the silver, 68% of the copper, 52% of Ni and 67% of the Zn were obtained. The sodium thiosulfate leaching resulted in a recovery of 78% of the Au, close to the values obtained using cyanide.

O objetivo deste trabalho é a extração de Au, Ag, Cu e Zn a partir de dois tipos de lodos galvânicos utilizando um processo híbrido de sulfatação seletiva e lixiviação com tiossulfato de sódio e amônio. Nos experimentos realizados, o lodo galvânico foi misturado com um agente promotor de sulfato (enxofre, sulfato de ferro ou pirita) e foi tratado por processos pirometalúrgicos a temperaturas até 750◦C. Nesta fase, este agente sulfatante é oxidado térmicamente, transformando a atmosfera do forno e os óxidos metálicos em sulfatos solúveis em água. Depois disso, os sulfatos foram tratados por lixiviação com água para a recuperação de Ag, Cu, Ni e Zn. Como o ouro não forma sulfatos nesta reação, foi realizada uma segunda fase de lixiviação utilizando tiossulfato de sódio e de amônio, reagentes eficazes e menos prejudiciais ao ambiente do que o cianeto. Diferentes parâmetros foram analisados como qual agente promotor de sulfatação apresentou a maior recuperação de metais em solução, a proporção ótima lodo galvânico/ agente sulfatação, a temperatura de forno, o tempo de aquecimento no forno e o tempo de lixiviação. Além disso, uma comparação da recuperação de ouro com cianeto e tiossulfato de sódio e de amônio foi realizada. A configuração que demonstrou a melhor recuperação de metal em solução tinha uma proporção de 1: 0,4 de lodo galvânico/enxofre, uma temperatura de forno de 550◦C, um tempo de aquecimento de 90 minutos e um tempo de lixiviação em água de 15 minutos. Usando estes parâmetros, as taxas de recuperação de 75% de prata, 68% de cobre, 52% de Ni e 67% de Zn foram obtidas. A lixiviação de tiossulfato de sódio resultou em uma recuperação de 78% do Au, próximos aos valores obtidos utilizando cianeto. / The purpose of this work is the selective extraction of Au, Ag, Cu and Zn from two types of galvanic sludge using a mixed process of sulfate roasting and sodium thiosulfate and ammonium thiosulfate leaching. In the experiments, the sludge was mixed with a sulfate promoter (sulfur, iron sulfate or pyrite) and treated by pyrometallurgical processes at temperatures up to 750◦C. At this stage, this agent is thermally oxidized, turning the furnace atmosphere and the metallic oxides into water-soluble sulfates. Afterward, the sulfates can be treated by leaching with water for recovery of Ag, Cu, Ni and Zn. The gold does not form sulfates in this reaction and was recovered through a second leaching stage using sodium and ammonium thiosulfate, an effective reagent and less harmful to the environment than cyanide. Different parameters as the sulfate promoter that achieves the highest recovery of metals, the proportion of galvanic sludge to sulfating agent, the temperature, the heating time in the oven and the leaching time were evaluated. Additionally, a comparison of gold recovery using cyanide versus sodium and ammonium thiosulfate was performed. The configuration that showed the best metal recovery included a 1:0.4 ratio of sludge to sulfur, an oven temperature of 550◦C, a roasting time of 90 minutes and a water leaching time of 15 minutes. Using these parameters, recovery rates of 75 % of the silver, 68% of the copper, 52% of Ni and 67% of the Zn were obtained. The sodium thiosulfate leaching resulted in a recovery of 78% of the Au, close to the values obtained using cyanide.

No description available.