Gold recovery from cyanideand chloride solution using activated carbon

Uusia keinoja kullan erottamiseksi malmista on etsitty viimeaikoina taloudellisista ja ympäristöllisistä syistä kautta maailman. Syanidointimenetelmä on hallinnut kullan talteenottoayli sata vuotta. Menetelmässä kulta liuotetaan laimeaan syanidiliuokseen, jostase otetaan talteen aktiivihiilen avulla. Syanidin käyttöä pyritään kuitenkin vähentämään sen myrkyllisyyden takia. Lisäksi nykyään louhitaan enenemässä määrin malmia, josta on hankala rikastaa kulta kustannustehokkaasti syanidia käyttäen. Kullan talteenottoa syanidi- ja kloridiliuoksesta on selvitetty kirjallisuuden avulla. Kullan kemiaan liuotuksen aikana on perehdytty ennen kullan talteenottoa aktiivihiilellä. Aktiivihiilen elinkaari kullan adsorbenttinaon käsitelty valmistuksesta hylkäämiseen mukaan lukien hiilen myrkyttyminen prosessissa ja regenerointi. Aktiivi-hiilen käyttäytyminen syanidi- ja kloridiliuoksessa on selvitetty erikseen. Kullan talteenottoa kuparipitoisista malmeista on käsitelty. Kullan talteenottoa kloridiliuoksesta aktiivihiiltä käyttäen on tutkittu kokeellisesti. Pääasialliset tutkimuskohteet ovat adsorption kinetiikka, kuparin vaikutus adsorptioon, aktiivihiilen vaikutus adsorptioonja adsorboituneiden metallien strippaus hiilestä selektiivisesti. Hapettavan stippauksen vaikutus kullan desorptioon hiilestä on tutkittu yksityiskohtaisesti. Kullan erotusmenetelmät kuparimalmista aktiivihiiltä käyttäen on selvitetty diplomityön tulosten pohjalta. Diplomityön keskeisten tulosten perusteella kulta ei välttämättä saostu aktiivihiilen pinnalle kloridiliuoksesta. Havainto varmistettiin ladattujen hiilipartikkelien pyyhkäisyelektronimikroskooppikuvista ja partikkeleille tehdyistä mikroanalyyseistä. Kullan pelkistyminen metalliseksi kullaksi aktiivihiilessä voitaneen välttää käyttämällä erittäin hapettavia olosuhteita. Aktiivihiili ilmeisesti hapettuu näissä olosuhteissa, mikä mahdollistaa kultakloridin adsorboitumisen hiileen.

Gold investments and short- and long-run price determinants of the price of gold

Tämän tutkielman tavoitteena on tutkia tekijöitä jotkavaikuttavat lyhyellä ja pitkällä aikavälillä kullan hintaan. Toiseksi tutkielmassa selvitetään mitä eri sijoitusmahdollisuuksia löytyy kultaan sijoitettaessa. Aineistona käytetään kuukausitasoista dataa Yhdysvaltain ja maailman hintaindekseistä, Yhdysvaltain ja maailman inflaatiosta ja inflaation volatiliteetista, kullan beetasta, kullan lainahinnasta, luottoriskistä ja Yhdysvaltojen ja maailman valuuttakurssi indeksistä joulukuulta 1972 elokuulle 2006. Yhteisintegraatio regressiotekniikoita käytettiin muodostamaan malli jonka avullatutkittiin päätekijöitä jotka vaikuttavat kullan hintaan. Kirjallisuutta tutkimalla selvitettiin miten kultaan voidaan sijoittaa. Empiirisettulokset ovat yhteneväisiä edellisten tutkimusten kanssa. Tukea löytyi sille, että kulta on pitkän ajan suoja inflaatiota vastaan ja kulta ja Yhdysvaltojen inflaatio liikkuvat pitkällä aikavälillä yhdessä. Kullan hintaan vaikuttavat kuitenkin lyhyen ajan tekijät pitkän ajan tekijöitä enemmän. Kulta on myös sijoittajalle helppo sijoituskohde, koska se on hyvin saatavilla markkinoilla ja eri instrumentteja on lukuisia.

Modeling of Gold Cyanidation

The chemistry of gold dissolution in alkaline cyanide solution has continually received attention and new rate equations expressing the gold leaching are still developed. The effect of leaching parameters on gold gold cyanidation is studied in this work in order to optimize the leaching process. A gold leaching model, based on the well-known shrinking-core model, is presented in this work. It is proposed that the reaction takes place at the reacting particle surface which is continuously reduced as the reaction proceeds. The model parameters are estimated by comparing experimental data and simulations. The experimental data used in this work was obtained from Ling et al. (1996) and de Andrade Lima and Hodouin (2005). Two different rate equations, where the unreacted amount of gold is considered in one equation, are investigated. In this work, it is presented that the reaction at the surface is the rate controlling step since there is no internal diffusion limitation. The model considering the effect of non-reacting gold shows that the reaction orders are consistent with the experimental observations reported by Ling et al. (1996) and de Andrade Lima and Hodouin (2005). However, it should be noted that the model obtained in this work is based on assumptions of no side reactions, no solid-liquid mass transfer resistances and no effect from temperature.

Catalysis by gold for biomass transformations

The development of new technologies to supplement fossil resources has led to a growing interest in the utilization of alternative routes. Biomass is a rich renewable feedstock for producing fine chemicals, polymers, and a variety of commodities replacing petroleumderived chemicals. Transformation of biomass into diverse valuable chemicals is the key concept of a biorefinery. Catalytic conversion of biomass, which reduces the use of toxic chemicals is one of the important approaches to improve the profitability of biorefineries. Utilization of gold catalysts allows conducting reactions under environmentally-friendly conditions, with a high catalytic activity and selectivity. Gold-catalyzed valorization of several biomass-derived compounds as an alternative approach to the existing technologies was studied in this work. Isomerization of linoleic acid via double bond migration towards biologically active conjugated linoleic acid isomers (CLA) was investigated. The activity and selectivity of various gold catalysts towards cis-9,trans-11-CLA and trans-10,cis-12-CLA were investigated in a semi-batch reactor, showing that the yield of the desired products varied, depending on the catalyst support. The structure sensitivity in the selective oxidation of arabinose was demonstrated using a series of gold catalysts with different Au cluster sizes in a shaker reactor operating in a semibatch mode. The gas-phase selective oxidation of ethanol was studied and the influence of the catalyst support on the catalytic performance was investigated. The selective oxidation of the lignan hydroxymatairesinol (HMR), extracted from the Norway spruce (Picea abies) knots, to the lignan oxomatairesinol (oxoMAT) was extensively investigated. The influence of the reaction conditions and catalyst properties on the yield of oxoMAT was evaluated. In particular, the structure sensitivity of the reaction was demonstrated. The catalyst deactivation and regeneration procedures were studied. The reaction kinetics and mechanism were advanced.

62 gold 60 silver 63 bronze

kuv., 10 x 13 cm

62 gold 60 silber 63 bronze

kuv., 10 x 13 cm

Pretreatment processes in gold recovery by thiosulphate leaching

This thesis describes several different pretreatment processes for gold concentrates and ores. The thesis is divided to theoretical part and experimental part. The theoretical part presents the operating principle of the main pretreatment methods and their suitability for thiosulphate leaching. In the theoretical part also the whole recovery process for gold from ore to elemental gold is presented. In the experimental part the study is focused on pretreatment of sulphidic refractory concentrates with mechanical activation and chemical oxidation under alkaline environment; and their effect on leachability in the thiosulphate leaching. In the experimental part a combined 2-step process, where chemical oxidation under ammoniacal environment is cascaded with thiosulphate leaching in the same conditions, is also tested. The main sulphuric mineral components in the studied refractory concentrate are pyrite (49.4 %) and arsenopyrite (27.7 %). The gold content in the concentrate is 11.3 ppm and silver content is 90 ppm. Without pretreatment the gold conversion in thiosulphate leaching was 30 %, which was analyzed at the time point of 9 hours. At that time the silver conversion was 17 %. By using mechanical activation the gold conversion reached was 59 % and silver conversion 26 %. With chemical oxidation under alkaline environment, where the used chemical was sodium hydroxide, the reached conversion of gold was 72 % and 31 % for silver. In the combined oxidation and leaching experiment the conversion of gold remained at 49 % and 18 % for silver.

A new climatic periodisation of the Gold and Guinea Coasts in West Africa, 1750-1798 : a reconstruction of the climate during the slave trade era, including an analysis of the climatically facilitated Trans-Atlantic slave trade

Avsikten med studien är att producera den första rekonstruktionen av det västafrikanska klimatet mellan 1750 och 1798. Kunskapen om det västafrikanska klimatet före 1800-talet är till dags dato bristfällig, vilket gör det svårare att förstå framtida klimatvariationer. Det är bristen på instrumentell meteorologisk data (temperatur, regnmängd, och lufttryck), vilket i princip bara täcker det senaste århundradet, som är orsaken till att tidigare klimat är bristfälligt kartlagda. Klimatet och miljön är även sådana att proxydata från ’naturens arkiv’ (såsom t.ex. trädringar) har begränsad användning. Således är historiska dokument, främst från gästande kulturer/nationer/intressenter, innehållande deskriptiv information om vädret och klimatet, klimatforskarens viktigaste källa. Genom att använda tidigare, för det här syftet, oanvända källor påvisade den här undersökningen att klimatet i västra Afrika och Guldkusten (Ghana) har ändrats sedan 1700-talet. Monsunregnen var svagare och kortvarigare, speciellt den sekundära regnperioden under hösten var betydligt svagare än idag. Det förekom kraftiga årliga variationer i monsunregnen, men sett ur längre tidsperspektiv utmärktes torrare och blötare perioder. Studien kunde också visa en viss korrelation mellan det globala väderfenomenet El Niño och regnperiodens intensitet längs med kusten. Flera torrperioder sammanföll med tidigare registrerade El Niño sekvenser. Speciellt slutet av 1760-talet påverkades kraftigt av El Niño och även det globala klimatet verkar ha genomgått graftiga förändringar just dessa år. På basis av den nya klimatrekonstruktionen genomfördes också en jämförelse av klimatets inverkan på den transatlantiska slavhandeln från 1750 till 1798, en fråga som historikerna gjort anspelningar på i över 30 år. Utförseln av slavar från västra Afrika var som kraftigast under 1700-talets andra hälft. Analysen visade att slavhandeln delvis tilltog i samband med klimatanomalierna.

Modeling of high pressure pretreatment process for gold leaching

Investigation of high pressure pretreatment process for gold leaching is the objective of the present master's thesis. The gold ores and concentrates which cannot be easily treated by leaching process are called "refractory". These types of ores or concentrates often have high content of sulfur and arsenic that renders the precious metal inaccessible to the leaching agents. Since the refractory ores in gold manufacturing industry take a considerable share, the pressure oxidation method (autoclave method) is considered as one of the possible ways to overcome the related problems. Mathematical modeling is the main approach in this thesis which was used for investigation of high pressure oxidation process. For this task, available information from literature concerning this phenomenon, including chemistry, mass transfer and kinetics, reaction conditions, applied apparatus and application, was collected and studied. The modeling part includes investigation of pyrite oxidation kinetics in order to create a descriptive mathematical model. The following major steps are completed: creation of process model by using the available knowledge; estimation of unknown parameters and determination of goodness of the fit; study of the reliability of the model and its parameters.

Terpenoid transformations over gold catalysts

Nowadays biomass transformation has a great potential for the synthesis of value-added compounds with a wide range of applications. Terpenoids, extracted from biomass, are inexpensive and renewable raw materials which often have a biological activity and are widely used as important organic platform molecules in the development of new medicines as well as in the synthesis of fine chemicals and intermediates. At the same time, special attention is devoted to the application of gold catalysts to fine chemical synthesis due to their outstanding activity and/or selectivity for transformations of complex organic compounds. Conversion of renewable terpenoids in the presence of gold nanoparticles is one of the new and promising directions in the transformation of biomass to valuable chemicals. In the doctoral thesis, different kinds of natural terpenoids, such as α-pinene, myrtenol and carvone were selected as starting materials. Gold catalysts were utilized for the promising routes of these compounds transformation. Investigation of selective α-pinene isomerization to camphene, which is an important step in an industrial process towards the synthesis of camphor as well as other valuable substrates for the pharmaceutical industry, was performed. A high activity of heterogeneous gold catalysts in the Wagner-Meerwein rearrangement was demonstrated for the first time. Gold on alumina carrier was found to reach the α-pinene isomerization conversion up to 99.9% and the selectivity of 60-80%, thus making this catalyst very promising from an industrial viewpoint. A detailed investigation of kinetic regularities including catalyst deactivation during the reaction was performed. The one-pot terpene alcohol amination, which is a promising approach to the synthesis of valuable complex amines having specific physiological properties, was investigated. The general regularities of the one-pot natural myrtenol amination in the presence of gold catalysts as well as a correlation between catalytic activity, catalyst redox treatment and the support nature were obtained. Catalytic activity and product distribution were shown to be strongly dependent on the support properties, namely acidity and basicity. The gold-zirconia (Au/ZrO2) catalyst pretreated under oxidizing atmosphere was observed to be rather active, resulting in the total conversion of myrtenol and the selectivity to the corresponding amine of about 53%. The reaction kinetics was modelled based on the mechanistic considerations with the catalyst deactivation step incorporated in the mechanism. Carvone hydrogenation over a gold catalyst was studied with the general idea of investigating both the activity of gold catalysts in competitive hydrogenation of different functional groups and developing an approach to the synthesis of valuable carvone derivatives. Gold was found to promote stereo- and chemoselective carvone hydrogenation to dihydrocarvone with a predominant formation of the trans-isomer, which generally is a novel synthetic method for an industrially valuable dihydrocarvone. The solvent effect on the catalytic activity as well as on the ratio between trans- and cis-dihydrocarvone was evaluated.

Interdependence of International Stock Markets, European Government Bond Market and Gold Market

This thesis examines the interdependence of international stock markets (the USA, Europe, Japan, emerging markets, and frontier markets), European government bond market, and gold market during the 21st century. Special focus is on the dynamics of the correlations between the markets, as well as on, spillovers in mean returns and volatility. The mean return spillovers are examined on the basis of the bivariate VAR(1) model, whereas the bivariate BEKK-GARCH(1, 1) model is employed for the analysis of the volatility spillovers. In order to analyze the spillover effects in different market conditions, the full sample period from 2000 to 2013 is divided into the pre-crisis period (2000–2006) and the crisis period (2007–2013). The results indicate an increasing interdependence especially within international stock markets during the periods of financial turbulence, and are thus consistent with the existing literature. Hence, bond and gold markets provide the best diversification benefits for equity investors, particularly during the periods of market turmoil.

Sustainable Gold Mining- Life Cycle Assessment of Cyanidation and Thiosulphate Leaching

With the increasing concern of the sustainable approach of gold mining, thiosulphate has been researched as an alternative lixiviant to cyanide since cyanide is toxic to the environment. In order to investigate the possibility of thiosulphate leaching application in the coming future, life cycle assessment, is conducted to compare the environmental footprint of cyanidation and thiosulphate leaching. The result showed the most significant environmental impact of cyanidation is toxicity to human, while the ammonia of thiosulphate leaching is also a major concern of acidification. In addition, an ecosystem evaluation is also performed to indicate the potential damages caused by an example of cyanide spill at Kittilä mine, resulting in significant environmental risk cost that has to be taken into account for decision making. From the opinion collected from an online LinkedIn discussion forum, the anxiety of sustainability alone would not be enough to contribute a significant change of conventional cyanidation, until the tighten policy of cyanide use. International Cyanide Code, therefore, is crucial for safe gold production. Nevertheless, it is still thoughtful to consider the values of healthy ecosystem and the gold for long-term benefit.

Improvement of Energy Efficiency in a Gold Mining Industry: Case Study of a Russian Gold Mining Company

The issue of energy efficiency is attracting more and more attention of academia, business and policy makers worldwide due to increasing environmental concerns, depletion of non-renewable energy resources and unstable energy prices. The significant importance of energy efficiency within gold mining industry is justified by considerable energy intensity of this industry as well as by the high share of energy costs in the total operational costs. In the context of increasing industrial energy consumption energy efficiency improvement may provide significant energy savings and reduction of CO2 emission that is highly important in order to contribute to the global goal of sustainability. The purpose of this research is to identify the ways of energy efficiency improvement relevant for a gold mining company. The study implements single holistic case study research strategy focused on a Russian gold mining company. The research involves comprehensive analysis of company’s energy performance including analysis of energy efficiency and energy management practices. This study provides following theoretical and managerial contributions. Firstly, it proposes a methodology for comparative analysis of energy performance of Russian and foreign gold mining companies. Secondly, this study provides comprehensive analysis of main energy efficiency challenges relevant for a Russian gold mining company. Finally, in order to overcome identified challenges this research conceives a guidance for a gold mining company for implementation of energy management system based on the ISO standard.