Ammonia regeneration in nickel matte chloride leaching

Ammonia can be used as a pH controller in chloride-based metal recovery processes. In chloride conditions, ammonia reacts to ammonium chloride which can be regenerated back to ammonia with lime. Although the regeneration process itself has been known for a long time, the concentrations, non-reacting species, conditions, and even goals are different when comparing the ammonia regeneration process in different industries. The main objective of this thesis was to study the phenomena, equipment, and challenges in ammonia regeneration in the nickel process and to make a preliminary process design. The study concentrated on the regeneration and recovery units. The thesis was made by process simulation and laboratory tests using the current processes as initial information. The results were combined from all of the information obtained during the studies to provide a total process solution, which can be used as a basis when designing an ammonia regeneration process to be used in industry. In particular, it was possible to determine ammonia recovery with a stripping column and the achievement of the desired ammonia water product within the scope of this thesis. The required mass flows and process conditions were also determined. The possible challenges and solutions or further studies to overcome them were provided as well to ease the prediction and design of the ammonia regeneration process in the future. On the basis of the results of this thesis, the ammonia regeneration process can be developed further and implemented in the nickel chloride leaching process.

Hydrometallurgical process modeling using advanced mathematical tools

Hydrometallurgical process modeling is the main objective of this Master’s thesis work. Three different leaching processes namely, high pressure pyrite oxidation, direct oxidation zinc concentrate (sphalerite) leaching and gold chloride leaching using rotating disc electrode (RDE) are modeled and simulated using gPROMS process simulation program in order to evaluate its model building capabilities. The leaching mechanism in each case is described in terms of a shrinking core model. The mathematical modeling carried out included process model development based on available literature, estimation of reaction kinetic parameters and assessment of the model reliability by checking the goodness fit and checking the cross correlation between the estimated parameters through the use of correlation matrices. The estimated parameter values in each case were compared with those obtained using the Modest simulation program. Further, based on the estimated reaction kinetic parameters, reactor simulation and modeling for direct oxidation zinc concentrate (sphalerite) leaching is carried out in Aspen Plus V8.6. The zinc leaching autoclave is based on Cominco reactor configuration and is modeled as a series of continuous stirred reactors (CSTRs). The sphalerite conversion is calculated and a sensitivity analysis is carried out so to determine the optimum reactor operation temperature and optimum oxygen mass flow rate. In this way, the implementation of reaction kinetic models into the process flowsheet simulation environment has been demonstrated.

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.

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.

Kullan uutto kloridiliuoksista

Työssä tutkittiin kullan neste-nesteuuttoa kloridiliuoksista kirjallisuustutkimuksen ja laboratoriokokeiden avulla. Uuttoreagenssina käytettiin Outotecin kehittämää kullanuuttoreagenssia. Teoreettisessa osassa tarkastellaan kullan käyttäytymistä happamissa vesiliuoksissa, jotka sisältävät kloridia ja bromidia. Lisäksi työssä käsitellään kultakloridiyhdisteiden käyttöturvallisuutta. Teollisuudessa vuonna 2012 käytettäviä neste-nesteuuttoon perustuvia kullan talteenottomenetelmiä esitellään lyhyesti. Kirjallisuusosassa käsitellään myös joidenkin teollisesti käytettävien polymeeristen rakennemateriaalien ominaisuuksia. Kokeellisessa osassa määritettiin kullanuuttoreagenssin fysikaalisia ominaisuuksia, kuten sen tiheys, viskositeetti, liukoisuus veteen sekä faasien selkeytyminen uuttoprosessissa. Tuloksista havaittiin, että eri modifiointiaineet vaikuttavat huomattavasti kullanuuttoliuoksen fysikaalisiin ominaisuuksiin. Kullan uuttoa tutkittiin pienen mittakaavan laboratoriokokein käyttämällä synteettisiä kultaa sisältäviä lähtöliuoksia. Kokeissa tutkittiin lähtöliuoksen happopitoisuuden ja bromidipitoisuuden, sekä uuttoreagenssin modifiointiaineiden vaikutuksia kullan uuttotasapainoon. Lisäksi tutkittiin joidenkin epäpuhtausmetallien myötäuuttautumista. Materiaalitutkimuksissa tarkasteltiin kullanuuttoreagenssin ja autenttisen kullan halidiliuoksen vaikutuksia polymeerimateriaaleihin pitkäaikaisessa kontaktissa. Uuttoliuosten havaittiin aiheuttavan turpoamaa sekä pinnan pehmenemistä joissakin teollisissa muoveissa.

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.

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.

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.

The leaching of nutrients from ash- and PK-fertilised peat

Tiivistelmä: ravinteiden huuhtoutuminen tuhka- ja PK-lannoitetusta turpeesta

Timing incorporation of different green manure crops to minimize the risk of nitrogen leaching

Selostus: Viherlannoituskasvuston kynnön viivyttäminen vähentää typen huuhtoutumista

Effects of sodium sulphate and potassium chloride fertilizers on the nutritive value of timothy grown on different soils

Selostus: Natrium- ja kaliumlannoituksen vaikutus timotein ravintoarvoon

Undersowing Italian ryegrass diminishes nitrogen leaching from spring barley

Selostus: Italian raiheinä aluskasvina vähentää typen huuhtoutumista ohranviljelyssä

Chlormequat chloride and ethephon affect growth and yield formation of conventional, naked and dwarf oat

Selostus: Kasvunsääteiden vaikutukset tavanomaisen, paljasjyväisen ja kääpiökauran kasvuun ja sadonmuodostukseen

Seasonal dry deposition and canopy leaching of base cations in a subtropical evergreen mixed forest, China

Abstract