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Abstract Zinc is a common metal, and has a central role in the production of galvanised bulk products, battery applications and fertilisers. Its production relies mainly on the leaching of zinc minerals with sulfuric acid, followed by purification and electrowinning. In this thesis an internally consistent thermodynamic model for the industrially important ZnSO₄-H₂SO₄-H₂O system was developed. Model parameters were optimised using available literature data and new experimental freezing point and density data determined in this work. With Gibbs energy minimisation algorithms embedded in commercial software, such as ChemSheet and FactSage, the developed model can be used to calculate easily phase equilibria and thermodynamic properties of aqueous zinc sulfate solutions and solid zinc sulfate phases, including activity coefficients, enthalpy changes, heat capacities, densities and solubilities, in a wide range of temperature, pressure and sulfuric acid concentrations. Solution non-ideality was treated with the original Pitzer model with electrostatic mixing terms included. Applicability of thermodynamic approach and the developed model was demonstrated by two separate case studies on the hydrometallurgical zinc process. Precipitation of amorphous silica during hot acid leach was studied experimentally. Its solubility in the process solution was also successfully predicted using the thermodynamic approach. To study crystallisation of gypsum during the gypsum precipitation stage, the model was expanded by addition of the Ca²⁺ ion. The model calculations showed good agreement with the experienced Ca²⁺ levels. The results of this thesis have found immediate use in understanding the various stages of the electrolytic zinc process. The obtained results also form a basis on which new, more advanced tools for managing and studying the process can be developed. / Tiivistelmä Sinkki on yleinen metalli, ja sillä on keskeinen rooli sinkittyjen terästuotteiden, paristojen ja jopa lannoitteiden valmistuksessa. Sen tuotanto perustuu sinkkipitoisten mineraalien rikkihappoliuotukseen, muodostuneen prossessiliuoksen puhdistukseen ja lopulta metallisen sinkin elektrolyysitalteenottoon. Tässä työssä kehitettiin termodynaaminen malli teollisesti tärkeälle ZnSO₄-H₂SO₄-H₂O -systeemille. Malliparametrit määritettiin kirjallisuudessa esitetyistä tuloksista ja tässä työssä tehdyistä uusista jäätymispiste- ja tiheysmittauksista. Käyttämällä kaupallisia Gibbsin energian minimointialgoritmiin perustuvia ohjelmistoja, kuten ChemSheet tai FactSage, tässä työssä kehitetyllä mallilla voidaan helposti kuvata sinkkisulfaattipitoisten vesiliuosten faasitasapainoja ja laskea systeemin termodynaamisia ominaisuuksia. Malliin sisällytettyihin ominaisuuksiin kuuluvat systeemin komponenttien aktiivisuudet, entalpiamuutokset, lämpökapasiteetit sekä tiheydet laajalla lämpötila-, paine- ja rikkihapon pitoisuusalueella. Liuoksen epäideaalisuutta kuvattiin Pitzerin ioniaktiivisuusmallilla. Työssä sinkkisulfaattiliuoksille kehitettyä mallia testattiin kahdessa sinkintuotannon kannalta keskeisessä tapaustutkimuksessa. Amorfisen piidioksidin saostumista vahvahappoliuotuksen aikana tutkittiin kokeellisesti ja laskennallisesti. Amorfisen piidioksidin liukoisuus prosessiliuokseen ennustettiin onnistuneesti. Kipsinpoistoprosessin tutkimusta varten mallia laajennettiin lisäämällä siihen Ca²⁺-ioni. Mallilla laskettiin kipsin liukoisuus prosessiliuokseen. Saadut tulokset vastasivat hyvin käytännössä havaittuja arvoja. Tutkimuksen tuloksia on suoraan hyödynnetty sinkintuotantoprosessin ymmärtämisessä. Ne myös mahdollistavat jatkossa edistyneempien työkalujen kehittämisen niin prosessin hallintaan kuin tutkimukseenkin.

Ever since it was identified as a speleogenetic process in the Guadalupe Mountains of New Mexico, USA, hypogene speleogenesis has become the focus of numerous research projects aimed at discerning between classical epigene caves and sulfuric acid or thermal caves. The first distinguishing characteristics that were recognized for hypogene caves were passage and cave morphology. The following step was the identification of rare minerals, specific for processes associated to hypogene speleogenesis. One other important step was the recognition of the importance of stable isotopes - mainly of S - in tracing the source of S and the chemical processes affecting it. Many of the caves now labeled as hypogene are fossil caves, in which presently the hypogene activity has long died off. Studies comparing stable isotopes from coexisting cave minerals and the waters that generate the cave are rarer. This extensive study encompasses a description of cave and passage morphologies, cave mineral assemblages, as well as hydrogeochemistry of thermomineral waters in a peculiar region of Romania. Băile Herculane (Cerna River Valley, SW Romania) is a spa town known since Roman times for its numerous thermal springs that were considered to have healing powers. These springs, along with wells drilled in the past century, are still being used for curative purposes in several treatment centers in Băile Herculane. The present study is important not only for the scientific data it produced, but also for economic purposes, as mixing of the thermomineral waters with meteoric sources is a major concern, due to the dilution it causes. The data presented here is based on multiple investigation methods, each specific to the analyzed material: powder X-ray diffractions, scanning electron microscope, electron microprobe (for mineral samples), sedimentological investigations (for cave sediments), stable isotope mass spectrometry (for water and mineral samples), field measurements (for water samples). The results presented here help to clarify the source of dissolved S species in the thermomineral water, the source of the water itself, as well as establish a connection between caves along the Cerna Valley and the thermomineral aquifers.

Sulphuric acid obtained as a byproduct of non-ferrous metal ore smelting is often the mandatory result of stringent environmental policies adopted in the industrialized countries to limit sulphur dioxide emissions. For the primary copper industry in the southwestern U.S., improvement of sulphuric acid marketing and distribution economies is a critical factor. In this thesis, through a comparison of the European and U.S. sulphuric acid market structure and organization, both the opportunity and the implications of adopting European acid marketing practices are discussed. A more centralized system of acid distribution, as in the European model, if applied to the U.S. smelter acid market, proves to be potentially beneficial for net revenue enhancement. A rationalization of the logistic aspects could substantially reduce acid transportation costs, allow repayment of at least average variable costs of production and improve southwestern smelter acid competitiveness in the domestic markets.

Epoxides have been recently identified as one of the intermediate species in the gas phase oxidation of alkenes. This study investigates the reaction of isoprene oxide and alpha-pinene oxide with sulfuric acid to identify the potential of epoxides as important secondary organic aerosol (SOA) precursors. The reaction was explored using different methods to understand the factors governing the reaction rate and the types of products formed under different conditions. Uptake experiments of epoxides on sulfuric acid using Ion drift-Chemical Ionization Mass Spectrometry (ID-CIMS) showed an irreversible uptake of epoxides at room temperature resulting in the formation of less volatile products like diols, organosulfates and acetals. However, at lower temperatures, dehydration of diols and some rearrangement was the preferred reaction pathway resulting in the formation of higher volatility compounds like hydroxy-alkenes and aldehydes. The uptake coefficients of isoprene oxide and alpha-pinene oxide at room temperature using 96% wt acid were found to be 4x10^-2 and 0.8x10^-2, respectively. Spectroscopic study using Attenuated total reflection-Fourier transform infrared technique (ATR-FTIR) revealed that for both the epoxides, diols were the major identifiable products at low acid concentrations. At higher acid concentrations, acetal formation was observed in case of isoprene oxide, while organosulfate formation was seen for alpha-pinene oxide. No products were identified under neutral conditions due to slow reaction. Bulk studies using Nuclear Magnetic Resonance (NMR) spectroscopy conducted at low acid concentrations showed the presence of 1,2- and 1,4-diols as the major products for isoprene oxide, similar to the results from the ATR-FTIR experiments. Additionally, aldehyde formation was also observed. For alpha-pinene oxide, organosulfate formation was observed in all NMR experiments, unlike ATR-FTIR results, where organosulfate formation was observed only at high acid concentrations. These observations can be attributed to the kinetic isotope effect (KIE) due to use of D2SO4/D2O in NMR experiments rather than H2SO4/H2O. The percent yield of organosulfate products was proportional to the amount of available acidic sulfate. The results from this study suggest that acid hydrolysis of epoxides can result in the formation of a wide range of products under different conditions, that can contribute to SOA growth. It proves that epoxides can be efficient SOA precursors for ambient conditions prevailing in an urban atmosphere.

No description available.

Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed Feb. 27, 2008). Vita. Includes bibliographical references.

Thesis (Ph.D.) -- McMaster University, 1999. / Includes bibliographical references (leaves 220-228). Also available via World Wide Web.

Inaugural-Dissertation zur Erlangung der Doktorwürde einer hohen naturwissenschaftlich-mathematischen Fakultät der Ruprecht-Karls-Universität zu Heidelberg.

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