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Author:Aaltonen, Mari
Title:The Dissolution Kinetics of Sphalerite Concentrates
Sphaleriittirikasteiden liukenemiskinetiikka
Publication type:Licentiate thesis
Publication year:2005
Pages:viii + 70 s. + liitt. 15      Language:   eng
Department/School:Kemian tekniikan osasto
Main subject:Fysikaalinen kemia   (Kem-31)
Supervisor:Kontturi, Kyösti
Instructor:Taskinen, Pekka
Electronic version URL: http://urn.fi/urn:nbn:fi:tkk-009853
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark TKK  4793   | Archive
Abstract (eng):In the literature part of the thesis, an overview of the mechanisms and kinetics of oxidative sphalerite dissolution was given.
The factors affecting the rate of dissolution and some methods of study were briefly described.

In the experimental part various methods were used.
In batch dissolution experiments with manganese dioxide and ferric ions as the oxidising species, it was found that MnO2 affects the dissolution of a sphalerite concentrate by two mechanisms: by directly oxidising the sulphur in the mineral and by regenerating the active ferric species.
The results also suggested further oxidation of the elemental sulphur layer by the manganese species.

The dissolution behaviour of two sphalerite concentrates was studied by batch dissolution experiments using ferric ions as the oxidant.
Fractions with particle sizes of < 37 µm and > 37 µm were used.
The measurement parameters were chosen to match those in industrial scale dissolution.
The average zinc conversions for the fractions were from 45 to 74 mass percent after 3 hours dissolution.
The conversions were strongly effected by the size fraction of the concentrate, temperature and the concentration of iron in the solution.
The effects of the sulphuric acid and zinc concentrations were on average negligible.
As expected, the concentrate fraction with the largest surface area per gram had the highest conversion and the conversions decreased with decreasing surface area.
The average conversion divided by the surface area of the concentrate was 15 m-% higher for the concentrate with a higher concentration of iron in the lattice.

A rotating ring disc electrode was constructed, in which a pressed concentrate pellet was used as the disc.
The Fe2+ ions formed by the dissolution of ZnS in the disc were detected on the platinum ring by oxidising them back to the ferric form.
The measured current was used to determine the rate of dissolution.
The method is fast and thus can be used for rapid comparison of the dissolution characteristics of different concentrate fractions under varying conditions.
In addition, the method allows for the effects of kinetics and transport processes on the current to be separated, allowing a closer study of the factors affecting the kinetics of the reaction.
Theoretical calculations of the rate of mass transfer showed, that kinetics are rate limiting under these conditions.
Increasing the mass transport in the solution will not increase the rate of the dissolution process; the conditions have to be made more favourable for faster kinetics.

A mineral-carbon paste electrode was constructed by mixing sphalerite concentrate with fine carbon powder and oil.
Cyclic voltammetric measurements showed the carbon-oil paste electrode to be inert under the conditions used.
The voltammetric and potentiostatic measurements conducted on the modified mineral electrode showed the effect of the electrode potential on the rate of dissolution.
The oxidation of the sulphide began above 0.8 V vs.
Ag/AgCl and the rate was increased with increasing potential until a maximum was reached at 1.2 V vs.
Ag/AgCl.
Abstract (fin):Työn kirjallisuusosassa annetaan yleiskuva sphaleriitin hapettavan liuotuksen mekanismeista ja kinetiikasta.
Liukenemisen nopeuteen vaikuttavat tekijät sekä joitain tutkimuksessa käytettäviä menetelmiä esitellään lyhyesti.

Työn kokeellisessa osassa käytettiin useita tutkimusmenetelmiä.
Suoraliuotuskokeissa, joissa käytettiin mangaanidioksidia sekä ferri-ioneita hapettajina, todettiin MnO2:n vaikuttavan sphaleriittirikasteen liukenemiseen kahdella tavalla: se suoraan liuottaa sulfidimineraalia sekä regeneroi hapettavaa ferri-ionia.
Tulokset myös viittaavat siihen, että mangaanidioksidi hapettaa partikkelien pinnalle muodostavaa elementääririkkikerrosta.

Kahden rikasteen liukenemiskinetiikkaa tutkittiin suoraliuotuskokeissa, joissa käytettiin ferrirautaa hapettimena rikkihappoliuoksissa.
Rikasteet oli jaettu fraktioihin < 37 µm ja > 37 µm ja koeolosuhteet oli valittu vastaamaan teollista tuotantoa.
Rikastefraktioiden keskimääriset sinkkikonversiot kolmen tunnin liuotuksen jälkeen olivat 45:stä 74:än massaprosenttiin.
Rikasteen kokofraktio sekä liuoksen lämpötila ja ferrirautapitoisuus vaikuttivat voimakkaasti konversioihin.
Hapon konsentraatiolla ja sinkkippitoisuudella ei ollut huomattavaa vaikutusta.
Odotetusti konversio oli suurinta rikastefraktiolla, jolla oli suurin ominaispinta-ala ja konversiot laskivat pienenevän pinta-alan mukaisesti.
Konversiot olivat keskimäärin 15 massaprosenttia korkeampia sillä rikasteella, jonka hilassa oli enemmän rautaa, kun keskimääräiset konversiot jaettiin rikasteiden ominaispinta-aloilla.

Tutkimusta varten tehtiin pyörivä rengas-levy-elektrodi, jossa käytettiin levyelektrodina rikasteesta puristettua nappia.
Ferrorauta, jota syntyi kun ferrirauta hapetti rikastetta, detektoitiin platinaisella rengaselektrodilla hapettamalla se takaisin ferrimuotoon.
Rengaselektrodin virran avulla määritettiin liuekenemisnopeus.
Menetelmä on nopea ja sopii rikasteiden liukenemisominaisuuksien vertailuun eri olosuhteissa.
Lisäksi menetelmän avulla saadaan erotettua aineensiirron ja kinetiikan vaikutukset, jolloin voidaan tarkemmin tutkia reaktiokinetiikkaan vaikuttavia tekijöitä.
Teoreettiset aineensiirtolaskut osoittivat, että kinetiikka on reaktionopeutta rajoittava vaihe.
Parantamalla aineensiirtoa liuoksessa ei voida nopeuttaa liukenemista, vaan olosuhteita tulee muuttaa kineettisten vaiheen nopeuttaiseksi.

Mineraali-hiilipastaelektrodi tehtiin sekoittamalla sphaleriittirikastetta hienon hiilijauheen ja öljyn kanssa.
Mitatut sykliset voltamogrammit osoittavat, että hiili-öljypastaelektrodi oli inertti käytetyissä olosuhteissa.
Modifioidulla mineraalielektrodilla tehdyillä voltametrisillä ja potentiostaattisilla mittauksilla tutkittiin potentiaalin vaikutusta liukenemisnopeuteen.
Sulfidin liukeneminen alkoi 0,8 V:n (vs.
Ag/AgCl) potentiaalissa ja reaktionopeus kasvoi potentiaalin noustessa 1,2 volttiin (vs.
Ag/AgCl) saakka.
ED:2005-12-13
INSSI record number: 34641
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