Sorption of metal ions to wood, pulp and bark materials

Ett huvudmål med denna avhandling var att erhålla ny information om växelverkan mellan metalljoner i vattenfas och träbaserade material såsom olika pappersmassor, ved och bark. Material av gran, tall och björk har studerats. En ny känslig kolonnkromatografisk metod utvecklades för bestämning av affinitetsordningar för 17 olika metalljoner. Av dessa bands trevärt järn och de mycket toxiska tungmetallerna bly, koppar och kadmium starkast till de studerade materialen. Växelverkan i dessa tvåfas system sker som jonbyte, huvudsakligen via komplexbildning av metalljoner till funktionella grupper i den fasta fasen. Vattenfasens pH är den viktigaste parametern som bestämmer totala halten av metalljoner som binds till materialen. Resultatet i denna avhandling kan delvis betraktas som grundforskning. En ny kunskap om metalljoners förekomst och kemiska reaktioner i dessa system är även av stor ekonomisk och ekologisk, betydelse, när man strävar till allt mera slutna system i moderna massafabriker. Avhandlingen visar också att trädbark har stor potential för biosorption av tungmetaller t.ex. från avfallsvatten. Trädbark har nästan lika stor bindningskapacitet som dyra syntetiska jonbytare.

The role of metal ions in selective and sustainable processes

Sustainability and recycling are core values in today’s industrial operations. New materials, products and processes need to be designed in such a way as to consume fewer of the diminishing resources we have available and to put as little strain on the environment as possible. An integral part of this is cleaning and recycling. New processes are to be designed to improve the efficiency in this aspect. Wastewater, including municipal wastewaters, is treated in several steps including chemical and mechanical cleaning of waters. Well-cleaned water can be recycled and reused. Clean water for everyone is one of the greatest challenges we are facing today. Ferric sulphate, made by oxidation from ferrous sulphate, is used in water purification. The oxidation of ferrous sulphate, FeSO4, to ferric sulphate in acidic aqueous solutions of H2SO4 over finely dispersed active carbon particles was studied in a vigorously stirred batch reactor. Molecular oxygen was used as the oxidation agent and several catalysts were screened: active carbon, active carbon impregnated with Pt, Rh, Pd and Ru. Both active carbon and noble metal-active carbon catalysts enhanced the oxidation rate considerably. The order of the noble metals according to the effect was: Pt >> Rh > Pd, Ru. By the use of catalysts, the production capacities of existing oxidation units can be considerably increased. Good coagulants have a high charge on a long polymer chain effectively capturing dirty particles of the opposite charge. Analysis of the reaction product indicated that it is possible to obtain polymeric iron-based products with good coagulation properties. Systematic kinetic experiments were carried out at the temperature and pressure ranges of 60B100°C and 4B10 bar, respectively. The results revealed that both non-catalytic and catalytic oxidation of Fe2+ to Fe3+ take place simultaneously. The experimental data were fitted to rate equations, which were based on a plausible reaction mechanism: adsorption of dissolved oxygen on active carbon, electron transfer from Fe2+ ions to adsorbed oxygen and formation of surface hydroxyls. A comparison of the Fe2+ concentrations predicted by the kinetic model with the experimentally observed concentrations indicated that the mechanistic rate equations were able to describe the intrinsic oxidation kinetics of Fe2+ over active carbon and active carbon-noble metal catalysts. Engineering aspects were closely considered and effort was directed to utilizing existing equipment in the production of the new coagulant. Ferrous sulphate can be catalytically oxidized to produce a novel long-chained polymeric iron-based flocculent in an easy and affordable way in existing facilities. The results can be used for modelling the reactors and for scale-up. Ferric iron (Fe3+) was successfully applied for the dissolution of sphalerite. Sphalerite contains indium, gallium and germanium, among others, and the application can promote their recovery. The understanding of the reduction process of ferric to ferrous iron can be used to develop further the understanding of the dissolution mechanisms and oxidation of ferrous sulphate. Indium, gallium and germanium face an ever-increasing demand in the electronics industry, among others. The supply is, however, very limited. The fact that most part of the material is obtained through secondary production means that real production quota depends on the primary material production. This also sets the pricing. The primary production material is in most cases zinc and aluminium. Recycling of scrap material and the utilization of industrial waste, containing indium, gallium and geranium, is a necessity without real options. As a part of this study plausible methods for the recovery of indium, gallium and germanium have been studied. The results were encouraging and provided information about the precipitation of these valuables from highly acidic solutions. Indium and gallium were separated from acidic sulphuric acid solutions by precipitation with basic sulphates such as alunite or they were precipitated as basic sulphates of their own as galliunite and indiunite. Germanium may precipitate as a basic sulphate of a mixed composition. The precipitation is rapid and the selectivity is good. When the solutions contain both indium and gallium then the results show that gallium should be separated before indium to achieve a better selectivity. Germanium was separated from highly acidic sulphuric acid solutions containing other metals as well by precipitating with tannic acid. This is a highly selective method. According to the study other commonly found metals in the solution do not affect germanium precipitation. The reduction of ferric iron to ferrous, the precipitation of indium, gallium and germanium, and the dissolution of the raw materials are strongly depending on temperature and pH. The temperature and pH effect were studied and which contributed to the understanding and design of the different process steps. Increased temperature and reduced pH improve the reduction rate. Finally, the gained understanding in the studied areas can be employed to develop better industrial processes not only on a large scale but also increasingly on a smaller scale. The small amounts of indium, gallium and germanium may favour smaller and more locally bound recovery.

Pohjakuonan käsittelyn ja hyötykäytön toimintamallin muodostaminen Kotkan Energia Oy:n jätteenpolttolaitokselle

Tavoitteena tässä diplomityössä oli selvittää Kotkan Energia Oy:n jätteenpolttolaitoksen toiminnassa syntyvän pohjakuonan hyötykäyttömahdollisuuksia ja kustannuksiltaan järkevin tapa käsitellä pohjakuona. Tarkasteltavia vaihtoehtoja hyötykäytön osalta olivat erilaiset maarakennustyöt sekä kaatopaikkojen peittäminen. Hyötykäyttövaihtoehdoille vaihtoehtoisena ratkaisuna tutkittiin kaatopaikkasijoituksen kannattavuutta. Pohjakuonan käyttöä maarakentamisessa, jätetäyttöjen peitemaina sekä pohjakuonan loppusijoitusta kaatopaikoille säätelee lainsäädäntö. Valtioneuvoston asetuksessa kaatopaikoista on määritelty loppusijoitettaville jakeille liukoisuus raja-arvot, joiden mukaisesti jätteet sijoitetaan joko pysyvän jätteen, tavanomaisen jätteen tai ongelmajätteen kaatopaikoille. Jätetäyttöjen peitemateriaalina käytettävän jakeen on myös täytettävä kyseisen kaatopaikkaluokan liukoisuusraja-arvot. Maarakennusasetus antaa puolestaan liukoisuus- ja pitoisuusraja-arvot maarakennuksessa hyödynnettäville jakeille. Pohjakuonan hyötykäyttö vaatii kuitenkin aina ympäristöluvan. Hyötyvoimalan pohjakuonasta tehtyjen analyysien perusteella voidaan todeta, että käsiteltyä pohjakuonaa olisi mahdollista käyttää esimerkiksi kenttien ja kaatopaikkojen pohjarakenteissa sekä kaatopaikoilla jätetäyttöjen peitemaina. Pohjakuonan hyödyntäminen kaukolämpötöiden maarakennuksessa vaatii vielä lisätutkimuksia putkien korroosioriskin osalta. Diplomityön tuloksena kehitettiin toimintamalli, jonka avulla Kotkan Energia Oy:n on mahdollista säästää kuonan käsittelyn ja hyötykäytön kustannuksissa. Kustannuksiltaan parhaaksi vaihtoehdoksi osoittautui kuonan käsittely omalla biopolttoaineiden välivarastolla sekä käsitellyn pohjakuonan hyödyntäminen välivaraston pohjarakenteissa. 

Artificial Ribonucleases: Oligonucleotides Conjugated with Metal Ion Chelates of Azacrowns

Ribonucleic acid (RNA) has many biological roles in cells: it takes part in coding, decoding, regulating and expressing of the genes as well as has the capacity to work as a catalyst in numerous biological reactions. These qualities make RNA an interesting object of various studies. Development of useful tools with which to investigate RNA is a prerequisite for more advanced research in the field. One of such tools may be the artificial ribonucleases, which are oligonucleotide conjugates that sequence-selectively cleave complementary RNA targets. This thesis is aimed at developing new efficient metal-ion-based artificial ribonucleases. On one hand, to solve the challenges related to solid-supported synthesis of metal-ion-binding conjugates of oligonucleotides, and on the other hand, to quantify their ability to cleave various oligoribonucleotide targets in a pre-designed sequence selective manner. In this study several artificial ribonucleases based on cleaving capability of metal ion chelated azacrown moiety were designed and synthesized successfully. The most efficient ribonucleases were the ones with two azacrowns close to the 3´- end of the oligonucleotide strand. Different transition metal ions were introduced into the azacrown moiety and among them, the Zn2+ ion was found to be better than Cu2+ and Ni2+ ions.

Metal-Ion-Binding Oligonucleotides: High-Affinity Probes for Nucleic Acid Sequences

Small non-coding RNAs have numerous biological functions in cell and are divided into different classes such as: microRNA, snoRNA, snRNA and siRNA. MicroRNA (miRNA) is the most studied non-coding RNA to date and is found in plants, animals and some viruses. miRNA with short sequences is involved in suppressing translation of target genes by binding to their mRNA post-transcriptionally and silencing it. Their function besides silencing of the viral gene, can be oncogenic and therefore the cause of cancer. Hence, their roles are highlighted in human diseases, which increases the interest in using them as biomarkers and drug targets. One of the major problems to overcome is recognition of miRNA. Owing to a stable hairpin structure, chain invasion by conventional Watson-Crick base-pairing is difficult. One way to enhance the hybridization is exploitation of metal-ion mediated base-pairing, i. e. oligonucleotide probes that tightly bind a metal ions and are able to form a coordinative bonds between modified and natural nucleobases. This kind of metallo basepairs containing short modified oligonucleotides can also be useful for recognition of other RNA sequences containing hairpin-like structural motives, such as the TAR sequence of HIV. In addition, metal-ion-binding oligonucleotides will undoubtedly find applications in DNA-based nanotechnology. In this study, the 3,5-dimethylpyrazol-1-yl substituted purine derivatives were successfully incorporated within oligonucleotides, into either a terminal or non-terminal position. Among all of the modified oligonucleotides studied, a 2-(3,5-dimethylpyrazol-1-yl)-6-oxopurine base containing oligonucleotide was observed to bind most efficiently to their unmodified complementary sequences in the presence of both Cu2+ or Zn2+. The oligonucleotide incorporating 2,6-bis(3,5-dimethylpyrazol-1-yl)purine base also markedly increased the stability of duplexes in the presence of Cu2+ without losing the selectivity.

Pyridyyliryhmän sisältävien erotusmateriaalien ominaisuudet ja soveltaminen hydrometallurgiassa

Diplomityössä tutkittiin silikarunkoisen, pyridyyliryhmän sisältävän erotusmateriaalin kykyä erottaa selektiivisesti kuparia, nikkeliä, kobolttia ja kadmiumia sinkkisulfaattiliuoksista. Erotuskykyä verrattiin kolonnikokein toiseen kaupalliseen polystyreenidivinyylibentseenirunkoiseen (PS-DVB) erotusmate-riaaliin, jonka funktionaalinen ryhmä on samantyyppinen. Silikarunkoisen erotusmateriaalin happo-emäsominaisuuksia selvitettiin titrauksin. Metallien sitoutumisen kinetiikkaa ja eluointia verrattiin PS-DVB-runkoisen erotus-materiaalin kirjallisuudessa esitettyihin tuloksiin. Lisäksi määritettiin kummankin erotusmateriaalin partikkelikokojakaumat. Silikarunkoisen materiaalin havaittiin turpoavan noin 4 % muutettaessa se vapaastaemäsmuodosta happomuotoon. Turpoaminen oli huomattavasti vähäisempää kuin PS-DVB-runkoisella materiaalilla. Silikarunkoisen erotus-materiaalin titrauksen tuloksena voitiin todeta, että se oli heikosti emäksinen. Titrauskäyrä muistutti PS-DVB-runkoisen erotusmateriaalin titrauskäyrää, vaikka erotusmateriaalien protonoitumisalueet olivat hieman erilaiset. Tämä johtuu siitä, että silikarunkoisen materiaalin funktionaaliset ryhmät poikkeavat rakenteeltaan hieman PS-DVB-runkoisesta materiaalista. Tasapainokokeet osoittivat, että silikarunkoinen erotusmateriaali adsorboi tutkituista metalleista eniten kuparia ja nikkeliä ja vähiten sinkkiä. Kaikkien tutkittujen metallien eluointi silikarunkoisesta erotusmateriaalista onnistui rikkihapolla toisin kuin PS-DVB-runkoisesta erotusmateriaalista, jonka regenerointiin tarvitaan rikkihappoa tai ammoniumhydroksidia riippuen siitä, mitä metalleja siihen on ladattu.

Wet Oxidation of Concentrated Wastewaters: Process Combination and Reaction Kinetic Modeling

The accumulation of aqueous pollutants is becoming a global problem. The search for suitable methods and/or combinations of water treatment processes is a task that can slow down and stop the process of water pollution. In this work, the method of wet oxidation was considered as an appropriate technique for the elimination of the impurities present in paper mill process waters. It has been shown that, when combined with traditional wastewater treatment processes, wet oxidation offers many advantages. The combination of coagulation and wet oxidation offers a new opportunity for the improvement of the quality of wastewater designated for discharge or recycling. First of all, the utilization of coagulated sludge via wet oxidation provides a conditioning process for the sludge, i.e. dewatering, which is rather difficult to carry out with untreated waste. Secondly, Fe2(SO4)3, which is employed earlier as a coagulant, transforms the conventional wet oxidation process into a catalytic one. The use of coagulation as the post-treatment for wet oxidation can offer the possibility of the brown hue that usually accompanies the partial oxidation to be reduced. As a result, the supernatant is less colored and also contains a rather low amount of Fe ions to beconsidered for recycling inside mills. The thickened part that consists of metal ions is then recycled back to the wet oxidation system. It was also observed that wet oxidation is favorable for the degradation of pitch substances (LWEs) and lignin that are present in the process waters of paper mills. Rather low operating temperatures are needed for wet oxidation in order to destruct LWEs. The oxidation in the alkaline media provides not only the faster elimination of pitch and lignin but also significantly improves the biodegradable characteristics of wastewater that contains lignin and pitch substances. During the course of the kinetic studies, a model, which can predict the enhancements of the biodegradability of wastewater, was elaborated. The model includes lumped concentrations suchas the chemical oxygen demand and biochemical oxygen demand and reflects a generalized reaction network of oxidative transformations. Later developments incorporated a new lump, the immediately available biochemical oxygen demand, which increased the fidelity of the predictions made by the model. Since changes in biodegradability occur simultaneously with the destruction of LWEs, an attempt was made to combine these two facts for modeling purposes.

Biohajoavat kompleksinmuodostajat mekaanisen massan peroksidivalkaisussa

Mekaanisen massan peroksidivalkaisussa on perinteisesti käytetty kahta kompleksinmuodostajaa, jotka ovat dietyleenitriamiinipentaetikkahappo (DTPA) ja etyleenidiamiinipentaetikkahappo (EDTA). Kompleksinmuodostajat saavat aikaan hyvän kelatointituloksen muodostamalla valkaisulle haitallisten metalli-ionien kanssa kompleksin ja estäen näin metalli-ionien valkaisutulosta huonontavan vaikutuksen. Perinteiset kompleksinmuodostajat DTPA ja EDTA eivät kuitenkaan ole biohajoavia ja niiden epäillään irrottavan metalleja vesistöjen sedimenteistä. Työssä selvitettiin kolmen eri biohajoavan kompleksinmuodostajan valkaisuteho verrattuna perinteisiin kompleksinmuodostajiin. Laboratoriossa suoritetut pesukokeet osoittivat, että mikään biohajoava kompleksinmuodostaja ei saavuttanut samaa pesutehoa kuin perinteiset kompleksinmuodostajat. Valkaisukokeet kuitenkin osoittivat, että biohajoava kompleksinmuodostaja ISA pääsi hyvin lähelle perinteisten kompleksinmuodostajien valkaisutuloksia suoritettaessa valkaisu siten, että massa esipestään kompleksinmuodostajalla ja sen jälkeen valkaistaan vakiokemikaaliannoksella alkalina ollessa natriumhydroksidi. Kaksi muuta biohajoavaa kompleksinmuodostajaa, ISA+EDDS ja HAS, eivät saavuttaneet samaa tasoa. HAS toimi kyllä stabilaattorina, muttei pystynyt nostamaan massan vaaleutta.

The Role of Surfactant Properties of Extractants in Hydrometallurgical LiquidLiquid Extraction Processes

The amphiphilic nature of metal extractants causes the formation of micelles and other microscopic aggregates when in contact with water and an organic diluent. These phenomena and their effects on metal extraction were studied using carboxylic acid (Versatic 10) and organophosphorus acid (Cyanex 272) based extractants. Special emphasis was laid on the study of phase behaviour in a pre neutralisation stage when the extractant is transformed to a sodium or ammonium salt form. The pre neutralised extractants were used to extract nickel and to separate cobalt and nickel. Phase diagrams corresponding to the pre neutralisation stage in a metal extraction process were determined. The maximal solubilisation of the components in the system water(NH3)/extractant/isooctane takes place when the molar ratio between the ammonia salt form and the free form of the extractant is 0.5 for the carboxylic acid and 1 for the organophosphorus acid extractant. These values correspond to the complex stoichiometry of NH4A•HA and NIi4A, respectively. When such a solution is contacted with water a microemulsion is formed. If the aqueous phase contains also metal ions (e.g. Ni²+), complexation will take place on the microscopic interface of the micellar aggregates. Experimental evidence showing that the initial stage of nickel extraction with pre neutralised Versatic 10 is a fast pseudohomogeneous reaction was obtained. About 90% of the metal were extracted in the first 15 s after the initial contact. For nickel extraction with pre neutralised Versatic 10 it was found that the highest metal loading and the lowest residual ammonia and water contents in the organic phase are achieved when the feeds are balanced so that the stoichiometry is 2NH4+(org) = Nit2+(aq). In the case of Co/Ni separation using pre neutralised Cyanex 272 the highest separation is achieved when the Co/extractant molar ratio in the feeds is 1 : 4 and at the same time the optimal degree of neutralisation of the Cyanex 272 is about 50%. The adsorption of the extractants on solid surfaces may cause accumulation of solid fine particles at the interface between the aqueous and organic phases in metal extraction processes. Copper extraction processes are known to suffer of this problem. Experiments were carried out using model silica and mica particles. It was found that high copper loading, aromacity of the diluent, modification agents and the presence of aqueous phase decrease the adsorption of the hydroxyoxime on silica surfaces.

EDTA- and DTPA-functionalized silica gel and chitosan adsorbents for the removal of heavy metals from aqueous solutions

Adsorbents functionalized with chelating agents are effective in removal of heavy metals from aqueous solutions. Important properties of such adsorbents are high binding affinity as well as regenerability. In this study, aminopolycarboxylic acid, EDTA and DTPA, were immobilized on the surface of silica gel, chitosan, and their hybrid materials to achieve chelating adsorbents for heavy metals such as Co(II), Ni(II), Cd(II), and Pb(II). New knowledge about the adsorption properties of EDTA- and DTPA-functionalizedadsorbents was obtained. Experimental work showed the effectiveness, regenerability, and stability of the studied adsorbents. Both advantages and disadvantages of the adsorbents were evaluated. For example, the EDTA-functionalized chitosan-silica hybrid materials combined the benefits of the silica gel and chitosan while at the same time diminishing their observed drawbacks. Modeling of adsorption kinetics and isotherms is an important step in design process. Therefore, several kinetic and isotherm models were introduced and applied in this work. Important aspects such as effect of error function, data range, initial guess values, and linearization were discussed and investigated. The selection of the most suitable model was conducted by comparing the experimental and simulated data as well as evaluating the correspondence between the theory behind the model and properties of the adsorbent. In addition, modeling of two-component data was conducted using various extended isotherms. Modeling results for both one- and twocomponent systems supported each other. Finally, application testing of EDTA- and DTPA-functionalized adsorbents was conducted. The most important result was the applicability of DTPA-functionalized silica gel and chitosan in the capturing of Co(II) from its aqueous EDTA-chelate. Moreover, these adsorbents were efficient in various solution matrices. In addition, separation of Ni(II) from Co(II) and Ni(II) and Pb(II) from Co(II) and Cd(II) was observed in two- and multimetal systems. Lastly, prior to their analysis, EDTA- and DTPA-functionalized silica gels were successfully used to preconcentrate metal ions from both pure and salty waters

Recovery and refining of manganese as by-product from hydrometallurgical processes

The consumption of manganese is increasing, but huge amounts of manganese still end up in waste in hydrometallurgical processes. The recovery of manganese from multi-metal solutions at low concentrations may not be economical. In addition, poor iron control typically prevents the production of high purity manganese. Separation of iron from manganese can be done with chemical precipitation or solvent extraction methods. Combined carbonate precipitation with air oxidation is a feasible method to separate iron and manganese due to the fast kinetics, good controllability and economical reagents. In addition the leaching of manganese carbonate is easier and less acid consuming than that of hydroxide or sulfide precipitates. Selective iron removal with great efficiency from MnSO4 solution is achieved by combined oxygen or air oxidation and CaCO3 precipitation at pH > 5.8 and at a redox potential of > 200 mV. In order to avoid gypsum formation, soda ash should be used instead of limestone. In such case, however, extra attention needs to be paid on the reagents mole ratios in order to avoid manganese coprecipitation. After iron removal, pure MnSO4 solution was obtained by solvent extraction using organophosphorus reagents, di-(2-ethylhexyl)phosphoric acid (D2EHPA) and bis(2,4,4- trimethylpentyl)phosphinic acid (CYANEX 272). The Mn/Ca and Mn/Mg selectivities can be increased by decreasing the temperature from the commonly used temperatures (40 –60oC) to 5oC. The extraction order of D2EHPA (Ca before Mn) at low temperature remains unchanged but the lowering of temperature causes an increase in viscosity and slower phase separation. Of these regents, CYANEX 272 is selective for Mn over Ca and, therefore, it would be the better choice if there is Ca present in solution. A three-stage Mn extraction followed by a two-stage scrubbing and two-stage sulfuric acid stripping is an effective method of producing a very pure MnSO4 intermediate solution for further processing. From the intermediate MnSO4 some special Mn- products for ion exchange applications were synthesized and studied. Three types of octahedrally coordinated manganese oxide materials as an alternative final product for manganese were chosen for synthesis: layer structured Nabirnessite, tunnel structured Mg-todorokite and K-kryptomelane. As an alternative source of pure MnSO4 intermediate, kryptomelane was synthesized by using a synthetic hydrometallurgical tailings. The results show that the studied OMS materials adsorb selectively Cu, Ni, Cd and K in the presence of Ca and Mg. It was also found that the exchange rates were reasonably high due to the small particle dimensions. Materials are stable in the studied conditions and their maximum Cu uptake capacity was 1.3 mmol/g. Competitive uptake of metals and acid was studied using equilibrium, batch kinetic and fixed-bed measurements. The experimental data was correlated with a dynamic model, which also accounts for the dissolution of the framework manganese. Manganese oxide micro-crystals were also bound onto silica to prepare a composite material having a particle size large enough to be used in column separation experiments. The MnOx/SiO2 ratio was found to affect significantly the properties of the composite. The higher the ratio, the lower is the specific surface area, the pore volume and the pore size. On the other hand, higher amount of silica binder gives composites better mechanical properties. Birnesite and todorokite can be aggregated successfully with colloidal silica at pH 4 and with MnO2/SiO2 weight ratio of 0.7. The best gelation and drying temperature was 110oC and sufficiently strong composites were obtained by additional heat-treatment at 250oC for 2 h. The results show that silica–supported MnO2 materials can be utilized to separate copper from nickel and cadmium. The behavior of the composites can be explained reasonably well with the presented model and the parameters estimated from the data of the unsupported oxides. The metal uptake capacities of the prepared materials were quite small. For example, the final copper loading was 0.14 mmol/gMnO2. According to the results the special MnO2 materials are potential for a specific environmental application to uptake harmful metal ions.

Electrocoagulation in the treatment of industrial waters and wastewaters

Chemical coagulation is commonly used in raw water and wastewater treatment plants for the destabilisation of pollutants so that they can be removed in the subsequent separation processes. The most commonly used coagulation chemicals are aluminium and iron metal salts. Electrocoagulation technology has also been proposed for the treatment of raw waters and wastewaters. With this technology, metal cations are produced on the electrodes via electrolysis and these cations form various hydroxides in the water depending on the water pH. In addition to this main reaction, several side reactions, such as hydrogen bubble formation and the reduction of metals on cathodes, also take place in the cell. In this research, the applications of electrocoagulation were investigated in raw water treatment and wastewater applications. The surface water used in this research contained high concentrations of natural organic matter (NOM). The effect of the main parameters – current density, initial pH, electric charge per volume, temperature and electrolysis cell construction – on NOM removal were investigated. In the wastewater treatment studies, the removal of malodorous sulphides and toxic compounds from the wastewaters and debarking effluents were studied. Also, the main parameters of the treatment, such as initial pH and current density, were investigated. Aluminium electrodes were selected for the raw water treatment, whereas wastewaters and debarking effluent were treated with iron electrodes. According to results of this study, aluminium is more suitable electrode material for electrocoagulation applications because it produces Al(III) species. Metal ions and hydroxides produced by iron electrodes are less effective in the destabilisation of pollutants because iron electrodes produce more soluble and less charged Fe(II) species. However, Fe(II) can be effective in some special applications, such as sulphide removal. The resulting metal concentration is the main parameter affecting destabilisation of pollutants. Current density, treatment time, temperature and electrolysis cell construction affect the dissolution of electrodes and hence also the removal of pollutants. However, it seems that these parameters have minimal significance in the destabilization of the pollutants besides this effect (in the studied range of parameters). Initial pH and final pH have an effect on the dissolution of electrodes, but they also define what aluminium or iron species are formed in the solution and have an effect on the ζ-potential of all charged species in the solution. According to the results of this study, destabilisation mechanisms of pollutants by electrocoagulation and chemical coagulation are similar. Optimum DOC removal and low residual aluminium can be obtained simultaneously with electrocoagulation, which may be a significant benefit of electrocoagulation in surface water treatment compared to chemical coagulation. Surface water treatment with electrocoagulation can produce high quality water, which could be used as potable water or fresh water for industrial applications. In wastewater treatment applications, electrocoagulation can be used to precipitate malodorous sulphides to prevent their release into air. Technology seems to be able to remove some toxic pollutants from wastewater and could be used as pretreatment prior to treatment at a biological wastewater treatment plant. However, a thorough economic and ecological comparison of chemical coagulation and electrocoagulation is recommended, because these methods seem to be similar in pollutant destabilisation mechanisms, metal consumption and removal efficiency in most applications.

Electroactive ion exchange membranes based on conducting polymers

Ion exchange membranes are indispensable for the separation of ionic species. They can discriminate between anions and cations depending on the type of fixed ionic group present in the membrane. These conventional ion exchange membranes (CIX) have exceptional ionic conductivity, which is advantageous in various electromembrane separation processes such as electrodialysis, electrodeionisation and electrochemical ion exchange. The main disadvantage of CIX membranes is their high electrical resistance owing to the fact that the membranes are electronically non conductive. An alternative can be electroactive ion exchange membranes, which are ionically and electronically conducting. Polypyrrole (PPy) is a type of electroactive ion exchange material as well as a commonly known conducting polymer. When PPy membranes are repeatedly reduced and oxidised, ions are pumped through the membrane. The main aim of this thesis was to develop electroactive cation transport membranes based on PPy for the selective transport of divalent cations. Membranes developed composed of PPy films deposited on commercially available support materials. To carry out this study, cation exchange membranes based on PPy doped with immobile anions were prepared. Two types of dopant anions known to interact with divalent metal ions were considered, namely 4-sulphonic calix[6]arene (C6S) and carboxylated multiwalled carbon nanotubes (CNT). The transport of ions across membranes containing PPy doped with polystyrene sulphonate (PSS) and PPy doped with para-toluene sulphonate (pTS) was also studied in order to understand the nature of ion transport and permeability across PPy(CNT) and PPy(C6S) membranes. In the course of these studies, membrane characterisation was performed using electrochemical quartz crystal microbalance (EQCM) and scanning electron microscopy (SEM). Permeability of the membranes towards divalent cations was explored using a two compartment transport cell. EQCM results demonstrated that the ion exchange behaviour of polypyrrole is dependent on a number of factors including the type of dopant anion present, the type of ions present in the surrounding medium, the scan rate used during the experiment and the previous history of the polymer film. The morphology of PPy films was found to change when the dopant anion was varied and even when the thickness of the film was altered in some cases. In nearly all cases the permeability of the membranes towards metal ions followed the order K+ > Ca2+ > Mn2+. The one exception was PPy(C6S), for which the permeability followed the order Ca2+ ≥ K+ > Mn2+ > Co2+ > Cr3+. The above permeability sequences show a strong dependence on the size of the metal ions with metal ions having the smallest hydrated radii exhibiting the highest flux. Another factor that affected the permeability towards metal ions was the thickness of the PPy films. Films with the least thickness showed higher metal ion fluxes. Electrochemical control over ion transport across PPy(CNT) membrane was obtained when films composed of the latter were deposited on track-etched Nucleopore® membranes as support material. In contrast, the flux of ions across the same film was concentration gradient dependent when the polymer was deposited on polyvinylidene difluoride membranes as support material. However, electrochemical control over metal ion transport was achieved with a bilayer type of PPy film consisting of PPy(pTS)/PPy(CNT), irrespective of the type of support material. In the course of studying macroscopic charge balance during transport experiments performed using a two compartment transport cell, it was observed that PPy films were non-permselective. A clear correlation between the change in pH in the receiving solution and the ions transported across the membrane was observed. A decrease in solution pH was detected when the polymer membrane acted primarily as an anion exchanger, while an increase in pH occurred when it functioned as a cation exchanger. When there was an approximately equal flux of anions and cations across the polymer membrane, the pH in the receiving solution was in the range 6 - 8. These observations suggest that macroscopic charge balance during the transport of cations and anions across polypyrrole membranes was maintained by introduction of anions (OH-) and cations (H+) produced via electrolysis of water.

Arvometallien liuospuhdistus jatkuvatoimisella ioninvaihdolla

Työn tarkoituksena oli tutkia arvometalleja sisältävän liuoksen puhdistamista jat-kuvatoimisella ioninvaihdolla. Teoriaosassa käsitellään ioninvaihdon periaate, sekä jatkuvatoimisen ioninvaihdon laiteratkaisuja ristivirta- ja vastavirtasysteemeissä. Lopuksi esitellään Simuloidun liikkuvapedin (SMB) virtausnopeuksien laske-miseksi käytettävä kolmiomenetelmä. Kokeellisen osan tarkoituksena on demonstroida laboratorioon rakennetun jatku-vatoimisen ioninvaihtimen, Simuloidun liikkuvapedin, käyttö arvometallia sisäl-tävän liuoksen puhdistamiseksi kahdenarvoisista metalli-ioneista. Kokeissa käy-tettiin hopeaa sisältävää NaCl-liuosta, josta pyrittiin puhdistamaan Mg2+, Ca2+, Pb2+ ja Zn2+-ionit ekstraktina. Laitteistolla suoritettiin kolme ajoa, joista kaksi edusti vastavirtasysteemiä ja yksi ristivirtasysteemiä. Ensimmäisessä vastavirta-ajossa sekä ekstrakti että raffinaattin erottuva hopealiuos tulivat puhtaina. Toisessa vastavirta-ajossa pyrittiin parantamaan tuottavuutta nostamalla syötön virtausnopeutta, jolloin raffinaatin puhtaus kärsi Pb2+ ja Mg2+-ionien kulkeutuessa liuosfaasin mukana raffinaattiin. Ristivirta-ajossa vain yksi kolmesta raffinaatista saavutti 100 % puhtauden. Kokeet osoittivat, että Mg2+, Ca2+, Pb2+ ja Zn2+-ionien erottaminen hopeaionista on mahdollista käyttämällämme SMB-laitteistolla. Tuottavuuden parantaminen syötön virtausnopeutta nostamalla kuitenkin heikentää puhtautta. Cross-flow-systeemin erilleenkytkettyjen kolonnien ansioista painehäviö on pienempi, mikä mahdollistaa korkeammat virtausnopeudet, mikäli ei vaadita 100 % puhtautta.

Metallien eluointi kelatoivasta ioninvaihtimesta

Kelatoivat ioninvaihtimet ovat yleensä makrohuokoisia hartseja, joiden avulla metalleja poistetaan ja otetaan mahdollisesti talteen teollisuuden puhdistettavista jätevirroista. Ne muodostavat metalli-ionien kanssa komplekseja runkomateriaaliin kovalenttisesti liitettyjen aktiivisten funktionaalisten ryhmiensä välityksellä. Ioninvaihtimen selektiivisyys eri metalli-ioneja kohtaan vaihtelee riippuen siihen liitetystä kelatoivasta ryhmästä. Työssä tutkitaan metallien tarttumista kelatoiviin ioninvaihtimiin, sekä niiden eluoitumista adsorbentistaan. Kelatoivat ioninvaihtimet sitovat metalli-ioneja tehokkaasti ligandiensa monihampaisuudesta johtuen. Metallien tarttuminen kelatoivaan ioninvaihtimeen ei kuitenkaan ole yksiselitteistä, vaan siihen vaikuttaa muun muassa pH yhdessä monen muun tekijän kanssa. Ioninvaihtimien selektiivisyyttä tarkastellaan työssä lähinnä kovien ja pehmeiden happojen ja emästen HSAB -teorian näkökulmasta. Regeneroinnilla ioninvaihdin saadaan jälleen alkuperäiseen muotoonsa, minkä jälkeen se voidaan käyttää uudelleen. Yleensä regenerointi suoritetaan kemiallisesti. Tässä työssä ioninvaihtimien regenerointia ja kohdemetallin eluointia tarkastellaan paitsi teoriassa, myös kokeellisessa osuudessa. Kokeellisessa osuudessa tutkitaan kuparin (Cu2+) eluoitumista kelatoivasta Dowex M-4195 kationinvaihtohartsista. Kokeissa hartsi ladattiin kuparilla erillisessä panoksessa kuparin ollessa syöttöliuoksessa kuparisulfaattina. Eluointiliuoksina käytettiin 2 ja 5 molaarista rikkihappoa, sekä 2 molaarista ammoniumhydroksidia. Eluointi suoritettiin panostoimisena kolonniajona ja eluaatista otetut näytteet analysoitiin atomiadsorptiospektrofotometrillä. Analyysitulokset esitetään läpäisykäyrinä, joiden perusteella 2M ammoniumhydroksidi on kolmesta tutkitusta eluentista tehokkain eluoimaan kuparia Dowex M-4195 hartsista.