Geopolymer matrix for the inertization of gold mine tailings

The mining industry produces a huge amount of solid waste materials during mining’s lifetime. Solid mine tailings typically contain many sulfide minerals and heavy metals. These fine-grained residues are usually deposited in impounding lakes near mining sites. Sulfides are oxidized in contact with water, which decreases the surrounding pH, and metal oxides are leached into the environment. This leachability causes short- and long-term environmental problems, such as contamination of surface and ground water. There is increasing interest in discovering new methods to manage mine tailings more effectively in the future. This interest is mainly focused on developing low-cost treatment or confinement processes. The possibility of immobilizing several heavy metals from gold mine tailings by reactive geopolymerization technique has been investigated in the present study. The chemical stability of geopolymers synthesized by the alkali activation of metakaolin and blast furnace slag with the addition of 40 to 50 wt% gold mine tailings is demonstrated. The geopolymers were cured at room temperature, and the effects of different Si/Al and Na/Al molar ratios and curing times were investigated. The inertization effectiveness was evaluated by means of leaching tests carried out according to standard EN 12457 after 7 and 28 days and after 18 months. The samples were immersed into the water for 1 day, and the leachable metals in the test solution were determined by ICP-OES. Please click Additional Files below to see the full abstract

Utilization of sulphidic mine tailings in alkali-activated materials

Disposal of mine tailings is one of the most important environmental issues during the mining lifetime. Especially sulphidic tailings can cause environmental and ecological risks because of their tendency to oxidize in the presence of water or air. Because of small particle size and harmful chemical properties, utilization possibilities of sulphidic mine tailings are limited. The aim of the present study was to develop technologies to utilize sulphidic mine tailings in alkali activated materials. Alkali-activated materials also known as geopolymers are nanosized zeolite type or slightly amorphous materials comparable to traditional Portland cement concrete, which can physically encapsulate or chemically stabilize the hazardous elements such as heavy metals into the 3D structure. Mine tailing based geopolymer aggregates were successfully produced from sulphidic mine tailings with good physical properties. The geopolymer aggregates performed as a concrete aggregate comparable to commercial lightweight aggregates. In addition, geopolymer mortars were prepared from mine tailings. In mortar application, there is a need to add some co-binder such as blast furnace slag in order to achieve high strength for the material. The mine tailing based geopolymer structure has an ability to stabilize a large number of cationic species into the structure while some anionic species were not able to immobilize by alkaline activation

Perustajaurakointi pientalotuotannossa

Perustajaurakoinnilla tarkoitetaan prosessia, jossa perustajaurakoitsija perustaa asunto- tai kiinteistöyhtiön, rakentaa sille rakennuksia ja markkinoi ja myy niiden hallintaan oikeuttavat osakkeet eteenpäin. Perustajaurakointi on suomalainen tapa toteuttaa rakentamista ja se sisältää useita eri asioita ja vaiheita sekä käytännön että juridiikan näkökulmasta. Tämän opinnäytetyön tavoitteena oli laatia kuvaus perustajaurakoinnin prosessista pientalotuotannossa. Tavoitteena oli käsitellä perustajaurakoinnin eri vaiheita ja soveltaa sitten hankittuja tietoja käytäntöön. Tavoitteena oli muodostaa selkeä ja looginen työ, jota työn toimeksiantaja Kiventerä Oy voisi tulevaisuudessa hyödyntää siirtyessään liiketoiminnassaan perustajaurakointiin. Aluksi käytiin läpi perustajaurakoinnin eri vaiheita ja niihin liittyviä lakeja sekä määräyksiä. Tämän jälkeen hankittuja tietoja sovellettiin käytäntöön malliyhtiön avulla. Opinnäytetyössä valittiin malliyhtiölle tontti ja tehtiin luonnokset rakennettavista asunnoista. Työmaalle laadittiin myös alustava yleisaikataulu. Perustettavalle asunto-osakeyhtiölle aadittiin malliyhtiöjärjestys sekä taloussuunnitelma. Opinnäytetyön perusteella onnistunut perustajaurakointiprosessi koostuu seuraavista neljästä vaiheesta: tarveselvitys, toimet ennen rakentamisen aloitusta, rakennusvaihe ja luovutusvaihe. Kannattava ja laadukas lopputulos edellyttää onnistumista jokaisessa edellä mainitussa vaiheessa.Founder contracting is a contracting process where the building company es-tablishes a housing cooperative, construct the buildings and market and sell the shares. This is a Finnish way to create new residences, offices or other build-ings. It is a complicated process in practical point of view and it is regulated by the law. The aim of this thesis was to describe the different steps of the founder con-tracting process. First, the different steps have been clarified in theory and then the new knowledge has been adapted in practice. The house building company Kiventerä Oy ordered this thesis because the company will start founder con-tracting in the future. This thesis is supposed to be a clear and logical starting material for this purpose. Founder contracting includes many different steps including laws and specifica-tions, which have been reported in the theoretical part. In practice a model company was established, property was chosen and the blueprints was made. A draft of the timetable was produced for the project. The details of the articles of association and economic plan for the model company was also made. According to the results of this thesis there are four different steps, which guar-antee high quality of the founder contracting process: the necessity report, the actions before starting the construction project, the main construction process and the actions after that. In addition, the profitability of the founder contracting is based on those four different steps

Stabilization of sulphidic mine tailings by different treatment methods:heavy metals and sulphate immobilization

Abstract Millions of tons of mine tailings are generated worldwide annually. Since many valuable metals such as Ag, Cu, Pb, Zn, Au and Ni are usually incorporated into sulphidic minerals, a large proportion of the tailings generated contain high amounts of sulphates and heavy metals. Some of these tailings are used as paste backfill material at mining sites, but large amounts are still being deposited into the tailings dams under water coverage. Sulphidic minerals are stable underground but after mining of the ore and several processing steps these minerals can be oxidized when they come into contact with water and air. This oxidation generates acid and thus reduces the pH of the surrounding environment. Furthermore, the heavy metals present in the mine tailings can be leached into the environment. This phenomenon, called Acid Mine Drainage (AMD), is one of the most critical environmental issues related to the management of sulphidic-rich tailings. Since AMD generation can still occur hundreds of years after closure of the mine, the mine tailings need stable, sustainable and economically viable management methods in order to prevent AMD production in the long term. The aim of this PhD thesis was to study various solidification/stabilization (S/S) methods for the immobilization of sulphidic mine tailings. The main focus was to develop a suitable chemical environment for achieving effective heavy metal (mainly arsenic) and sulphate immobilization while simultaneously ensuring good mechanical properties. Three treatment methods were tested: alkali activation, stabilization using hydrated lime (Ca(OH)2) and blast furnace slag (GBFS), and calcium sulphoaluminate-belite (CSAB) cement stabilization. The mine tailings used in this study contained large amounts of sulphates and heavy metals such as Cr, Cu, Ni, Mn, Zn, V and As. The leaching of arsenic and sulphates from powdered tailings exceeded the legal limits for regular and inert waste. All treatment methods were found to generate a hardened matrix that was suitable for use as a backfilling or construction material, but the calcium-based binding system was the most suitable for effective immobilization of all the heavy metals (including arsenic) and the sulphates. Precipitation in the form of calcium sulphates/calcium arsenate and the formation of ettringite are the main stabilization methods employed in calcium-based stabilization/solidification (S/S) systems. Some evidence of physical encapsulation occurring simultaneously with chemical stabilization was noted. These results can be exploited further to develop more sustainable mine tailing management systems for use in the future. The tailings could be stored in a dry landfill area instead of in tailing dams, and in this way a long-term decrease in AMD generation could be achieved, together with a high potential for recycling.Tiivistelmä Monet arvometallit kuten kulta, kupari ja nikkeli ovat sitoutuneena sulfidipitoisiin mineraaleihin. Louhittaessa ja rikastettaessa näitä sulfidimineraaleja syntyy miljoonia tonneja sulfidipitoisia rikastushiekkoja vuosittain. Rikastushiekat voivat sisältää myös runsaasti erilaisia raskasmetalleja. Osa rikastushiekoista hyödynnetään kaivostäytössä, mutta suurin osa rikastushiekoista läjitetään edelleen ympäristöön rikastushiekka-altaisiin veden alle. Kun sulfidipitoinen malmi kaivetaan ja käsitellään, sulfidiset mineraalit hapettuvat ollessaan kosketuksissa veden ja hapen kanssa. Hapettuessaan ne muodostavat rikkihappoa, laskien ympäristön pH:ta jolloin useimmat raskasmetallit liukenevat ympäristöön. Muodostuvia happamia kaivosvesiä voi syntyä vielä pitkään kaivoksen sulkemisen jälkeen ja ovat näin ollen yksi suurimmista kaivosteollisuuteen liittyvistä ympäristöongelmista. Lisäksi suuret rikastushiekka-altaat voivat aiheuttaa vaaraa myös ihmisille, mikäli altaan rakenteet pettävät. Rikastushiekkojen kestäviä ja ympäristöystävällisiä varastointimenetelmiä täytyy kehittää, jotta näitä ongelmia voidaan tulevaisuudessa ehkäistä. Tässä työssä tutkittiin menetelmiä, joilla kultakaivoksella syntyvät sulfidipitoiset vaaralliseksi jätteeksi luokitellut rikastushiekat saataisiin stabiloitua tehokkaasti. Työssä keskityttiin kolmeen erilaiseen menetelmään: alkali-aktivointiin, stabilointiin kalsiumhydroksidin ja masuunikuonan avulla ja stabilointiin CSAB sementin avulla. Valmistettujen materiaalien mekaanisia ja kemiallisia ominaisuuksia arvioitiin. Tavoitteena oli ymmärtää, miten eri menetelmät soveltuvat raskasmetallien (erityisesti arseenin) ja sulfaattien sitoutumiseen ja mikä on eri komponenttien rooli reaktioissa. Alkali-aktivoimalla rikastushiekkaa sopivan sidosaineen kanssa saavutettiin hyvät mekaaniset ominaisuudet ja useimmat haitta-aineet sitoutuivat materiaaliin. Ongelmia aiheuttivat edelleen sulfaatit ja arseeni. Kalsiumpohjaiset menetelmät sitoivat raskasmetallit (myös arseenin) ja sulfaatit tehokkaimmin. Sulfaatit ja arseeni saostuivat muodostaen niukkaliukoisia komponentteja kalsiumin kanssa. Samanaikaisesti rakenteeseen muodostui ettringiittiä, jolla on tutkitusti hyvä kyky sitoa erilaisia raskasmetalleja rakenteeseensa. Raskasmetallit myös kapseloituivat rakenteen sisään. Työn tuloksia voidaan hyödyntää, kehitettäessä rikastushiekkojen turvallista varastointia. Kun materiaalille saavutetaan riittävän hyvä lujuus ja kemiallinen stabiilius, rikastushiekat voitaisiin läjittää tulevaisuudessa kuivalle maalle altaan sijaan. Näin vältyttäisiin rikastushiekka-altaiden rakentamiselta ja voitaisiin vähentää happamien kaivosvesien muodostumista pitkällä ajanjaksolla. Saavutettujen tulosten perusteella rikastushiekkoja voidaan mahdollisesti tulevaisuudessa hyödyntää myös erilaisissa betonin tapaisissa rakennusmateriaaleissa

Influence of alkali source on properties of alkali activated silicate tailings

Abstract Mining activities are inevitable for the growing industrialization and urbanization in the world. Disposal of mine tailings creates a severe impact to the environment and ultimately to the society. Identifying the applications of mine tailings as potential secondary raw materials would help the mining industries in achieving circular economy. Alkali activation of tailings for their utilization as building materials or backfill in mining sites is one such popular technique. In this paper, mechanically treated silicate tailings rich in magnesium/aluminum content were chosen, to be used as aluminosilicate precursors. The effect of different alkaline sources was accessed by using sodium silicate (Na₂SiO₃), sodium sulphate (Na₂SO₄) and sodium carbonate (Na₂CO₃) as activators. Alkali activated tailings pastes were studied by examining the compressive strength and microstructural properties. High magnesium tailings show good strength results with sodium silicate activator whereas sulphate-based activator performed well in high alumina tailings. Sodium carbonate seems to be efficient in early phases but does not display improvement in later ages. This behavior of alkali activated tailings with different alkali sources were tried to be correlated with the mineralogy of the tailings and its reactivity using FTIR, XRD and TGA

Inertization of mine tailing via cold consolidation in geopolymer matrix

he consolidation via geopolymerisation is a room temperature alkaline chemical reaction of condensation between SiO2 and AlO2 monomers. Such a matrix can retain a large number of cations to compensate for the Al+3 in place of Si+4 in the tetrahedra. Arsenic-rich mine tailings from a gold mining site were activated with NaOH solution and commercial Na-Silicate (Na2O/SiO2 = 3) to produce a no-hazardous final material. Granulated blast furnace slag and metakaolin were used as co-binders to optimize the formulations. Leaching test was used to evaluate the inertization capability of the matrix after curing times of 7 and 28 days. The leaching results show that increasing curing time there is a significant decrease of As leaching due to the better consolidation of the material. Leaching of Cu, V, Ba and Zn significantly decrease, while Ni and Cr remain almost constant and Sb slightly increases

Utilization of sulphidic mine tailings in alkali-activated materials

Disposal of mine tailings is one of the most important environmental issues during the mining lifetime. Especially sulphidic tailings can cause environmental and ecological risks because of their tendency to oxidize in the presence of water or air. Because of small particle size and harmful chemical properties, utilization possibilities of sulphidic mine tailings are limited. The aim of the present study was to develop technologies to utilize sulphidic mine tailings in alkali activated materials. Alkali-activated materials also known as geopolymers are nanosized zeolite type or slightly amorphous materials comparable to traditional Portland cement concrete, which can physically encapsulate or chemically stabilize the hazardous elements such as heavy metals into the 3D structure. Mine tailing based geopolymer aggregates were successfully produced from sulphidic mine tailings with good physical properties. The geopolymer aggregates performed as a concrete aggregate comparable to commercial lightweight aggregates. In addition, geopolymer mortars were prepared from mine tailings. In mortar application, there is a need to add some co-binder such as blast furnace slag in order to achieve high strength for the material. The mine tailing based geopolymer structure has an ability to stabilize a large number of cationic species into the structure while some anionic species were not able to immobilize by alkaline activation

Inertization of mine tailing via cold consolidation in geopolymer matrix

The consolidation via geopolymerisation is a room temperature alkaline chemical reaction of condensation between SiO2and AlO2monomers. Such a matrix can retain a large number of cations to compensate for the Al+3in place of Si+4in the tetrahedra. Arsenic-rich mine tailings from a gold mining site were activated with NaOH solution and commercial Na-Silicate (Na2O/SiO2= 3) to produce a no-hazardous final material. Granulated blast furnace slag and metakaolin were used as co-binders to optimize the formulations. Leaching test was used to evaluate the inertization capability of the matrix after curing times of 7 and 28 days. The leaching results show that increasing curing time there is a significant decrease of As leaching due to the better consolidation of the material. Leaching of Cu, V, Ba and Zn significantly decrease, while Ni and Cr remain almost constant and Sb slightly increases

Solidification/stabilization of gold mine tailings using calcium sulfoaluminate-belite cement

Abstract In this study, calcium sulfoaluminate-belite cement (CSAB) was used to stabilize gold mine tailings, which are challenging materials to effectively immobilize due to high heavy metal and sulfate content. The hydration of CSAB cement yields ettringite and monosulfate with good capability for immobilizing sulfates and oxyanions in their crystal structure, in addition to physical encapsulation/solidification in a cementitious matrix. Different mix designs of CSAB cement and mine tailings were prepared, and the samples were cured at room temperature. Mechanical strength and heavy metal leaching were analyzed after 7 days, 28 days, and 90 days of curing, and the phase composition (XRD), thermogravimetric analysis (TGA), and microstructure (FESEM) were also studied. All harmful elements (cationic and oxyanion elements) were effectively immobilized during 7 days of curing, and the heavy metal immobilization remained constant after longer curing, according to an environmental leaching test. High mechanical strength results and good sulfate immobilization were obtained with mine tailing content up to 50 w-% of total binder material. With higher mine tailing content (75 w-% and 90 w-%), the mechanical strength and immobilization ability substantially decreased

Upcycling of mechanically treated silicate mine tailings as alkali activated binders

Abstract Mining activity is inevitable in human societies, and thus, disposal of mining waste in a proper and effective way is crucial to preserving our environment. In this context, studies on the reuse potential for mine tailings in the construction sector are booming. However, utilizing tailings as binder material is complicated due to the high variation in mineralogical composition and the low reactivity of these materials. In this study, an attempt was made to understand the effect of mechanical treatment on silicate mine tailings in order to improve their properties for use as a sole precursor in alkali-activated binders. Two different silicate tailings from Finland were studied: one rich in tremolite, which is high in magnesium (HM tailings) and one rich in anorthite and epidote, which is high in aluminum (HA tailings). Interestingly, grinding activity performed at different durations affected the properties of the tailings with various intensities, including their mineralogical and physical properties and characteristics and, thus the reactivity of tailings. Tremolite does not respond to milling for longer durations, and layered anorthite was easily distorted by the mechanical disturbance. Irrespective of the type of tailings, the compressive strength of alkali-activated milled tailings increased with an increase in grinding time from 1 to 16 min. However, the percentage of compressive strength increase varied with the type of tailings and their mineralogy