Alternative ye’elimite (CSA) cement clinkers from industrial byproducts

Abstract The production of ordinary Portland cement (OPC) is responsible for ~8% of global anthropogenic CO2. Two thirds of the emissions arise from the calcination of limestone (CaCO3 -> CaO + CO2). Meanwhile, huge volumes of inorganic industrial sidestreams with necessary ingredients for cement production (Al2O3, CaO, SiO2, and Fe2O3) are landfilled across the globe. Locally these raw materials can be used to replace virgin raw materials of cement manufacture and provide a source of already decarbonized CaO that can reduce the carbon footprint of cement manufacture while promoting the circular economy. The driving factors for industry to utilize their industrial sidestreams are to find a way to enhance waste valorization, to cover the rising expenses of landfilling due to taxation and regulations, and to tackle resource scarcity. The aim of this thesis is to utilize Finnish metallurgical slags (argon oxygen decarburization (AOD) slag, ladle slag (LS), fayalitic slag (FS), burned jarosite slag (Fe slag)), and phosphogypsum (PG) which is a byproduct of fertilizer production as a raw material source for the production of two alternative ye’elimite (CSA) cement clinkers; CSAB (calcium sulfoaluminate belite), and AYF (alite-ye’elimite-ferrite). The chemical composition of ye’elimite clinkers requires less calcium than conventional OPC and allows the use of sulfur- and aluminum-containing raw materials. To allow the use of iron-containing slags, the produced clinkers had a high ferrite phase content. The main concern to use industrial sidestreams as raw materials are the impurities that may affect the clinkering parameters and mineralogy. Detailed microstructural analyses were performed on the clinker to reveal the clinker composition, as well as the partition of the minor elements. The usability of the raw materials for cement manufacture was first tested in laboratory-scale experiments and was then translated to a pilot demonstration in a 7-meter semi-industrial kiln. It was found through mineralogical analysis that impurities from raw materials affected the produced clinker phases in both clinker types when compared to natural raw materials. CSAB clinker was found to be successful in a pilot demonstration. The raw meal of pilot CSAB was composed of 85% industrial residues, and the CO2 emissions caused by chemical reactions were 90% lower than that of PC cement made with virgin raw materials. CSAB clinker from pilot demonstration was mixed with anhydrite, sand, and water to make concrete mortars that led to 28-day performance equaling reference PC cement (CEM II/B-M (S-LL) 42,5 N). AYF clinker was successfully produced in laboratory conditions, but the use of fluorine-containing AOD slag was found challenging in a pilot-scale demonstration and requires further experiments.Tiivistelmä Sementtiteollisuus aiheuttaa 8 % kaikista ihmisen aiheuttamista CO2 päästöistä, joista kaksi kolmasosaa (2/3) syntyy kalkkikiven kalsinoinnista (CaCO3 -> CaO + CO2). Samanaikaisesti teollisuus tuottaa maailmanlaajuisesti suuret määrät läjitettäviä epäorgaanisia jätemateriaaleja, joiden sisältämät alkuaineet (Al2O3, CaO, SiO2 ja Fe2O3) sopivat sementin raaka-aineeksi. Paikallisesti näitä materiaaleja voitaisiin hyödyntää sementin valmistuksessa, ne tarjoavat lähteen CO2 vapaalle kalkille (CaO), joka voisi alentaa sementin valmistuksen CO2 päästöjä samalla edistäen kiertotaloutta. Tiukentuva lainsäädäntö ja verotus läjitettävälle jätteelle on ajava voima yrityksille löytää keinoja hyödyntää ja tuotteistaa jätemateriaaleja. Väitöskirjatutkimuksessani tutkin ye’elimiitti (kalsiumsulfoaluminaatti eli CSA) pitoisten sementtien valmistusta hyödyntäen metallurgisen teollisuuden kuonia (AOD-kuona, senkkakuona, fayaliittikuona ja pyrometallurgisesti käsitelty jarosiittikuona), sekä fosforilannoitteen valmistuksessa syntyvää fosforikipsiä. Vaihtoehtoiset sementit nimetään yleisesti niissä ilmenevien päämineraalien mukaan. Tässä työssä valmistetut vaihtoehtoiset sementtiklinkkerit ovat CSAB (ye’elimiitti-beliitti) ja AYF (aliitti-ye’elimiitti-ferriitti). Tutkimuksessa kehitettyjen CSA-sementtien perusidea on korvata perinteisen sementin päämineraaleja alhaisemman kalkkipitoisuuden omaavilla mineraaleilla, joka mahdollistaa sulfaatti-, rauta- ja alumiinioksidipitoisten jätemateriaalien monipuolisen käyttämisen raaka-aineena. Työssä valmistetut sementit sisälsivät tavanomaista sementtiä korkeamman pitoisuuden rautapitoista brownmilleriitti (ferriitti) mineraalia, joka mahdollisti rautapitoisten kuonien käytön. Jätemateriaalien sisältämien epäpuhtauksien vaikutusta sementtiklinkkerin mikrorakenteeseen ja muodostuviin mineraaleihin tutkittiin monipuolisesti. Jätemateriaalien käyttöä sementin raaka-aineina tutkittiin aluksi laboratoriomittakaavassa, jonka jälkeen valmistusta kokeiltiin 7-metrisessä pilottimittakaavan jatkuvatoimisessa sementtiuunissa. Mineralogisissa analyyseissä huomattiin, että jätemateriaalien epäpuhtaudet johtivat muutoksiin valmistettujen sementtiklinkkerien mineralogiassa ja mineraaleissa verrattaessa puhtaista raaka-aineista valmistettuihin verrokkeihin. CSAB-klinkkerin valmistus onnistui laboratoriossa ja pilottimittakaavassa. Valmistetussa sementtiklinkkerissä parhaimmillaan 85 % raaka-aineista oli korvattu teollisuuden jätemateriaaleilla ja raaka-aineista peräisin olevat CO2-päästöt alenivat 90 % verrattuna kalkkikivestä valmistettuun OPC-sementtiklinkkeriin. CSAB-sementtiklinkkeristä, anhydriitistä (CaSO4), vedestä ja hiekasta valmistettujen betonikappaleiden 28 päivän lujuusominaisuudet vastasivat kaupallisen OPC-sementin (CEM II/B-M (S-LL) 42,5 N) lujuutta. AYF-sementtiklinkkereitä pystyttiin valmistamaan laboratorio-olosuhteissa, mutta pilottimittakaavassa fluoria sisältävän AOD-kuonan käyttö osoittautui vaikeaksi ja vaatisi lisätutkimusta

Effect of gypsum content on CSAB cement-based immobilization of Se and SO₄ from industrial filter sludge and sodium–selenium salts

Abstract Release of different heavy metals from various industries is a significant environmental hazard worldwide. In order to reduce the threat from these chemicals, different treatment methods are needed to make them harmless. This study approaches the problem by examining the effect of gypsum content for immobilization of selenium oxyanions selenite and selenate, and sulfate, with calcium sulfoaluminate belite (CSAB) cement-based ettringite binder systems. The study has two experimental sections. In the first section, an industrial filter sludge with high concentrations of selenium and sulfate is immobilized with CSAB and varying amounts of gypsum. The immobilization is efficient and reducing the gypsum amount in the hydrating mixture enhances the incorporation of both selenium and sulfate. The binding occurs through encapsulation and incorporation into ettringite and other hydrated phases. In the second section, two reagent grade sodium–selenium salts, sodium selenite and sodium selenate, are mixed with CSAB and varying amounts of gypsum. The immobilization is not effective and ettringite is not formed in large quantities, most likely due to high sodium content in the reacting system

Hazardous industrial filter sludge immobilization with mayenite and gypsum

Abstract Heavy metals escaping from industrial processes and industrial waste are a significant environmental hazard all around the globe. Since they cannot be destroyed, the only way to manage the pollution is to capture and contain the hazardous components. This study focuses on stabilization-solidification of a highly toxic industrial filter slag that contains a range of different heavy metals in extremely high quantities. The stabilization-solidification treatment was executed with a mayenite and gypsum based solid cementitious binder. The major components that were monitored during the study were selenium, lead and sulphate. Different ratios of gypsum addition were tested in order to observe the effect of total sulphate content in the system to the immobilization efficiency of anionic selenium and sulphate. During the experiments, all cationic heavy metals were immobilized efficiently, most of them achieving the immobilization efficiencies of more than 99.9%. By adjusting the sulphate content of the system, the immobilization efficiency of selenium was improved from 95.669% to 99.925% and the immobilization efficiency of sulphate raised from 96.069% to above 99.964%. Controversially, the immobilization of lead was at its highest (99.999%) with high sulphate content and dropped to 98.162% as the sulphate rate decreased. The results show clearly that mayenite has good potential for stabilization-solidification applications

Immobilization of heavy metals, selenate, and sulfate from a hazardous industrial side stream by using calcium sulfoaluminate-belite cement

Abstract Release of heavy metals from different industries and industrial waste is a major global threat for as well humans as ecosystems. In this study, immobilization of an industrial filter sludge (FS) with an extremely high content of several heavy metals (24.6 wt% Pb, 21.7 wt% Hg, and 9.00 wt% Se) and sulfate via calcium sulfoaluminate-belite (CSAB) cement was tested. The ratios of 25%, 50% and 75% of CSAB addition were tested, and the target was to achieve immobilization of the hazardous components. The leaching of Pb, Hg, SeO₄, SO₄, Ni, Cd, Cu, and As was monitored, and the structure of the immobilized materials was examined via X-ray powder diffraction (XRD) and field emission scanning electron microscopy-energy dispersive spectroscopy (FESEM-EDS) analysis. It was observed that Hg, Cu, As, Cd, and Ni were immobilized completely and leaching of Pb was reduced by 69% from the theoretical release. On the other hand, the leaching of SeO₄ and SO₄ experienced major increase when CSAB was added. XRD indicated significant ettringite formation as the amount of added CSAB increased, and the formation of gypsum as the amount was decreased. FESEM-EDS indicated that the immobilization was largely based on encapsulation into the CSAB binder, but chemical immobilization into the ettringite binder was also observed. It was concluded that the increased release of SO₄ and SeO₄ might have resulted from an excess amount of sulfates (added gypsum) during hydration

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

Production and properties of ferrite-rich CSAB cement from metallurgical industry residues

Abstract Blast furnace slag from the steel industry is commercially utilized as a cement replacement material without major processing requirements; however, there are many unutilized steel production slags which differ considerably from the blast furnace slag in chemical and physical properties. In this study, calcium sulfoaluminate belite (CSAB) cement clinkers were produced using generally unutilized metallurgical industry residues: AOD (Argon Oxygen Decarburisation) slag from stainless steel production, Fe slag from zinc production, and fayalitic slag from nickel production. CSAB clinker with a target composition of ye’elimite-belite-ferrite was produced by firing raw materials at 1300 °C. The phase composition of the produced clinkers was identified using quantitative XRD analyses, and the chemical composition of the clinker phases produced was established using FESEM-EDS and mechanical properties were tested through compressive strength test. It is demonstrated that these metallurgical residues can be used successfully as alternative raw materials for the production of CSAB cement that can be used for special applications. In addition, it is shown that the available quantities of these side-streams are enough for significant replacement of virgin raw materials used in cement production

The effect of fluoride and iron content on the clinkering of Alite-ye’elimite-ferrite (AYF) cement systems

Abstract Alite–ye’elimite–ferrite (AYF) cement is a more sustainable alternative to Portland cement (PC) that may offer improved mechanical, rheological, and chemical performance. Using traditional raw materials and conventional clinker processing conditions, alite (C₃S) and ye’elimite (C₄A₃), the major phases in PC and calcium sulfoaluminate (CSA) cements, respectively, cannot be coproduced. The typical formation temperature in the kiln for alite is >1350°C, but ye’elimite normally breaks down above 1300°C. However, with careful composition control and in the presence of fluoride, alite can be mineralized and formed at lower temperatures, thus enabling the production of AYF clinkers in a single stage. In this study, the production of AYF cement clinkers with different chemical compositions is attempted at 1250°C. The sensitivity of the fluoride content is initially assessed with a fixed target clinker composition to determine the optimal requirements. The effect of altering the target ferrite (C₄AF) and alite (C₃S) contents is also assessed followed by the effect of altering the target C₄AF and C₄A₃ contents. It is shown that AYF clinkers can be produced in a single stage through the careful control of the fluoride content in the mix; however, the formation/persistence of belite and mayenite could not be avoided under the conditions tested. It is also shown that ∼10 wt% ferrite in the target composition provides sufficient AYF clinker burnability and the amount of fluoride needs to be controlled to avoid stabilization of mayenite

Blending eco-efficient calcium sulfoaluminate belite ferrite cement to enhance the physico–mechanical properties of Portland cement paste cured in refrigerated and natural winter conditions

Abstract The acceleration impacts of calcium sulfoaluminate belite ferrite (CSABF)—a cement produced from industrial side streams—on the hydration and strength development of Portland cement (PC) paste cured at −5 °C with and without pre-curing at room temperature were investigated. The impacts of eco-friendly CSABF cement content and pre-curing on the setting time and hardened properties of pastes were investigated. Freezing point of the paste and the amount of freezable water (FW) decreased with CSABF cement content and pre-curing. Hydration rate increased with CSABF cement content. By adding an optimal CSABF cement content, the compressive strength of paste cured at −5 °C increased by 500%. The effects of pre-curing on the compressive strength of the subzero-cured pastes were highly dependent on CSABF cement content and curing period. After 6 months, the outdoor-cured 70%PC/30%CSABF paste gained compressive strength comparable to that in the 90-day-old pair cured at −5 °C and continuous strength gain was detected up to one-year. The microstructural observations and porosity results are consistent with compressive strength measurements

Removal of sulphate and arsenic from wastewater using calcium sulfoaluminate (ye’elimite)

Abstract Chemical precipitation is one of the most widely known methods for treatment of industrial wastewaters with high sulphate content, where sulphate can be precipitated as practically insoluble ettringite (Ca₆Al₂(SO₄)₃(OH)₁₂·26H₂O). This treatment method is also widely recognised for solidifying hazardous components and toxic elements e.g. arsenic in wastewater. In the ettringite precipitation process, lime and aluminium salts are typically used as starting materials, in stoichiometric amounts to form ettringite from the sulphate-containing water, leading to a pH rise to ∼11.5 and ettringite precipitation. In the current study, for the first time, ye’elimite mineral (Ca₄Al₆O₁₂SO₄), also known as calcium sulfoaluminate (CSA) in cements, is used in order to investigate its suitability to form ettringite precipitate from sulphate and arsenic containing synthetic wastewater and industrial wastewater solutions. The dissolution of ye’elimite prior to dosing, optimal precipitation pH, and arsenic co-precipitation were studied. The effluent and precipitates were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM-EDS) and inductively coupled plasma atomic emission spectroscopy (ICP-OES). The results showed that high percentage of sulphate removal (98% in the synthetic wastewater and 87% in the industrial wastewater) can be achieved using ye’elimite as the aluminium source in ettringite precipitation. Additionally, up to 95% arsenic removal was achieved in arsenic co-precipitation experiments from the synthetic wastewater. The current developed technology can be used as a novel ecological and cost-effective approach for removal of sulphate and toxic elements from wastewater

Ferritic calcium sulfoaluminate belite cement from metallurgical industry residues and phosphogypsum:clinker production, scale-up, and microstructural characterisation

Abstract The production of ferrite-rich calcium sulfoaluminate belite (CSABF) cement clinker, also containing MgO, from ladle slag, Fe-slag, and phosphogypsum was translated from a lab-scale to a pilot demonstration in a 7-metre kiln at 1260 °C. An account of the pilot trials/manufacturing is presented, and the process was robust. Laboratory tests prior to scale-up showed that gehlenite formation can be inhibited in the CSABF clinker by adding excess CaO in the raw meal; however, this reduces the amount of iron (Fe) that can be incorporated into ye’elimite and leads to higher ferrite (C₆AF₂) content. Detailed microstructural analyses were performed on the clinker to reveal the clinker composition as well as the partition of the minor elements. Different ferrite phases with varying amounts of titanium and iron are distinguished. Eighty-five percent of the clinker raw meal was comprised of side-stream materials and the clinker produced in the kiln had chemical raw-material CO₂ emissions 90% lower than that of Portland cement made from virgin raw materials. These results can have a significant impact in regions with a prospering metallurgical industry, enabling industrial decarbonisation and resource efficiency