SMART geopolymers, an ERA-MIN project

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Near-zero-waste processing of low-grade, complex primary ores and secondary raw materials in Europe: technology development trends

With an increasing number of low-grade primary ores starting to be cog-effectively mined, we are at the verge of mining a myriad of low-grade primary and secondary mineral materials. At the same time, mining practices and mineral waste recycling are both evolving towards sustainable near-zero-waste processing of low-grade resources within a circular economy that requires a shift in business models, policies and improvements in process technologies. This review discusses the evolution towards low-grade primary ore and secondary raw material mining that will allow for sufficient supply of critical raw materials as well as base metals. Seven low-grade ores, including primary (Greek and Polish laterites) and secondary (fayalitic slags, jarosite and goethite sludges, zincrich waste treatment sludge and chromium-rich neutralisation sludge) raw materials are discussed as typical examples for Europe. In order to treat diverse and complex low-grade ores efficiently, the use of a new metallurgical systems toolbox is proposed, which is populated with existing and innovative unit operations: (i) mineral processing, (ii) metal extraction, (iii) metal recovery and (iv) matrix valorisation. Several promising novel techniques are under development for these four unit-operations. From an economical and environmental point of view, such processes must be fitted into new (circular) business models, whereby impacts and costs are divided over the entire value chain. Currently, low-grade secondary raw material processing is only economic and environmentally beneficial when the mineral residues can be valorised and landfill costs are avoided and/or incentives for waste processing can be taken into account

Early age microstructural transformations of an inorganic polymer made of fayalite slag

Three types of binders were investigated by combining a water granulated fayalite slag and three different activating solutions (NaOH, SH; Na‐silicate, SS; and a 1:1 mixture of the two, SH + SS). A reactivity test proved that the slag dissolves in the alkaline environment, releasing both Si and Al. Through rheological measurements it was found that the most alkaline solution (SH) led to a very fast structure build‐up, followed by the activating solution SS+SH; when SS was used, the storage modulus did not increase even after 2 h. A similar trend was observed by calorimetry, where the paste with SH resulted in heat release within minutes, followed by SH + SS. These transformations were also followed by in situ ATR‐FTIR, indicating changes in the vibrational bands attributed to asymmetric stretching vibration of [SiO4] with 3 or 4 NBO/Si. In the case of the sample activated with SH, a new band appeared after 96 h and continued to increase in intensity at later times. For SS + SH activating solution, a new band appeared after 96 h, increasing over time, whereas the originally present band at 940 cm−1 became more distinct. For the sample with only SS, no vibrational changes were detected after 24 h. In conclusion, the fayalite slag is a reactive material that can undergo microstructural changes toward new reaction products, with the choice of the activating solution being a crucial factor in the process.status: publishe

Influence of mechanical activation on the kinetics of non ferrous metal sulphides oxidation

The paper presents experimental research results on a new concept of oxidation in aqueous medium (solution of sodium carbonate) of copper sulphide concentrate in autoclave under air pressure in the temperature range 100 to 135 °C for 5 h, partial air pressure 5 aim in the presence of 30% excess of sodium carbonate more then stoichiometrical necessary for oxidation. Determinations were made in parallel on not-milled concentrate and mechanically activated concentrate. Based on the results obtained, the influence of mechanical activation on the kinetics of oxidation of sulphide concentrates was studied. By prolonged milling of copper concentrate, the activation energy decreases from 118.65 kJ · mol-1 to 25.75 kJ· mol -1.status: publishe

Boosting the use of bauxite residue (red mud) in cement : production of an Fe-rich calciumsulfoaluminate-ferrite clinker and characterisation of the hydration

In the present work, calciumsulfoaluminate-ferrite clinker was produced using 35 wt% of bauxite residue in combination with alumina, clay, limestone and gypsum. At a temperature of 1300 degrees C, the hydraulic phases ye'elimite, ferrite and C2S were formed. Computed thermochemical predictions were a significantly better match for the real mineralogy than modified Bogue equations. Hydration of the clinker led to the formation of ettringite and monosulfate, resulting in compressive strengths of 17 MPa after 28d. Compressive strengths of 40 MPa after 2d, and 28d-strengths exceeding 50 MPa, were reached in blends with 10 wt% of anhydrite. The strength development was due to the rapid formation of ettringite, mainly originating from ye'elimite, which did not convert to AFm phases and led to a compact microstructure. Only when the ye'elimite dissolution decreased, did the ferrite phase react. In pastes with additional sulfates, ferrite hydration led to the formation of ettringite and to hydrogarnet. Cement nomenclature is used in this work

Transformation of stainless steel slag toward a reactive cementitious binder

Argon oxygen decarburization (AOD) slag represents more than 50 wt% of the slag from stainless steel production. Although some applications are available,e.g., as aggregates for road constructions or fertilizers, they are characterized by low economic value and limited applicability. In order to increase the economic value of AOD slag, alternative applications have been proposed, e.g., as partial or full replacement for Ordinary Portland Cement (OPC). The work presented here investigates whether the adaptation of the AOD slag chemistry within a high temperature process leads to an improvement of its hydraulic properties and thereby can demonstrate its potential to be converted into a hydraulic binder suit able for OPC replacement. For this purpose, three synthetic AOD slags with basicities(CaO/SiO2) of 2.0, 2.2, and 2.4 were synthesized, and the effect of the CaO/SiO2 ratio on the material stability, the amount of tri-calcium silicate formed, and their hydraulic properties investigated. X-ray diffraction, scanning electron microscope(SEM), and isothermal calorimetry analysis were used to characterize the microstructure and the hydraulic activity. The results show that the proposed method is indeed a promising way to stabilize a stainless steel AOD slag and con-vert it into a hydraulic binder.status: publishe

Pozzolanic activity of thermally treated bauxite residue in blends with ordinary portland cement

<p>The present paper reports on the possibility to use modified bauxite residue (BR) as a pozzolanic material, suitable for the replacement of cement clinker.</p

The influence of curing conditions on the mechanical properties and leaching of inorganic polymers made of fayalitic slag

This study reports on the impact of the curing conditions on the mechanical properties and leaching of inorganic polymer (IP) mortars made from a water quenched fayalitic slag. Three similar IP mortars were produced by mixing together slag, aggregate and activating solution, and cured in three different environments for 28 d: a) at 20 °C and relative humidity (RH) ~ 50% (T20RH50), b) at 20 °C and RH≥90% (T20RH90) and c) at 60 °C and RH ~ 20% (T60RH20). Compressive strength (EN 196-1) varied between 19 MPa (T20RH50) and 31 MPa (T20RH90). This was found to be attributed to the cracks formed upon curing. Geochemical modelling and two leaching tests were performed, the EA NEN 7375 tank test, and the BS EN 12457-1 single batch test. Results show that Cu, Ni, Pb, Zn and As leaching occurred even at high pH, which varied between 10 and 11 in the tank test’s leachates and between 12 and 12.5 in the single batch’s leachates. Leaching values obtained were below the requirements for non-shaped materials of Flemish legislation for As, Cu and Ni in the single batch test.status: publishe

Mechanochemical activation of copper concentrate and the effect on oxidation of metal sulphides

This work presents the effect of mechanochemical activation in an attrition mill, in water medium and for different time internals, on the particle size distribution and microstructure of copper concentrate as well as, on the oxidation of the metal sulphides after treatment in an autoclave. Results show that the mean particle size decreased after 30 minutes of milling almost 10 times and the specific surface increased from 0.1 to 4.3 m2/g. Regarding the micro-structural changes, it was found that during the mechanochemical activation the average crystallite size of chalcopyrite decreased, following an exponential trend towards a limiting value of approximately 20 nm, assuming spherical or equiaxed crystallites. The enhanced structural disorder of chalcopyrite is also highlighted by the linear increase of lattice strain with the milling time. Finally, results from the leaching experiments, demonstrated that the mechanical treatment improved the oxidation of sulphides by lowering the reaction temperature and increasing the reaction rates. The above data suggest that the mechanochemical activation of copper concentrate is an efficient method to enhance the hydrometallurgical oxidation of copper concentrate and chalcopyrite in particular.status: publishe

Near-zero-waste processing of low-grade, complex primary ores and secondary raw materials in Europe: technology development trends

status: publishe