In this work, the processes occurring during geopolymerization of low‐calcium iron‐rich (19.3% Fe2О3) fly ash (FA) mechanically activated in a planetary mill were investigated. Sodium hydroxide solution was used as an alkaline agent and curing was at 20 ± 2°C. Analysis of the initial and mechanically activated FA by selective acid dissolution method showed that after mechanical activation (MA) for 180–400 s the total reactive SiО2 and Al2О3 increased by 1%–2% while the total reactive Fe2О3 more than doubled. The compressive strengths of the geopolymers prepared using the FA mechanically activated for 0, 180, and 400 s were 1.8, 15.0, and 14.0 MPa, respectively, after curing for 28 days. Considerably greater compressive strength of the geopolymers based on the mechanically activated FA was explained by the higher reactivity of the FA induced by MA. This was evidenced by analyses of the geopolymers using Fourier transform infrared spectroscopy, thermogravimetry, and scanning electron microscopy. As shown by microprobe analysis, the geopolymers synthesized using the mechanically activated FA were characterized by considerably higher iron oxide content in the aluminosilicate hydrogel than the geopolymers prepared using the initial FA. The advantage of MA was not only to increase the overall reactivity of FA but also to include Fe in the geopolymerization process, which improved the geopolymer strength.

The paper presents the results of studying the binding properties of a mechanically activated composition including fly ash from the Apatity Thermal Power Plant with increased calcium content, calcite concentrate produced from apatite-carbonatite ores of the Kovdorsky deposit and natural gypsum stone. It was found that the composition, depending on the mixing ratio and curing conditions, displays characteristics of both hydraulic binder similar to lime-ash one and air binder similar to gypsum.

This study reports the effect of natural dolomite addition to fly ash and the mechanical activation of this blend on the geopolymerization process. Dolomite was replaced with fly ash at 1, 3, 5, and 10 wt.%. Geopolymers were synthesized at ambient temperature using NaOH solution as an alkaline agent. The geopolymerization process, reactivity of the raw material, compressive strength, and microstructure were studied using X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetry, and scanning electron microscopy. It was shown that blending fly ash with dolomite and mechanical activation improved the geopolymer strength, especially during the early age of curing. For geopolymers prepared using a 90% fly ash + 10% dolomite blend cured for 7 d, the strengths were 8.2-, 2.3-, and 1.4-fold higher than those for geopolymers prepared using 100% FA for 30 s, 180 s, and 400 s milling times, respectively. A simple method for evaluating the increments of mechanical activation, carbonate additives, and the synergistic effect in the increase in the compressive strength of the composite geopolymer is proposed.

Аннотация.Исследованы вяжущие свойства геополимерной механоактивированной композиции на

The issues of improved reactivity in geopolymerization reactions developed under effect of mechanical activation are examined in the fly ash obtained from the Apatity Heat and Electric Power Plant. The effect of normal and hydrothermal hardening of ash activated with sodium hydroxide solution is explored from the standpoint of changing the strength of geopolymers obtained.

The development of apatite and rare-metal deposits of the Khibiny and Lovozero—the world’s largest ultrabasic massifs located in the Kola Alkaline Province—is accompanied by accumulation of huge amounts of sandy tailings dumps, about half consisting of nepheline. These tailings, on the one hand, pose a real threat of environmental pollution. On the other hand, they are “technogenic deposits” that contain reserves of valuable components (Na2O, K2O, Al2O3, etc.). In this paper, methods of processing of the nepheline-containing mining waste using mechanical activation to produce binding materials—geopolymers and blended cements—are observed. The advantages of combining the nepheline containing tailings dumps with other mining wastes accumulated in the region, such as Cu–Ni slag, are presented.

The problems of increasing the reactivity of fly ash of the Apatity thermal power plant in the reactions of geopolymerization occurring under the influence of mechanical activation were considered. The effect of the normal and hydrothermal curing of fly ash activated with sodium hydroxide solution on the strength of the resulting geopolymers was studied.

Синтез геополимеров на основе золы уноса с применением механоактивацииКалинкин А.М., Гуревич Б

Blends of fly ash and natural calcite, mechanically activated for 0–400 s in a planetary mill, were used to synthesize geopolymers at ambient temperature. The calcite content in the blends was 0–10 wt.%. Sodium hydroxide solution was used as an alkaline agent. Mechanical activation of the raw material considerably enhanced its reactivity with respect to the alkaline agent, as was observed using Fourier-transform infrared spectroscopy, isothermal conduction calorimetry, thermogravimetry coupled with mass spectrometry analysis of the evolved gas, and SEM/EDS. The addition of calcite to the fly ash improved the compressive strength of the geopolymers, especially during the early age of curing. For 7 d aged geopolymers based on the 90% fly ash + 10% calcite blend, the strength was 8.0-, 3.5- and 2.9-fold higher than that for the geopolymers based on the unblended fly ash for 30 s, 180 s and 400 s mechanical activation time, respectively. Using Mössbauer spectroscopy, it was revealed that iron present in the fly ash did not play a significant part in the geopolymerization process. The dominant reaction product was sodium containing aluminosilicate hydrogel (N-A-S-H gel). Calcite was found to transform, to a small extent, to vaterite and Ca(OH)2 in the course of the geopolymerization.

Аннотация.В работе изучена возможность использования механоактивированных серпентинсодержащих горнопромышленных отходов без

Antigorite is a very common rock-forming mineral and it is often present in mining wastes. Utilization of these wastes is a very important issue from the environmental point of view. A potential use for mining wastes is for the production of building materials. This study investigated the alkali activation of antigorite and antigorite-containing ore dressing tailings (AT) milled in a planetary ball mill in an air or CO2 atmosphere. The specific surface area, amorphisation, and dehydroxylation of milled antigorite and AT were examined, and their effect on the cementitious properties was investigated. Binders were prepared by mixing the milled antigorite or AT with liquid glass and curing at 20 ± 2 °C in dry (relative humidity of 65 ± 5%) or humid (relative humidity of 95 ± 5%) conditions for up to 28 days. Curing at dry conditions was found to produce binders with increased strengths. The compressive strength of the alkali-activated binder also increased with increased milling time. For AT milled in air for 4 min and cured in dry conditions for 28 days, the compressive strength was 49 MPa. The milling atmosphere (air or CO2) influenced the cementitious properties of the alkali activated binder to a small extent.

Hydration behavior of mechanically activated magnesia-ferriferous slag has been investigated by isothermal calorimetry. The slag is a waste of pyrometallurgical processing of Cu–Ni ores. Hydration activity of the slag is low in comparison to that of blast furnace slag. It has been shown that mechanical activation of the magnesia-ferriferous slag in CO2 atmosphere considerably increases its hydration activity. In the course of milling in planetary mill in CO2, the slag absorbs carbon dioxide molecules in the form of carbonate ions not only on the surface, but also in the bulk of the slag particles. This accelerates dissolution of the slag in water and the consequent formation of hydration reaction products. As a result, the slag is hardened at ambient temperature without addition of alkali agents or other chemical activators. Calorimetric measurements show that for the slag milled in CO2 the acceleration period comes without the induction period immediately following the initial exothermal peak. For the slag milled in air, the induction period lasts for about 20 days. Milling of the slag in CO2 results in higher intensity of the main heat evolution rate peak and larger cumulative hydration heat as compared to those for the slag milled in air. The compressive strength of the slag milled in CO2 is 12–14 MPa after the main hydration stage, whereas that of the slag milled in air is only about 1 MPa. This can be explained by the mechanically induced carbonization of the slag resulting in its higher reactivity and faster hydration relative to those for the slag milled in air.

Using in situ X-ray diffraction in conjunction with the Rietveld method, we have studied the dynamics of phase formation in the early stages of hardening of mechanically activated blended binders based on Portland cement and mineral admixtures: granulated magnesia-ferriferous slag and nepheline concentrate. The results demonstrate accelerated clinker hydration in the composition of the blended cements compared to admixture-free Portland cement, which correlates with the compressive strength of the samples.

The effect of carbon dioxide as milling medium on the ability of magnesia-ferriferous slag to dissolve in alkali solutions was examined. The degree of extraction of silicon and aluminum from the slag into a sodium hydroxide solution was studied in relation to the milling time in a ball mill, milling atmosphere, and NaOH concentration. The surface of slag particles mechanochemically carbonated upon grinding in a carbon dioxide atmosphere exhibits enhanced reactivity, which is consistent with an increase in the compression strength of geopolymer samples prepared on the basis of this slag. The experimental results are in good agreement with the results of thermodynamic modeling of the interaction of slags with alkali using Selektor program complex.

Copper and nickel waste slag are claimed to pollute the environment with heavy metals. With a view to recycling of waste slag, research has been carried out to recover non-ferrous metals from them and get silica to be used in production of binding materials. It is shown that preconcentrates of non-ferrous metals can be obtained at the floatation concentration and hydrochemical treatment stages. Silica-containing products resulting from separation of non-ferrous metals can be efficiently used in slag portland cement, fine concrete and magnesia binding material. The use of hydrochloric or sulfuric acid leaching and silica powders with high-surface area (270-753 m 2 /g) from copper and nickel slag resulted in water-resistant high-strength magnesia binding material not prone to cracking.

Методом рентгеновской дифракции in situ в сочетании с методом Ритвельда исследована динамика фазообразования на ранних стадиях твердения механоактивированных смешанных вяжущих на основе портландцемента и минеральных добавок: гранулированного магнезиально-железистого шлака и нефелинового концентрата. Показано, что по сравнению с бездобавочным портландцементом наблюдается ускоренная гидратация клинкера в составе смешанных цементов, что согласуется с данными по прочности при сжатии образцов.

We have studied the feasibility of improving the reactivity of ferromagnesian slag through the mechanical activation of the slag with small additions of carbonate minerals in a centrifugal planetary mill. The results demonstrate that, like in the case of the mechanical activation of the slag in a carbon dioxide atmosphere, the process leads to a similar carbonization product, which is considerably more capable of hydraulic hardening than is the slag mechanically activated in air. The highest strength is offered by slag-carbonate materials containing 0.25–1 wt % carbonate (in terms of CO 2 ).

The production of geopolymer material (alkali-activated cement) is investigated as a result of the interaction of the mechanoactivated granular magnesite-ferriferrous slag, which is the processing waste of copper-nickel ores and alkali silicate. The preliminary mechanoactivation of the slag in carbon dioxide is demonstrated to result in an increase in the strength of geopolymer samples in comparison to similar processes in air. The mechanism of the effect of CO2 as a medium for slag mechanoactivation on the physical-mechanical properties of geopolymer is proposed.