Two dimensions comminution of kaolinite clay particles

A review: Alkali-activated cement and concrete production technologies available in the industry

A growing interest in alternative cements has emerged with the sole purpose of reducing the environmental footprint associated with cement production. One of the promising alternatives is to use non-carbonate materials such as alkali-activated materials. They have demonstrated to have a similar performance as traditional Portland cement and have the potential to significantly reduce CO₂ emissions. This paper reviews the main relevant technologies that are already available in the construction industry and explains how to consider them for alkali-activated cement and concrete production. This includes aluminosilicate pre-treatment methods (drying, grinding, and calcining) to increase the precursor's reactivity and degree of amorphization, alkali activation by two-part or one-part mix, as well as, mixing and casting fresh alkali-activated concrete ensuring low porosity and adequate strength development. This review also presents an overview of the alkali-activated cements market, providing examples of commercialized products, estimating related CO₂ and costs, as well as future considerations for standardization and commercialization. Most of the commercialized alkali-activated materials are two-part mixes despite their limitations for in-situ applications. CO₂ emissions can be reduced by more than 68% when compared to Portland cements. However, they have been estimated to be 2 to 3 times more expensive and the cost is primarily dependent on the aluminosilicate and alkali activators source.

Improved holding and releasing capacities of coal gangue toward phosphate through alkali-activation

Activation is an effective method to improve adsorption capacity of coal gangue, however, most activated gangues reported have limited adsorption capacity for phosphate because of the electronegativity, affecting their use in agricultural production and environmental protection. In order to enhance the phosphate absorption capacity of coal gangue through alkali-activation, three alkali-activated silicate coal gangue according to fine-size (AS-FCG¹), medium-size (AS-MCG²), and large-size (AS-LCG³) were prepared through grinding, calcining (800 °C) and stimulating with Ca(OH)₂ solution (0.1 M), and raw coal gangue (RCG⁴) was used as control. The results revealed that AS-FCG has the best modified effects, its maximum phosphate adsorption capacity, according to Langmuir model, was 11.796 mg g^-1, which was 4.41, 8.16 and 73.73 times higher than that of AS-MCG, AS-LCG and RCG, respectively. The adsorption penetration time of AS-FCG packed column was over 30 h, which was longer than that of other samples. Besides, when the AS-FCG packed column loaded with phosphate was desorbed with distilled water, the phosphate concentration of filtrate was low and rapidly tended to 0 mg L^-1, while when it was desorbed with NaHCO₃ solution, the concentration remained high sustainably. The best adsorption performance of AS-FCG were associated with generation of calcium silicate hydrate gel and ettringite, which provided more Ca²⁺, Al³⁺, hydroxyl and larger specific surface area. It is suggested that alkali-activation is able to truly realize the recycling of solid waste, AS-FCG is an inexpensive, durable and eco-friendly material, which could not only be used to hold phosphate, but also release it slowly as fertilizer.

Hallmarks of mechanochemistry: from nanoparticles to technology

The aim of this review article on recent developments of mechanochemistry (nowadays established as a part of chemistry) is to provide a comprehensive overview of advances achieved in the field of atomistic processes, phase transformations, simple and multicomponent nanosystems and peculiarities of mechanochemical reactions. Industrial aspects with successful penetration into fields like materials engineering, heterogeneous catalysis and extractive metallurgy are also reviewed. The hallmarks of mechanochemistry include influencing reactivity of solids by the presence of solid-state defects, interphases and relaxation phenomena, enabling processes to take place under non-equilibrium conditions, creating a well-crystallized core of nanoparticles with disordered near-surface shell regions and performing simple dry time-convenient one-step syntheses. Underlying these hallmarks are technological consequences like preparing new nanomaterials with the desired properties or producing these materials in a reproducible way with high yield and under simple and easy operating conditions. The last but not least hallmark is enabling work under environmentally friendly and essentially waste-free conditions (822 references).

Preparation of Nano-Scale Piece of Sericite by Using Mechanical Exfoliation Method and Ultrasonic Method

The structure of sericite is very stable, so it is hard to peel it directly using traditional methods. In this article, the sericite which was processed through thermal activation, acid treatment, Na-modification and CTAB intercalation was used as raw material to do the exfoliation. The mechanical exfoliation method and ultrasonic method were used respectively to exfoliate the modified sericite. The grain size of final product using mechanical exfoliation method reached 16.6nm and the grain size of final product using ultrasonic method reached 8.1nm. Alongside with the result of TEM images, the ultrasonic method is thought to be better.

Preparation of Delaminated Nano-Kaolinite by Intercalation of Chemical Assistants

A process for preparing of the delaminated kaolinite was developed with intercalation of hydrazine, urea or potassium acetate followed by removing the chemical assistants. Delaminated kaolinite was characterized by XRD, solid-state NMR, thermal analyses, particle-size distribution analyses, etc. The particle size was reduced to ca. 440 nm in diameter and ca.15 nm in thickness in contrast to about 7 μm and 800 nm for untreated precursor respectively. The dehydroxylation temperature of kaolinite was shifted from 514°C to 490°C by the delamination. Additionally, a greater mass lost was also observed for the delaminated particles by dehydroxylation.

The effect of ultrasound on the particle size and structural disorder of a well-ordered kaolinite

The present study examined the effect of sonication on the particle size and structure of a well-crystallized (KGa-1) kaolinite from Georgia. Sonication produced an important delamination effect as well as a reduction of the other particle-size dimensions. The experiments, carried out under different experimental conditions, showed that particle-size reduction can be controlled through different variables such as power of ultrasonic processor, amount of sample (kaolinite + water), and time of treatment. As a consequence of this particle-size reduction the surface area increases sharply with the sonication time from 8.5 to 83 m2/g after 20 h with the most energetic treatment. Contrary to what is observed in the grinding treatment, sonication did not cause the amorphization of kaolinite, as observed by XRD and FTIR data. Nevertheless, ultrasound treatment increased the structural disorder, which consisted in increases in the proportion of specific translations (-a/3+b/3) between adjacent layers in the first hours of treatment, followed by increases in the proportion of random translations between layers.