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The scientific community's interest in geopolymers keeps on growing under environmental and climate change pressures. Although most studies concern metakaolin or industrial by-products as aluminosilicate precursors, few are those concerning clay cuttings characterized by little or no kaolinite content. This study proposes a method to activate illitic clay in order to obtain a geopolymer with high mechanical performances. The tested illitic material contained 53 wt% of illite/muscovite, 22 wt% quartz, 7 wt% feldspars and low content of calcite. The innovation consists in coupling thermal and mechanical activations favoring both the clay dehydroxylation and the destruction of the clay crystalline structure. Such increase of amorphous rate in the precursor is required to make the material reactive. The evolution of the precursor material after activation was followed by ThermoGravimetric Analysis (TGA/DTG), X-Ray Diffraction (XRD), Fourier-Transform InfraRed spectroscopy (FTIR) and Scanning Electron Microscopy coupled to Energy Dispersive X-ray spectrometry (SEM-EDX). The impact of the variations of the mechanical activation duration and ball:powder mass ratio (b:p) were mainly explored, as well as the Liquid:Solid mass ratio (L:S) which is a key parameter of the geopolymerization. Finally, an optimized geopolymer with a mechanical compressive strength reaching 126 MPa after 28 days has been manufactured with a grinding duration of 240 min, a b: p = 15 and a L:S = 0.5. The demonstration was done that a geopolymer can be manufactured from 100% illitic clay precursor, in addition to a relatively low amount of alkaline solution (L:S mass ratio of 0.5) then lowering the cost and the environment impact of the final geopolymer material. The resulting illitic clay based geopolymers can display very high mechanical resistance (compressive strength up to 126 MPa after 28 days), fully competitive with conventional building materials. • Illitic geopolymer from clayey soil reached a 126 MPa compressive strength after 28 days • Illitic geopolymer from clay soil reached a 126 MPa of Rc after 28 days. • The grinding time, heating temperature, L:S and b:p ratios allowed to increase Rc. • Only a 50% amorphous content after precursor amorphization was enough for high Rc. • Incomplete amorphization of illitic precursor induced non or partially reacted particles • Non or partially reacted particles in geopolymer hardened paste impacted Rc. [ABSTRACT FROM AUTHOR]

Humic substances (HS) are frequently incorporated into soils to improve soil health and nutrient availability. However, existing literature presents discrepancies regarding the soil-HS interactions and their impact on orthophosphate (inorganic phosphorus (IP)) adsorption, specifically, concerning the influence of soil clay mineralogy on these interactions. This study aims to investigate whether the impact of soluble humic acid (HA) on IP adsorption in semi-arid Mediterranean soils is contingent upon their clay mineralogy. This was tested by constructing IP- adsorption isotherms in the presence and absence of HA of four illite/smectite (I/S) or kaolinitic dominated soils. The results revealed that the addition of HA increased IP adsorption to I/S soils by up to 80%, yet IP did not affect HA adsorption to these soils. This suggests that while HA and IP are adsorbed onto different sites on the I/S clay, HA adsorption probably increases the number of adsorption sites accessible for IP. In contrast, IP and HA adsorption onto the kaolinitic soil was fully competitive: IP reduced HA adsorption and vice versa. It is suggested that new adsorption sites for IP resulted from the HA interactions with the I/S clay planar surfaces. In addition, HA moieties containing cationic (ionized) nitrogen, could possibly interact with clays to increase the number of platelets per tactoid. Unlike I/S clays, kaolinite that possesses low degree of isomorphic substitution, low net negative charge, and high degree of platelets stacking, does not tend to such interactions with HA. Instead, HA will be adsorbed mostly onto the clay edges, competing with IP on adsorption sites. • Humic acid (HA) – inorganic P (IP) adsorption to kaolinitic soil is competitive. • Dissolved HA increases IP adsorption to illite/smectite (I/S) soils by 5 to 72%. • HA increases IP adsorption through interactions with negatively charged clay surfaces. • HA increases the IP-buffering capacity of the I/S soils by up to 60%. [ABSTRACT FROM AUTHOR]

This study is aimed at evaluating the performance of low-alkali activated clay-fly ash liners as an environmentally friendly approach to attrap heavy metals cations and prevent the leachate containing such hazardous materials from spreading through the soil medium. For this purpose, a series of unsaturated experimental column leaching tests is carried out on clay-fly ash samples containing 20% fly ash activated by 1, 2 and 4 M NaOH solutions, leading to different Na/fly ash ratios. The leachate, synthesized by various equal concentrations of copper sulfate CuSO 4 and zinc nitrate Zn(NO 3) 2 , i.e. 50 mg/L , 100 mg/L and 150 mg/L, is monitored while passing through various treated clayey soils to assess their time-dependent attenuation capacity and permeability at three different leaching times so as to select the sample with the best overall performance. The leaching test is then continued for the corresponding sample until 57 days in order to determine the unsaturated breakthrough curve and effective diffusion coefficient of the pollutants. The results of experiments show the mutual contribution of hydroxide precipitation and physical adsorption to the attenuation process, where the lower alkali concentration favors the former; thus the clay-fly ash liner activated by 1 M NaOH solution exhibits the best attenuation performance, achieving appreciably high removal rates of >99.71% for Zn(II) and 94.47% for Cu(II), after 192 h of leaching. Furthermore, having a lower breakthrough time and effective diffusion coefficient, 1 M alkali-activated clay-fly ash is observed to considerably work better than the untreated clay in the long-run attenuation. Microstructural analyses also reveal the presence of new crystalline phases and rise in amorphous content, referring to new chemical bonds produced due to the immobilization of heavy metals. [Display omitted] • Performance of low-alkali activated clay-fly ash liners to attrap heavy metals is evaluated. • Unsaturated experimental column leaching tests is performed on clay-fly ash liners. • Attenuation capacity, permeability, breakthrough curve and diffusion coefficient are evaluated. • Mutual contributions of hydroxide precipitation and physical adsorption are assessed. [ABSTRACT FROM AUTHOR]

Due to cyclic loading, clays composed of different mineral compositions exhibit non-linear viscoelastic characteristics. This study quantified the effect of the mineral composition on the non-linear viscoelastic properties of clays. Large-amplitude oscillatory shear rheological tests and cryo-electron microscopy tests were conducted on clays containing quartz, feldspar, montmorillonite, and kaolinite (Q, F, Mt., and Kaol). The results indicated that as the clay content in the soil sample increased, so did the value of relative intensity(I 3 / 1), the Lissajous curves shifted from elliptical to rectangular, and the absolute values of the overall non-linear viscoelasticity parameters (N E and N V) were also larger. In addition, its non-linear viscoelasticity was more prominent, supported by the cryo-electron microscopy test outcomes. Montmorillonite played a more significant role than kaolinite in increasing the nonlinear viscoelasticity of the soil samples. The study findings have significant academic and practical value, facilitating an in-depth understanding of the viscoelastic behavior of clays, rheological studies of other types of clay soils, and geotechnical engineering applications. • Studying clay non-linear viscoelastic behavior (NLVEB) using rheology. • Quantifying NLVEB of clay using overall characterization parameters (N E and N V). • Clay mineral composition and content have a great influence on the NLVEB in clays. • Montmorillonite is extremely important for the NLVEB in clays. [ABSTRACT FROM AUTHOR]