This work analyzes the effect of Mechanochemical Activation (MA) of a Commercial low-grade kaolinite and low-grade illite, a feldspar, a diatomite and a clayey soil (non-commercial) as supplementary cementitious materials. Milling was conducted at different times for up to 360 min. MA decreased the particles size and increased the specific surface area except for low-grade illite. However, prolonged milling produced agglomeration in feldspar, diatomite and clayey soil. MA partially reduced diffractogram peaks and modified the dehydroxylation losses of mass in the thermogravimetric tests. MA's effect over the solubility of SiO 2 and Al 2 O 3 was not conclusive, with differences among aluminosilicate minerals and with no relationships with their physical parameters or chemical structures. Feldspar was the only one not to show Strength Activity Index (SAI) increases due to MA. Low-grade illite, feldspar and diatomite combinations surpassed 75 % on the SAI. No clear relationships were observed between the combinations SAI and their physical parameters, chemical structure or SiO 2 and Al 2 O 3 availability. • Milling times exceeding the optimal produced particles agglomeration. • Mechanochemical activation (MA) partially amorphized the samples. • MA demonstrated its effectiveness in the Strength Activity Index test.

Waste Cooking Oils (WCOs) are generated worldwide through industrial food processing and household use, posing environmental concerns upon disposal. Bentonites often showed to be effective in removing minor contaminants in vegetable oil refining. The present research focused on the processing of raw WCOs using four bentonites, two commercials and two obtained by ball milling of the latest. The different bentonites (hydrophobic and hydrophilic) were characterized before and after ball milling (BM) procedure, including an exhaustive analyses of crystal structure, morphology and surface area via x-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and N2-physisorption technique. Optimization of BM processing in terms of milling time was achieved within 60 min. The milled powders were then tested as adsorbents for recycling WCOs with different degrees of decomposition (expressed in terms of free fatty acids, FFAs, content). Employing a design of experiments approach, the impact of five parameters (FFAs content, temperature, specific surface area, stirring, BM time) on the resulting pour point (PP), taken as a quality benchmark for recycled oil, was assessed. Quantitative multivariate statistical analysis revealed temperature's negligible role and identified the significant impact of two characteristics of the bentonite (specific superficial area and ball milling time), as well as the relevant role of the stirring during the treatment. At the end, hydrophilic bentonite resulted able to improve the PP of waste oils with a low content of free fatty acids of about 10 °C.

In this research, chemometric tools (Partial Least-Squares Regression, Principal Component Regression, Linear Discriminant Analysis for example) allowed estimating firing temperatures and to identify the type of meta-clay based on their infrared spectra.The 3 min phases observed in clay thermal degradation were: (i) a dehydroxylation reaction between 400 and 500–600 °C leading to the formation of a non-crystalline meta-clay, (ii) a continuous thermal degradation reaction of the meta-clay involving the SiO bonds between 500 and 850 °C, (iii) the formation of secondary silicates above 850 °C.The 10 Latent Variables of the Partial Least-Squares Regression model led to accurate predictions (Root Mean Squared Error of Prediction = 66.6) and provided a good correlation between predicted and actual temperatures, without any estimation bias related to the type of clay, the presence of other minerals or iron concentration. These models give greater importance to the infrared absorption bands of the bonds involved in thermal degradation: Si-O-Si (1026 and 461 cm−1), Si-O-Al (526 cm−1), SiO or AlO (1095 cm−1), and infrared bands resulting from the formation of meta-clays (486 et 562 cm−1).Finally, a Linear Discriminant Analysis model is proposed in order to identify the type of meta-clay between different types of meta-kaolinites, meta-nacrite and meta-smectite in 96 % of cases. The meta-clays produced by the firing of halloysite, dickite and kaolinite were too close in terms of infrared spectra to be distinguished.

Ion composition in groundwater at the spent nuclear fuel repositories is a relevant uncertainty for predicting the shear behavior of the bentonite buffer. However, only a few studies investigated the range of shear strength variation with in-situ groundwater conditions. This paper examines the ultimate shear strength of compacted Wyoming-type bentonite, focusing on the effect of pore water salinity. Triaxial tests were performed under effective confining pressures up to 10 MPa with different types of pore water representing: 1) extremely low, 2) current, and 3) maximal salinity conditions at the repositories, while tracking the evolution of exchangeable cation composition. The results revealed that pore waters with typical Ca2+ concentrations at the repositories strengthen the sodium bentonite through Na+-Ca2+ cation exchange. The observed salinity-dependent strength of the bentonite was described by the ultimate shear strength line and its apparent mobilization in the deviatoric stress-mean effective stress plane. The upper limit of the increase in strength was found to be 0.74 MPa. Previous triaxial test results with deionized water were compared to refine the shape of the ultimate shear strength line. Lessons learned from the triaxial testing of saturated bentonite were elucidated to offer recommendations to address the challenges associated with high swelling potential and low permeability. The findings in this paper have implications for accurate assessment of shear behavior in the deep geological disposal system as well as effective laboratory measurements of the shear strength parameters of compacted bentonite.