Abstract This study examines the influence of acid activation (HCl) of an Ypresian clay on the synthesis of porous materials and the clarification of soybean oils. The clay was collected from the Palaeocene–Eocene transition between the El Haria and Chouabine formations in the Meknassy–Mezzouna basin, central Tunisia, and was subjected to chemical and mineralogical characterization. The clay consists of smectite, sepiolite and palygorskite, with smectite dominating and accessory quartz and dolomite. The clay has a relatively high specific surface area (50.47 m 2 g –1 ), which increases to 100 m 2 g –1 after activation by HCl. The optimal activation conditions were obtained at 75°C for 4 h with 3 N HCl. Acid activation disrupted the smectite structure (causing leaching of structural cations), dissolved dolomite, formed amorphous porous material and caused H for Ca ion exchange in the smectite interlayer. The acid-activated smectitic clay provided encouraging results regarding the clarification of neutral soybean oil after comparison with the Tonsil commercial bleaching earth product. The bleaching capacity of the activated clay was 78.08%, which is higher than that of Tonsil (56.12%). This was corroborated by visual examination of the clarified oils.
Abstract The brick production industry faces increasing environmental pressure due to high energy demands during firing, necessitating the optimization of firing conditions. This study investigates an eco-friendly stepped firing process as a sustainable alternative to conventional direct heat treatment using clayey raw materials from the Ouled Mansour area, north-east Morocco. To evaluate this approach, raw materials were characterized using X-ray diffraction, X-ray fluorescence, infrared spectroscopy, simultaneous thermal analysis, Atterberg limits and particle-size distribution analysis. Brick specimens were then prepared and fired under both conventional and stepped heating processes. Their thermophysical properties (thermal conductivity, thermal diffusivity, porosity, water absorption and density) and compressive strength were assessed. Non-destructive tests (ultrasonic pulse velocity and Schmidt hammer tests) together with mineralogical and microstructural analyses were also performed. The stepped firing process reduces porosity and defects, thereby increasing the ultrasonic pulse velocity from 3197 to 3508 m s –1 and improving compressive strength by up to 21%. Thermal conductivity and density slightly increase, from 0.57 to 0.58 W mK –1 and from 1.60 to 1.62 g cm –3 at 770°C, respectively. The proposed eco-friendly firing process enhances the physico-mechanical performance of bricks while supporting their energy-efficient production, with potential reductions in energy consumption during both manufacturing and the building service life.
Abstract Engineering muck (EM) is an underutilized construction waste rich in clay minerals. The mechanical properties, composition, microstructures and reaction mechanisms of various EM-based geopolymers produced via acid or alkali activation are comprehensively compared and discussed in this study. The results indicate that EM mainly contains clay minerals (kaolinite, halloysite and dioctahedral mica), feldspar and quartz. The geopolymerization reactivity of EM was improved following crushing and calcination pretreatments, which destroyed the microstructure of the clay minerals and formed a reactive amorphous phase. Acid activation of calcined EM (EM 700°C ) resulted in greater geopolymerization reactivity than alkali activation. The highest 7 and 28 day compressive strengths of phosphoric acid-activated EM-based geopolymers reached 27.31 and 24.37 MPa, respectively, under a water/binder mass ratio of 0.7 and an Al/P molar ratio of 0.9. Comparatively, the maximum 7 and 28 day compressive strengths of alkali-activated EM-based geopolymers were only 7.82 and 11.66 MPa, respectively, under a water/binder mass ratio of 0.6 and a SiO 2 /Na 2 O molar ratio of 1.75. For phosphoric acid activation, reactive Al 3+ mainly from calcined clay (e.g. metakaolinite) in EM 700°C geopolymerized with PO 4 3– and silica, forming phosphate-containing phases and amorphous silico-aluminophosphate (SAP; Si–O–Al–O–P) gels. In contrast, reactive SiO 2 and Al 2 O 3 from EM 700°C participated in the geopolymerization process in alkaline solution, forming sodium aluminosilicate hydrate (N–A–S–H) gels and the byproduct faujasite. The geopolymerization reactivity of EM 700°C and the resulting composition variations in various solutions contributed to the differences in the compressive strengths of EM-based geopolymers. This study provides a theoretical basis for preparing acid/alkali-activated geopolymers from EM.
Abstract Natural zeolites modified with iron(II) ions or iron(III) phases represent two promising approaches for treating hexavalent chromium contamination in water due to their reduction and adsorption capacities, respectively. However, comprehensive comparative analysis of their efficiency remains limited. Fe(II)-modified zeolites can reduce Cr(VI) to the less toxic and insoluble Cr(III) form, while Fe(III)-modified zeolites primarily remove Cr(VI) through surface adsorption. This study evaluates the effectiveness of Fe(II)- and Fe(III)-modified zeolites using synthetic Cr solutions and real contaminated surface water. The materials were characterized via X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray fluorescence spectroscopy to assess their chemical, structural and morphological changes before and after chromium sorption. Batch and column tests determined Cr(VI) removal capacity, while Cr isotopes were used to track reduction reactions. The Fe(II) enrichment via cation exchange was highly effective. The Fe(II)-modified zeolite demonstrated a greater capacity for Cr(VI) removal from contaminated solutions, primarily through a reduction mechanism that converted Cr(VI) to Cr(III), as was confirmed by isotopic analysis. Its performance improved under higher-salinity conditions. However, it required prolonged contact time with the contaminant to achieve optimal efficiency. The Fe(III)-modified zeolite exhibited a heterogeneous distribution of iron oxide/hydroxide phases on its surface. This material showed some favourable characteristics in batch and column tests, including a notably faster Cr removal rate due to direct Cr(VI) sorption. However, it could only perform well when no other competitive ions were present in the solution, severely impacting its application in complex, real matrices.
Abstract Claystones and related sedimentary lithologies are considered as potential host rocks for the storage of high-level radioactive waste. The properties of claystones, which govern their barrier performance, can vary significantly between sites and formations. This study summarizes relevant barrier properties, with a particular emphasis on those dependent on burial history and maximum rock temperatures. Given the large number of properties influencing barrier quality, ranking them by relative importance is necessary. The predictable, non-linear behaviour of certain characteristics with geological burial depth allows for a substantial reduction in the number of properties requiring determination. Based on a set of representative repository-relevant rock lithologies, a case study comparison of potential claystone host rocks is presented. Hydraulic conductivity was assumed to be the most critical barrier property, with optimal values in rocks that reached peak diagenesis at burial depths exceeding 2000 m. To further distinguish claystone types and related lithologies in terms of barrier suitability, either cation-exchange capacity, reflecting the content of smectitic layers, or maximum temperature of palaeoburial heating ( T maxgeo ) can be used as an example. Pore-size distribution, correlating with the average particle distance, was particularly suited to estimating maximum burial depth, as it is less affected by thermal anomalies, pore fluid composition or cementation effects. Overall, combining key barrier properties with burial depth-dependent behaviour enables efficient assessment and comparison of claystone formations for deep high-level radioactive waste disposal. A quantitative comparison of various claystones, however, requires establishing a reactive solute transport model that simulates radionuclide release fluxes at specific timescales.
