Phosphogypsum and Black Steel Slag as Additives for Ecological Bentonite-Based Materials: Microstructure and Characterization

peer reviewedThe Black Steel slag (Ss) and phosphogypsum (PG) are industrial wastes produced in Morocco. In order to reduce these two wastes and to evaluate their pozzolanic reactivity in the presence of water, they were incorporated into bentonite (B) mixed with lime (L). The studied mixtures (BLW, BL–PG–W and BL–PG–Ss–W) were analyzed by X-ray diffraction, Infrared spectroscopy, Raman spectroscopy and SEM/EDX analysis. Compressive strength tests were performed on hardened specimens. The results obtained show that the hydration kinetics of the B–L–W and B–L–PG–W mixtures are slow. The addition of PG to a bentonite––lime mixture induces the formation of new microstructures such as hydrated calcium silicate (C–S–H) and ettringite, which increases the compressive strength of the cementitious specimens. The addition of the Ss to a mixture composed of 8%PG and 8%L–B accelerates the kinetics of hydration and activates the pozzolanic reaction. The presence of C2S in the slag helps to increase the mechanical strength of the mixture B–L–PG–Ss. The compressive strength of the mixtures BL–W, BL–PG–W and BL–PG–Ss–W increases from 15 to 28 days of setting. After 28 days of setting, 8% of Sc added to the mixture 8% PG–8%L–B is responsible for an increase of the compressive strength to 0.6 MPa

Physico-mechanical properties of phosphogypsum and black steel slag as aggregate for bentonite-lime based materials

This study aim to valorizing phosphogypsum (PG) and steel slag (Sc) in geotechnical applications by incorporating them in bentonite (B) stabilized by lime (L). Mineralogical (XRD), spectroscopic (IR-FTIR), geotechnical (Atterberg limits) analyzes were carried out on the raw material. Resistance to axial compression (UCS) was performed on cylindrical specimens prepared for mixtures B-L, B-L-PG, B-L-PG-Sc and cured for 3, 7, 15 and 28 days. The results obtained revealed that the mechanical strength increases with the addition of PG, and reaches its maximum value for a water content equal to 46%. Slag improves the strength of the B-L-PG mixture. The pH and the electrical conductivity of the solutions containing in porosity of the various mixtures decrease over time. The observed decrease is greatest for B-L-PG and B-L-PG-Sc mixtures due to pozzolanic reactions

Reduction of phosphogypsum to calcium sulfide (CaS) using metallic iron in a hydrochloric acid medium

peer reviewedOur study aims to decompose phosphogypsum (PG), mainly composed of CaSO4.2H2O, by reduction in an acidic medium. We evaluated the decomposition of PG by various reaction mechanisms. Sulfate ions from the acid digestion of PG are reduced to sulfide by the hydrogen gas produced in the solution by hydrochloric attack of the metal iron. The solid residues obtained have been determined and monitored by X-Ray Diffraction, Fourier-Transform Infrared spectroscopy and Ultraviolet-visible spectroscopy. The microstructure of residues was observed by scanning electron microscope (SEM). The results show that hydrogen gas formed by hydrochloric acid attack of iron reduces the sulfur from S(VI) to S(-II). CaSO4.2H2O, insoluble in water, gives a residue containing CaS, which is only sparingly soluble in water. The residue also contains anhydrite, bassanite and ferrous chloride. The monitoring of the quantities of residue obtained under varying experimental conditions (temperature, attack time, mass of iron and PG and volume of acid on PG) and volume of HCl showed that the amounts of residue obtained are less than 32% of mass. When the volume of the HCl added increases, the obtained mass of the solid residue decreases sharply. The residue stabilizes at 10% of mass when the volume of HCl added is higher than that required to attack metal iron

Etude expérimentale du relargage des polluants du mélange smectite-chaux-phosphogypse-scories noires en vue de leur valorisation

Le phosphogypse (PG) et les scories d’aciérie (Ss) ont été étudiés pour une éventuelle valorisation comme matériaux pour remblai routier et comme ajouts à la stabilisation des sols gonflants. Ils ont été ajoutés en faible quantité au mélange smectite-chaux. La bentonite et le ghassoul sont deux minerai argileux riches en smectite. La bentonite est riche montmorillonite/beidellite dioctaédrique tandis que le ghassoul est riche en saponite/stevensite trioctaédrique. La structure de la bentonite est déstabilisée par la chaux. Il se forme un gel cimenté qui est le silicate de calcium hydraté (C-S-H) à la surface des grains. L’ajout de PG au mélange bentonite-chaux avantage la formation du gel (C-S-H) et de l’ettringite. L’ajout des scories au mélange bentonite-chaux-PG accélère la cinétique d’hydratation et active les réactions pouzzolaniques et augmente la résistance mécanique à la compression. La réactivité du ghassoul avec la chaux est différente de celle de la bentonite. Le gel C-S-H ne se forme pas et la structure de la smectite n’est pas altérée par l’alcalinité agressive de la chaux. Une étude de lixiviation des éprouvettes préparée par la bentonite, chaux, PG et scories a été réalisée. Les éléments métalliques, potentiellement relarguée par la matière première, sont détectés à faibles concentrations dans les lixiviats des éprouvettes des mélanges. La concentration en activité alpha des élément 210Po, 234U et 232Th trouvée dans les lixiviats des éprouvettes est très faible par rapport au lixiviat du PG seul. Pour mieux comprendre le mécanisme de déstabilisation de la structure de la montmorillonite dans un milieu hyper alcalin, l’ajout des bases fortes CaO, MgO, NaOH et KOH a été également étudié. Si le CaO réagit avec la montmorillonite et permet la formation d’hydrates, le MgO se substitue au calcium et au sodium dans l’espace interfoliaire de la smectite sans altérer la structure de la smectite. L'ajout de NaOH provoque la dissolution de la montmorillonite et la formation de sodalite et de cancrinite. L'ajout de KOH à la bentonite permet la formation de kaolinite et probablement de l’illite, de carbonate de potassium sesquihydraté et d'oxyde de potassium et d'aluminium hydraté.9. Industry, innovation and infrastructur

Development of a new ecological material based on Moroccan industrial waste for road construction

Currently, the recovery of industrial waste to reduce their quantities and their impact on the environment is one of the problems to be tackled in research. The Phosphogypsum (PG) is an industrial waste produced by the attack of sulfuric acid on natural phosphate. PG contains harmful elements to the ecosystems and human health, in particular heavy metals and radionuclides [1]. The electric steel is a growth industry worldwide, in particular in the United States, it raised from less than 50% in 2000 to more than 68% in 2018 (Létard, 2019). This growth is accompanied by a significant increase in slag waste. In Morocco, OCP (Jorf Lasfar) generates more than 15 million tonnes per year of and the steel company (SONASID) produces slag waste (SC) 150,000 tonnes per year. Adding this waste to concrete may increase its mechanical strength. The Aim of this study is to incorporate these wastes with Bentonite of deposit Trebia (Nador, Morocco) stabilized by Lime to assess stabilization effect of bentonite in the presence of water (W). For this purpose the mixtures (BLW), (BL-PG-W) and (BL-PG-Ss-W), cured for 3, 7, 15 and 28 days, were analyzed by X-ray diffraction (XRD), infrared (IR), thermal analysis (DTA/TGA or DSC/TGA), scanning electron microscopy (SEM) and unconfined compressive strength (UCS). The kinetics setting and hardening of B-L and B-L-PG mixtures are slow. The addition of PG to the mixture (B-L) allows ettringite formation after 7 days of hydration and stratlingite after 28 days. The Slag accelerates the setting of the mixture and activates the pozzolanic reactions of bentonite. Mechanical strength is accelerated for the mixture (B-L-PG-Ss) comparable to other mixtures; it increases only after 3 days of setting. This improvement was confirmed for other curing times. The presence of Ye’elimite and other hydraulic binder phases present in slag could explain the increased hardening showed for B-L-PG-Ss mixtur

Thermodynamics and kinetics of the removal of methylene blue from aqueous solution by raw kaolin

Remediation of contaminated water with organic dyes originated from variety of industrial processes deserves increased attention. Raw clay is an effective low-cost and eco-environmentally friendly adsorbent for the removal of methylene blue (MB) from solution. This study aims to determine kinetics and thermodynamics of MB adsorption onto raw kaolin clays (halloysite and kaolinite/illite) from northeast of Morocco. The apportion capacity of the two kaolin clays to adsorb the MB dye by varying temperature and pH conditions was studied. The thermodynamic parameters show that the sorption of MB is spontaneous and endothermic for halloysite-rich clay, whereas adsorption onto kaolinite/illite is inhibited by electrostatic exothermic effects and the sorption is thermodynamically unfavorable. The kinetic study showed that the adsorption capacity of MB on halloysite is greater than on kaolinite. The intraparticle diffusion process controls the adsorption reaction, and the kinetic is more important for halloysite

Physico-mechanical behavior of solid waste-bentonite-lime based mixtures

This study aim to valorizing phosphogypsum (PG) and steel slag (Sc) in geotechnical applications by incorporating them in bentonite (B) stabilized by lime (L). Mineralogical (XRD), spectroscopic (IR-FTIR), geotechnical (Atterberg limits) analyzes were carried out on the raw material. Resistance to axial compression (UCS) was performed on cylindrical specimens prepared for mixtures B-L, B-L-PG and B-L-PG-Sc and after 3, 7, 15 and 28 days of hardening. The results obtained revealed that the mechanical strength increases with the addition of PG, and reaches its maximum value for a water content equal to 46%. Slag improves the strength of the B-L-PG mixture. The pH and the electrical conductivity of the solutions containing in porosity of the various mixtures decrease over time. The observed decrease is greatest for B-L-PG and B-L-PG-Sc mixtures

Mechanical properties and durability of lime mortar using aggregate made from phosphogypsum and steel mill slag

The present investigation deals with the utilization of phosphogypsum and steel mill slag combined with lime and raw bentonite as a cementitious material used for road construction and durability of mortar. The result reveals that the stabilization of bentonite by lime enhances mechanical strength of the material, mainly due to the alkaline environment promoting the formation of aluminates and silicates found in Portland cement. Additionally, the addition of phosphogypsum increases the compressive strength by 7 times, with an increase of 20% compared to lime-bentonite aggregate. This is partially due to stratlingite formation, obtained by reaction of CAH10 with C-S-H. The steel mill slag further increases this compressive strength by 10 times, because the occurrence of dicalcium silicate and metal flakes.Waste valoraisatio

Élaboration de nouveau matériau pour la construction routière à base des déchets industriels locaux : scories noires d’aciérie électrique et phosphogypse

The Black Steel slag (Ss) and phosphogypsum (PG) are industrial wastes produced in Morocco. In order to reduce these two wastes and to evaluate their pozzolanic reactivity in the presence of water, they were incorporated into bentonite (B) mixed with lime (L). The studied mixtures (BLW, BL–PG–W and BL–PG–Ss–W) were analyzed by X-ray diffraction, Infrared spectroscopy, Raman spectroscopy and SEM/EDX analysis. Compressive strength tests were performed on hardened specimens. The results obtained show that the hydration kinetics of the B– L–W and B–L–PG–W mixtures are slow. The addition of PG to a bentonite––lime mixture induces the formation of new microstructures such as hydrated calcium silicate (C–S–H) and ettringite, which increases the compressive strength of the cementitious specimens. The addition of the Ss to a mixture composed of 8%PG and 8%L–B accelerates the kinetics of hydration and activates the pozzolanic reaction. The presence of C2S in the slag helps to increase the mechanical strength of the mixture B–L–PG–Ss. The compressive strength of the mixtures BL–W, BL–PG–W and BL–PG–Ss–W increases from 15 to 28 days of setting. After 28 days of setting, 8% of Sc added to the mixture 8% PG–8%L–B is responsible for an increase of the compressive strength to 0.6 MPa

Physico-chemical, mineralogical, and technological characterization of stabilized clay bricks for restoration of Kasbah Ait Benhadou- Ouarzazate (south-east of Morocco)

Due to ageing, the unfired brick masonry may detach and fall off, or deteriorate to such an extent that it becomes necessary to restore them. Such is the case, for instance, of the Ksar of Ait Benhadou in Ouarzazate, Morocco. Our study aims to provide compatible and sustainable earthen bricks to restore this monument. Samples were collected from facades that were under conservation/restoration at the time when sampling was performed. Clayey soil samples were collected vicinity to the Ksar and analyzed by X-ray diffraction and X-ray fluorescence. A representative sample was stabilized with three aggregates (lime, cement and straw). The effect of ageing of the stabilized briquettes on shrinkage, water absorption, mechanical and thermal properties, compressive strength and thermal conductivity was studied on stabilized specimens. The samples consist mainly of clay minerals, calcite and quartz. They are rich in iron, aluminium and potassium. These samples are sandy with low plasticity (PI = 7%), which is slightly lower than the plasticity value required by the Moroccan standard for earth constructions. The results showed that the stabilized clayey soils have suitable properties such as density, porosity, water absorption and high thermal insulation. The best compressive strength performance is obtained for clay-stabilized samples with a high sand fraction. The thermal conductivity of clay-stabilized specimens increases as the specimens become denser and more compact, lime and straw have the opposite effect. Copyright 2022 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 3rd International Congress on Materials & Structural Stabilit