Halloysite nanotubes (HNTs) are clay minerals with a hollow nanotubular structure. There is growing interest in these nanomaterials, due to their biocompatibility, potential applications and availability. The surface chemistry of HNTs is versatile for the targeted chemical modification of the inner lumen and outer surface. Functionalized halloysite constitutes a valuable support for metal nanoparticles, promoting catalytic applications with tunable properties. The peculiar tubular shape of HNTs favors the dispersion and surface availability of the supported metal nanoparticles that are active in the catalytic path. Moreover, the presence of an empty lumen opens new perspectives for the production of nanoarchitectures with synergistic catalytic effects, due to the increase in local concentrations and confinement. The main focus of this review is the research on modified halloysite nanotubes for the preparation of valuable supports for metal nanoparticles and their applications in catalytic processes.

Halloysite Nanotubes as Support for Metal-Based Catalysts

This study aimed to develop non-metal elements for doping carbon quantum dots (CQDs) with nitrogen and sulfur (N, S-CQDs), which loaded inside hexagonal mesoporous silica (HMS) in order to effectively remove methylene blue dye (MB) from an aqueous solution. The histidine and cysteine amino acids were used as the source for synthesis N, S-CQDs through the hydrothermal method. Morphology and structure of the N, S-CQDs, and adsorbent (N, S-CQDs/HMS) were characterized by using different microscopic and spectroscopic techniques. The adsorption parameters such as adsorbent dosage (0.25–1 g/L), pH (2–10), contact time (15–75 min), and initial MB dye concentration (20–300 mg/L) were investigated. The maximum adsorption capacity and removal efficiency of MB were determined at 370.4 mg/g and 97%, respectively, under optimum conditions at 303 K. The adsorption isotherm studies were fitted with the Freundlich isotherm equation, and the dye removal kinetics of the adsorbent followed the pseudo-second-order model. Thermodynamic studies showed that the adsorption process had exothermic and spontaneous behavior. The removal of MB next to the Rhodamine B and Reactive Black 5 dyes indicated that the N, S-CQDs/HMS had excellent selective behavior for MB absorption. This prepared adsorbent could be well recycled with suitable activity after four repeated adsorption–desorption cycles. Results revealed that the porous characters, surface area, charge properties, reduction in the bandgap, and quantum yield of the N, S-CQDs/HMS were essential factors that affected dye adsorption.

/pdf/n-s-doped-carbon-quantum-dots-inside-mesoporous-silica-for-23d2z0dkwk.pdf

N, S doped carbon quantum dots inside mesoporous silica for effective adsorption of methylene blue dye

Phosphogypsum (PG), the main industrial by-product of phosphate fertilizer industry, primarily consists of calcium sulfate dihydrate. However, it contains various impurities with variable quantities depending on the origin of the phosphate rock. These impurities can restrict the reuse of phosphogypsum as a secondary primary resource. Consequently, large quantities of produced PG are stored in surface stockpiles that occupy extensive land areas and may pose a significant risk of ecological contamination to the surroundings. Researchers have shown growing interest in addressing the worldwide accumulation of this waste material. To gain a comprehensive understanding of the environmental impact of phosphogypsum, it is crucial to explore its properties (e.g., chemistry, mineralogy, radioactivity), and how it interacts with the surrounding environment, enabling well-informed decisions decision regarding its management and its valorization. In this review, we will i) explore the chemical, radiological and mineralogical characteristics of PG; ii) discuss the environmental concerns related to land discharge and sea disposal; and iii) examine the latest advancements in various valorization techniques developed including agriculture, REE extraction, environmental application, chemical and thermal transformation, and also construction sector. Outlining their limitations and challenges restrict in the global variability of phosphogypsum (PG), technical and economic limitations, and the potential for secondary pollution in select valorization approaches. This requires a thorough assessment and comparison with conventional disposal alternatives. 

Exploring the potential reuse of PG: A waste or a resource?

Development and optimization of phosphogypsum-based geopolymer cement

Study of adsorption mechanism of Malachite Green (MG) and Basic Yellow 28 (BY28) onto smectite rich natural clays (Ghassoul) using DFT/B3LYP and DOE/FFD

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.

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

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

https://orbi.uliege.be/bitstream/2268/268651/1/1-s2.0-S221478532200534X-main.pdf

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

Mining dumps, particularly inactive or abandoned mines located near makeshift mining towns, have significant environmental and social impacts. The Touissit-Boubker lead mine, operated for years by the Touissit Mining Company (CMT) and abandoned without rehabilitation, is an example of this socio-economic and environmental collapse. Large quantities of harmful solid waste containing clayey aggregates rich in lead sulphide have been dumped in dykes on the edge of the village of Touissit. These mining wastes were rewashed to extract galena causing a depletion of lead sulphide. The objective of this study is to evaluate the possibility of using washed mining waste as sandy aggregate for the manufacture of masonry mortar. Cylindrical mortar tests, made with various proportions of sand and mine waste were characterized by X-ray diffraction, scanning electron microscopy and mechanical analysis by uni-axial compressive strength after curing for 3, 14, 28 and 60 days. The results obtained revealed that the mining waste consists of dolomite, quartz and clay. The dehydration rate of the mortar specimens is strongly affected by the amount of the waste added and the grain size. The mechanical strength of the mortar specimens mostly depends on the grain-size of the aggregates than on the amount of mine waste added. The microstructure of the mortar did not change when sand was replaced by mine waste of the same grain size.

/pdf/assessment-of-a-mining-waste-dump-of-galena-mine-in-the-east-1ygrvf0o.pdf

Assessment of a Mining-Waste Dump of Galena Mine in the East of Morocco for Possible Use in Civil Engineering

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 BL-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 by 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.

https://www.preprints.org/manuscript/202009.0762/v1/download

Development of a New Ecological Material Based on Moroccan Industrial Wastes for Road Construction

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