LTA and FAU-X Iron-Enriched Zeolites: Use for Phosphate Removal from Aqueous Medium

Unlocking the potential of Tunisian dam sediment: optimizing zeolite X synthesis via Taguchi and Box-Behnken methods for sustainable resource recovery and versatile applications

The Tunisian Lebna dam sediment was utilized to create the zeolite faujasite type Na-X. The aim of this investigation is to optimize the yield of Na-X zeolite using alkaline fusion hydrothermal treatment. Taguchi orthogonal array design was employed with nine trials to explore operating parameters including fusion temperature and time, activator type, and sediment type. The efficiency of alkaline fusion was evaluated using acid solubility. After dissolving the optimal alkali-fused sample in water, the Box-Behnken plan was used to identify the influence of L/S ratio, crystallization temperature, and time on zeolite Na-X yield. Rietveld analysis identified the mineral phases in the sediment as quartz (82.0%), calcite (8.8%), kaolinite (6.0), and illite (1.2%). With a NaOH activator, 850 °C fusion temperature for 30 min, 15 L/S ratio, and 75 °C crystallization temperature for 4 days, highly crystalline zeolite Na-X was created. FTIR, TGA, N2 adsorption-desorption isotherm, and X-ray diffraction were used to thoroughly describe this sample. The findings reveal the substantial zeolitization potential of the raw Lebna dam sediment, resulting in a high yield of zeolite Na-X.

Evidence of electronic influence in the adsorption of cationic and zwitterionic dyes on zeolites

The adsorption of a cationic dye, Methylene blue (MB), and a zwitterionic dye, 8-Hydroxyquinoline (8-HQ), onto zeolites synthesized from different clays has been investigated. The presence of certain metals and the Si/Al ratio of the parent clay has an overall effect on the type of zeolites produced. Zeolites LTA and FAU Y were obtained using the hydrothermal method. X-ray diffraction and Fourier transform infrared spectroscopy (FTIR) spectral analysis was used to study the adsorption phenomena of the adsorbates on the adsorbents. The adsorption profile of MB (Topological Polar Surface Area (TPSA) 43.9 Å2 and 8-HQ (TPSA 33.1 Å2) compared favourably with a Freundlich isotherm with R2 > 0.9 for all the zeolitic materials synthesized. Adsorption capacities of zeolite FAU was significantly different from zeolite LTA for MB removal. The higher adsorption capacity of zeolite FAU was attributed to geometric effects resulting in greater shrinkage in the inter lattice spacing of zeolite LTA leading to a reduction in surface area. Adsorption of the relatively smaller 8-HQ however, did not show significant difference in the two zeolite types. Surface and structural characterization showed that adsorbates/adsorbents interactions were driven by both geometric (inter lattice spacing which imparts higher surface area of the adsorbent) and electronic (electrostatic repulsions through electron back donation from metals in the zeolitic structure) considerations.

From Waste to Added-Value Product: Synthesis of Highly Crystalline LTA Zeolite from Ore Mining Tailings

The use of wastes is necessary to contribute to environmental sustainability. In this study, ore mining tailings were used as the raw material and precursor for the synthesis of LTA zeolite, a value-added product. Pre-treated mining tailings were submitted to the synthesis stages under specific established operational conditions. The physicochemical characterization of the synthesized products was performed with XRF, XRD, FTIR and SEM, to identify the most cost-effective synthesis condition. The LTA zeolite quantification and its crystallinity were determined as effects of the SiO₂/Al₂O₃, Na₂O/SiO₂ and H₂O/Na₂O molar ratios used, as well as the influence of the synthesis conditions: mining tailing calcination temperature, homogenization, aging and hydrothermal treatment times. The zeolites obtained from the mining tailings were characterized by the LTA zeolite phase accompanied by sodalite. The calcination of mining tailings favored the production of LTA zeolite, and the influence of the molar ratios, aging and hydrothermal treatment times were determined. Highly crystalline LTA zeolite was obtained in the synthesized product at optimized conditions. Higher methylene blue adsorption capacity was associated with the highest crystallinity of synthesized LTA zeolite. The synthesized products were characterized by a well-defined cubic morphology of LTA zeolite and lepispheres of sodalite. The incorporation of lithium hydroxide nanoparticles over LTA zeolite synthesized (ZA-Li⁺) from mining tailings yielded a material with improved features. The adsorption capacity towards cationic dye was higher than for anionic dye, especially for methylene blue. The potential of using ZA-Li⁺ in environmental applications related to methylene blue deserves detailed study.

Adsorption of Phosphate and Ammonium on Waste Building Sludge

Two selected waste building sludges (WBS) were used in this study: (i) sludge from the production and processing of prestressed concrete pillars (B) and (ii) sludge from the production of technical stone (TS). The materials were used in their original and Fe-modified forms (B_Fe/TS_Fe) for the adsorption of NH₄⁺ and PO₄^3- from contaminated waters. The experiments were performed on a model solution simulating real wastewater with a concentration of 1.7 mmol·L^-1 (NH₄⁺) and 0.2 mmol·L^-1 (PO₄^3-). The adsorption of PO₄^3- had a high efficiency (>99%) on B, B_Fe and TS_Fe, while for TS, the adsorption of PO₄^3- was futile due to the high content of available P in the raw TS. The adsorption of NH₄⁺ on all sorbents (B/B_Fe, TS/TS_Fe) had a lower efficiency (<60%), while TS proved to be the most effective. Leaching tests were performed according to the CSN EN 12457 standard for B/B_Fe and TS/TS_Fe before and after NH₄⁺ and PO₄^3- sorption when the contents of these ions in the leachates were affected by adsorption experiments in the cases of B and TS. For B_Fe and TS_Fe, the ion content in the leachates before and after the adsorption experiments was similar.

Using Iron Tailings for Phosphate Removal in Cemented Phosphogypsum (PG) Backfill

Compared with the post-treatment of pollutants, such as the removal of phosphate from wastewater, it is more important to develop effective emission control strategies to reduce phosphate pollution. Phosphogypsum (PG) is a typical solid waste byproduct of phosphate production and contains high amounts of residual phosphate. In order to control the phosphate emissions during the recycling of PG aggregates for cemented backfill, another solid waste product—iron tailings (ITs)—was added during the preparation of backfill slurry. The results showed that the ITs effectively accelerated the phosphate removal in cemented PG backfill, enabling the quick reduction in the phosphate concentration to the discharge standard (<0.5 mg/L) within 15 min. This means that the emissions of phosphate to bleeding water were effectively controlled. The adsorption experiment showed that phosphate was adsorbed by the ITs, and the adsorption data fitted well with the Langmuir adsorption model (R2 = 0.98) and pseudo-second-order kinetic model (R2 = 0.99), indicating that the phosphate adsorption of ITs was a monolayer chemical adsorption. Furthermore, an unconfined compressive strength (UCS) test was performed on the backfill with the addition of ITs. Compared to the control group (without ITs), the UCS of backfill with 20% ITs increased from 1.08 MPa to 1.33 MPa, indicating that the addition of solid waste could be beneficial to the strength development of the backfill by mitigating the interference of phosphate with the hydration process. The backfill cured for 28 d was selected for the toxic leaching test, and the phosphate concentration in the leachates was always below 0.02 mg/L, indicating that ITs can effectively immobilize phosphate in backfill for a long time.

Fe3+/Mn2+ (Oxy)Hydroxide Nanoparticles Loaded onto Muscovite/Zeolite Composites (Powder, Pellets and Monoliths): Phosphate Carriers from Urban Wastewater to Soil

The development of an efficient adsorbent is required in tertiary wastewater treatment stages to reduce the phosphate-phosphorous content within regulatory levels (1 mg L^-1 total phosphorous). In this study, a natural muscovite was used for the preparation of muscovite/zeolite composites and the incorporation of Fe³⁺/Mn²⁺ (oxy)hydroxide nanoparticles for the recovery of phosphate from synthetic wastewater. The raw muscovite MC and the obtained muscovite/sodalite composite LMC were used in the powder form for the phosphate adsorption in batch mode. A muscovite/analcime composite was obtained in the pellets PLMCT₃ and monolith SLMCT₂ forms for the evaluation in fixed-bed mode for continuous operation. The effect of pH, equilibrium and kinetic parameters on phosphate adsorption and its further reuse in sorption-desorption cycles were determined. The characterization of the adsorbents determined the Fe³⁺ and Mn²⁺ incorporation into the muscovite/zeolite composite's structure followed the occupancy of the extra-framework octahedral and in the framework tetrahedral sites, precipitation and inner sphere complexation. The adsorbents used in this study (MC, LMC, PLMCT₃ and SLMCT₂) were effective for the phosphate recovery without pH adjustment requirements for real treated wastewater. Physical (e.g., electrostatic attraction) and chemical (complexation reactions) adsorption occurred between the protonated Fe³⁺/Mn²⁺ (oxy)hydroxy groups and phosphate anions. Higher ratios of adsorption capacities were obtained by powder materials (MC and LMC) than the pellets and monoliths forms (PLMCT₃ and SLMCT₂). The equilibrium adsorption of phosphate was reached within 30 min for powder forms (MC and LMC) and 150 min for pellets and monoliths forms (PLMCT₃ and SLMCT₂); because the phosphate adsorption was governed by the diffusion through the internal pores. The adsorbents used in this study can be applied for phosphate recovery from wastewater treatment plants in batch or fixed-bed mode with limited reusability. However, they have the edge of environmentally friendly final disposal being promissory materials for soil amendment applications.

Effect of Mn2+/Zn2+/Fe3+ Oxy(Hydroxide) Nanoparticles Doping onto Mg-Al-LDH on the Phosphate Removal Capacity from Simulated Wastewater

A parent Mg-Al-LDH was upgraded in its adsorption properties due to the incorporation of tri-metal species oxy(hydroxide) nanoparticles obtaining Mn²⁺/Zn²⁺/Fe³⁺/Mg-Al-LDH composite for the phosphate recovery from simulated urban treated wastewater. The physicochemical properties of the synthesized Mn²⁺/Zn²⁺/Fe³⁺/Mg-Al-LDH make promising for real application without being environmentally harmful. The performance of Mn²⁺/Zn²⁺/Fe³⁺/Mg-Al-LDH composite was evaluated through batch adsorption assays. The support of iron, manganese, and zinc (oxy)hydroxide nanoparticles onto the parent Mg-Al-LDH structure was performed by precipitation, isomorphic substitution, and complexation reactions. The main improvement of the Mn²⁺/Zn²⁺/Fe³⁺/Mg-Al-LDH composite was the highest phosphate adsorption capacity (82.3 mg∙g^-1) in comparison to the parent Mg-Al-LDH (65.3 mg∙g^-1), in a broad range of concentrations and the effective phosphate adsorption at neutral pH (7.5) near to the real wastewater effluents conditions in comparison to the conventional limitations of other adsorbents. The effectiveness of Mn²⁺/Zn²⁺/Fe³⁺/Mg-Al-LDH composite was higher than the conventional metal LDHs materials synthesized in a single co-precipitation step. The phosphate adsorption onto Mn²⁺/Zn²⁺/Fe³⁺/Mg-Al-LDH composite was described to be governed by both physical and chemical interactions. The support of Mn²⁺/Zn²⁺/Fe³⁺ oxy(hydroxide) nanoparticles over the parent Mg-Al-LDH was a determinant for the improvement of the phosphate adsorption that was governed by complexation, hydrogen bonding, precipitation, and anion exchange. The intra-particular diffusion also described well the phosphate adsorption onto the Mn²⁺/Zn²⁺/Fe³⁺/Mg-Al-LDH composite. Three specific stages of adsorption were determined during the phosphate immobilization with an initial fast rate, followed by the diffusion through the internal pores and the final equilibrium stage, reaching 80% of removal and the equilibrium within 1 h. The Mn²⁺/Zn²⁺/Fe³⁺/Mg-Al-LDH was strongly selective towards phosphate adsorption in presence of competing ions reducing the adsorption capacity at 20%. The Mn²⁺/Zn²⁺/Fe³⁺/Mg-Al-LDH has limited reusability, only 51% of the adsorbed phosphate could be recovered in the second cycle of the adsorption-desorption process. Around 14% of phosphate was loosely-bond to Mn²⁺/Zn²⁺/Fe³⁺/Mg-Al-LDH which brings the opportunity to be a new source of phosphorus. The use of eluted concentrates and the final disposal of the exhausted adsorbent for soil amendment applications can be an integral nutrient system (P, Mn, Zn, Fe) for agriculture purposes.