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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+/Zn, Peer Reviewed, Postprint (published version)

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, Peer Reviewed, Postprint (published version)

Hydrothermally synthesized Linde type A (LTA) and faujasite X (FAU-X) zeolites are low-cost and environmentally benign inorganic carriers for environmental applications. In this study, (oxy)hydroxides were incorporated onto LTA and FAU-X zeolites to promote the phosphate adsorption. The performance of LTA-Fe and FAU-X-Fe was evaluated through batch adsorption assays. A complete evaluation was performed to recover phosphate from synthetic wastewater. The effect of pH, concentration, equilibrium, and kinetic parameters on phosphate adsorption and its further reuse in sorption–desorption cycles were evaluated. LTA-Fe and FAU-X-Fe are effective for adsorption of phosphate at neutral (e.g., pH 7.0 ± 0.2) and in a broad range of phosphate concentrations. Higher ratios of adsorption capacities were obtained by synthetic zeolites enriched with iron in comparison to their parent forms. The phosphate adsorption occurred through hydrogen bonding and complexation reactions between protonated iron hydroxyl groups and phosphate anions. The phosphate monolayer adsorption was followed by diffusion through the internal pores and 80% of the equilibrium adsorption was reached within 50 min. The LTA-Fe and FAU-X-Fe can be used for phosphate recovery from wastewater treatment plants. The use of LTA-Fe and FAU-X-Fe in a tertiary wastewater treatment stage could allow to reduce the phosphate–phosphorous content, reaching the regulatory levels (equal 1 mg L-1 total phosphorous). The phosphate adsorption using LTA-Fe and FAU-X-Fe does not require pH adjustment, and it is endothermic. The reusability of both iron zeolites is limited, and they can be finally disposed for soil amendment applications., Peer Reviewed, Postprint (published version)

The aim of this work was to investigate the properties of two clays and a natural zeolite available in Ecuador, for the removal of Arsenic (III), (As (III)), in synthetic aqueous solutions. The adsorbents were prepared from the powdered solids, shaped as cylindrical extrudates of 0.5 cm in length by 0.2 cm in diameter approximately, and characterized by X-ray Diffraction (XRD), X-ray Fluorescence (FRX) and specific area ( Ae). Arsenic adsorption in aqueous systems was determined by charging load experiments, using a dosage of 0.1 L of solution per grame of adsorbent, at 30 ° C in a stirred system (100 r. p. m.). The Arsenic content was determined by means of atomic absorption spectrophotometry with a hydride generator. The kinetics absorption was analyzed by following the variation of the concentration of an 80 mg As/L solution, taken at different times for an extended period of 24 hours. The experimental data showed a good fit using a pseudo-first-order equation for the natural zeolite and pseudo-second-order equation for the two clays. The maximum adsorption capacity of As was higher for clays (13-15 ) compared to zeolite (5-6 ). These values are lower compared to those reported in the literature, however, the solids studied have the advantage of requiring a simple preparation process and they represent an abundant cheap raw material in the country., El objetivo fue investigar las propiedades de dos arcillas y una zeolita natural disponibles en Ecuador, para la remoción de Arsénico (III) (As (III)) en soluciones acuosas sintéticas. Los adsorbentes fueron preparados a partir de los sólidos en polvo, conformados como extruidos cilíndricos de 0,5 cm de longitud por 0,2 cm de diámetro, aproximadamente, y caracterizados mediante difracción de rayos X (DRX), fluorescencia de rayos X (FRX) y área específica (Ae). La adsorción de As (III) en sistemas acuosos se realizó en experimentos por carga, usando una dosificación de 100 mL de solución por gramo de adsorbente, a 30 °C en un sistema agitado (100 r. p. m.) y pH 7. El contenido de As se determinó mediante espectrofotometría de absorción atómica con generador de hidruros. La cinética de adsorción se estudió siguiendo la variación en la concentración de una solución de 80 mg de As/L, tomada a diferentes tiempos durante 24 h. Los datos experimentales se ajustaron bien mediante una ecuación de seudoprimer orden para la zeolita natural y seudosegundo orden para las dos arcillas. La capacidad máxima de adsorción de As fue mayor para las arcillas (13-15 ) comparada con la zeolita (5-6 ). Estos valores son menores comparados con algunos reportados en la literatura; sin embargo, los sólidos estudiados tienen la ventaja de requerir un proceso de preparación simple y son una materia prima barata y abundante en el país.

Natural inorganic adsorbents are attractive for pollutants removal due to the easy operation, non-toxic char- acteristics and low cost. In this study, two raw clays (C1 and C2) were doped with iron and evaluated for the recovery of phosphate from simulated urban treated wastewater. The adsorbents' performances were evaluated through batch adsorption assays. Iron was stably retained in doped clays (C1-Fe and C2-Fe) at basal and edge surface at adsorption and desorption stages. Clay adsorbents were effective for adsorption of phosphate at neutral pH 7 and in broad range of phosphate concentrations. The maximum phosphate adsorption capacity values were 21, 38, 21 and 38 for C1, C1-Fe, C2 and C2-Fe, respectively. The equilibrium sorption data of raw and iron-doped clays were well described by the Langmuir isotherm model (R2 > 0.97). Therefore, monolayer phosphate adsorption occurred through hydrogen bonding and complexation between protonated hydroxyl groups and phosphate anions. The raw and iron-doped clay adsorbents reached the equilibrium within 10 min and the equilibrium attainment data were well described by the intraparticular diffusion model (R2 > 0.96). The phosphate monolayer adsorption was followed by diffusion through the internal clay pores. The phosphate adsorption by clays in presence of competing ion was inhibited by the higher ionic charge of sulphate. Besides, the less hydrated chloride and bicarbonate anions promoted the reduction of the sorption capacity of phosphate. Finally, the reusability of iron-doped clays is limited. Therefore, saturated iron-doped clays as single-use ad- sorbents can be disposed for soil amendment applications., Peer Reviewed, Postprint (author's final draft)

The usefulness of a nutrient-enriched zeolite (NEZ) obtained from simultaneous ammonium (NH4+) and phosphate (PO43-) recovery from urban wastewaters was evaluated as soil amendment through the early growth of sunflower (Helianthus annuus). The NEZ systems were applied to sandy (acid) and clayey (basic) soils from Mediterranean agricultural areas (Spain). Some plant growth indicators were measured: evapotranspiration, plant moisture content, plant biomass, root/shoot ratio, nitrogen and phosphorous uptake and the C/N ratio. The experimental data exhibited differences in the growth indicators for un-amended and amended soils. The addition of the NEZ system increase the plant water content of sunflowers grown on clay soils. The plant biomass of sunflower was improved by the incorporation of NEZ system in all treatments for the two soils studied. A reduction of the root/shoot ratio for the treatments of clay soil by application of NEZ systems were observed. The content of ammonium and phosphorous in tissues increased considerably with the addition of amendment material. Besides, the ammonium, nitrate and inorganic phosphorous in the post-test soils revealed that nutrients were still available for a second growth cycle. As demonstrated in previous work, the NEZ system releases nutrients continuously controlled by soil pH and mineral composition as well as the irrigation conditions provided. Therefore, this approach of amendment materials for soil seems to be a promising alternative for agricultural practice, where the dose selection must be balanced according to the plant's nutrient needs and soil properties by adjusting the growth conditions, Peer Reviewed, Postprint (author's final draft)