Efficient adsorption of acid orange 7 from wastewater using novel bio-natural granular bentonite-sawdust-corncob (GBSC): Mixture optimization, adsorption kinetic and regeneration.

The removal of dyes from industrial wastewater is one of the most environmental challenges that should be addressed through sustainable technologies. In this study, a novel green and cost-effective granular from bentonite and bio-wastes of sawdust and corncob (GBSC) was prepared for sustainable treatment of acid orange 7 (AO7) dye wastewater. The d-optimal mixture method was employed to determine the optimum combination of the GBSC in terms of dye adsorption and structure stability. Characterizations of the GBSC were investigated using SEM, XRD, FTIR and BET analyses and compared with bentonite powder (BP), modified bentonite powder (MBP), and granular modified bentonite (GMB). According to the results, a mixture of bentonite 60 wt%, sawdust 20 wt% and corncob 20 wt% at 550 °C yielded the optimal combination of the GBSC which resulted to the highest adsorption capacity 135.22 mg/g, the lowest mass loss 3.1% and maximum crushing strength 12.275 N. The kinetic and isotherm of the adsorption data were fitted well by the pseudo-second-order model and Langmuir isotherm. Our finding suggested a green circular economy model by utilizing agriculture wastes (sawdust and corncob) to synthesize GBSC for sustainable dye wastewater treatment, which offers a cost-effective adsorbent (0.907 $/g) with high regeneration (4 times reusability with 40.5% removal rate) to keep them in circulation for as long as possible.

A graphene oxide based composite granule for methylene blue separation from aqueous solution: Adsorption, kinetics and thermodynamic studies.

Graphene oxide and chitosan composite material using as a high-efficiency and low-cost granular adsorbent for methylene blue removal was fabricated via self-assembling method. The effects of pH value, contact time, initial concentration, adsorbent dose, temperature, and recyclic stability on the adsorption performance of methylene blue in aqueous solution were investigated in detail. Desorption process with the effects of solvents, contact time, and temperature were also conducted carefully in this study. The adsorption kinetics and adsorption isotherm of dye adsorption process showed that dye adsorption process was fitted to the pseudo-second-order kinetic model and the Freundlich adsorption isotherm, indicating a physical adsorption process with multilayer adsorption. The intra-particle diffusion model indicated that the dye adsorption by the granular adsorbent was strongly happened during the first 4 h. The thermodynamic study showed that the adsorption was a spontaneous and exothermic process and dye ions were condensed onto the surface of adsorbent. The maximum adsorption capacity of dye on the granular adsorbent was calculated as 951.35 mg/g and the adsorbent could maintain its adsorption performance after six cycles. In general, this study provided an efficient, cost-effective, and recyclable the granular adsorbent for dye separation from aqueous solution.

Mechanism of Phosphate Desorption from Activated Red Mud Particle Adsorbents.

Herein, activated red mud particles are used as adsorbents for phosphorus adsorption. HCl solutions with different concentrations and deionized water are employed for desorption tests, and the desorption mechanism under the following optimal conditions is investigated: HCl concentration = 0.2 mol/L, desorbent dosage = 0.15 L/g, desorption temperature = 35 °C, and desorption time = 12 h. Under these conditions, the phosphate desorption rate and amount reach 99.11% and 11.29 mg/g, respectively. Notably, the Langmuir isothermal and pseudo-second-order kinetic linear models exhibit consistent results: monomolecular-layer surface desorption is dominant, and chemical desorption limits the rate of surface desorption. Thermodynamic analysis indicates that phosphorus desorption by the desorbents is spontaneous and that high temperatures promote such desorption. Moreover, an intraparticle diffusion model demonstrates that the removal of phosphorus in the form of precipitation from the surface of an activated hematite particle adsorbent primarily occurs via a chemical reaction, and surface micromorphological analysis indicates that desorption is primarily accompanied by Ca dissolution, followed by Al and Fe dissolutions. The desorbents react with the active elements in red mud, and the vibrations of the [SiO4]4- functional groups of calcium-iron garnet and calcite or aragonite disappear. Further, in Fourier-transform infrared spectra, the intensities of the peaks corresponding to the PO43- group considerably decrease. Thus, desorption primarily involves monomolecular-layer chemical desorption.

Evaluation of the adsorption of ammonium-nitrogen and phosphate on a granular composite adsorbent derived from zeolite.

To remove the extra ammonium-nitrogen (NH3-N) and phosphorus (P) from contaminated water, a novel granular adsorbent (GAZCA) was fabricated with zeolite powders and Al-Mn binary oxide (AMBO) via the compression method. The SEM-EDS and mapping and XRD results illustrated the microstructure of GAZCA: the homogeneous aggregation of zeolite and AMBO nanoparticles with their crystal integrity and the uniform distribution of Al/Mn/Si/O elements on the adsorbent surface. FTIR and XPS results demonstrated the existence of impregnated sodium cations and hydroxyl groups, which were responsible for the removal of NH3-N and P, respectively. The results of BET analysis and compression tests exhibited a high surface area (14.4 m2/g) and a satisfactory mechanical strength of GAZCA. Kinetic adsorption results showed a fast adsorption rate for NH3-N and P, and mutual inference was not observed between the adsorption kinetics of NH3-N and P in the bi-component system. The adsorption isotherm results demonstrated that the maximum adsorption capacities of NH3-N and P were calculated as 12.9 mg/g and 9.3 mg/g via the Langmuir model, respectively. In the bi-component system, the adsorption capacities of NH3-N and P were maintained at low and moderate concentrations and decreased at high concentrations due to the blockage effects of NH4MnPO4·H2O precipitates. The removal efficiency of NH3-N could be maintained in a wide pH range of 4~10, while P adsorption was inhibited at alkali conditions. The solution of sodium bicarbonate (0.4 M) was used for the regeneration of saturated adsorbents, which permitted GAZCA to keep 98% and 78% of its adsorption capacity for NH3-N and P even after three regeneration and reuse cycles. Dynamic experiments illustrated that a satisfactory performance was obtained for the in situ treatment of simulated N- and P-contaminated water by using a column reactor packed with GAZCA, thus further confirming its great potential for the control of eutrophication.

Adsorptive removal of fluoride from water by granular zirconium-aluminum hybrid adsorbent: performance and mechanisms.

Granular zirconium-aluminum hybrid adsorbent (GZAHA) was fabricated for efficient defluoridation of groundwater in filter application. GZAHA was formed through the aggregation of massive Zr/Al oxide nanoparticles with an amorphous pattern. This adsorbent has a satisfactory mechanical strength, a specific surface area of 29.55 m2/g, and numerous hydroxyl groups on the surface. F adsorption equilibrium could be achieved within 12 h, and the sorption process followed a pseudo-second-order reaction rate. The maximum adsorption capacity of F estimated from the Langmuir model was 65.07 mg/g at 25 °C, being greater than most of other granular adsorbents. The removal efficiency of F could be maintained in a wide pH range of 5~9. The presence of phosphate posed an adverse effect on F adsorption due to the competition mechanisms. The saturated adsorbents could be regenerated and reused for four times by using sodium hydroxide solution as an eluent, and the adsorption capacity remained around 80%. Besides electrostatic attraction and Al-F complex, surface complexation and anion exchange were also involved in the adsorption process. Continuous adsorption experiments illustrated that 808 bed volumes of F-contaminated water (F = 5 mg/L) were treated successfully by a GZAHA-packed column without second pollution.

Granular tri-metal oxide adsorbent for fluoride uptake: Adsorption kinetic and equilibrium studies.

A novel adsorbent embedding Mg-Al-Zr mixed oxides with millimetre-sized calcium alginate beads (SA-CMAZ) was synthesized, characterized, and applied for the secondary removal of fluoride from wastewater. Key factors affecting the fluoride adsorption, including initial fluoride concentration, contact time, initial pH and coexisting anions, were investigated. The results showed that fluoride could be removed by SA-CMAZ over a wide pH range, from 4 to 10. The presence of coexisting anions weakened the adsorption of fluoride, and the decreasing order of the removal towards fluoride was PO43->CO32->SO42->NO3-. The adsorption follows a pseudo second order kinetic with theoretical adsorption capacity (Qe,cal) and experimental adsorption capacity (Qe,exp) close to each other at the temperatures of 303K, 308K, and 313K. The equilibrium data could be fitted by the Freundlich isotherm model as the SA-CMAZ is a heterogeneous. The value of the thermodynamic parameter indicated an endothermic adsorption process. A negative value shows the feasibility and spontaneity of the material-anion interaction.

Removal of arsenic(III,V) by a granular Mn-oxide-doped Al oxide adsorbent: surface characterization and performance.

In order to remove arsenic (As) from contaminated water, granular Mn-oxide-doped Al oxide (GMAO) was fabricated using the compression method with the addition of organic binder. The analysis results of XRD, SEM, and BET indicated that GMAO was microporous with a large specific surface area of 54.26 m2/g, and it was formed through the aggregation of massive Al/Mn oxide nanoparticles with an amorphous pattern. EDX, mapping, FTIR, and XPS results showed the uniform distribution of Al/Mn elements and numerous hydroxyl groups on the adsorbent surface. Compression tests indicated a satisfactory mechanical strength of GMAO. Batch adsorption results showed that As(V) adsorption achieved equilibrium faster than As(III), whereas the maximum adsorption capacity of As(III) estimated from the Langmuir isotherm at 25 °C (48.52 mg/g) was greater than that of As(V) (37.94 mg/g). The As removal efficiency could be maintained in a wide pH range of 3~8. The presence of phosphate posed a significant adverse effect on As adsorption due to the competition mechanisms. In contrast, Ca2+ and Mg2+ could favor As adsorption via cation-bridge involvement. A regeneration method was developed by using sodium hydroxide solution for As elution from saturated adsorbents, which permitted GMAO to keep over 75% of its As adsorption capacity even after five adsorption-regeneration cycles. Column experiments showed that the breakthrough volumes for the treatment of As(III)-spiked and As(V)-spiked water (As concentration = 100 µg/L) were 2224 and 1952, respectively. Overall, GMAO is a potential adsorbent for effectively removing As from As-contaminated groundwater in filter application.