Enhancing removal and recovery of magnesium from aqueous solutions by using modified zeolite and bentonite and process optimization

Natural Zeolite for The Purification of Saline Groundwater and Irrigation Potential Analysis

Groundwater is one of the main sources of water for irrigation used worldwide. However, the application of the resource is threatened by the possibility of high saline levels, especially in low-lying coastal regions. Furthermore, the lack of readily accessible materials for successful treatment procedures makes the purification of such water a constant challenge. Based on the fact that natural zeolite is one of the easily accessible and relatively cheap filter materials, this study examined the potential use of high-salinity groundwater filtered by natural zeolite for irrigation. Zeolite-filled filters at two different depths (0.5 m and 1 m) were studied. The samples were collected from the low-lying areas of Dar es Salaam City, Tanzania. The study observed that when the raw groundwater samples were exposed to the 0.5 m column depth, sodium (Na⁺) had the lowest removal efficiency at 40.2% and calcium (Ca²⁺) had the highest removal efficiency at 98.9%. On the other hand, magnesium (Mg²⁺) had the lowest removal efficiency, at about 61.2%, whereas potassium (K⁺) had up to about 99.7% removal efficiency from the 1 m column depth treatment system. Additionally, from the salinity hazard potential analysis, most of the samples fell within C4 (based on the electrical conductivity), which is a "very high salinity" class, and based on the quality it means the water cannot be directly applied for irrigation purposes. From the 0.5 m column depth, most of the samples fell within C3 (the "high salinity" class), and from the 1 m column depth most of the samples fell within C1 ("low salinity" class). The findings of this study offer some valuable insight into the prospective use of natural zeolite for the filtration of saline groundwater before its application for irrigation.

Ethylenediaminetetraacetate functionalized MgFe layered double hydroxide/biochar composites for highly efficient adsorptive removal of lead ions from aqueous solutions

The application of layered double hydroxides (LDHs) of MgFe and its composites with biochar of Eucalyptus camdulensis (Eb) and ethylenediaminetetraacetic acid (EDTA) was explored in a batch study to mitigate toxic lead ions (Pb²⁺) from synthetic wastewater solutions. SEM images revealed that MgFe/LDH composites with Eb were successfully formed, while FTIR spectra confirmed the successful adsorption of Pb²⁺ onto the MgFe/LDH and composite adsorbents. Batch equilibrium was attained after 60 min, then the adsorption capacity gradually increased. An increase in adsorption capacity (and a 60% decrease in the percentage removal) was observed by increasing the initial Pb²⁺ concentration, and the highest value was 136 mg g^-1 for MgFe/LDH-Eb_EDTA. A 50–60% increase in both the adsorption capacities and percent removal was seen in the pH range of 2–6. The second-order kinetic model had a nearly perfect fitting, suggesting that chemisorption was the mechanism controlling adsorption. The Langmuir isotherm model best presented the adsorption data, suggesting that the Pb²⁺ adsorption was monolayer, and predicted a better affinity between the adsorbent surface and absorbed Pb²⁺ for MgFe/LDH-Eb_EDTA in comparison to the other two adsorbents. The D–R isotherm suggested that the adsorption system was physical based on E values for all three adsorbents, while the Temkin isotherm model suggested that Pb²⁺ adsorption was heterogeneous. Finally, the Sips and R–P isotherms predicted that the adsorption of Pb²⁺ on the surface of the adsorbents was homogeneous and heterogeneous.

Effective Removal of Calcium and Magnesium Ions from Water by a Novel Alginate-Citrate Composite Aerogel

In this work, a novel alginate/citrate composite aerogel (CA-SC) was synthesized by chemical grafting technology combined with vacuum freeze-drying method, and CA-SC was used for removing calcium (Ca2+) and magnesium (Mg2+) ions from water. The experimental results indicate that the as-prepared CA-SC has a high affinity for Ca2+ and Mg2+ and can remove 96.5% of Ca2+ (or 96.8% of Mg2+) from the corresponding solution. The maximum adsorption capacities of CA-SC for Ca2+ and Mg2+ are 62.38 and 36.23 mg/g, respectively. These values are higher than those of the most reported Ca2+-sorbents and Mg2+-sorbents. The CA-SC adsorbent can be regenerated through a simple pickling step, and its adsorption performance keeps stable after repeated use. Analysis of the adsorption mechanism shows that the CA-SC combines Ca2+ and Mg2+ in water mainly through coordination effect.

Effective decontamination of Ca2+ and Mg2+ hardness from groundwater using innovative muscovite based sodalite in batch and fixed-bed column studies; dynamic and equilibrium studies

A novel form of sodalite was synthesized from muscovite (M.SD) as low-cost softening material for both Ca²⁺ and Mg²⁺ ions from real groundwater in batch and column studies. The sodalite sample showed significant surface area (105 m²/g) and ion exchange capacity (87.3 meq/100 g) which qualifies it strong for softening applications. The incorporation of the M.SD as a fixed bed in column system at a fixed thickness of 4 cm and flow rates of 5 mL/min resulted in removal percentages of 90.5% and 92.2% for Ca²⁺ and Mg²⁺, respectively at pH 7.6. Considering the real concentrations of the ions (Ca²⁺ (233 mg/L) and Mg²⁺ (114 mg/L)), the M.SD bed has the ability to reduce their concentrations according to the recommended limits (75 mg/L for Ca²⁺ and 50 mg/L for Mg²⁺). These conditions resulted in purification of about 8.1 L and 8.7 L with breakthrough intervals of 1380 min and 1440 min; and saturation interval more than 1620 min for Ca²⁺ and Mg²⁺, respectively. The M.SD columns' performances were described considering the assumption of the Thomas model, Adams-Bohart model, and Yoon-Nelson model. The batch studies demonstrate the uptake of both Ca²⁺ and Mg²⁺ ions according to the Pseudo-First order kinetics and Langmuir equilibrium behaviour. Considering the values of Gaussian energies (0.77 KJ/mol (Ca²⁺) and 1.36 KJ/mol (Mg²⁺)), the uptake of these ions occurred by homogenous reactions of monolayer form and physical nature. The thermodynamic studies declared the spontaneous properties of the reactions and their exothermic properties.

Preparation and application of modified zeolites as adsorbents in wastewater treatment

Natural zeolite has been recognized as a useful adsorbent for wastewater treatment for removing cations. Natural zeolite is a kind of porous material with large specific surface area but limited adsorption capacity. In recent years, emphasis has been given to prepare the surface modified zeolite using various procedures to enhance the potential of zeolite for pollutants. Modification treatment for zeolite can greatly change surface chemistry and pore structure. The article describes various modification methods of zeolite, and introduces the removal mechanisms of common pollutants such as ammonium, phosphorus and heavy metals. In addition, this review paper intends to present feasibility of applying modified zeolite to constructed wetlands which will be beneficial to achieve higher removal effect.

Significance, evolution and recent advances in adsorption technology, materials and processes for desalination, water softening and salt removal

Desalination and softening of sea, brackish, and ground water are becoming increasingly important solutions to overcome water shortage challenges. Various technologies have been developed for salt removal from water resources including multi-stage flash, multi-effect distillation, ion exchange, reverse osmosis, nanofiltration, electrodialysis, as well as adsorption. Recently, removal of solutes by adsorption onto selective adsorbents has shown promising perspectives. Different types of adsorbents such as zeolites, carbon nanotubes (CNTs), activated carbons, graphenes, magnetic adsorbents, and low-cost adsorbents (natural materials, industrial by-products and wastes, bio-sorbents, and biopolymer) have been synthesized and examined for salt removal from aqueous solutions. It is obvious from literature that the existing adsorbents have good potentials for desalination and water softening. Besides, nano-adsorbents have desirable surface area and adsorption capacity, though are not found at economically viable prices and still have challenges in recovery and reuse. On the other hand, natural and modified adsorbents seem to be efficient alternatives for this application compared to other types of adsorbents due to their availability and low cost. Some novel adsorbents are also emerging. Generally, there are a few issues such as low selectivity and adsorption capacity, process efficiency, complexity in preparation or synthesis, and problems associated to recovery and reuse that require considerable improvements in research and process development. Moreover, large-scale applications of sorbents and their practical utility need to be evaluated for possible commercialization and scale up.