Novel approach for selective phosphate removal using colloidal layered double hydroxide nanosheets and use of residue as fertilizer

Anion Selectivity of Layered Double Hydroxides: Effects of Crystallinity and Charge Density

“…The last two samples for each COP-and HYD-LDH, which were produced at the preparation stage Mg/Al ratios of 6.0 and 6.5, contain minor Mg(OH) 2 phases in addition to the LDHs. Mg(OH) 2 has been confirmed to have no influence on this adsorption of SO 4 2-and NO 3 -, as will be mentioned in the next section. When the Mg/ Al ratio in the product increases (the charge density of the host layers decreases), the results for both types of LDHs indicate that SO 4 2-removals begin to decrease at an Mg/Al ratio of about 3, and there is an abrupt drop when the Mg/Al ratio exceeds about 3.5.…”

“…Mg(OH) 2 has been confirmed to have no influence on this adsorption of SO 4 2-and NO 3 -, as will be mentioned in the next section. When the Mg/ Al ratio in the product increases (the charge density of the host layers decreases), the results for both types of LDHs indicate that SO 4 2-removals begin to decrease at an Mg/Al ratio of about 3, and there is an abrupt drop when the Mg/Al ratio exceeds about 3.5. After that drop, removal percentages become almost constant again at Mg/Al ratios greater than 4.3 and 4.9 for COP-LDHs and HYD-LDHs, respectively.…”

“…Excessive use of fertilizer and inappropriate disposal of livestock excrement are potential pended on the Mg/Al molar ratio, compared with low-crystallinity LDHs with smaller particle sizes. When the Mg/Al ratio increased, selectivity of high-crystallinity LDHs for SO 4 2-and F -decreased, whereas that for NO 3 -increased. In the case of F -, the diameter of which is smaller than the height of the flat orientation of NO 3 -, this result indicates that an ion sieve effect is not the only factor that determines selectivity.…”

“…[1][2][3][4][5] LDHs are a class of lamellar materials in which metal hydroxide layers lie on top of each other, and anions and water molecules are located in the interlayer space. Although a wide variety of LDHs have been reported in terms of the constituent metals, the general formula of the LDHs that have most commonly been studied can be written as [M , and M 3+ are diand trivalent metal cations, and A n-refers to charge-balancing anions, which can often be a group of different anions.…”

Evaluation of Layered Double Hydroxide Synthesised from a Green Biogenic Precursor for Phosphate Removal: Characterisations and Isotherms

“…Sharp and intense symmetric peaks at low 2θ values and relatively less intense and symmetric basal reflections at higher 2θ values, characteristics of LDH-materials indicates the presence of Ca-Cr LDHs in the prepared materials [10][11]. Notably, the diffract graph of LDH1 sample differs from that of LDH2 and LDH4 samples in peak positions, intensities and basal lattice positions.…”