Study on the sorption–desorption–regeneration performance of Ca-, Mg- and CaMg-based layered double hydroxides for removing phosphate from water

Abstract

Various layered double hydroxides (LDHs) were prepared by the co-precipitation method using the most common divalent and trivalent metal precursors. The resulting LDHs were studied for their performance in removing phosphate from aqueous test solution. The results have clearly demonstrated the influence of Ca and Mg as precursor metals in synthesizing LDH compounds for removing phosphate. For the same LDH's dose, more phosphorus was removed by Ca-based LDHs than Mg-based LDHs. Real effluent from a wastewater treatment plant with high phosphate concentration (3.4-10.4 mg-P/L) can also be treated with >90% removal by both Ca-and Mg-based LDHs depending on the selection of suitable dose. For Ca-based LDHs, the main removal process was observed to be as calciumphosphate precipitation. Due to the loss of layered structure after first sorption/precipitation operation, Ca-(Fe or Al)-LDHs cannot be regenerated for reuse. However, Mg-based LDHs showed potentially applicable for the regeneration and reuse due to their stable nature in aqueous phase than Ca-based LDHs. On the other hand, when choosing CaMg-based LDHs for the phosphorus removal, the nature of Ca dissolution from such LDHs needs to be taken into account although they were demonstrated to be reusable with the efficiency of phosphate removal up to 64% at the fourth cycle.

Using Chemically Treated Organic Recycling Materials to Enhance Freshwater Purification

“…The deposit of calcium presented in this study allowed between 71% and 90% reduction of phosphate concentration (Table 3), which corresponds with the range obtained in other studies (75-98%) [29][30][31]. The lower efficiency observed during the second laboratory experiment with the higher phosphate inflow (Table 3 and Fig.…”

Polyethyleneimine as a novel desorbent for anionic organic dyes on layered double hydroxide surface

“…Generally, NaCl-NaOH, Na 2 CO 3 , or high-press CO 2 is employed as efficient desorbents to remove adsorbed anions from LDH materials via anion exchange process [11][12][13][14]. However, these desorbents require to be in high concentrations (e.g., 20% NaOH) [11] and desorption efficiencies are unsatisfactory (about 50%) [12,13]. Therefore, it is extremely necessary to investigate a new strategy to improve the desorption efficiency of anionic dyes from LDHs.…”

“…However, considerable examples have been reported on adsorptive properties of LDHs toward anionic dyes, few studies have addressed desorption of anionic dyes [10]. Generally, NaCl-NaOH, Na 2 CO 3 , or high-press CO 2 is employed as efficient desorbents to remove adsorbed anions from LDH materials via anion exchange process [11][12][13][14]. However, these desorbents require to be in high concentrations (e.g., 20% NaOH) [11] and desorption efficiencies are unsatisfactory (about 50%) [12,13].…”

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

“…Mineralogical composition of the phosphate laden LDH 2 sample indicated the formation of whitlockite, hydroxyapatite (Ca 5 (PO 4 ) 3 .OH) and calcite [23][24]. Calcium -based LDHs are believed to exhibit this phenomenon due to formation of amorphous phosphate salts (precipitates) of Ca on the surface of the LDH sample during the sorption process [1]. The LDH readily releases Ca 2+ into the liquid phase which leads to the increase in Ca 2+ concentration observed after P uptake (Table 4) as a result of its high solubility product (5.02 X 10 -6 ) to precipitate with phosphate [25].…”

“…Layered double hydroxides (LDH) are laminar anionic clay materials also known as hydrotalcite compounds and characterized with high exchange capacity [1]. The structure of layered double hydroxides is patterned after the brucitelike structure of Mg (OH) 2 /M 3+ ratio alters the charge density and the anion exchange capacity of the LDHs [2].…”