Application of zinc-aluminium layered double hydroxides for adsorptive removal of phosphate and sulfate: Equilibrium, kinetic and thermodynamic

Abstract

In this study, a series of layered double hydroxide (ZxAy LDH) material was synthesized with different molar ratios and calcination temperatures to remove phosphate and sulfate ions from synthetic solution. ZxAy LDH was characterized by XRD, FTIR, BET and SEM analysis. The highest removal was obtained by Z3A200 LDH that is LDH with a Zn-Al molar ratio of 3 and calcined at 200 °C. The leaching of Zn and Al was more under highly acidic pH compared to pH 5 and 8. Adsorption isotherms data had a good fit with Langmuir model and maximum adsorption under optimum conditions led to 2.6-2.72 and 1.02-1.31 mmol/g for phosphate and sulfate, respectively. Kinetic studies have been performed by applying reaction based models and diffusion-based models, which indicated the chemisorption interaction for Z3A200 by a controlling step of the macro-pore and micro-pore diffusion for phosphate and sulfate adsorption process onto Z3A200, respectively. Thermodynamic studies showed that adsorption process onto Z3A200 was endothermic and spontaneous. Thus, phosphate and sulfate adsorption by using optimized Zn-Al LDH appears to be a promising adsorbent for their removal.

Phosphate Sequestration From Aqueous Solutions Using A Zeolite in The Zinc Form.

“…For this case, the pH pzc value of Z-Zn is 8.5. Comparing with bibliographic information on other types of adsorbents that have used zinc in their composition, data such as double hydroxides of zinc and aluminum are found in layers where the value of the zero charge point pHpzc is 10.05, (Iftekhar, Küçük, Srivastava, Repo, & Sillanpää, 2018).…”

“…According to the graph, the values are similar in pH 4 to 6 and pH 9 and 10, (Iftekhar et al, 2018); however, there is a variation in pH 7 and 8 promoting a reduction in phosphate elimination. FIGURE 3 describes the distribution of phosphate species as a function of pH.…”

Layered Double Hydroxide Sorbents for Removal of Selenium from Power Plant Wastewaters

“…Many studies have shown the highest P removal at low pH (< 4) where the LDH is partially dissolved; in these cases, the Mg 2+ and Al 3+ in solution along with hydroxides can act as coagulants to remove the phosphate [92,93]. Interlayer ion-exchange and surface adsorption is the predominant mechanism at intermediate pH, with phosphate removal usually decreasing > pH 8 due to repulsion by the negative surface charge of the LDH [94,95]. In our case, the high effluent pH and absence of breakthrough for P as was seen for Se and S suggested a different removal mechanism.…”

Development of magnesium–iron layered double hydroxide and application to nitrate removal

“…The LDH is generally represented by [M 2+ 1−X M X 3+ (OH) 2 ][A x/n n− ‧yH 2 O], where M 2+ is a divalent cation, M 3+ a trivalent cation, and A an anion. Many types of LDH exist including magnesium-aluminum [8,9], magnesium-iron [10], zinc-aluminum [11], zinc-iron [12], nickel-aluminum [13], and nickel-iron [14]. The charge variation of LDH is its driving force for anion adsorption.…”