Capacity, selectivity, and reversibility for nitrate exchange of a layered double‐hydroxide (LDH) mineral in simulated soil solutions and in soil

Abstract

The leaching of nitrate is an important way of N losses from agricultural soils in humid regions. Nitrate leaching is difficult to control as most soils under crop production do not have anionexchange properties, and nitrate remains mobile in the solution. The present work evaluated the potential use of a synthetic layered double-hydroxide (LDH) mineral as a nitrate exchanger in soil. The LDH used was a chloride form of a magnesium-aluminum layered double hydroxide with the formula: [Mg 2+ 0.82 Al 3+ 0.18 (OH) 2 ] 0.18+ [(Cl -) 0.18 0.5(H 2 O)] 0.18-. Experiments were carried out in aqueous solutions as well as in soil with the following objectives: (1) to characterize the nitrate adsorption capacity on the LDH, (2) to study its selectivity for nitrate adsorption in solution, (3) to evaluate the reversibility for nitrate exchange, and (4) to study the nitrate adsorption capacity and nitrate diffusion towards the LDH in soil. In aqueous solutions, the nitrate adsorption capacity was determined to be 1.54 mol c kg -1 LDH at nitrate concentrations typically encountered in soils under crop production. In solution, the LDH showed a high selectivity for nitrate adsorption compared to other anions. The LDH exchanged nitrate reversibly without a measurable reduction of the exchange capacity for at least 15 times. Under soil conditions, the extension of the nitrate depletion zone from the LDH surface reached up to about 8 cm within one week, confirming its high nitrate adsorption capacity also in soil. The LDH mineral evaluated in this work has the potential to be used as a nitrate exchanger in crop production, aiming to control the movement of nitrate in soil and thereby reducing the risks of nitrate leaching.

Relationship between the particle size and dosage of LDHs and concrete resistance against chloride ingress

“…Ca-Al-NO 3 LDHs is synthesized by using a co-precipitation method because of its facile and low cost features. In order to promote the real scale engineering application, LDHs are prepared under ambient conditions [33,[46][47][48]. However, in the present study, the pH value of the solution is changed to prepare LDH nano-platelets with different sizes.…”

Layered Double Hydroxides: Nanomaterials for Applications in Agriculture

“…Studies have reported the use of LDH as slow release source of nutrients to plants. Torres-Dorante et al (2008) studied the potential use of MgAl-Cl-LDH, as a NO − 3 adsorber in soils, controlling its losses and availability. It was examined the adsorption capacity of NO − 3 by LDH in aqueous solution as well as anion adsorption selectivity.…”

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

“…Actually, some studies have reported the potential use of LDHs as adsorbents or reservoirs of nitrate. [9,10,[13][14][15][16][17][18] However, the selectivity of LDHs for nitrate is generally considered not to be high, and a large number of studies have reported that anions with a higher charge density tend to be more preferentially intercalated into LDHs. [6][7][8]19,20] According to a report by Miyata, [19] the order of exchange selectivity for monovalent anions in the case of Mg-Al LDHs (Mg/ Al = 2.3) is OH -> F -> Cl -> Br -> NO 3 -> I -, and according to a report by Costa et al, [20] the order of exchange selectivity based on a computational simulation with Zn-Al LDHs (Zn/Al = 2) is CO 3 2-> OH -> F -> Cl -> Br -> NO 3 -.…”