Improvement of nitrate-leaching control technology using an anion exchange compound on agriculture 1: synthesis of a Mg-Fe system layered double hydroxide and its anion exchange characteristics

Figures & data

Figure 1. NO₃^– adsorption properties of prepared samples.

Table 1. Chemical composition of PA_1.5.

element	cmol kg^−1
Mg	1178
Fe	271
Cl	170

Table 2. X-ray powder diffraction data.

Kohls and Rodda (1967) ^a		Braithwaite et al. (1994) ^a		Present work
dobs (pm)	R.I.meas^b	dobs (pm)	R.I.meas^b	dobs (pm)	R.I.meas^b	h	k	l
810.9	100	804.3	10	802.2	100	0	0	3
404.7	40	404.0	5	405.5	61	0	0	6
269.7	<1					0	0	9
263.9	17	263.7	4	262.7	52	0	1	2
236.3	27	235.3	4	234.5	51	0	1	5
201.9	23	201.4	4	201.1	30	0	1	8
180.5	4	179.1	<1			1	0	10
171.0	5	170.5	1			0	1	11
156.0	8	156.6	1	155.5	81	1	1	0
153.0	13	153.6	2	153.0	49	1	1	3

^a Data of Iowaites.

^b Relative intensity.

Figure 2. SEM image of PA_1.5 surface.

Table 3. The pH value at equilibrium and AEC of PA_1.5.

	AEC
pH	(cmolc kg^−1)
9.8	166

AEC: Anion Exchange Capacity.

Figure 3. NO₃^– exchange isotherm of the PA_1.5. The approximated curve was drawn by the formula of Langmuir.

Figure 4. Relationship between NO₃^– adsorption and the Cl^–desorption. Simple regression analysis was done by Excel software.

Table 4. The anion adsorption, selectivity coefficient (K_GT), and the distribution coefficient (K_d) for each anion on the equilibrium solution containing one kind of anion.

Anion				Cl^–
		Solution phase	Solid phase	Solution phase	Solid phase		Kd
Anions	pH	(mmol dm^−3)	(mmol kg^−1)	(mmol dm^−3)	(mmol kg^−1)	log KGT	(dm^3 kg^−1)
NO3^−	8.8	0.9	530	2.9	980	0.2	604
PO4^3−(HPO4^2−)	8.9	1.6	344	2.0	1210	−2.9	212
SO4^2−	9.8	1.4	393	3.3	872	−1.9	276

K_GT, Gaines–Thomas selectivity coefficient.

Table 5. The anion adsorption and distribution coefficient (K_d) for each anion on the equilibrium solution containing three kinds of anion.

		Solution phase	Solid phase	Kd
Anions	pH	(mmol dm^−3)	(mmol kg^−1)	(dm^3 kg^−1)
NO3^−		1.4	413	306
PO4^3− (HPO4^2−)	9.1	1.7	333	200
SO4^2−		2.1	230	111

Table 6. The competitive adsorption for each anion in the imitative soil solution.

Anions	Equilibrium		Adsorption ratio (%)	Kd (dm^3 kg^−1)
	Solution phase (mmol dm^−3)	Solid phase (mmol kg^−1)
Cl^−	8.3	–	–	–
NO3^−	6.4	900	36	141
PO4^3− (HPO4^2−)	0.0	250	100	–
SO4^2−	1.7	68	14	39

Kohls DW, Rodda JL 1967: Iowaite, a new hydrous magnesium hydroxide-ferric oxychloride from the precambrian of Iowa. Am. Mineralogist, 52, 1261–1271.

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Braithwaite RSW, Dunn PJ, Pritchard RG, Paar WH 1994: Iowaite, a re-investigation. Mineral. Mag., 58, 79–85.

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